Manejo Integrado da Praga do Weevil da Banana

Prévia do material em texto

Integrated Pest Management Reviews 6: 79–155, 2001.
© 2003 Kluwer Academic Publishers. Printed in the Netherlands.
Biology and integrated pest management for the banana weevil
Cosmopolites sordidus (Germar) (Coleoptera: Curculionidae)
Clifford S. Gold1, Jorge E. Pena2 & Eldad B. Karamura3
1IITA-ESARC, P.O. Box 7878, Kampala, Uganda
2TREC, University of Florida, 18905 SW 280th Street, Homestead, Florida 33031-3314, U.S.A.
3INIBAP/ESA, IPGRI, P.O. Box 24384, Kampala, Uganda
Key words: banana, banana weevil, Beauveria bassiana, biological control, Cosmopolites sordidus, cultural
control, host plant resistance, integrated pest management, neem, plantain
Abstract
The banana weevil Cosmopolites sordidus (Germar) is the most important insect pest of bananas and plantains
(Musa spp.). The larvae bore in the corm, reducing nutrient uptake and weakening the stability of the plant. Attack
in newly planted banana stands can lead to crop failure. In established fields, weevil damage can result in reduced
bunch weights, mat die-out and shortened stand life. Damage and yield losses tend to increase with time. This
paper reviews the research on the taxonomy, distribution, biology, pest status, sampling methods, and integrated
pest management (IPM) of banana weevil. Salient features of the weevil’s biology include nocturnal activity, long
life span, limited mobility, low fecundity, and slow population growth. The adults are free living and most often
associated with banana mats and cut residues. They are attracted to their hosts by volatiles, especially following
damage to the plant corm. Males produce an aggregation pheromone that is attractive to both sexes. Eggs are laid
in the corm or lower pseudostem. The immature stages are all passed within the host plant, mostly in the corm. The
weevil’s biology creates sampling problems and makes its control difficult. Most commonly, weevils are monitored
by trapping adults, mark and recapture methods and damage assessment to harvested or dead plants. Weevil pest
status and control options reflect the type of banana being grown and the production system. Plantains and highland
bananas are more susceptible to the weevil than dessert or brewing bananas. Banana production systems range
from kitchen gardens and small, low-input stands to large-scale export plantations. IPM options for banana weevils
include habitat management (cultural controls), biological control, host plant resistance, botanicals, and (in some
cases) chemical control. Cultural controls have been widely recommended but data demonstrating their efficacy
are limited. The most important are clean planting material in new stands, crop sanitation (especially destruction
of residues), agronomic methods to improve plant vigour and tolerance to weevil attack and, possibly, trapping.
Tissue culture plantlets, where available, assure the farmer with weevil-free material. Suckers may be cleaned by
paring, hot water treatment and/or the applications of entomopathogens, neem, or pesticides. None of these methods
assure elimination of weevils. Adult weevils may also invade from nearby plantations. As a result, the benefits of
clean planting material may be limited to a few crop cycles. Field surveys suggest that reduced weevil populations
may be associated with high levels of crop sanitation, yet definitive studies on residue management and weevil pest
status are wanting. Trapping of adult weevils with pseudostem or corm traps can reduce weevil populations, but
material and labour requirements may be beyond the resources of many farmers. The use of enhanced trapping with
pheromones and kairomones is currently under study. A combination of clean planting material, sanitation, and
trapping is likely to provide at least partial control of banana weevil.
Classical biological control of banana weevil, using natural enemies from Asia, has so far been unsuccessful.
Most known arthropod natural enemies are opportunistic, generalist predators with limited efficacy. Myrmicine ants
have been reported to help control the weevil in Cuba, but their effects elsewhere are unknown. Microbial control,
using entomopathogenic fungi and nematodes tend to be more promising. Effective strains of microbial agents are
known but economic mass production and delivery systems need further development.
80 C.S. Gold et al.
Host plant resistance offers another promising avenue of control. Numerous resistant clones are known, including
Yangambi-km 5, Calcutta 4, and Pisang awak. Resistance is most often through antibiosis resulting in egg or larval
failure. Banana breeding is a slow and difficult process. Current research is exploring genetic improvement through
biotechnology techniques including the introduction of foreign genes.
Neem has also shown potential for control of banana weevil. Studies on the use of other botanicals against
banana weevil have failed to produce positive results. Chemical control of banana weevil remains a common and
effective method for larger scale producers but is beyond the reach of resource-poor farmers. However, the weevil
has displayed the ability to develop resistance against a broad range of chemicals.
In summary, cultural control remains the most available approach for resource-poor farmers. A combination of
several cultural methods is likely to reduce weevil pressure. Among the methods currently under study, microbial
control, host plant resistance and neem appear to offer the most promise.
Part 1: Biology and Pest Status of
Banana Weevil
The banana weevil, Cosmopolites sordidus (Germar),
is an important pest of banana, plantain, and ensete.
Weevil attack can prevent crop establishment, cause
significant yield reductions in ratoon cycles and con-
tribute to shortened plantation life. For example, the
weevil has been implicated as a primary factor con-
tributing to the decline and disappearance of East
African highland cooking banana (Musa spp., genome
group AAA-EA) from its traditional growing areas
in central Uganda (Gold et al. 1999b) and western
Tanzania (Mbwana & Rukazambuga 1999).
The banana weevil is a difficult pest to work on.
The adult is nocturnally active and seldom observed,
while the immatures stages may be deep within the
banana corm. Damage often occurs well beneath the
soil surface. The insect’s biology creates a number
of sampling difficulties. Damage assessment requires
destructive sampling that can affect the vigour and sta-
bility of other plants on the mat. Adult population esti-
mates are costly and there is only a modest relationship
between estimated adult densities and weevil damage.
All of the above factors have implications for the
integrated pest management (IPM) of banana weevil.
The damaging larval stage is protected against most
natural enemies by virtue of its cryptic lifestyle within
the host plant. Control methods directed at the more
vulnerable adult stage may not be directly translated
into reductions in larval damage or may require con-
siderable lag times before effects are felt. Control
options requiring labour or costly inputs are depen-
dent upon farmer objectives, management priorities,
and allocation of limited resources.
Research results suggest that no single control strat-
egy will be likely to provide complete control for
banana weevil. Therefore, a broad IPM approach
might provide the best chance for success in control-
ling this pest. This paper provides a review of the
available literature and unpublished data on banana
weevil biology, pest status, and management options.
The paper concludes with recommendations for the
way forward in developing management strategies for
this pest.
I. Banana Morphology and Phenology
The genus Musa evolved in southeast Asia (Stover &
Simmonds, 1987). Edible bananas (Musa spp., Eumusa
series) originated from two wild progenitors, Musa
acuminata and M. balbisiana, producing a series of
diploids, triploids, and tetraploids through natural
hybridisation. Simmonds & Shepherd (1955) provided
a key by which these naturallyhybridised bananas may
be divided into six genome groups (AA, AAA, AAB,
AB, ABB, ABBB) based on the relative contributions
of M. acuminata and M. balbisiana. Triploids tend to
be more vigorous and productive than diploids and
comprise the majority of currently cultivated bananas.
Differences among these cultivars allow for differ-
ent end products, i.e. dessert, cooking, roasting, and
brewing bananas. Some of these clones supply impor-
tant international markets, while others are largely
restricted to subsistence production or domestic trade.
Bananas are grown from sea level to >2000 masl, under
a range of different rainfall and soil conditions and
in production systems ranging from kitchen garden to
large-scale commercial plantations.
Bananas are herbaceous plants ranging in height
from 0.8 to 15 m (Turner 1994) that are vegetatively
propagated. A mat (=stool) consists of an underground
corm (rhizome) from which one or more plants (shoots)
Biology and IPM for banana weevil 81
emerge. The apparent stem or pseudostem is composed
of leaf sheaths. The true stem arises from the api-
cal meristem after leaf production has terminated and
grows through the centre of the pseudostem (Stover &
Simmonds 1987). The true stem bears a single ter-
minal inflorescence. After the fruit matures, the stem
dies back to the corm. Farmers normally cut harvested
plants between ground level and 1 m.
New plants are produced by suckers emerging from
lateral buds in the corm. These can be left in situ
(i.e. ratoon crops) or serve as a source of planting
material, in which case they are removed and planted
elsewhere. Plant density is controlled by desucker-
ing. Normally, a banana mat consists of three or more
plant generations (=ratoons or crop cycles) at any one
time. As banana stands age, mats ‘divide’ and the rela-
tionship between plants (e.g. sharing of a common
corm) becomes more tenuous; thus, in older stands,
mat definition becomes unclear. Suckers used to estab-
lish new fields are called the mother plant or plant
crop (Stover & Simmonds 1987; Turner 1994). In
older stands, bananas are harvested throughout the year.
Yield is normally expressed in kg/area/year and reflects
both the number and size of bunches harvested.
II. Banana Weevil Taxonomy and Morphology
The banana weevil was first identified by Germar
in 1824 from specimens collected in Java and given
the name Calandra sordida. In 1885, Chevrolat
changed this to its currently recognised name
C. sordidus (Germar) (Viswanath 1976). Sphenophorus
striatus Fahreus 1845 (collected in Brazil) and
S. cribricollis Walker 1859 (collected in Ceylon)
are considered synonyms of C. sordidus and these
names have been suppressed (Zimmerman 1968a,b).
The genus Cosmopolites belongs to the subfam-
ily Rhynchophorinae of the family Curculionidae
(weevils and snout beetles). A single congeneric
species, C. pruinosus, is associated with bananas in
Indonesia, the Philippines and the Caroline Islands
(Zimmerman 1968b,c). Taxonomic keys are presented
by Zimmerman (1968a), while adult morphology
has been described by Moznette (1920), Beccari
(1967), Zimmerman (1968b), Viswanath (1976), and
Nahif et al. (1994), reproductive system morphology
by Cuille (1950), Beccari (1967), Uzakah (1995),
and Nahif (1998, 2000), and larval morphology
by Moznette (1920) and Viswanath (1976). The
ultrastructure of the spermatazoan has been described
by Lino Neto & Dolder (1995).
The banana weevil’s limited mobility suggests the
existence of discrete populations with limited gene flow
and the likely evolution of local biotypes. Studies on
the possible biotypes of banana weevils are currently
being concluded at ICIPE in Nairobi, Kenya (Ochieng
2001; Ochieng et al. unpubl. data). Genetic diversity
of banana weevils from East and West Africa, Asia,
Australia, and the Americas were compared using ran-
dom amplified polymorphic DNA polymerase chain
reaction (RAPD-PCR) with five universal primers and
46 RAPD markers. The data show that considerable
variation exists between banana weevil populations
from different parts of the world. Populations with
greatest levels of genetic similarity often came from
geographically disparate areas (e.g. East Africa and the
Caribbean), while populations from the same region
sometimes showed high levels of genetic diversity.
Further examination of populations from different parts
of Uganda showed distinct genetic variability, although
much less than that found across regions.
III. Origin and Distribution
The banana weevil is believed to have originated in the
Indo-Malayan region (Simmonds 1966; Zimmerman
1968b; Waterhouse 1993), coincident with the area
of origin of bananas (Stover & Simmons 1987). The
weevil has since spread to all major banana-growing
regions of the world, presumably through the move-
ment of infested planting material. By 1900, the
insect was reported in Indonesia, China, Australia,
and Brazil (Table 1). Within 20 years, it was also
reported in sub-Saharan Africa, Central America,
Pacific, and the Caribbean (Simmonds 1966). It is
currently found throughout Asia, Oceana, Australia,
Africa, and the Americas and absent only from banana-
growing regions of North Africa (Cuille & Vilardebo
1963).
In many countries, the banana weevil was prob-
ably established long before it was first recorded.
For example, bananas are believed to have entered
sub-Saharan Africa by multiple introductions between
the first and sixteenth centuries A.D. (Price 1995a;
Karamura 1998). It is likely that the weevil entered the
region well before the first reports of its presence in the
early 1900s. Similarly, the weevil was first observed in
Cuba in 1944 although it was believed to have arrived
many years earlier (Roche 1975).
82 C.S. Gold et al.
Table 1. First reports of the banana weevil C. sordidus in different
countries
Region/Country Year Source
Asia
Indonesia 1824∗ Zimmerman (1968a)
Sri Lanka 1859∗ Zimmerman (1968a)
Sri Lanka 1885 Chevrolat (1885) in
Viswanath (1976)
China 1885 Chevrolat (1885) in
Viswanath (1976)
Vietnam 1885 Chevrolat (1885) in
Viswanath (1976)
Taiwan 1909 Tsai (1986)
India 1914 Moznette (1920)
Malaysia 1914 Jepson (1914)
Vietnam 1914 Jepson (1914)
Philippines 1916 Moznette (1920)
Oceana
Fiji 1908 Moznette (1920)
Borneo 1914 Jepson (1914)
New Guinea 1914 Jepson (1914)
Seychelles 1914 Jepson (1914)
Guam 1936 Gressitt (1954)
Hawaii 1981 Gettman et al. (1992)
Australia
Queensland 1896 Franzmann (1976)
New South Wales 1916 Hely et al. (1982)
Africa
Madagascar 1903 Moznette (1920)
Sao Tome 1907 Gravier (1907)
Uganda 1908 Hargreaves (1940)
Congo (Zaire) 1913 Ghesquierre (1925)
Tanzania 1922 Harris (1947)
South Africa 1924 Cuille (1950)
Sierra Leone 1925 Cuille (1950)
Cote d’Ivoire 1938 Cuille (1950)
French Guinee 1938 Cuille (1950)
Canary Islands 1945 Carnero et al. (2002)
Cameroon 1947 Nonveiller (1965)
Americas
Brazil 1845∗ Zimmerman (1968a)
Brazil 1885 Arleu et al. (1984)
Guadeloupe 1889 Harris (1947)
Lesser Antilles 1912 Moznette (1920)
Peru 1914 Jepson (1914)
Dominican Republic 1916 Moznette (1920)
Jamaica 1916 Moznette (1920)
Guadeloupe 1916 Moznette (1920)
Trinidad 1916 Moznette (1920)
USA (Florida) 1917 Moznette (1920)
Puerto Rica 1921 Wolcott (1948)
Cuba 1944 Roche (1975)
Colombia 1947 Gallego (1956),
Cardenas (1983)
∗From type specimens.
Nevertheless, surveys do suggest recent spread of
the pest in some areas. For example, the weevil
is believed to have been absent from the important
banana-growing region of Bukoba district, Tanzania
until 1940 (Harris 1947) and from Kabarole district,
Uganda until after 1957 (Whalley 1957; Gold et al.
1993). Similarly, it was first recorded in the Colombian
departments of Caldas in 1979, Quindio in 1981, and
Cesar in 1982 (Castrillon 1991, 2000). In the depart-
ment of Risaralda, the banana weevil was found on
nearly all farms during a survey in 1999 whereas it had
been found on only four farms in 1976 and on only 12%
of farms between 1977 and 1981 (Castrillon 2000).
Hargreaves (1940) estimatedit would take 10 years for
the weevil to achieve pest status following its arrival in a
region.
Where present, severity of attack may be influ-
enced by ecological conditions, clonal susceptibility,
and management practices. Froggatt (1928) believed
that the hot weather conditions of low elevations in
the banana-growing zones of Australia reduced weevil
activity. However, the weevil thrives in the hot, humid
conditions of coastal Nigeria (C. Gold pers. observ.)
and Honduras (Sponagel et al. 1995).
Valentine & Valentine (1957) found the banana
weevil to be abundant at low elevations in Haiti but
did not observe it over 1200 masl. Lescot (1988) sur-
veyed 45 sites and found a negative correlation (r =
−0.75) of weevil damage with elevation with the great-
est damage below 1000 masl and very low damage
between 1500 and 1600 masl. The weevil was absent
above 1600 masl. Lescot (1988) also cited similar ele-
vation thresholds in Burundi, Rwanda, and Colombia.
In a later survey conducted in Colombia, the weevil
was most important at 1300–1400 masl (Anonymous
1992).
However, in the Department of Risaralda, Colombia,
Castrillon (2000) captured 1244 (2.5/trap) and 684
(1.4/trap) banana weevils in plantain stands on farms
at 1600 and 1700 masl, respectively. This is the only
record in the literature of significant weevil populations
above 1600 masl. At three other sites above 1600 masl
in this study, trap captures ranged from 0 to 0.2 weevils
per trap.
In Uganda surveys, weevil damage to highland
banana clones (AAA-EA) was most severe between
1000 and 1300 masl, although considerable variabil-
ity existed at each elevation level (Gold et al. 1994a).
Damage was not observed at the two sites above
1600 masl. Gold & Okech (unpubl. data) have since
trapped banana weevils (0.1–0.6 weevils/trap) and
observed low levels of damage on 10 farms between
1600 and 2000 masl in Mbarara district, Uganda.
The upper elevation threshold for banana weevil
is likely to be temperature related. Cuille (1950),
Mesquita & Alves (1983), and Lescot (1988) suggest
Biology and IPM for banana weevil 83
minimal thermal thresholds for adult activity at
15–18◦C, while thermal preferences have been esti-
mated at 25◦C (Cuille 1950), 23–26◦C (Minost 1992),
and 20–30◦C (Gomes 1985). In a controlled study,
Traore et al. (1993, 1996) found minimal thermal
thresholds of 12◦C for eggs and 10◦C for larvae
with highest rates of eclosion and larval develop-
ment between 25◦C and 30◦C. These data suggest that
extended periods with low night-time temperatures at
higher elevations may become bottlenecks for larval
development and/or adult survival. In Cameroon, for
example, nocturnal temperatures fall below <12◦C at
1300 masl (Lescot 1988).
IV. Host Range
The banana weevil is a narrowly oligophagous
pest, attacking wild and cultivated clones in the
related genera Musa (banana, plantain, abaca) and
Ensete. Reports of alternative hosts, including sugar
cane (Saccharum officinarum L.), yams (Dioscorea
batatas Dene), cocoyam (Xanthosoma sagittifolium
(L.) Schott) (summarised by Moznette 1920; Beccari
1967; Arleu & Neto 1984), have not been substanti-
ated and appear to be in error. For example, gravid
females placed in pots with Colocasia esculenta Schott,
X. saggittifolium, and X. violaceum Schott failed to
oviposit, while larvae inserted into these plants quickly
died (Martinez & Longoria 1990). Nevertheless, Traore
(pers. comm.) was able to maintain larvae through
several instars using a factitious host (processed
X. saggittifolium), while Pavis (1988) and Schmitt
(1993) had modest success rearing larvae on artificial
diets.
V. Adult Biology
1. Longevity, tropisms, feeding, and distribution
The banana weevil displays a classical ‘K’ selected
life cycle (Pianka 1970) with long life span and low
fecundity. Adults have been widely reported to live
upto 2 years (Froggatt 1925; Harris 1947; Nonveiller
1965; Beccari 1967; Crooker 1979; Waterhouse &
Norris 1987; Treverrow et al. 1992). In Uganda, marked
weevils were recovered in experimental trials 4 years
after release (Rukazambuga & Gold unpubl. data).
Mean longevity under field conditions is not clear.
Jardine (1924) reported that the adult lived 5–8 months,
while Froggatt (1925) thought there was high mortality
soon after emergence. In Thailand, Jirasurat et al.
(1989, cited in Vittayaruk et al. 1994) estimated male
and female longevity at 88 and 128 days, respectively.
The banana weevil adult is nocturnally active
and characterised by negative phototropism, strong
hygrotrophism, thigmotactism, gregariousness, and
death mimicry (Jardine 1924; Delattre 1980; Ittyeipe
1986; Tsai 1986; Treverrow & Bedding 1993;
Uzakah 1995; Braimah 1997; Aranzazu et al. 2000;
Padmanaban et al. 2001). The adults have been widely
reported to favour crop residues and moist environ-
ments, including in or under newly cut or rotting
pseudostems, decaying stalks, cut or damaged corms,
moist trash, and burrowed under the soil surface
(Weddell 1945; Swaine 1952; Whalley 1957; Vilardebo
1960, 1973; Nonveiller 1965; McNutt 1974; Roche &
Abreu 1983; Jones 1986; Pavis 1988; Treverrow et al.
1992; Silva & Fancelli 1998; Aranzazu et al. 2000).
Additionally, the adults can penetrate the soil to depths
of 50–70 cm (Cardenas & Arango 1986; Rukazambuga
unpubl. data). Moznette (1920), Vilardebo (1960),
Saraiva (1964), Treverrow et al. (1992), and Silva &
Fancelli (1998) reported adults to be closely associ-
ated with the banana mat, being primarily in the leaf
sheaths, around the roots, under loose fibres surround-
ing the base of the plant and, occasionally, in larval
galleries. Silva & Fancelli (1998) reported that, during
the day, the adults may also be found in wet, shaded
areas under shrubs.
In Uganda, banana plots were systematically
searched to determine field distribution of banana
weevil adults (Gold et al. 1999d). Most banana weevil
adults were within or attached to the banana plants
(mainly in leaf sheaths) (41%), or in the soil at the
base of the mat (24%) (Gold et al. 1999d). Weevil den-
sity was greatest in or around flowered plants, although
adults were also commonly found on pre-flowered
plants and harvested stumps. Significant numbers of
weevils (28%) were attached to cut and prostrate
residues >0.5 m away from the mats, while negli-
gible numbers were found in the leaf litter (6%) or
buried in soil >0.5 m from the banana mat (1%). A few
marked weevils had re-entered the corm or pseudostem
of living plants through existing galleries. Distribution
patterns of males and females were similar.
The adults feed on rotting banana tissue (Budenberg
et al. 1993b) or, occasionally, on young suckers
(Castrillon 2000), but it is likely that resulting dam-
age is negligible. The weevil can survive without food
for extended periods (2–6 months) in moist environ-
ments (Moznette 1920; Froggatt 1924, 1925; Cuille &
Vilardebo 1963; Viswanath 1976; Crooker 1979;
84 C.S. Gold et al.
Mitchell 1980; Aranzazu et al. 2000; Castrillon 2000).
In one exceptional case, females were maintained for
17 months without food (Franzmann 1976). Under
field conditions, the weevil reportedly can survive
3–6 months once all banana plants and residues are
removed (Froggatt 1924; Peasley & Treverrow 1986;
Allen 1989).
However, the weevil is very susceptible to desic-
cation and will die within 1–10 days if kept in a
dry substrate (Froggatt 1925; Cuille 1950; Vilardebo
1960; Cuille & Vilardebo 1963; Viswanath 1976; Gold
1998a). For example, Viswanath (1976) maintained
weevils in moist soil without food for 112 days, but
the weevils died in 10 days when kept in dry soil. As a
result, the weevil is strongly hygrotropic and searches
for the highest available air humidity and for liquid
water (Cuille 1950; Roth & Willis 1963). In labora-
tory studies, males and females were unsettled at low
humidity and sedentary at high humidity (Roth & Willis
1963). Koppenhofer (1993a) suggested that females
deposit eggs on living plants further below the soilsurface during the dry season. Masanza (unpubl. data)
found a higher proportion of oviposition on buried
corms (i.e. chopped below the soil surface) in the dry
season than in the wet season.
2. Sexual dimorphism and sex ratio
Males can be distinguished from females on the basis of
punctuation on the rostrum extending beyond the point
of insertion of the antennae (McCarthy 1920 cited in
Longoria 1968; Viswanath 1976), a shorter and less
accentuated curvature of the rostrum (Longoria 1968;
Mestre 1995) and greater curvature of the last abdom-
inal sternite (Roth & Willis 1963). Males tend to be
uniform black or dark-brown, while the rostrum of
females may be redder in colour than the rest of their
body (Longoria 1968). Punctuation of the rostrum and
curvature of the last abdominal sternite appear to be
the most reliable methods for sexing weevils and are
widely used. In Uganda, dissections suggested >95%
accuracy in sexing weevils on the basis of these traits
(Rukazambuga et al. 2002; Abera & Gold unpubl.
data).
The range in adult size has been reported as
10–16 mm (Nonveiller 1965), 8.8–13.2 mm (Beccari
1967), 11–14.5 mm (Viswanath 1976), 11–14 mm
(Sponagel et al. 1995; Carnero et al. 2002), and
15–20 mm (Aranzazu et al. 2000, 2001; Castrillon
2000), although mean sizes of 12.5–13.0 mm were
similar in such disparate populations as those in
India (Viswanath 1976), Cameroon (Lescot 1988),
and Honduras (Anonymous 1989; Sponagel et al.
1995). On average, females are >20% longer (Cuille
1950; Beccari 1967; Sponagel et al. 1995) and
weigh 11–17% more than males (Edge 1974; Gold
et al. 1999a,d).
Sex ratios (female : male) of field-collected weevils
have been reported as 1 : 1 in Guinee (Cuille 1950),
Kenya (Koppenhofer & Seshu Reddy 1994), and the
Canary Islands (Carnero et al. 2002), 1.2 : 1 in Tonga
(Litsinger 1974), 1 : 1.4 in India (Viswanath 1976),
and 1 : 2.2 in Honduras (Sponagel et al. 1995). In
Cameroon, Delattre (1980) found a sex ratio of 1 : 1 for
laboratory-reared weevil and attributed a higher pro-
portion of females among field-trapped weevils in the
rainy season to sexual differences in behaviour. In a
survey of 50 farms in Ntungamo district, Uganda, the
overall sex ratio for trapped weevils (N = 15,376) was
1.07 : 1, although on individual farms it ranged from
1.67 : 1 to 1 : 1.56 (Gold et al. 1999d; Gold & Okech
unpubl. data).
3. Daily and seasonal activity periods
Banana weevil adults are negatively phototropic and
tend to be sedentary during daylight hours. They are
active between 1800 and 0600 hours (Cuille 1950;
Uzakah 1995) with greatest activity between 2100 and
0400 hours (Uzakah 1995). Padmanaban et al. (2001)
collected weevils in freshly set traps during daytime
hours in mulched fields suggesting at least some diur-
nal weevil activity in these systems. A substantial pro-
portion of the population may be inactive for extended
periods (S. Lux pers. comm.).
Seasonal differences in trap captures have been
reported by many authors. Trap captures, however, do
not provide meaningful estimates of population den-
sity (Vilardebo 1973), which require mark and recap-
ture methods (Price 1993; Gold & Bagabe 1997). Most
likely such apparent seasonal differences reflect weevil
activity patterns more than population fluctuations.
In Latin America (primarily Brazil and Cuba), trap
captures reported in a number of studies suggest
reduced adult activity in the rainy season (Yaringano &
van der Meer 1975; Reinecke 1976; Zem & Alves
1976; Mesquita et al. 1981; Arleu & Neto 1984 (one
study); Gomes 1985; Durans Pinheiro & Batista de
Carvalho Filho 1985; Bendicho & Gonzales 1986;
Batista Filho et al. 1992). In contrast, other researchers
(including most African and some Latin American
studies) found greater weevil activity and trap captures
Biology and IPM for banana weevil 85
in the rainy season (Cuille 1950; Roy & Sharma 1952;
Whalley 1957; Cuille & Vilardebo 1963; Saraiva 1964;
Delattre 1980; de Souza et al. 1981; Vilardebo
1984; Marcelino & Quintero 1991; Pinese & Piper
1994; Price 1995b). Still others found no relationship
between climatic factors (rainfall, relative humidity,
and/or temperature) and trap captures (Sen & Prasad
1953; Oliveira et al. 1976; Delattre 1980; Arleu 1982;
Pulido 1982, 1983; Arleu & Neto 1984 (second study);
Van den Enden & Garcia 1984; Cardenas & Arango
1986; Pavis 1988; Boscan de Martinez & Godoy
1989). Uzakah (1995) reported activity in the labo-
ratory to be positively correlated to relative humidity
and negatively correlated with temperature and light
intensity. These conflicting results provide an unclear
picture of when adults are most active and, hence, most
vulnerable to control interventions.
Banana weevil populations may show year to
year fluctuations reflecting environmental conditions
(e.g. drought). For example, in a study evaluating the
control potential of pseudostem trapping, weevil pop-
ulations on nine control farms declined from a mean of
13,400/ha to 11,400/ha (farm mean change = −38%)
in 1 year (Gold et al. 2002b). In this study, however,
populations declined by 42% during the first 6 months
in which rainfall was 635 mm and then increased by
12% during the next 6 months during which rainfall
was 245 mm (Gold et al. unpubl. data).
4. Dispersal and movement
a. Crawling
Dispersal by means of crawling appears to be lim-
ited and slow. Moznette (1920) reported most adults
to remain near their sites of emergence. Delattre
(1980) found 90% of weevils recaptured after 3 days
to be at the point of release. Whalley (1957) and
Cardenas & Arango (1986) each reported that most
weevils moved less than 10 m over a period of sev-
eral months. Maximum weevil movement has been
recorded as 6 m in a night (Wallace 1938), 15 m in a
night (Cendana 1922), 21 m in 14 days (Wallace 1938),
35 m in 3 days (Gold & Bagabe 1997), and 60 m in
5 months (Delattre 1980). Most of these trials con-
cerned tracking weevils released at a single point, with
probability of recapture declining at greater distances
from the release point.
Wallace (1938) found few weevils were able to
cross grass barriers of 4–10 m. In a series of trials
lasting several years and in which plots (15 × 15 m2
and 15 × 25 m2) were separated by 20 m grass alleys,
Gold et al. (1998b, unpubl. data) found that less than
3% of marked weevils appearing in pseudostem traps
were captured in plots other than those in which
they had been released. Nevertheless, Vilardebo (1984)
found weevils attracted to house lights 200 m from the
nearest banana stand.
Mestre & Rhino (1997) released five marked females
and five marked males each in a series of pseudostem
traps, which they then monitored for 17 days. The
percentage of marked weevils in these traps declined
rapidly; after 17 days, 25% of the released weevils
had remained in the traps. Mestre & Rhino (1997)
observed much faster disappearance of females that
they hypothesised was associated with their search for
oviposition sites.
In a study at the Kawanda Agricultural Research
Institute near Kampala, Uganda, 2000 weevils were
individually marked with distinctive patterns, released
in banana stands and tracked by pseudostem trapping
for 1 year. Results from the first 10 weeks have been
published (Gold et al. 1999d). Two weeks after release,
49% of the weevils in a mulched plot and 79% in an
unmulched plot were found at the site of release. By
10 weeks after release, 17% and 36% of the weevils
were recovered at the release point in mulched and
unmulched plots, respectively. During the same time
period, 60% of the weevils had moved >10 m in the
mulch, while 27% had moved >10 m in the unmulched
plot. Six months after release, 42% of recaptured
weevils were found within 5 m of the point of release,
39% had moved 6–15 m and only 3% had moved more
than 25 m (Gold & Kagezi unpubl. data). These results
suggest that adults may be sedentary for extended
periods and that soil moisture stimulates activity
and movement. Females tended to be more active
than males,leaving the site of release quicker and
moving longer distances (Gold & Kagezi unpubl.
data).
b. Flight
Although the banana weevil has functional wings, most
observers report that the weevil seldom if ever flies
(Froggatt 1925; Nonveiller 1965; Gordon & Ordish
1966; Wardlaw 1972; Cardenas & Arango 1986;
Greathead 1986; Waterhouse & Norris 1987; Pinese &
Piper 1994; Sponagel et al. 1995). At ICIPE, flight
was never observed during laboratory studies on noc-
turnal weevil behaviour (Uzakah 1995; S. Lux pers.
comm.). In the laboratory, a few weevils were observed
to open their wings in response to extreme drought, the
latest stages of insecticide influence (Whalley 1957)
86 C.S. Gold et al.
or being tethered (Viswanath 1976), but did not fly.
Gold & Nankinga (unpubl. data) placed weevils on hot
plates but could not induce flight by gradually increas-
ing the temperature until the weevils died. Reports of
banana weevil flight (Cuille & Vilardebo 1963; Haarer
1964; Simmonds 1966) are often anecdotal.
Nevertheless, the possibility of dissemination by
flight remains unclear. Few workers have made obser-
vations on the weevil during it periods of greatest
activity (i.e. 2100–0400 hours) and flight may be stim-
ulated only under certain environmental conditions.
Castrillon (pers. comm.) believes that weevils read-
ily fly at night following the removal of host plants
in recently uprooted banana stands. In Cameroon,
Messiaen (2002) captured 14 adult banana weevils
over a 40-week period in window traps placed 0.5–
1.5 m above the ground on the edge of a 0.8 ha
banana stand. Moreover, weevil attack of isolated
fields planted with tissue culture plants in Malaysia
and Uganda (C. Gold pers. observ.) suggests that dis-
persal by flight may be greater than most observers
believe.
c. Dispersal
In summary, the data suggest that banana weevils are
relatively sedentary and dissemination by crawling or
flight of adults is limited. Adult weevils can move
within banana stands and across contiguous plantings.
However, movement across barriers of >20 m may be
limited. Moreover, the banana weevil’s narrow host
range and limited dispersal capability mitigate against
immigration of adults into isolated or newly planted
banana stands (Gold et al. 1998b, 1999d).
It has been widely recognised that dispersal of
banana weevil is primarily through infested plant-
ing material (Froggatt 1925; Ghesquierre 1925;
Hargreaves 1940; Vilardebo 1960; Haarer 1964;
Nonveiller 1965; Cardenas & Arango 1986; Jones
1986; Rodriguez 1989; Pinese & Piper 1994; Gold et al.
1998a,b; Castrillon 2000). Infested planting material is
likely to contain adults in the leaf sheaths and imma-
ture stages in the pseudostem and corm. For exam-
ple, Abera et al. (1999) reported 0.4–1.5 eggs per plant
(cv Atwalira, AAA-EA) for peepers and suckers, while
Gold et al. (1998a) found mean larval infestation levels
per sucker of 0.3 for Gonja (AAB), 0.6 for Atwalira,
and 1.1 for Nsowe (AAA-EA). This suggests that the
use of clean planting material is an important factor in
establishing healthy banana stands and retarding weevil
build-up.
5. Teneral stage
The teneral stage of newly emerged adults is most
often passed in the pupal chamber within the plant
(Jardine 1924; Longoria 1972). Teneral adults are
reddish-brown and turn dark-brown to black as their
exoskeletons harden. Under tropical conditions, the
teneral stage can last from 2 to 14 days (Jardine 1924;
Froggatt 1925; Montellano 1954; Viswanath 1976;
Mestre 1997). In contrast, Cuille (1950) described a
teneral stage in which the weevil required 22–60 days
to reach its final black colour.
6. Mating
Mating is most often at night (Delattre 1980; Jones
1986; Uzakah 1995). Courtship and mating behaviour
of the banana weevil have been described by Uzakah
(1995) and Viana & Vilela (1996). Mating lasted
3–24 min (mean 7.5 min). Following mating, males
often guard the females to prevent further mating. The
weevils may oviposit for up to 11 months without
renewed mating (Cuille 1950). Treverrow et al. (1992)
reported production of up to 100 eggs following a single
mating.
7. Sexual maturity and preoviposition period
In Kenya, male sexual maturity (i.e. the ability to
inseminate females) was attained at 18–31 days after
emergence (DAE) (Uzakah 1995). Spermatogenesis
occurred at emergence, but sperm were non-motile
in the female following insemination. This suggested
that secretions from an accessory gland activate sperm.
Female sexual maturity was at 5–20 DAE, the first
oocytes were observed at 11–28 DAE, chorionated
eggs first appeared at 25 DAE, and first oviposition
occurred at 27–41 DAE (Uzakah 1995). This suggests
that oocytes require about 2 weeks to mature. Only
mated females produced chorionated eggs (Uzakah
1995). In Tonga, 4% of the females were infertile
(Litsinger 1974).
First oviposition has also been reported at 7–10 days
(Treverrow & Bedding 1993), 21 days (Viswanath
1976), 33–36 days (Cuille 1950), and >60 days
(Pulido 1982). Froggatt (1925), Arleu (1982) and
Silva & Fancelli (1998) reported greater oviposi-
tion rates in young females, while Cuille (1950) and
Treverrow et al. (1992) found that females more than
1-year-old produced as many eggs as young females.
Biology and IPM for banana weevil 87
Viswanath (1976) observed maximum oviposition dur-
ing the 7th month with greatly reduced oviposition after
11 months.
8. Oviposition potential
The banana weevil has telotrophic ovaries with each
containing two ovarioles (Uzakah 1995; Nahif 1998),
although a few individuals may have only one ovar-
iole per ovary (Abera & Gold unpubl. data). There
is normally continual development of oocytes in
the ovaries (Froggatt 1925), although in the labora-
tory studies undernourished weevils ceased oviposit-
ing and their ovaries may became non-functional
(Cuille 1950; Cuille & Vilardebo 1963). Cuille (1950)
found 4 oocytes per ovary and suggested that food
deficiency arrests oviposition and leads to reabsorp-
tion. According to Nahif (1998), each calyx can
hold 4 eggs. In contrast, Uzakah (1995) and Abera
(1997) reported up to 17 (mean 5) and 22 (mean 10)
chorionated eggs, respectively, retained in the
calyces.
Dissections of 1140 females after being maintained
in the laboratory for 30 days on oviposition substrates,
revealed an average of 1.7 mature eggs (range 0–16),
2.0 medium-sized oocytes (range 0–10), and 4.9 small
oocytes (range 0–13) per weevil (Gold et al. 2002a,
unpubl. data). The total number of eggs and oocytes
averaged 8.5 (range 0–24).
9. Realised oviposition
Egg production of the banana weevil is low, with ovipo-
sition in the laboratory most commonly estimated at
1–4 eggs/week (Cuille 1950; Vilardebo 1960, 1984;
Cuille & Vilardebo 1963; Haarer 1964; Gordon &
Ordish 1966; Delattre 1980; Pulido 1983; Arleu &
Neto 1984; Treverrow et al. 1992; Minost 1992;
Treverrow & Bedding 1993; Koppenhofer 1993a;
Lemaire 1996) and 10–270 in the lifetime of the insect
(Cuille 1950; Viswanath 1976; Arleu & Neto 1984;
Castrillon 1989; Treverrow et al. 1992; Treverrow &
Bedding 1993; Aranzazu et al. 2000, 2001). In con-
trast, Montellano (1954) reported oviposition rates of 1
and occasionally 2 eggs/day. Further laboratory studies
in Uganda found oviposition rates of 4–14 eggs/week
(Rukazambuga 1996; Abera 1997; Griesbach 1999;
Gold et al. 2002a). Females may also pass extended
periods without any oviposition (Cuille 1950; Longoria
1972; Cardenas 1983).
In India, Viswanath (1976) found a mean ovipo-
sition of 43 eggs (range 36–53) in the lifetime of
the weevil. The oviposition period averaged 471 days
(range 313–556 days), suggesting 1 egg every 11 days.
Maximum oviposition (4 eggs/month) occurred dur-
ing the 7th month. Females more than 11 months old
produced less than 1 egg/month. All oviposition was
at night. The post-oviposition period lasted 35 days
(range 14–57 days).
Under field conditions near Kampala, Uganda,
oviposition was estimated at 0.5–1.4 eggs/week (Abera
1997). Seasonal effects on ovipositionare unclear.
Uzakah (1995) found oviposition rates related to
temperature but not to relative humidity or rain-
fall. However, Cuille (1950) and Cuille & Vilardebo
(1963) reported oviposition of 7.8 eggs/female/month
in the rainy season and 0.4 eggs/female/month in
the dry season. Similarly, Nonveiller (1965) and
Simmonds (1966) report reduced oviposition in the dry
season.
Although Uzakah (1995) found no relationship
between female size and egg production, Griesbach
(1999) reported smaller weevils produce fewer
eggs. Griesbach divided field-collected banana weevil
females into ‘large’ (mean weight 0.11 g) and ‘small’
(mean weight 0.06 g) individuals. The large females
laid significantly more eggs (mean = 0.43/day) than
small females (0.28/day) (T = 4.76; p < 0.01).
Large weevils also produced significantly larger eggs
(0.47 mg) with higher rates of eclosion (81%) than eggs
produced by small weevils (0.41 mg; 73%).
In a separate experiment, Abera et al. (unpubl. data)
found that large and small field-collected weevils con-
tained similar numbers of chorionated eggs (4.0 and
4.3). When held in the laboratory for 2 or 6 weeks
without exposure to an oviposition substrate, larger
weevils maintained twice as many chorionated eggs
(10.5 and 11.3, respectively) as did small weevils (5.0
and 4.6). These data suggest that weevils reabsorb eggs
and oocytes and that the rate of reabsorption may be
greater for smaller individuals.
In Uganda, available data suggest that weevils are
more active under conditions of higher soil moisture
(i.e. rainy season or under mulches) and it is likely that
oviposition is greater at this time. Ovipisition rates may
also be influenced by weevil density and temperature
(Rukazambuga 1996; Silva & Fancelli 1998; Gold et al.
2002a, unpubl. data). In Brazil, for example, Silva &
Fancelli (1998) report higher oviposition rates at 24◦C
than at 28◦C.
88 C.S. Gold et al.
In summary, weevil dissections indicate that females
produce four or more oocytes per week, have the capac-
ity to store eggs until a favourable substrate is found
and can reabsorb eggs under unfavourable conditions.
However, realised oviposition in the field may be con-
siderably less than the weevil’s potential fecundity.
Why this may be is unclear since banana stands con-
tain an abundance of host substrate for oviposition. Low
oviposition rates may, in part, explain the slow build-up
of weevil populations over time. It also suggests that
strategies targeting adults may have a long-term impact
on weevil numbers and subsequent damage.
10. Oviposition preferences: Timing of attack
Timing of oviposition with respect to host phenolog-
ical stage has implications for understanding yield
loss (e.g. possible critical periods of attack), screen-
ing methods for host plant resistance (larval success
may vary by age of plant), timing of interventions and
strategies for managing crop residues (i.e. sanitation).
Banana weevils oviposit on all stages of banana
plants ranging from peepers (i.e. newly emerged
suckers) to crop residues (Abera et al. 1999). Females
are attracted to freshly cut corms making young
suckers, recently detached from mother plants, espe-
cially vulnerable. Suckers planted in or proximal to
infested fields may fail to establish due to weevil attack
(McIntyre et al. 2002).
Vilardebo (1973, 1984), Haddad et al. (1979) and
Mesquita & Caldas (1986) suggested that oviposit-
ing weevils favour plants during flowering and
bunch maturation. In the laboratory, Cerda et al.
(1995) found weevils oriented more towards corms
of flowered than of pre-flowered plants. In contrast,
Cuille (1950) reported that the weevil prefers to
oviposit on young plants, while Treverrow & Maddox
(1993) noted heavy attack on pre-flowered plants.
Ittyeipe (1986) suggested that ovipositing weevils
do not discriminate among bananas on the basis of
plant age. In a field trial in Uganda (cv Atwalira,
AAA-EA), weevils released at a density of 20 per mat
oviposited on 23% of peepers (0.6 eggs/plant), 35% of
maiden suckers (1.2 eggs/plant), 74% of pre-flowered
plants (6.0 eggs/plant), and 90% of flowered plants
(13.8 eggs/plant) (Abera et al. 1999). Egg density per
unit surface area was 2.5–4 greater on flowered plants
than earlier stages.
The banana weevil will also oviposit in crop residues
(Froggatt 1925; Vilardebo 1960; Koppenhofer 1993a;
Gold & Bagabe 1997; Abera et al. 1999). Prostrate
stems are considered favoured breeding grounds for
the weevil (Treverrow & Maddox 1993). Abera et al.
(1999) found oviposition on 88% of the residues of har-
vested highland banana plants (19 eggs/plant), while
Rukazambuga (unpubl. data) collected 200 eggs from
a single stump (cv Atwalira).
In Uganda, the cultivar Kisubi (AB, Ney Poovan sub-
group) is resistant to banana weevil attack, yet high lev-
els of damage may be found in crop residues (more so
on prostate rather than standing stems) (Gold & Bagabe
1997). In Indonesia, Gold & Hasyim (pers. observ.)
found up to 100 larvae on prostrate stems, while stand-
ing and recently harvested stumps were virtually free
of attack. Abera (1997) and Kiggundu (2000) sug-
gested that damage on residues of resistant clones
reflect larval success rather than ovipositional prefer-
ences. This would imply the breakdown of biochemical
(antibiotic) defences following harvest. Greater suc-
cess on prostrate stems may also reflect exposure of the
true stem to ovipositing females. Banana weevil larvae
prefer to feed on the corm and true stem and are uncom-
monly found feeding in the pseudostem. In contrast,
young weevil larvae on stumps and unharvested plants
often have to tunnel from oviposition sites through the
pseudostem to reach their preferred feeding sites.
Montellano (1954) found eight times as many eggs
on fresh versus decomposing corms, while tissues in
states of advanced deterioration were rejected entirely.
However, Masanza (unpubl. data) found oviposition on
moist residues up to 120 days after harvest, although
most oviposition was on residues less than 30 days old.
11. Oviposition sites
Eggs (0.5 × 2 mm2) are deposited singly in the host
plant in orifices (1–2 mm deep) excavated by the
female weevil with her rostrum. Oviposition sites have
been described by many authors although few stud-
ies have quantified egg distribution within the plant
under field conditions. In general, it is believed that
oviposition is usually at the base of the plant, at or
near soil level, in the leaf sheaths at the base of the
pseudostem (Jepson 1914; Moznette 1920; Jardine
1924; Pinto 1928; Harris 1947; Swaine 1952;
Montellano 1954; Viswanath 1976; Arleu 1982;
Suplicy Fo & Sampaio 1982; Arleu & Neto
1984; Pinese & Piper 1994; Pavis & Lemaire 1997;
Abera 1997), in leaf scars (Saraiva 1964; PANS
1973; Treverrow 1985; Allen 1989; Waterhouse &
Sands 2001), the corm (Pinto 1928; Montellano
1954; Beccari 1967; Koppenhofer 1993a; Abera 1997;
Biology and IPM for banana weevil 89
Silva & Fancelli 1998; Nkakwa 1999; Castrillon 2000;
Gold & Kagezi unpubl. data), and in the weevil gal-
leries in the interior of the corm (Montellano 1954;
Martinez & Longoria 1990; Koppenhofer 1993a).
Oviposition on roots is uncommon (Abera 1997).
There is some disagreement whether eggs are placed
above or below the soil surface. Oviposition place-
ment may be influenced by weather, plant stage, the
presence or absence of high mat and the availability
of crop residues (Koppenhofer 1993a; Abera 1997).
The location of eggs will affect vulnerability to nat-
ural enemies (Koppenhofer 1993a); those below the
soil surface are likely to be relatively protected against
possible parasitoids and predators. In laboratory exper-
iments, Cuille & Vilardebo (1963) found 69% of the
eggs on the corm with the remainder on the pseu-
dostem. Of those in the corm, 16% were in basal third,
31% in the middle, and 53% in the upper third. In pot
trials, Koppenhofer (1993a) found egg distribution to
be 33% in crown area, 5% superficially in base of roots,
29% insideof abandoned tunnels, 22% in remaining
parts of corm, and 11% in base of leaf sheaths. The
majority of eggs were below the soil surface, with both
adults and eggs found to a depth of 50 cm.
In field studies, Abera (1997) found 96% of eggs
on plants without high mat to be in the leaf sheaths,
4% in the corm and 1% on the roots. Seventy-five
percent of the eggs were placed below the soil surface.
Oviposition reached 15 cm above the collar although
60% of the eggs on the pseudostem were <5 cm above
the collar. High mat increased both total oviposition,
the proportion of eggs on the corm and the percent-
age of eggs placed above the ground (Abera 1997).
Koppenhofer (1993a) estimated that 50% of the eggs
were accessible to predators, while Abera’s (1997) data
suggest that a lower percentage of eggs may actually
be vulnerable to predation.
Crop residues are also attractive to ovipositing
weevils. On prostrate stems, most eggs are placed
within 12–18 inches of basal end or, if part of the corm
is attached, just above the crown (Froggatt 1925). Most
eggs placed on residues are probably vulnerable to
natural enemy attack.
VI. Development of Immatures
Banana weevil developmental rates determined under
ambient temperatures (reviewed by Schmitt 1993;
Traore et al. 1993) show wide variability in stage
duration: 3–36 days for eggs, 12–165 days for larvae,
1–4 days for prepupae, 4–30 days for pupae, and
24–220 days from egg to adult. The longest stage dura-
tions were found in Australia where seasons are pro-
nounced and the range in weevil development times
large: In cold seasons, development rates were up to
four times as long as recorded anywhere else. While
temperature is certainly the most critical factor in deter-
mining developmental rates, relative humidity, cultivar,
age of plant, food quality, and population density may
also be involved (Mesquita et al. 1984; Schmitt 1993).
1. Egg stage duration and eclosion rates
Most studies on egg stage duration have been con-
ducted under ambient temperatures. Under tropical
conditions, the egg stage has been most commonly
found to last 6–8 days (Pinto 1928; Cuille
1950; Montellano 1954; Vilardebo 1960; Saraiva
1964; Woodruff 1969; Longoria 1972; Viswanath 1976;
Mesquita & Alves 1983; Pinese & Piper 1994;
Vittayaruk et al. 1994; Seshu Reddy et al. 1998; Gold
et al. 1999d), although some researchers reported an
egg stage of 8–10 days (Montellano 1954; Vilardebo
1960; Ingles & Rodriguez 1989; Padmanaban et al.
2001). However, eclosion may occur in as few as
3–4 days (Froggatt 1924; Cuille 1950; Longoria 1972;
Franzmann 1976; Mesquita & Alves 1983; Pinese &
Piper 1994) or as many as 14–15 days (Montellano
1954; Vilardebo 1960; Trejo 1969; Mesquita & Alves
1983).
In Cotonou, Benin (mean temperature 26.8◦C),
Traore et al. (1993) monitored egg stage duration
under six constant temperatures ranging from 15◦C
to 34◦C and determined a developmental threshold
of 12◦C and thermal requirement of 89 degree-days.
The duration of the egg stage decreased from 35 days
at 15◦C to 5 days at 30◦C. Highest rates of eclo-
sion occurred between 25◦C and 30◦C. Eggs did not
hatch above 32◦C. In Brazil, Ferreira (1995) deter-
mined egg stage duration to be seven to nine days (mean
8.0 days) at 25◦C.
Local biotypes may exist and immatures may display
optimal development at the prevailing temperatures for
a given site. Nevertheless, estimates of degree-day ther-
mal requirements for banana weevil eggs in Kampala,
Uganda (mean temperature 22.5◦C) (Gold et al. 1999c)
suggested conformity to developmental periods estab-
lished for West African banana weevil populations by
Traore et al. (1993).
Eclosion rates of over 80% have been recorded
(Bakyalire 1992; Griesbach 1999) and it is likely that
90 C.S. Gold et al.
field eclosion on susceptible cultivars may approach
100%. However, in the laboratory, egg mortality
may be very high (Gomes 1985; Minost 1992;
Ogenga-Latigo 1992; Traore et al. 1993; Treverrow &
Bedding 1993; Lemaire 1996; Carnero et al. 2002)
due to handling, desiccation, and fungal attack.
Koppenhofer & Seshu Reddy (1994) found lower
hatchability for eggs in pseudostems, possibly due
to higher water content or metabolites. Kiggundu
(2000) suggested that viscosity and metabolites of
plant sap in resistant clones might also reduce egg
success.
2. Larval stage
a. Distribution, feeding, and damage
First-instar larvae emerging in the leaf sheaths tend
to move downward into the corm. Jardine (1924),
Vilardebo (1960), Ittyeipe (1986), and Sponagel et al.
(1995) suggested that the larvae prefer the cortical tis-
sue to the central cylinder. In Ugandan surveys, Gold
et al. (1994b) estimated damage to the central cylin-
der and cortex in 7000 recently harvested plants and
found that 43% of weevil damage in plantain was in the
central cylinder compared to 36% in highland banana,
26% in Pisang awak, 22% in Gros Michel, and 17% in
AB clones. Within the highland banana group, the pro-
portion of damage found in the central cylinder ranged
from >40% of total damage in Namwezi, Muskala,
and Nakitembe to 25% in Kibuzi, Mbwazirume, and
Nakyetengu.
The larvae feed throughout the corm but there is
limited information on their vertical distribution rel-
ative to the soil surface and distance below the col-
lar. In the Ugandan surveys, Gold et al. (unpubl. data)
consistently found greater damage at 10 cm below
the collar than at the collar. Englberger & Toupu
(1983), Price (1994), and Gold & Kagezi (unpubl. data)
found highest levels of damage on the lower third of
the corm.
The larvae may also enter the true stem after flower-
ing. In severe attacks, the larvae may feed on leaf tis-
sue in the pseudostems or move from the mother plant
into young suckers (Vilardebo 1960; Champion 1975;
C. Gold pers. observ.). In exceptional circumstances,
larval galleries can reach 30–100 cm above the collar
(Moznette 1920; Sen & Prasad 1953; Treverrow 1985).
In one case, Froggatt (1925) observed three larvae in
the stalk of the fruit.
Measuring gallery size is difficult because of
the larva’s meandering feeding habit within the
corm. Beccari (1967) suggested that first-instar lar-
vae tunnel 7–8 cm before moulting. Maximum gallery
diameter has been reported to range from 0.8 cm
(Sponagel et al. 1995; Seshu Reddy et al. 1998) to
1.2 cm (Montellano 1954), while gallery length has
been variously reported as 30 cm (Treverrow 1985),
60 cm (Cuille 1950), 63 cm (Montellano 1954), 70 cm
(Beccari 1967), 120 cm (Sponagel et al. 1995), and
150 cm (Seshu Reddy et al. 1998). The wide range in
reported gallery size makes it difficult to estimate the
number of larvae that cause observed levels of damage
in a corm.
b. Instars
The banana weevil has been variously reported to
have 5 (Cendana 1922; Beccari 1967; Lemaire 1996;
Carnero et al. 2002), 6 (Cuille 1950; Montellano 1954;
Koppenhofer et al. 1994), 7 (Viswanath 1976; Pulido
1982; Ferreira 1995), 4–6 (Traore et al. 1996), 4–7
(Mestre 1997), 5–7 (Schmitt 1993), 5–8 (Mesquita
et al. 1984; Mesquita & Caldas 1986; Gold et al.
1999c), or 6–7 instars (Cuille 1950; Arleu & Neto
1984). The variable number of larval instars in some
studies suggest that banana weevils may display devel-
opmental polymorphism, i.e. the occurrence of instar
number other than those which are thought to be
‘customary’ for a particular species (c.f. Schmidt &
Lauer 1977).
Developmental polymorphism in banana weevil has
been attributed to temperature (Schmitt 1993; Traore
et al. 1996), nutrition (Cuille & Vilardebo 1963), clone
(Haddad et al. 1979; Mesquita et al. 1984; Mesquita &
Caldas 1986), plant stage (Mesquita et al. 1984;
Mesquita & Caldas 1986), and rearing method (Gold
et al. 1999c). Adverse conditions or resistant clones
increased the numbers of moults, prolonged stage dura-
tion and resulted in smaller pupae (Mesquita & Caldas
1986; Gold et al. 1999c).
Gold et al. (1999c) set up frequency distribution
polygons of head capsule-widths to separate instars
for laboratory-reared and field-collectedlarvae. Mean
head capsule-widths for the first four instars showed
close agreement among laboratory-reared and field-
collected populations. The method of analysis was not
sensitive enough to separate later instars. However,
field-collected larvae were larger than those reared in
the laboratory, thus forming distinct frequency distri-
bution curves. Traore (1995) and Sponagel et al. (1995)
also present ranges of head capsule sizes for different
instars but did not attempt to fit these sizes to frequency
distribution curves.
Biology and IPM for banana weevil 91
c. Larval stage duration
Using weevils collected in southern Benin and Onne,
Nigeria, Traore et al. (1996) determined developmental
thresholds and thermal requirements for each instar for
larvae kept under five constant temperatures ranging
from 16◦C to 30◦C. The total larval period (including
prepupal stage) was inversely related to temperature
ranging from 34 days at 30◦C to 70 days at 16◦C.
Development in each of the six observed instars showed
a similar inverse relationship with temperature. The
developmental threshold for the larval stage was 8.8◦C
with a total thermal requirement of 538 degree-days.
Optimal development occurred at 29.6◦C. Stage dura-
tion was progressively longer for later instars. However,
in this study, the prepupal stage was not differentiated
from the sixth instar.
Ferreira (1995) determined the duration of each
instar at a single temperature, 25◦C, while Viswanath
(1976) and Gold et al. (1999c) measured instar dura-
tion under ambient conditions in India (in different
months with temperatures not reported) and Uganda
(20–27◦C), respectively. Combining the results of these
three studies suggest that the relative proportion of time
spent in each instar was: first instar (10%); second instar
(11%); third instar (13%); fourth instar (14%); fifth
instar (15%); >sixth instar and prepupa (37%).
Under ambient temperatures in tropical environ-
ments, the larval stage has been variously reported
as 2–3 weeks (Moznette 1920; Seshu Reddy et al.
1998), 2–6 weeks (Simmonds 1966; Gordon & Ordish
1966; Anonymous 1989), 3 weeks (de Villiers 1973;
Waterhouse & Norris 1987), 3–5 weeks (Castrillon
2000), 4 weeks (Gomes 1985), 5 weeks (Vittayaruk
et al. 1994), 3–6 weeks (Godonou 1999), 4–5 weeks
(Carnero et al. 2002), 4–7 weeks (Longoria 1972),
4–8 weeks (Trejo 1969; Mesquita & Caldas 1986),
5–8 weeks (Padmanaban et al. 2001), 6 weeks (Ingles &
Rodriguez 1989), 6–7 weeks (Cuille 1950), 7–8 weeks
(Ferreira 1995), 6–9 weeks (Castrillon 1991; Aranzazu
et al. 2000, 2001), 7–10 weeks (Padmanaban et al.
2001), 7–17 weeks (Montellano 1954), 11–13 weeks
(Velasco 1975). In Australia, the larval period can
last 23 weeks during winter months (Froggatt 1924).
Mesquita et al. (1984) and Mesquita & Caldas (1986)
determined the prepupal stage to be about 3 days, while
Gold et al. (1999c) found it to be 4 days.
High variability in larval stage duration has even
been observed at the same locality, suggesting the influ-
ence of food source and rearing methods on develop-
mental rates. At one site near Kampala, Gold et al.
(1999c) found the total larval and prepupal period
averaged 25 days. Rearing the larvae on thin corm slices
(precluding formation of galleries) extended this to
36 days. In contrast, Bakyalire (1992), working 20 km
away and at a similar elevation, found the larval (and
prepupal) period to range from 41 days (laboratory) to
51 days (screenhouse).
The duration of the larval stage may be affected by
climate, food source, weevil density, and plant stage
(Arleu & Neto 1984; Mesquita et al. 1984; Mesquita &
Caldas 1986). For example, Mesquita & Caldas (1986)
found the larval period was shorter on younger plants.
Our calculations on their presented data for differ-
ent clones show a mean larval stage of 29 days on
young plants, 44 days on flowered plants and 52 days
on crop residues. The larval period also ranged from
35 to 44 days when different clones were used as
hosts.
d. Survivorship or survival
Larval survivorship or survival in the laboratory may
be reduced by handling and/or deterioration of the food
source (Mestre 1997). However, Mesquita & Caldas
(1986) successfully reared 87% of larvae to the pupal
stage on young plants, 67% on flowered plants and 50%
on crop residues. In addition, the developmental period
was longer and pupal weights lowest on residues,
suggesting this to be an inferior quality food. Traore
et al. (1996) successfully reared 50% of the larvae
tested, with greatest mortality occurring in the first two
instars. This may have reflected disturbance during the
handling of small larvae.
Under field conditions, mortality in the egg and first-
instar stages appears to be high. Abera (1997) found
6–12 times as many eggs as mid- to late-instar lar-
vae during dissections of banana mats. Concurrent with
low oviposition rates, this may contribute to the slow
population build-up and greater importance of banana
weevil in ratoon crops (Mitchell 1980; Lescot 1988;
Rukazambuga 1996).
3. Pupal stage
Pupation is in a bare chamber excavated by the larvae
near the corm surface of the host plant (Vilardebo 1960;
Longoria 1972). Godonou (1999) found all pupae to be
in the corm and most to be >5 cm below the collar.
In Benin, the pupal stage ranged from 5.5 days at
30◦C to 23.0 days at 16◦C, with 10–19% mortality
(Traore et al. 1996). The developmental threshold was
10.1◦C with a thermal requirement of 121 degree-days.
Optimal development occurred at 33.3◦C.
92 C.S. Gold et al.
Ferreira (1995) estimated the duration of the pupal
stage at 25◦C to be 8.3 days. Under ambient tropi-
cal conditions, the pupal stage has been most com-
monly reported at 6–8 days (Froggatt 1925; Vilardebo
1960; Haarer 1964; Saraiva 1964; Longoria 1972;
de Villiers 1973; Viswanath 1976; Mesquita & Alves
1983; Mesquita et al. 1984; Ingles & Rodriguez
1989; Pinese & Piper 1994; Seshu Reddy et al. 1998;
Godonou 1999; Castrillon 2000; Carnero et al. 2002)
although stage durations of 6–12 days (Aranzazu et al.
2001), 9 days (Padmanaban et al. 2001) and 11–13 days
have also been reported (Montellano 1954; Gomes
1985).
VII. Distribution and Population Dynamics
1. Population density and severity of attack
Densities of adult banana weevils in banana stands
have been estimated by mark and recapture methods.
In Cameroon, Delattre (1980) estimated weevil densi-
ties in two fields to be 15,600/ha and 2600/ha, respec-
tively; density within the fields varied from 1.1 to
37.4 weevils/m2. Assuming a plant spacing of 3×3 m2,
this would represent a range of 10–337 adults per mat.
In Mubende district, Uganda, Gold & Bagabe
(1997) estimated weevil density at 900 adults/ha
(3.4/mat) in a stand of cooking banana (cv Kibuzi,
AAA-EA) and 2100/ha (4.8/mat) in an adjacent stand
of brewing bananas (Kisbui, AB, Ney Poovan sub-
group), while Rukazambuga (1996) found a density
of 19,000 adults/ha in a banana stand (cv Atwalira,
AAA-EA) in Mpigi District. In Uganda surveys, high
variability in weevil numbers and damage were also
found among farms within-sites (Table 2). For exam-
ple, population estimates ranged from 850 weevils/ha
(1.5 weevils/mat) to 149,000 (240 weevils/mat) (Gold
et al. 1997; Tinzaara & Gold unpubl. data).
Table 2. Estimated banana weevil population densities per
hectare at selected sites in Uganda (N = 50–60 farms per site)
Site Range Median weevil
number per matLow High Median
Ntungamo1 1600 149,000 9300 15
Ntungamo2 2200 44,900 7900 13
Mbarara 850 15,000 3500 6
Masaka 2000 41,000 10,000 17
1Survey conducted in 1996.
2Survey conducted in 1998.
Sources: Gold et al. (1997), Masanza et al. (unpubl. data), Gold
et al. (unpubl. data).
This within-site variability suggests that manage-
ment plays an important role in regulating weevil pop-
ulations. Weevil pressure has been widely believed to
be associated with low levels of management, stressed
plants, bad drainage, acid or low fertility soils, weedy
fields, inadequate sanitation, extended droughts,and
nematode infestations (Froggatt 1925; Veitch 1929;
Wallace 1938; Harris 1947; Gordon & Ordish 1966;
Ostmark 1974; Loebel 1975; Yaringano & van der Meer
1975; Firman 1970; Ambrose 1984; Van den Enden &
Garcia 1984; Mesquita & Caldas 1986; Sebasigari &
Stover 1988; Allen 1989; Boscan de Martinez & Godoy
1989; Sikora et al. 1989; Bakyalire 1992; Treverrow
et al. 1992; Speijer et al. 1993; Garcia et al. 1994;
Pinese & Piper 1994; Stanton 1994; Gowen 1995;
Sponagel et al. 1995; Schill et al. 1997). In central
Uganda, farmers associated increasing banana weevil
pressure with reduced management, and cited this as
an important factor in the decline and disappearance
of highland cooking banana in the region (Gold et al.
1999b).
In the Ntungamo survey, however, characterisation
of study farms failed to reveal any important rela-
tionships between management practices and weevil
severity (Gold et al. 1997). Additionally, Rukazambuga
(1996) and Rukazambuga et al. (2002) found sim-
ilar levels of weevil attack in stressed (intensively
intercropped) and vigorous (mulched) banana systems
(see below). Within banana stands, neither Treverrow
(1993) nor Rukazambuga (1996) found any evidence
to suggest that smaller or thinner plants were predis-
posed to greater levels of weevil attack than occurred
in healthier plants. Moreover, weevil adult populations
may be as much as 2.5 times higher in mulched than
in unmulched plots because of more favourable soil
moisture conditions (Price 1994; Rukazambuga et al.
2002).
In Ghana, weevil damage in plantain stands was
often low in spite of susceptible germplasm, favourable
temperatures and low management levels (Schill 1996).
Shifting agricultural systems predominated with most
plantain abandoned after two crop cycles. As such,
short plantation life may preclude adequate time to
allow weevil populations to build up to damaging lev-
els. Weevil problems became increasingly evident in
plantain stands maintained beyond two cycles (Schill
1996).
In Uganda, weevil damage was very variable
across survey sites (Gold et al. 1993, 1994a, 1999b).
Damage was especially severe throughout much of
the central zone where banana stands received limited
Biology and IPM for banana weevil 93
management attention and banana was in rapid decline.
In these areas, banana weevil damage averaged 10% of
surface area in the cortex and in the central cylinder
(as measured in cross cut sections, Gold et al. 1994b).
Elsewhere, however, it was difficult to discern why
some sites had higher levels of weevil damage than
others.
2. Population build-up
Banana weevils have limited dispersal capacity and
are most often disseminated through infested planting
material. However, suckers used as planting material
usually support only a small number of weevil eggs
and larvae (Gold et al. 1998a; Abera et al. 1999), so
initial populations are often low. With low fecundity,
weevil build-up tends to be slow and several cycles may
be required before populations are fully established
(Arleu & Neto 1984). In a survey of 52 sites in Ghana,
Schill (1996) found cross section damage increased
from 2% in the plant crop, to 3% in the first ratoon and
7% in the second ratoon. However, a large population
of banana weevils may quickly become established in
new banana stands placed in or near previously infested
fields.
In Uganda, Rukazambuga (1996) monitored popula-
tions with mark and recapture methods for 3 years fol-
lowing release of 8750 weevils (mean of 9 weevils/mat)
in a field trial 9 months after planting and 3 months
before flowering. The released weevils had been col-
lected from traps in a farmer’s field and were of uncer-
tain age distribution. The population initially declined
by 44% to 4904 weevils at 8 months after release, then
recovered to 9632 weevils at 12 months after release
and peaked at 19709 weevils 32 months after release
(a 4.5-fold increase in 24 months). Median cross sec-
tion damage levels increased from 7% in the first ratoon
to 10% in the second ratoon and >20% in the third
ratoon.
With existing estimates of weevil longevity, disper-
sal capacity and fecundity, slow rates of population
build-up in young stands, and population fluctuations in
established plantations suggest either high mortality in
the egg and larval stages and/or the influence of density
dependent factors on oviposition and survivourship.
In laboratory rearing experiments, Mesquita &
Caldas (1986) reported 17–50% mortality in the larval
stage and 11–16% in the pupal stage, while Bakyalire &
Ogenga-Latigo (1992) found 27–38% mortality in the
egg stage, 9–23% in the larval stage and 0–4% in the
pupal stage. Traore (1995) observed 43–53% mortality
in the larval stage, primarily in the first two instars. Lar-
val performance will be influenced by clone and host
plant defence mechanisms. Under field conditions, sap
or other antibiotic factors might cause additional mor-
tality to the egg and first-instar larvae that might not be
realised in the laboratory (Kiggundu 2000). It is unclear
how environmental factors might influence plant
defence and mortality levels of weevils immatures.
3. Adult populations and damage
Shillingford (1988) and Gowen (1995) have suggested
that weevil adult density may not be closely related to
damage levels. Gold et al. (1997) estimated weevil pop-
ulations, percentage weevil damage and area (i.e. cm2)
damaged (i.e. to account for between-farm differences
in plant size) in cross sections of recently harvested
plants on 50 farms in Ntungamo district, Uganda.
Further analysis of the survey data sets revealed poor
relationships between weevil populations and percent-
age damage (r = 0.11) and between weevil popula-
tions and area damaged (r = 0.22) (Gold et al. unpubl.
data).
These data have implications for control strategies
of banana weevil. Methods targeting adult weevils
may require a considerable lag time before popula-
tion reductions are translated into reduced damage and
increased yields.
4. Density dependence
Two factors suggest the possible existence of density
dependence effects on banana weevil oviposition in
the field. First, the rate of population build-up is often
slower than expected, given the adult’s longevity and
limited dispersal capacity. Second, weevil damage may
be poorly related to population density suggesting the
possibility of reduced oviposition at higher densities
(see below). However, Koppenhofer (1993a) felt that
densities under field conditions would never reach the
point of adversely affecting oviposition rates, in light of
the weevil’s low reproductive potential and abundance
of host plants.
Density dependent effects on banana weevil oviposi-
tion were first reported by Cuille (1950) who found that
grouped weevils produced only 28–38% as many eggs
as isolated individuals. Dissections of grouped females
showed they had fewer oocytes (of which some were
malformed) than ungrouped weevils.
Rukazambuga (1996) compared oviposition rates
over 4 weeks for densities of 2, 5, 10, 20 and 40 females
94 C.S. Gold et al.
(with equal numbers of males) on potted plants.
Individual females at the highest two densi-
ties produced 3.5–4.4 eggs/week compared to
12.4–14.5 eggs/week at lower densities. As a result,
groups of 40 females produced only 4.9 and 2.3 times
as many eggs as groups of 2 and 5 females, respectively.
In another study (Gold et al. 2002a), offered pieces of
corm to different densities of weevils maintained in
buckets. Mean oviposition rates per female at densi-
ties of 10, 20, and 40 females per bucket were 29%,
37%, and 53%, respectively, lower than that at a density
of five females. Nevertheless, total oviposition for the
same groups was 1.4, 2.5, and 3.7 times higher than that
of the five-female group. Oviposition rates were sim-
ilar on corms changed daily and those changed every
5 days, suggesting that the presence of eggs did not
deter further oviposition. Under field conditions, esti-
mated oviposition per female declined with increasing
weevildensity with averages of 1.4 eggs/week at a den-
sity of 5 females/mat, 0.8 eggs/week at 20 females/mat
and 0.5 eggs/week at 40 females/mat (Abera 1997).
Koppenhofer & Seshu Reddy (1994) suggest that
high larval populations can result in cannibalism and
dwarfism of adults. In contrast, Gold et al. (2002a)
found larval survivourship was only slightly higher at
lower densities of immatures following insertion of
different densities of eggs or first-instar larvae into
banana corms. Gold et al. (2002a) concluded that
density dependent factors can influence oviposition
rates of individual weevils and survivourship of imma-
tures but are likely to exert only modest influence in
reducing banana weevil population growth under field
conditions. More likely, high mortality of weevil imma-
tures, independent of density, and/or higher rates of
adult mortality and emigration than previously pos-
tulated contribute to the slow population build-up of
this pest.
VIII. Semiochemicals
1. Host plant location
Olfactory cues may be utilised by banana weevils
in locating host plants, conspecifics and/or mates.
Cuille (1950) was the first to propose and test
‘chemotropisms’ of banana weevil. In a series of exper-
iments using lures and olfactometers, both male and
female weevils regularly oriented to corm material or
water, acetone and ether extracts of banana from dis-
tances of up to 20 cm. The weevils were more attracted
to pseudostem than to corm material, but oviposition
was greater on the latter. This suggested to Cuille that
olfactory cues were most important in host location,
while chemoreception played the predominant role in
host acceptance. Cuille concluded that chemorecep-
tion is probably more important than olfaction for a
sedentary insect like banana weevil.
Although Cuille (1950) and, later, Sumani (1997)
found greater attraction to pseudostems than corm,
traps containing corm material tend to be more effective
than those made from pseudostems alone. Moreover, it
has long been recognised that freshly cut corms or suck-
ers are especially attractive to the weevils (Sein 1934;
Franzmann 1976; Jaramillo 1979; Treverrow 1994).
In still-air olfactometers, both male and female
weevils oriented towards freshly chopped corm
and pseudostem material, as well as to associated
Porapak-trapped volatiles from susceptible highland
cooking (AAA-EA) and resistant dessert (AB) bananas
(Budenberg & Ndiege 1993; Budenberg et al. 1993b).
Males and females also showed similar electroan-
tennogram (EAG) responses to plant volatiles, suggest-
ing that weevil orientation is to food sources rather
than oviposition sites. Budenberg et al. (1993b) found
the weevils demonstrated a somewhat lower response
to resistant AB than to susceptible AAA-EA clones,
implying that antixenosis may contribute to host plant
resistance. However, in other studies, no differences
were found in attractivity to a wide range of clones
(Pavis & Minost 1993; Abera 1997; Kiggundu 2000).
Budenberg et al. (1993b) found that the major compo-
nents of trapped volatiles did not elicit any response
indicating that minor components are responsible for
weevil activity. Weevil orientation to plant volatiles
could be demonstrated over only a few centimetres
(Budenberg & Ndiege 1993; Budenberg et al. 1993b;
Braimah 1997).
Jones (1968) reported that banana weevils appear
to be highly attracted to certain lipophilic plant and
Annalose-11 volatiles from the cultivar Valery (AAA).
More recently, Ndiege et al. (1991) and Lemaire (1996)
identified mono- and sesquiterpenes as major compo-
nents of volatiles from pseudostems and attractive to
weevils. Ndiege et al. (1996a) found 1,8 cineole in
susceptible or tolerant bananas and absent in resistant
clones.
Using olfactometers and tests in laboratory arenas,
Braimah (1997) and Braimah & van Emden
(1999) found weevils were more attracted to dead
banana leaves that had undergone natural senes-
cence on the plant than to the corm or pseudostem
Biology and IPM for banana weevil 95
(i.e. their oviposition sites). Surprisingly, the weevils
were more attracted to dead yam leaves and equally
attracted to hay as to banana leaves. They then tested the
individual chemical components that had been identi-
fied (and previously tested collectively) by Ndiege et al.
(1991, 1996a) as attractants, repellents or arrestants in
searching behaviour of weevil. None of the chemicals
constituents tested were more attractive than a distilled
water control, while some acted as repellents. These
findings agree with those of Budenberg et al. (1993b)
and suggest that unidentified minor elements, non-
volatiles factors, and/or different proportions of volatile
components are required to attract banana weevils.
Braimah & van Emden (1999) concluded that banana
weevil attraction to host plants is a stepwise-mediated
process, by which senescing leaves draw weevils to the
vicinity of the host plant.
In other work on volatiles using choice chambers,
Padmanaban et al. (2001) found some attraction to
leaf sheaths, but that most weevils were attracted to
corm pieces or leaf sheaths treated with corm extracts.
Castrillon (2000) reported the weevil to be attracted to
volatiles from leaf veins and pseudostems, while Cerda
et al. (1995) and Reyes-Rivera (2000) found weevils
equally attracted to corms and pseudostems.
2. Pheromones and aggregation response
Cuille (1950) observed an aggregation response of
banana weevils that he attributed to both olfactory
and tactile cues. He reported that olfactory cues
brought weevils of the different sexes together, while
thigmotaxis stabilised aggregations.
Budenberg et al. (1993a) tested the presence of
pheromones by extracting volatiles from the head
spaces above males and females, and by surface washes
and extracts from the hindgut of each sex. These were
used in behavioural bioassays and EAG recordings.
Both sexes were attracted to and made longer visits
to live males and male volatiles. Both sexes also had
EAG responses to male volatiles and hindgut extracts,
while there was no response by either sex to female
volatiles, washes or extracts. These results suggested
that the males release an aggregation pheromone via
the hindgut that is attractive to both males and females.
Braimah (1997) confirmed the presence of a male
aggregation pheromone in male frass and hind parts.
He concluded that the males were first attracted to the
proximity of banana mats by dead leaves, followed by
shorter range attraction to the mats themselves and,
once arriving at the mat, produced a male aggregation
pheromone attractive to both sexes. In olfactometers,
weevils were more attracted to corm pieces which had
previously supported male and female feeding than to
controls or corms fed only on by females. Viana (1992)
also suggested that chemical cues from the host plant
were needed to stimulate pheromone production.
Following on the results of Budenberg et al. (1993a),
Beauhaire et al. (1995) identified and synthesised a
male-produced banana weevil aggregation pheromone.
Six male-specific compounds were isolated of which
80% was comprised by a single compound (C11H20O2)
with a formula as (1S∗, 3R∗, 5R∗, 7S∗) 2,8-dioxa,
3,5,7-trimethyl bicylo (3,2,1) octane 1d. This com-
pound, named sordidin, is related to known ketal
pheromones produced by scolytids. Mori et al. (1996)
identified the natural configuration of sordidin, while
Jayaraman et al. (1997) synthesised four isomers
(exo-B, endo-B, endo-A, exo-A) of sordidin. All four
occur naturally in ratio of 1 : 4 : 4 : 44. Exo-B and
exo-A evoked similar levels of antennal response in
spite of their proportional differences. Ndiege et al.
(1996b) and Jaramayan et al. (1997) found that a mix-
ture of isomers were more attractive than single iso-
mers. Wardrop & Forslund (2002) have also provided
a synthesis for sordidin.
The use of pheromones and attractive plant volatiles
(i.e. kairomones) as a means of controlling banana
weevil through mass trapping or in baits for delivery of
Beauveriabassiana was first proposed by Budenberg
et al. (1993a) and Kaaya et al. (1993). Jayaraman et al.
(1997) also suggested semiochemical-enhanced mass
trapping could overcome the low reproductive capac-
ity of the insect and lead to successful control. They
also suggested that pheromones could be used in the
delivery of entomopathogenic nematodes. Chemtica
International, Inc. in Costa Rica has begun commercial
production of banana weevil pheromones (enhanced
with kairomones) in a product called Cosmolure+
(Oehlschlager pers. comm.) which is being tested in
Latin America, India and Africa.
IX. Sampling Methods
Accurate assessment of banana weevil population
levels and damage are necessary to understand the
weevil’s pest status, for screening germplasm and as
a prerequisite in evaluating the impact of any inter-
vention strategies. Sampling of banana weevil is diffi-
cult and there are no agreed upon sampling protocols.
The seclusive behaviour of the adult weevils and the
96 C.S. Gold et al.
difficulties in measuring larval damage in the interior
of the corm (much of it below ground level) in a peren-
nial crop has resulted in a multitude of scoring and
evaluation systems. These include monitoring adult
numbers through trapping; measuring damage to the
corm periphery; and measuring internal corm damage
(e.g. through cross and longitudinal sections). Some of
these methods are subjective, making it hard to interpret
results or to compare studies conducted by different
researchers.
Damage evaluations require destructive sampling
and are most often taken on recently harvested or dead
plants. However, the weevil is an indirect pest and
it is not clear what types of damage have the great-
est impact on yield. In evaluating sampling methods,
researchers should consider (1) ease of data collection;
(2) precision; (3) accuracy of population or damage
estimates; (4) degree of subjectivity and ability for
other researchers to interpret the data (5) reflection of
pest status (Gold et al. 1994b).
1. Trapping
Trapping of adults as a means of assessing banana
weevil population levels has been employed since
1912 (Knowles & Jepson 1912; Froggatt 1928; Cuille
1950) and continues to be widely used (Arleu 1982;
Bujulu et al. 1983; Allen 1989; Anonymous 1989;
Ogenga-Latigo & Bakyalire 1993; Mestre & Rhino
1997). Most commonly traps are made out of crop
residues (i.e. recently harvested corms and pseuod-
stems). A variety of trap types, including disk on
stump, corm disk, split pseudostem, sandwich, wedge,
and canoe, have been described by Castrillon (1989,
1991) and Aranzazu et al. (2000). Trap catches of up
to 50 weevils have been reported (Suplicy Filho &
Sampaio 1982).
Traps utilising corm material are generally more
attractive to banana weevils than those made from pseu-
dostems (Edwards 1925; Hord & Flippin 1956; Saraiva
1964; Martinez 1971). Yaringano & van der Meer
(1975), Cardenas & Arango (1986) and Moreira et al.
(1986) captured four to ten times as many weevils in
corm-based traps (e.g. disk on stump) than in pseu-
dostem traps. Most recommendations, however, con-
cern the use of pseudostem traps for which material is
more readily available and can be placed anywhere.
Traps made from the lower part of the pseudostem
(e.g. 30–70 cm above the collar) may be more attrac-
tive to weevils than those from higher on the plant
(Mestre & Rhino 1997). Adding crushed corm to
pseudostem traps can triple weevil captures (Bakyalire
1992).
Recommended trap densities for monitoring weevil
populations range from ≤10/ha (de Villiers 1973;
Crooker 1979; Castrillon 2000), 20–30/ha (Moreira
1979; Suplicy Filho & Sampaio 1982; Arleu 1983;
Castrillon 1991; Sponagel et al. 1995) to 40–60/ha
(Allen 1979; Arleu 1982; Peasley & Treverrow 1986;
Treverrow et al. 1992). Pest assessment based on
trap catches has operated on the assumption that
the numbers captured are proportional to the pop-
ulation size (Minost 1992). Action thresholds have
been suggested at >1 weevil/trap (McNutt 1974; Allen
1989), 2 weevils/trap (Mitchell 1978; Moreira 1979;
Treverrow et al. 1992; Pinese & Piper 1994 (southeast
Queensland)), 3 weevils/trap (Cuille & Vilardebo
1963), 4–5 weevils/trap (Pullen 1973; Arleu 1983;
Boscan de Martinez & Godoy 1989; Pinese & Piper
1994 (north Queensland); Treverrow 1993; Batista
Filho et al. 1995b; Smith 1995; Aranzazu et al.
2000), >6/weevils/trap (Stanton 1994) and (in Central
America) >15 weevils/trap (Roberts 1955; Vilardebo
1960; Pullen 1973; Anonymous 1989; Sponagel et al.
1995). However, few studies have related trap catches
to damage or to yield loss and there appears to be little
justification for any of these recommendations.
The use of trap catches as a means of assess-
ing banana weevil populations has been criticised by
Vilardebo (1960, 1973). With long adult life (estimated
at 10–18 months) and a slow rate of increase, weevil
populations should be relatively constant in established
stands. However, trap catches can vary by a factor of
3 or more within-sites during a single year. This sug-
gests that the number of weevils coming to a trap are
influenced by trap quality, humidity, temperature and
any other factors influencing the behaviour of insect.
For example, Bakyalire (1992) found that pseudostem
trap catches were affected by type of trap material
(clone, age), size, location, number, soil moisture, and
the elapsed time between setting and checking traps.
Trap catches may also be a poor indicator of eco-
nomic status if a high population estimate reflects
attack of residues rather than maturing plants. Gold &
Bagabe (1997) collected twice as many weevils from
traps in a stand of resistant beer banana (Kisubi, AB)
than in an adjacent stand of susceptible cooking banana
(Kibuzi, AAA-EA). Traps also provide no information
on which clones within a field may be most prone to
attack. Weevils may also have more effect on plants
with smaller corms. For example, Vilardebo (1960)
suggests that a given number of weevils cause 5 times
Biology and IPM for banana weevil 97
more damage on Gros Michel than on Cavendish due
to differences in timing of attack and corm size.
The use of different clones serving for trap material
can greatly influence weevil captures, although results
have not been consistent. Martinez (1971) reported that
traps from Giant Cavendish collected more weevils
(4.0/trap) than from Dwarf Cavendish (0.8/trap) and
that traps from harvested pseudostems caught more
weevils (4.9) than traps from young pseudostems
(2.7). Haddad et al. (1979) found traps from AAB
clones more attractive than from AAA clones. In
Uganda, traps made from Gros Michel attracted more
weevils (2.8 adults/trap) than traps made from high-
land cooking banana, plantain, Ndiizi, or Kayinja
(1.4–1.8/trap) (Bakyalire 1992), while in Kenya, traps
from highland cooking banana caught 2–12 times as
many weevils as traps from Gros Michel (K.V. Seshu
Reddy pers. comm). Gold & Bagabe (1997) collected
more than twice as many weevils in traps made from
Kisubi than from Kibuzi. Sumani (1997) reported trap
catches on Lusumba (AAA-EA) and Ndizi (AB) to
be more than twice those on Mbidde (AAA-EA) and
Nakyetengu (AAA-EA).
Trap placement can also influence trap captures.
Traps placed against banana mats caught four times as
many weevils as those placed >10 cm away (Bakyalire
1992). Traps next to older plants and stumps caught
4 times as many weevils than those proximal to younger
plants.
Recommended trap sizes have ranged from
25–30 cm (Schmidt 1965; de Villiers 1973; Bujulu et al.
1983; Masanza 1995), 40 cm (Batista Filho et al. 1990)
to 50–60 cm (Cuille & Vilardebo 1963; Simmonds
1966; Arleu 1982; Suplicy Filho & Sampaio 1982). In
one study, larger traps caught more weevils than smaller
traps, but smaller traps were twice as effective per unit
length than larger traps (i.e. 8.1 weevils per 35-cm trap;
2.7 weevils per 5-cm trap) (Bakyalire 1992).
Recommended collection time intervals following
placement of traps also vary: 1–3 days(Hord & Flippin
1956; Vilardebo 1960; Delattre 1980; Bakyalire 1992;
Aranzazu et al. 2000), 4–8 days (Wallace 1938; Cuille
1950; Mitchell 1978; Arleu 1982; Bujulu et al. 1983;
Treverrow 1985) to 14 days or more (Cardenas &
Arango 1986). Gold et al. (1997, 2001) used 3–5 day
intervals between placement of pseudostem traps and
weevil collection, as traps often deteriorated after
5 days (C. Gold pers. observ.).
In contrast, Mestre & Rhino (1997) found weevil
captures peaked at 7 days after trap placement
although numbers were statistically similar between
5 and 14 days. Weevils became increasingly concen-
trated under the true stem, which remained moist, com-
pared to under the leaf sheaths, which tended to dry out
over time. Equal numbers of males and females were
attracted to fresh traps (i.e. at 2 and 4 days), but males
constituted 63% and 57% of the weevils collected in
7- and 14-day-old traps, respectively. Mestre & Rhino
(1997) recommended collection of weevils 7–9 days
after trap placement.
A number of authors have reported a poor relation-
ship between weevil trap captures and corm damage
(Haddad et al. 1979; Crooker 1979; Ogenga-Latigo &
Bakyalire 1993). In one trial, trap catches had correla-
tions of 0.27 with peripheral damage to the corm and
0.05 and 0.28, respectively, with internal corm dam-
age estimates taken in cross and longitudinal sections,
respectively (Ogenga-Latigo & Bakyalire 1993).
In contrast, Mestre & Rhino (1997) found that dam-
age closely followed trap catches in the third and fourth
cycle of a trial. They concluded that trapping does
give a good indicator of damage and recommended
that this should be done at the time of plant flower-
ing. It is unclear, however, how this should be done in
established systems where flowering occurs through-
out the year. Moreover, all indications do suggest that
trap captures are clearly influenced by climatic and
other factors. For example, capture rates in one of
Mestre and Rhino’s trials varied over time from 1.5
to 5.0 weevils/trap, from 0.1 to 9.2 weevils/trap in a
second trial and from 0.6 to 8.5 weevils/trap in a third.
In a screening trial against banana weevil, Kiggundu
(2000) also found no relationship between trap cap-
tures at the base of the different clones and the damage
occurring in those clones. Similarly, Abera et al. (1999)
trapped comparable numbers of weevils on three high-
land cooking clones, two highland brewing clones
and Kayinja (ABB), yet each of the highland clones
had much greater damage levels than Kayinja. Batista
Filho et al. (1992) found similar trap catches (three
weevils/trap) on the banana clones Nanica and Prata,
even though Prata was found to be much more suscep-
tible to the weevil. Ogenga-Latigo & Bakyalire (1993)
found more weevils trapped on AB than AAA-EA
clones but 4–8 times more damage on the latter.
The relationship between trap catches and weevil
populations is likewise unclear. Reinecke (1976) found
four times as many weevils in uprooted plants than in
traps, while Cardenas & Arango (1987) suggest that
5–7 times as many weevils are attracted to the banana
mat as to traps. Due to the large variation in meth-
ods employed and environmental conditions, trapping
98 C.S. Gold et al.
provides imprecise estimates of weevil populations that
are inconsistent, statistically unreliable, and difficult
to compare and interpret (Ogenga-Latigo & Bakyalire
1993).
Weevil populations can be more accurately esti-
mated using standard mark and recapture methods
(Delattre 1980; Price 1993; Gold & Bagabe 1997; Gold
et al. 1997) including trapping, marking, releasing, and
subsequent re-trapping. Many adult weevils are inac-
tive for extended periods (S. Lux pers. comm.), sug-
gesting that a 1-week interval elapse between weevil
release and re-trapping to allow for a thorough mixing
within the field population. It is also important that an
adequate number of traps be placed randomly within
the banana stand.
Using mark and recapture methods, Price (1993) and
Rukazambuga (1996) found greater weevil density in
mulched plots than in unmulched plots, even though
trap captures were higher in the latter treatment. In
other words, trap efficiency was lower in the mulched
systems. These results highlight the weaknesses in
using simple weevil trap capture rates to estimate
weevil populations or to serve as action thresholds.
2. Plant damage
Assessment of weevil damage to banana corms requires
destructive sampling and is most often conducted on
harvested plants. In some clones (e.g. Kisubi), there is
substantial attack of residues (Gold & Bagabe 1997)
which will have no bearing on plant yield. Therefore,
it is important that sampling be done as soon after
harvest as possible. All existing sampling methods
measure cumulative weevil attack throughout the life
of the plant and cannot determine when this attack
occurred. Timing of attack must be inferred through
studies on oviposition (Abera 1997) and larval per-
formance (Mesquita & Caldas 1986) on different host
phenological stages.
a. Proportion of damaged plants
Vilardebo (1960) first proposed estimating the percent-
age of harvested plants with weevil damage in the
periphery as an alternative to trapping. He felt that a
proportion greater than 10% justified treatment.
Mestre (1997) and Mestre & Rhino (1997) com-
pared the percentage of plants attacked (grouped into
five classes) with an estimate of damage to the corm
periphery (modified from Vilardebo’s (1973) coeffi-
cient of infestation (CI) and grouped into four classes).
A strong curvilinear relationship and close correlation
(r = 0.98) existed between the two sets of values.
Based on this, Mestre proposed that percentage of
plants attacked is a better indicator of pest status than
actual damage measurements because it requires less
work. Heavy damage could be said to exist when more
than 50% of the plants have been attacked. However, in
Uganda surveys,>50% attack of plants was observed at
all sites under 1600 masl, even though peripheral dam-
age varied by a factor of >3 among sites (Gold et al.
1994a, unpubl. data). Moreover, no comparisons were
made in the Mestre (1997) study between the percent-
age of plants attacked and damage parameters (i.e. to
the central cylinder or cortex) that may have greater
impact on yield (Ogenga-Latigo & Bakyalire 1993;
Rukazambuga 1996).
b. Number of weevil tunnels
Vilardebo (1960) offered that visual observations on
larval damage are a better indicator of weevil pest status
than trap counts and recommended counting the num-
ber of galleries exposed on the corm periphery. Roman
et al. (1983) and Ogenga-Latigo & Bakyalire (1993)
counted tunnel points on cross sections through the
corm, while Treverrow et al. (1992) estimated the num-
ber of galleries >4 mm in diameter in 75% of the area
of a single cross section through the corm. Although
tunnel points are sometimes clear (especially at low
levels of damage), in many cases they are not, as they
may converge or be associated with rots.
c. Harvested plants – peripheral damage
Vilardebo (1973) was the first to propose using area
attacked as a means of estimating the degree of dam-
age to the plant. He suggested that this was preferable
to counting the number of galleries, which often con-
tained a high degree of error. According to Vilardebo,
weevil larvae prefer the upper cortical zone of the corm,
while under conditions of heavy attack, the larvae may
spread first to the lower parts of the corm, then the
interior of the corm and, finally, to the pseudostem and
followers. To measure this damage, Vilardebo (1973)
developed the ‘coefficient of infestation’ (CI) which
entails paring the corm below the collar to a depth of
1–2 cm. The CI then represents an estimate of the pro-
portion of the corm surface (i.e. 0–100%) with weevil
galleries. Although this is a destructive technique, it
can often be done ‘in situ’ with minimal damage to the
stability of the mat.
Vilardebo (1973) recommended a sample size
for estimating weevilpest status of at least
30 plants/ha/date. Vilardebo (1973) also provided rela-
tionships between trap catches and damage scores and
between damage scores and yield loss. However, it
Biology and IPM for banana weevil 99
is unclear how these relationships were determined
as no experimental designs, data sets or analyses
were described. Therefore, they must be regarded with
caution.
The CI has been widely used as a means of estimat-
ing weevil damage (Crooker 1979; Haddad et al. 1979;
Englberger & Toupu 1983; Kehe 1985; Lescot 1988;
Fogain & Price 1994; Smith 1995). However, the CI
scoring system was not clearly defined and remains
highly subjective, making interpretation of reported
scores difficult. A damage assessor must visualise a
grid by which he can evaluate the area of the corm with
weevil damage. This grid can be fine or coarse. As a
result, different scorers may assign a wide range of
values for similar levels of damage. Thus, it is unclear
if the CI values reported by researchers in Australia,
Cameroon, Cote d’Ivoire, Tonga, and Venezuela are
comparable.
To standardise the scoring system, Mitchell
(1978, 1980) developed a ‘percentage coefficient of
infestation’ (PCI). This method entails removal of
10 cm of topsoil and exposure of a band (7 cm wide
and 1
2
-cm deep) at the widest point of the corm.
Presence/absence of peripheral weevil damage is
recorded in 10 sections, each covering 18◦ of the corm
surface with the PCI representing the number of sec-
tions with weevil damage (i.e. 0–10). However, the PCI
tends to saturate quickly and may underestimate highly
clumped damage (Bridge & Gowen 1993; Gold et al.
1994b). Gold et al. (1994a,b) employed a modified PCI
by increasing the grid to 20 sections but found this pro-
vided no greater resolution in damage scores (i.e. the
correlation of the two PCI measurements was >0.9).
Given the weaknesses in both the CI and PCI meth-
ods, Gold et al. (1994b) developed a scoring system
for ‘peripheral damage’ that entailed paring the half
the corm for 10 cm below the collar and estimating
the percentage of surface area consumed by weevil
larvae (i.e. taken up by galleries). Other measure-
ments of peripheral damage include a coefficient of
health (Sampaio et al. 1982) and a mean CI (Mestre
1997) (both derived from the CI scale), a coefficient
of damage (Bujulu et al. 1983), and a weevil coeffi-
cient of infestation (WCI) based on the length of weevil
galleries (Bosch et al. 1996).
d. Harvested plants – internal damage
Internal damage within the corm is more likely to have a
greater impact on banana growth and bunch filling than
damage to the corm periphery. Moreover, the ability
of the weevil to penetrate the corm may be cultivar
related; as such, the CI and PCI serve as poor estimates
of internal corm damage (Ogenga-Latigo & Bakyalire
1993; Gold et al. 1994b).
Crooker (1979) was the first to measure internal
weevil damage to banana corms, which was done by
examining galleries in cross cuts (‘cut corm method’).
Mesquita (1985) proposed taking a longitudinal cut
on one-fourth of the corm circumference at its widest
point, with scores ranging from 0% to 100%. In both
methods, it is unclear if the scoring system was derived
from Vilardebo’s (1973) CI or represented the propor-
tion of surface area consumed by weevil larvae (i.e. in
galleries). Lescot (1988) employed the CI for tangential
cuts in the corm.
Taylor (1991) proposed adapting a presence/absence
scoring system for a grid applied to five sections
(i.e. modified PCI) of a transverse cut made at the
collar of the banana corm. Smith (1995) suggested
scoring presence/absence of nine sections in a similar
longitudinal cut in the corm periphery to that employed
by Mesquita (1985). Treverrow (1993) used cross sec-
tions, divided the surface into quarters and sampled all
but the quarter facing the follower. Damage was ranked
0–3 in the remaining quarters (giving a range of 0–9)
on the basis of the number of gallery points.
The most detailed scoring of internal damage was
carried out by Gold et al. (1994a,b) and Rukazambuga
(1996). Two cross cut sections were made (at the col-
lar and 10 cm below the collar). In each section, they
estimated the percentage of surface area consumed by
weevil larvae in the central cylinder and in the outer
cortex. In addition, the area of each section was esti-
mated by taking the diameter of the central cylinder and
of the corm. The central cylinder and cortex contain
roughly the same area (Rukazambuga 1996), allow-
ing the derivation of total internal damage to the cortex
(mean value of cylinder and cortex scores). These mea-
surements also allowed for conversion of percentage
area into square centimetres damaged.
In most cases, measurements of internal damage
require partially or totally digging out of the corm, with
resulting weakening of the stability of the mat. All of
the proposed sampling procedures measure damage to
the top 10 cm of the corm. However, damage may be
much more severe in the lower third than the upper
third of the corm (Englberger & Toupu 1983; Price
1994; Gold & Kagezi unpubl. data).
e. Harvested plants – damage scales
Many of the scoring systems are imprecise or
subjective. For example, the CI depends on the asses-
sor’s interpretation of the Vilardebo scale, while
presence/absence systems may saturate quickly and
100 C.S. Gold et al.
do not account for clumping of damage. Estimates
of the surface area taken up by weevil galleries are
more precise but remain subjective as the scorer must
determine what is weevil damage and then estimate
proportions.
Therefore, a number of researchers have indepen-
dently proposed or employed damage scales with
4–6 categories ranging from no attack to very severe
(Liceras et al. 1973; Bendicho & Gonzalez 1986;
Van den Enden & Garcia 1984; Treverrow et al. 1992;
Bridge & Gowen 1993; Price 1994; Pinese & Piper
1994; Sumani 1997). These scores are useful for com-
paring treatment effects within studies but may not be
replicable by different research teams.
X. Pest Status and Yield Loss
The banana weevil has been considered a major biotic
constraint in Africa (Persley & de Langhe 1987;
INIBAP 1988a,b; Gold et al. 1993), Asia and the Pacific
(Valmayor et al. 1994) and Latin America (Arleu &
Neto 1984; Mesquita et al. 1984; Arroyave 1985; Pena
et al. 1993; Schmitt 1993; Castrillon 2000). The banana
weevil has been implicated as an important cause
of the decline and disappearance of highland banana
(AAA-EA) in its traditional growing areas in East
Africa (Gold et al. 1999b; Mbwana & Rukazambuga
1999).
Yield losses to banana weevil have been associ-
ated with sucker mortality, reduced bunch weights and
shorter stand longevity. Ovipositing weevils are
attracted to cut corms (e.g. detached suckers used as
planting material), and can be serious pests during
the crop establishment phase. In newly planted fields
with existing weevil populations and no alternative host
stages, plant mortality may be high (Ambrose 1984;
Price 1994; Gowen 1995; McIntyre et al. 2002). A sin-
gle larva can kill a sucker if it attacks the growing point
(C. Gold pers. observ.).
In one trial in Uganda, 40% of newly planted, weevil-
free (i.e. pared and hot water treated) highland cooking
banana suckers were killed by banana weevils remain-
ing from an earlier trial (McIntyre 2002). Messiaen
et al. (2000) found mortality of weevil-free plantain
suckers at 34% in control plots during the first 3 months
after planting. Afreh-Nuamah (1993) also found high
mortality of suckers planted in clean fields, when plant-
ing material had been obtained from a heavily infested
field.
In fields with minor initial infestations of banana
weevils, population build-up is slow with problems
likely to become increasingly important in ratoon crops
(Reinecke 1976; Arleu 1982; Kehe 1985; Allen 1989;
Staver 1989; Afreh-Nuamah 1993; Rukazambuga et al.
1998; Gold et al. 1998b). Reinecke (1976) suggested
that yield reductions first appear in the second ratoon,while Allen (1989) reported weevil problems to be
relatively minor for 5 or 6 cycles. In a trial with high-
land cooking banana, Rukazambuga et al. (1998) esti-
mated yield loss to increase 5-fold from the first to third
ratoons.
Nevertheless, the pest status of banana weevil
remains controversial. The banana weevil has vari-
ously described as being an ‘important’, ‘serious’ or
‘major’ banana production constraint in a region to
being of local, restricted or no importance (Table 3).
In Colombia, for example, the banana weevil has been
reported as being of ‘restricted importance’ (Castrillon
1987; Anonymous 1992), the ‘most important and
widely distributed pest’ on banana (Cardenas & Arango
1987; Castrillon 1989) to being a ‘major economic
pest’ (Londono et al. 1991). In the Philippines, Davide
(1994) suggested the weevil was a major produc-
tion constraint and second in importance to nema-
todes on Cavendish plantations, while Dawl (1985)
felt the weevil pest problems were restricted to a few
plantations.
Banana weevil pest status may reflect banana type,
clone selection, ecological conditions and manage-
ment systems. Bananas are grown from sea level
to >2000 masl, under a range of different rainfall
and soil conditions and in production systems rang-
ing from kitchen garden to large-scale commercial
plantations. Weevil damage levels are likely to be
very different on Cavendish bananas (AAA) grown
in commercial plantations than on highland cooking
banana (AAA-EA) or plantains (AAB) grown in small-
holdings. Pest status within genome groups is also
in dispute. For example, recommended action thresh-
olds on Cavendish banana vary from 2 weevils/trap
in Brazil (Moreira 1979) to 15–25 weevils/trap in
Central America (Anonymous 1989; Sponagel et al.
1995).
Few studies have attempted to quantify yield loss to
banana weevil. On-farm assessments have mostly con-
cerned evaluation of plant loss through toppling and
snapping which can be attributed to banana weevils.
Some of these studies failed to partition damage effects
of weevils and nematodes and yield loss estimates are,
thus, confounded. Additionally, on-station trials are
most appropriate if yield losses are followed for several
crop cycles. Only limited information is available on
Biology and IPM for banana weevil 101
Table 3. Summary of literature reporting different pest status of the banana weevil C. sordidus and suggested mechanisms of yield loss
a. Pest status
‘Major’ pest or constraint
Jardine (1924), Hargreaves (1940), Sen & Prasad (1953), Hall (1954), Vilardebo (1960), Gorenz (1963), Wolfenberger (1964),
Nonveiller (1965), Singh (1970), Edge (1974), McNutt (1974), Suplicy Fo & Sampaio (1982), Arleu & Neto (1984), Van den Enden &
Garcia (1984), Arroyave (1985), Kehe (1985), Prando et al. (1987), Stover & Simmonds (1987), Tezenas du Montcel (1987), Lescot
(1988), Swennen et al. (1988), Sikora et al. (1989), Sarah (1990), Batista Filho et al. (1991), Londono et al. (1991), Taylor (1991),
Minost (1992), Varela (1993), Gold et al. (1993, 1999b), Simon (1993), Davide (1994), Pone (1994), Price (1994), Mukandala
et al. (1994), Sarah (1994), Stanton (1994), Vittayaruk et al. (1994), Bosch et al. (1996), Cerda et al. (1995), Ahiekpor (1996), Seshu
Reddy et al. (1998), Nkakwa (1999), Aranzazu et al. (2000, 2001), Castrillon (2000), Carnero et al. (2002)
Regional importance
Vilardebo (1984), Waterhouse (1993), Gowen (1995)
Local, restricted, or of no importance
Ostmark (1974), Firman (1970), Stephens (1984), Dawl (1985), Kusumo & Sunaryono (1985), Sebasigari & Stover (1988), Boscan
Martinez & Godoy (1989), Anonymous (1992), Schill et al. (1997), Sponagel et al. (1995)
b. Mechanisms of yield loss
Sucker loss
Moznette (1920), Hargreaves (1940), Weddell (1945), Stover & Simmonds (1987), Boscan de Martinez & Godoy (1989), Pena &
Duncan (1991), Afreh-Nuamah (1993), Pinese & Piper (1994), Price (1994), Ndege et al. (1995), McIntyre et al. (2000), Messiaen et al.
(2000)
Root initiation
Montellano (1954), Vilardebo (1960, 1977), Cuille & Vilardebo (1963), Singh (1970), Waterhouse & Norris (1987), PCAARD (1988),
Allen (1989), Castrillon (1989, 1991), Treverrow (1985, 1993), Treverrow et al. (1992)
Root death, reduced root number
Swaine (1952), Montellano (1954), Nonveiller (1965), Singh (1970), Wright (1977), Castrillon (1989, 1991), Kehe (1985, 1988), Lescot
(1988), Londono et al. (1991), Musabyimana (1999)
Nutrient uptake/transport
Moznette (1920), Montellano (1954), Vilardebo (1960, 1977), Cuille & Vilardebo (1963), Nonveiller (1965), McNutt (1974), Medina
et al. (1975), Kehe (1985, 1988), Treverrow (1985, 1993), Waterhouse & Norris (1987), PCAARD (1988), Allen (1989), Boscan de
Martinez & Godoy (1989), Castrillon (1989, 1991), Sponagel et al. (1995), Masso & Neyra (1997), Musabyimana (1999), McIntyre
et al. (2000)
Leaf senescence
Harris (1947), Cuille (1950), Nonveiller (1965), PANS (1973), Medina et al. (1975), Hely et al. (1982), Jones (1986), Cardenas &
Arango (1987), Prando et al. (1987), Waterhouse & Norris (1987), Allen (1989), Ingles & Rodriguez (1989), Londono et al. (1991),
Pinese & Piper (1994), Ndege et al. (1995), Sponagel et al. (1995), Masso & Neyra (1997)
Reduced plant size/vigour
Froggatt (1925), Harris (1947), Cuille (1950), Montellano (1954), Roberts (1958), Cuille & Vilardebo (1963), Shell (1967), Deang et al.
(1969), Trejo (1969), Singh (1970), Medina et al. (1975), Reinecke (1976), Kehe (1985, 1988), Jones (1986), Prando et al. (1987),
Boscan de Martinez & Godoy (1989), Sikora et al. (1989), Pinese & Piper (1994, Ndege et al. (1995), Seshu Reddy et al. (1995),
Rukazambuga (1996), Masso & Neyra (1997), Rukazambuga et al. (1998), Ngode (1998), Musabyimana (1999)
Increased susceptibility to drought/disease
Harris (1947), Ambrose (1984), Uzakah (1995)
Slower growth rate
Roberts (1958), Franzmann (1976), Rukazambuga (1996), Rukazambuga et al. (1998), Gold et al. (1998b)
Secondary invasion
Montellano (1954), Hord & Flippin (1959), Mesquita et al. (1984), PCAARD (1988), Londono et al. (1991), Sponagel et al. (1995),
Musabyimana (1999), Godonou et al. (2000)
Castniomera humboldti
Arroyave (1985), Castrillon (1989, 1991), Carballo & de Lopez (1994), Londono et al. (1991), Carnero et al. (2002)
Pseudomonas (Ralstonia) solanacearum
Vilardebo (1960, 1977), Trejo (1969), Arroyave (1985), Batista Filho et al. (1987), Castrillon (1989, 1991, 2000), Londono
et al. (1991), Carballo & de Lopez (1994), Aranzazu et al. (2000, 2001)
Fusarium oxysporum
Trejo (1969), Suplicy Filho & Sampaio (1982), Arroyave (1985), Castrillon (1989, 1991), Londono et al. (1991)
Rots
Hord & Flippin (1959), McNutt (1974), Mesquita et al. (1984), Kehe (1985, 1988), Williams et al. (1986), Waterhouse & Norris (1987),
Shillingford (1988), Castrillon (1989, 1991), Treverrow et al. (1992)
102 C.S. Gold et al.
Table 3. (Continued)
Plant loss
Hargreaves (1940), Simmonds & Simmonds (1953), Vilardebo (1960, 1977), Trejo (1969), Ambrose (1984), Prando et al. (1987),
Castrillon (1989, 1991), Deang et al. (1989), Londono et al. (1991), Carballo & de Lopez (1994), Sponagel et al. (1995), Rukazambuga
(1996), Masso & Neyra (1997), Rukazambuga et al. (1998), Aranzazu et al. (2000, 2001), McIntyre et al. (2000), Messiaen et al.
(2000), Carnero et al. (2002), Gold et al. (unpubl. data)
Snapping
Hord & Flippin (1959), de Villiers (1980), Treverrow (1985, 1993), Shillingford (1988), Sikora et al. (1989), Taylor (1991), Stanton
(1994), Gowen (1995), Sponagel et al. (1995), Bosch et al. (1996), Rukazambuga (1996)
Toppling
Swaine (1952), Sen & Prasad (1953), Simmonds & Simmonds (1953), Braithwaite (1958), Roberts (1958), Vilardebo (1960, 1977),
Cuille & Vilardebo (1963), Nonveiller (1965), Trejo (1969), PANS (1973), McNutt (1974), Medina et al. (1975), Jaramillo (1979),
Roman et al. (1983), Ambrose (1984), Mesquita et al. (1984), Kehe (1985, 1988), Jones (1986), Williams et al. (1986), Prando et al.
(1987), Waterhouse & Norris (1987), Stover & Simmonds (1987), Lescot(1988), Shillingford (1988), Ingles & Rodriguez (1989),
Deang et al. (1989), Sikora et al. (1989), Marcelino & Quintero (1991), Pena & Duncan (1991), Pinese & Piper (1994), Ndege et al.
(1995), Sponagel et al. (1995), Uzakah (1995), Rukazambuga (1996), Masso & Neyra (1997), Musabyimana (1999), Godonou et al.
(2000), Ysenbrandt et al. (2000)
Reduced bunch size/number1
Sen & Prasad (1953), Roberts (1958), Vilardebo (1960, 1973, 1977), Braithwaite (1967), Shell (1967), PANS (1973), Franzmann
(1976), Reinecke (1976), Roman et al. (1983), Kehe (1985, 1988), Jones (1986), Cardenas & Arango (1987), Shillingford (1988),
Castrillon (1989, 1991), Sikora et al. (1989), Carballo & de Lopez (1994), Ndege et al. (1995), Sponagel et al. (1995), Rukazambuga
(1996), Masso & Neyra (1997), Alpizar et al. (1998), Gold et al. (1998b), Rukazambuga et al. (1998), Ngode (1998), Aranzazu et al.
(2000, 2001), Ysenbrandt et al. (2000), Carnero et al. (2002)
Reduced plantation life
Gold et al. (1993, 1999b), Masso & Neyra (1997), Castrillon (2000)
Reduced number of suckers
Froggatt (1925), Sen & Prasad (1953), Franzmann (1976), Reinecke (1976), Roman et al. (1983), Ambrose (1984), Arroyave (1985),
Jones (1986), Prando et al. (1987), Castrillon (1989, 1991), Uronu (1992), Ndege et al. (1995), Seshu Reddy et al. (1995), Sponagel
et al. (1995)
Reduced vigour of suckers
Froggatt (1925), Roberts (1958), Ambrose (1984), Arroyave (1985), Jones (1986), Uronu (1992), Pinese & Piper (1994), Ndege et al.
(1995)
Water suckers
Braithwaite (1958), Uronu (1992), Sponagel et al. (1995), Bosch et al. (1996)
1Implicit in most reports but not always explicitly stated.
the physiological basis of yield loss in banana resulting
from banana weevil attack.
1. Weevil damage mechanisms
Various authors have proposed that banana weevil
attack can kill young suckers, interfere with root ini-
tiation in growing plants, kill existing roots, reduce
nutrient uptake and transport, lead to premature leaf
senescence, reduce plant size, vigour and tolerance of
other stresses, retard maturation rates, increase sus-
ceptibility to other pests and diseases, lead to plant
loss through death before producing a bunch, top-
pling and snapping, reduce the number of harvested
bunches and bunch weights, and affect the number
and vigour of followers (Table 3). Many of these
reports appear to be based on conjecture or field
observations without supporting data. Some may also
confound the combined effects of weevil and nematode
attack.
In established plants, timing and location of weevil
attack within the corm may have distinct effects on
plant development and yield. Weevil larvae may move
from the mother plant and can kill young suckers.
However, ovipositing females prefer flowered plants
(Abera 1997) and this may explain, in part, why larval
damage has more impact on bunch weight than on plant
size and maturation time (Rukazambuga et al. 1998).
Larvae feeding on the corm periphery (as measured
by the CI and PCI) can cut through root points of attach-
ment (Montellano 1954; Singh 1970; Londono et al.
1991). In Uganda, the number of detached roots in
highland banana was proportional to the area of corm
surface attacked (A. Abera & C. Gold unpubl. data).
By contrast, internal damage has been hypothesised
to affect root initiation, nutrient transport, and stem
Biology and IPM for banana weevil 103
growth, while more peripheral damage may detach
roots or adversely affect root development (Taylor
1991; Gold et al. 1994b). Larval feeding can inter-
fere with root initiation and development (Lescot 1988;
Boscan Martinez & Godoy 1989; Castrillon 1991;
Treverrow et al. 1992) resulting in production of
fewer roots or premature root death (Swaine 1952;
Montellano 1954; Vilardebo 1960; Cuille & Vilardebo
1963; Nonveiller 1965; Cerda et al. 1995). Damage
to the central cylinder has the greatest effect on the
vascular system and may stunt stem growth while dam-
age to the cortex may adversely affect root development
and lead to snapping and toppling (Taylor 1991; Gold
et al. 1994b). In Uganda, Gold et al. (1994a) found dif-
ferences among genome groups and clones in degree
of penetration into the central cylinder: Plantains had
extensive damage throughout the corm, while in Gros
Michel (AAA), Ndizi (AB), and Ney Poovan (AB)
larval feeding was largely restricted to the cortex. The
combined effects of weevil damage to the root and
vascular system have been reported to disrupt nutri-
ent uptake and transport (Moznette 1920; Montellano
1954; Vilardebo 1960; Cuille & Vilardebo 1963;
Nonveiller 1965; McNutt 1974; Castrillon 1991; Gold
1998a) resulting in premature leaf senescence, stunted,
weak plants and reduced bunch filling (i.e. lower
yields).
Montellano (1954) suggested that larvae do more
damage when tunnelling near attachment points of
roots in the central cylinder or when near vascular bun-
dles in cortex. Rukazambuga (1996) also concluded
that damage to the central cylinder had more effect on
plant growth and yield than damage to the cortex. In
contrast, Boscan de Martinez & Godoy (1989) postu-
lated that larval feeding on the corm surface proximal
to the roots caused the greatest damage by impeding
nutrient uptake.
Nevertheless, there are few available data quantify-
ing the effect of weevil damage on nutrient uptake and
few controlled studies documenting its effect on leaf
life, growth and yield. In a series of trials in Uganda,
McIntyre et al. (2002, unpubl. data) and Ssali et al.
(unpubl. data) concluded that weevil infestations pre-
vented plants from taking advantage of nutrient amend-
ments to the soil. Hassan (1977) observed that damage
prevents water from reaching the leaves causing them
to yellow and wither, while, according to Jones (1986)
attacked plants have dull, flaccid leaves.
Rukazambuga (1996) and Rukazambuga et al.
(1998) demonstrated that the effects of weevil damage
on yield was influenced by the levels of weevil damage
to the mat in earlier cycles; i.e. weevil attack influenced
the vigour of followers. Gold et al. (unpubl. data) found
>35% of highland banana mats died out in 5 years in
plots infested with weevils, compared to 2% mat loss
in controls. This suggests that the weevil can severely
reduce stand life. Farmers in central Uganda reported
that the weevil had contributed to reductions in stand
life from >30 years to 4 years (Gold et al. 1999b),
while in Colombia the weevil can reduce stand life to
2–3 crop cycles (Castrillon 2000).
2. Toppling and snapping
Toppling is often attributed to plant parasitic nematodes
(e.g. Radopholus similis, Pratylenchus spp.) that attack
the root system, thereby reducing anchorage (Gowen
1995). However, it is likely that weevil damage reduces
root number and can contribute to toppling. For exam-
ple, in Ugandan field trials, Rukazambuga (1996) found
extensive toppling in mats with high levels of weevil
damage and negligible levels of nematodes and root
necrosis. Similar observations have also been made on
farms in Bukoba District, Tanzania (N. Rukazambuga
pers. comm.). Snapping (i.e. breaking of the corm) may
also occur on plants with severe weevil damage (Gowen
1995). Most often, toppling and snapping occur on
older plants bearing the weight of a mature bunch.
Nevertheless, toppling and snapping of maiden suckers
may also occur, especially following strong winds.
3. Plant stress and banana weevil attack
Stressed plants have been reported as being more attrac-
tive or suitable for banana weevils than vigorously-
growing plants (Wallace 1938; Nonveiller 1965;
Ambrose 1984; Mesquita et al. 1984; Vilardebo
1984; Allen 1989; Speijer et al. 1993; Mestre 1997).
For example, banana weevil damage may be
higher on nematode infested plants (Speijer et al.
1993; Treverrow 1993) although data are limited.
However, Rukazambuga (1996) found that initial attack
(i.e. following release of weevils in an established
stand) was independent of plant size and vigour.
Stressed plants have also been reported as dis-
proportionatelyaffected by banana weevil damage,
while vigorous plants have been reported to be more
tolerant to weevil damage (Froggatt 1925; Harris
1947; Cuille & Vilardebo 1963; Pinese & Piper 1994;
Sponagel et al. 1995). Rukazambuga (1996) found that
bananas in a mulched stand had a higher damage thresh-
old than intensively intercropped bananas, but above
104 C.S. Gold et al.
that threshold, percentage reductions in bunch weight
were similar.
Larval feeding may provide entry point for
disease agents such as Pseudomonas (Ralstonia)
solanacearum (Moko disease) and other organisms
causing rots (Table 3). Reports on the weevil vector-
ing or providing entry points for Fusarium oxysporum
Schlecht f.sp. cubense (E.F. Smith) Snyder & Hansen,
a fungal pathogen causing Fusarium wilt (Suplicy Fo &
Sampaio 1982; Castrillon 1991; Londono et al. 1991),
have not been substantiated and may be in error.
In Latin America, the moth borer, Castniomera
humboldti, has been reported as utilising weevil gal-
leries to gain entrance into banana corms (Arroyave
1985; Castrillon 1991; Carballo & de Lopez 1994).
Ants (e.g. Ondotomachus troglodytes Sanschi) occa-
sionally nest in and enlarge weevil galleries in living
plants although more often they enter crop residues
(Gold pers. observ.). It has also been suggested
that weevil damaged plants are more susceptible to
drought and disease stresses (Harris 1947; Ambrose
1984).
4. Pest status in Asia
The banana weevil is presumed to have evolved in
southeast Asia (especially the Indo-Malay region)
from which it has spread to all of the world’s
major banana-growing regions (Zimmerman 1968b;
Neuenschwander 1988; Waterhouse 1993). Cuille
(1950) suggested that the banana weevil was not a
pest in Indonesia due to the prevalence of resistant
clones and climate. However, data on the weevil’s
pest status (e.g. distribution, incidence, severity, yield
loss) in its area of origin are sparse (Waterhouse
1993; Valmayor et al. 1994). Scattered reports of
weevil problems in south India (Viswanath 1976),
Thailand (Nanthachai 1985) and Indonesia (Kusomo &
Sunaryono 1985) are not supported by population or
yield loss data and lack confirmation. Nevertheless,
reviews by Viswanath (1976), Geddes & Iles (1991),
Waterhouse (1993), and Gold (1998b) suggest that
banana weevil is an important pest in Malaysia
and of moderate importance in parts of Indonesia,
the Philippines, Sri Lanka, and Vietnam. Hasyim (pers.
comm.) also believes the weevil to achieve pest status
in parts of Indonesia. An understanding of weevil pest
status and population dynamics in Asia will be critical
for the development of a classical biological control
programme.
5. Yield losses to banana weevil
Yield loss to banana weevil may be affected by a
number of inter-related factors including weevil den-
sity, clone, age of stand, environmental conditions
(elevation, rainfall, soil type) management practices,
and presence of other stresses. In Uganda, banana
weevil damage was greater: (1) on plantains (AAB)
and highland banana (AAA-EA) than on Pisang awak
(ABB) or Ney Poovan (AB); (2) on farms not employ-
ing sanitation practices; and (3) at elevations under
1400 masl (Gold et al. 1994a, 1997). Farmers are
well aware that weevil damage is more important in
older stands and on-station trials have shown increas-
ing yield losses over time (Rukazambuga et al. 1998,
2002). Thus, single cycle yield loss trials may be
misleading.
Yield losses attributed to banana weevil range
from 0% to 100% (Table 4). Methods for estimat-
ing yield loss include field observations on the pro-
portion of dead suckers, plant loss through mortality,
toppling and snapping (Liceras et al. 1973; Ambrose
1984; Sengooba 1986; Ingles & Rodriguez 1989;
Sikora et al. 1989; Marcelino & Quintero 1991)
and controlled trials quantifying bunch weight or
yield (tonnage/ha/year) reductions (Reinecke 1976;
Sponagel et al. 1995; Rukazambuga 1996; Mestre &
Rhino 1997; Rukazambuga et al. 1998, 2002).
Unfortunately, it is often unclear how yield loss fig-
ures presented in the literature were derived and what
they might represent (i.e. a single trial or losses within
a region). In some cases, estimates represent combined
loss to weevil and nematodes (Roman et al. 1983;
Sengooba 1986; Sikora et al. 1989; Gold et al. 1998b),
while in some reports it is difficult to tell if yield losses
included nematode effects or not (Montellano 1954;
Ingles & Rodriguez 1979; Job et al. 1986; Marcelino &
Quintero 1991).
In yield loss trials on highland banana in Uganda,
Rukazambuga et al. (1998, 2002) related levels of
weevil damage in the central cylinder to plant growth,
maturation rates, and yield. Weevils were released
at the base of banana mats 9 months after planting.
Weevil populations, corm damage, plant growth, and
yield were assessed over four crop cycles. Plant loss
was attributable to weevils if dead, toppled or snapped
plants showed heavy signs of weevil attack. In one trial,
damage to the central cylinder increased from 4% in
the plant crop to 17% in the third ratoon (Table 5a)
(Rukazambuga unpubl. data). Root necrosis was low
Biology and IPM for banana weevil 105
Table 4. Reported levels of yield loss to banana weevil C. sordidus
Country Yield loss (%) Clone Methods Reference
Latin America
Brazil 30 Moreira
20–50 Gallo (1978)
Bahia Abandoned Observ. Arleu & Neto (1984)
Colombia? Up to 80∗ Marcelino & Quintero (1991)
Up to 60 Castillon (2000)
Cuba 22–34 Trials Reinecke (1976)
>19 Trials Calderon et al. (1991)
20 Trials Masso & Neyra (1997)
Ecuador 20–40 Champion (1975)
Honduras 8–26 Roberts (1955)
Trials 0 Trials Sponagel et al. (1995)
Peru 48∗ Liceras et al. (1973)
Puerto Rico 30–70∗ Ingles & Rodriguez (1989)
902 Trials Roman et al. (1983)
Africa
Cameroon 20–90 Lescot (1988)
Congo Up to 90 Ghesquiere (1925)
Ghana 25–90 AAB Gorenz (1963)
Ghana 33 AAB Udzu (1997)
Kenya 24–90 AAA-EA Trials ICIPE (1991)
16–53 AAA-EA Trials Ngode (1998)
Up to 100 AAA-EA Koppenhofer (1993a–c)
22–76 AAA-EA Trials Musabyiamana (1999)
Tanzania
Kagera 30 AAA-EA Walker et al. (1983)
30∗,2 AAA-EA Sikora et al. (1983)
15 Trials Uronu (1992)
Uganda 5–44 AAA-EA Trials Rukazambuga et al. (1998)
40–502 AAA-EA Trials Gold et al. (1998)
Central 20–60 AAA-EA Damage1 Gold et al. (1999)
Masaka Up to 100∗ AAA-AE Observ. Sengooba (1986)
Rakai Up to 100∗ AAA-AE Observ. Sengooba (1986)
>50% AAA-AE Observ. Sebasigari & Stover (1988)
West Africa 5–44 AAB Trials Sery (1988)
Asia/Pacific
India 352 Trials Job et al. (1986)
Tonga <10 Damage2 Crooker (1979)
30–60 Damage2 Englberger & Toupu (1983)
Up to 80∗ Observ. Pone (1994)
∗Percentage plant loss due to toppling and snapping attributable to weevils.
1Estimated from Rukazambuga et al. (1998) data sets.
2Composite weevil and nematode.
in all cycles suggesting that effects were most likely
due to the weevils alone.
The effect of damage was greater on bunch weight
than on plant growth and rate of development.
Moderate to heavy banana weevil attack reduced the
number of functional leaves at flowering, plant girth,
plant height, and maturation period (sucker emergence
to harvest). Plant loss attributable to banana weevil
attack in two trials increased from 4% in the plant
crop to 29% in the third ratoon (Table 5b). The cumu-
lative effect of heavy damage sustained over several
crop cycles resulted in greater reduction in bunch
weight than that inflicted by similar levels of damage
in a single cycle (i.e. by weakening the mat’s corm
leading to weaker followers). Weevil damage >10%
reduced bunch weights on harvested plants by 20–45%
(Table 5c), while yield losses increased from 9% in the
first ratoon to 48% in the fourth cycle.
106 C.S. Gold et al.
Table 5. Effect of banana weevil damage in the central cylinder on
plant loss, bunch weight and related yield loss in a trial (cv Atwalira)
at the Kawanda Agriculture Research Institute, Kampala, Uganda
1991–1995
Damage
class
Plant
crop
Ratoon cycle
First Second Third
a. Number of plants displaying level ofdamage
0–5% 74% 38% 24% 6%
>5–10 19 31 30 14
>10–15 5 18 19 18
>15–20 2 4 8 10
>20 — 8 19 52
Mean damage 4.2% 8.2% 10.8% 16.9%
b. Plants lost without producing harvestable bunches
0–5% 2 5 10 0
>5–10 4 13 14 0
>10–15 2 5 14 3
>15–20 4 3 6 7
>20 — 13 43 80
Percent 3 9 19 29
c. Bunch weights by damage class (mean damage per mat
for given and preceding cycles) (kg)
0–5% 12.2 12.9 16.8
>5–10 10.1 11.7 14.3
>10–15 9.8 9.3 11.2
>15–20 7.1 9.9 8.3
>20 7.0 7.4 9.1
d. Yield loss by cycle
PC Crop cycle
1 2 3
Expected yield1 4153 5175 5130 5127
Actual yield 3961 4709 4281 2896
Yield loss 5% 9% 17% 44%
PC: Plant crop.
Adopted from Rukazambuga et al. (1998).
In a second trial employing four treatments to create
different levels of host plant vitality, overall yield loss
in the trial increased from 6% in the plant crop to 21%
in the third ratoon (Rukazambuga et al. 2002). In the
fourth cycle, yield losses were 27% each in the most
highly stressed (i.e. intercropped with finger-millet)
and most vigorous-growing banana (i.e. mulched with
grass). This translated into a loss of 2.5 tonnes/ha in
the intercrop and of 6.3 tonnes/ha in the mulch. These
data suggest that banana weevil can be an important
constraint in well-managed banana stands.
In Honduras, Sponagel et al. (1995) attempted to
assess weevil pest status through the use of pesticide
checks. Chemical applications resulted in 48–80% pop-
ulation decreases compared to the control. However,
the reductions in weevil populations was not reflected
in either reductions in damage or increases in yield.
Sponagel et al. (1995) concluded that the weevil was
not an economic pest in Honduras. However, it is
unclear how this conclusion was reached since corm
damage was similar among treatments. The data do
suggest the possibility of lag effects between killing
of adults in established plantations and reducing corm
damage.
Part 2: Integrated Pest Management of
Banana Weevil
Current research results suggest that no single con-
trol strategy will provide complete control for banana
weevil. Therefore, a broad IPM approach, combin-
ing a range of methods, might offer the best chance
for success in controlling this pest. The components
of such a programme include habitat management
(cultural control), biological control, host plant resis-
tance, botanicals, and (in some cases) chemical control.
XI. Habitat Management (Cultural Control)
Habitat management offers a first line of defence
against herbivores (Altieri & Letourneau 1982) by
creating an environment which reduces pest immigra-
tion and/or encourages reduced tenure time and emi-
gration, promotes host plant vigour and tolerance of
pest attack, and/or is unfavourable to pest build-up.
For banana weevil control, habitat management options
include the use of clean planting material, selection
of cropping systems, improved agronomic practices to
promote plant vigour, management of crop residues
(i.e. sanitation), and trapping (Table 6). Peasley &
Treverrow (1986) have summarised this approach as
‘start clean, stay clean’.
1. Clean planting material
The use of clean planting material can reduce initial
banana weevil infestations and retard pest build-up for
several crop cycles. At the same time, it can protect
new banana stands against nematodes and some dis-
eases. Infested planting material provides the princi-
pal entry point of banana weevils into newly planted
fields. Suckers used as planting propagules often con-
tain weevil eggs, larvae, and, occasionally, adults.
Removing these weevils from planting material elim-
inates the most important source of infestation in new
plantations. The insect’s low fecundity and slow popu-
lation growth further suggest that a reduction in initial
infestation level might result in lower damage to newly
Biology and IPM for banana weevil 107
Table 6. Cultural practices for control of banana weevil: Literature recommending, reviewing or reporting research with favourable results
Crop rotation or fallow to clean fields
Froggatt (1924), Pinto (1928), Aguero (1976), Greathead et al. (1986), Jones (1986), Pinese (1989), Sikora et al. (1989), Seshu Reddy
et al. (1993, 1998), Pinese & Piper (1994), Pone (1994), Price (1994), Stanton (1994), Nkakwa (1999)
Clean planting material
1. Tissue culture plantlets
Peasley & Treverrow (1986), Pone (1994), Aranzazu et al. (2001)
2. Selection of clean suckers
Froggatt (1925), Pinto (1928), Sein (1934), Hargreaves (1940), Weddell (1945), Haarer (1964), Saraiva (1964), Nonveiller (1965),
Gordon & Ordish (1966), Trejo (1969), Wardlaw (1972), de Villiers (1973), McNutt (1974), Aguero (1976), Franzmann (1976),
Suplicy Filho & Sampaio (1982), Jones (1986), Peasley & Treverrow (1986), Williams et al. (1986), INIBAP (1988b), Allen
(1989), Anonymous (1989), Pinese (1989), Londono et al. (1991), Pinese & Piper (1994), Sponagel et al. (1995), Aranzazu et al.
(2000, 2001), Tushemereirwe et al. (2000)
3. Paring
Froggatt (1925), Veitch (1929), Sein (1934), Weddell (1945), Harris (1947), Nonveiller (1965), Gordon & Ordish (1966), Firman
(1970), Wardlaw (1972), de Villiers (1973), McNutt (1974), Aguero (1976), Franzmann (1976), Mau (1981), Dawl (1985), Jones
(1986), Peasley & Treverrow (1986), INIBAP (1988b), Rodriguez (1989), Londono et al. (1991), Pinese & Piper (1994), Simon
(1994), Sponagel et al. (1995), Gold (1998b), Gold et al. (1998a,b), Seshu Reddy et al. (1998), Mbwana & Rukazambuga (1999),
Nkakwa (1999), Aranzazu et al. (2000, 2001), Tushemereirwe et al. (2000)
4. Treatment with Creolina
Aranzazu et al. (2000, 2001)
5. Water submersion
Ghesquierre (1924, 1925)
6. Hot water treatment
Ghesquiere (1924), Sein (1934), Hildreth (1962), Barriga & Montoya (1972), Castano (1973), PANS (1973), Jurado (1974),
McNutt (1974), Arroyave (1985), Stover & Simmonds (1987), Sebasigari & Stover (1988), Londono et al. (1991), Seshu Reddy
et al. (1993, 1998), Pone (1994), Prasad & Seshu Reddy (1994), Simon (1994), Gold (1998b), Gold et al. (1998a,b), Mbwana &
Rukazambuga (1999), Tushemereirwe et al. (2000)
7. Heat sterilisation
Stein (1934)
8. Quick planting to prevent re-infestation
Veitch (1929), Sein (1934), Saraiva (1964), Franzmann (1976), Sponagel et al. (1995), Aranzazu et al. (2000, 2001)
Crop management
1. Intercropping with coffee
Kehe (1985, 1988)
2. Weeding & trash removal
Wallace (1938), Haarer (1964), Saraiva (1964), Simmonds (1966), Trejo (1969), Firman (1970), de Villiers (1973), PANS (1973),
Ostmark (1974), Franzmann (1976), Jaramillo (1979), Treverrow (1985), Greathead et al. (1986), Kelly (1986), Castrillon (1989,
1991), Mau (1991), Pinese & Piper (1994), Simon (1994), Vittayaruk et al. (1994), Smith (1995), Sponagel et al. (1995), Seshu
Reddy et al. (1998), Nkakwa (1999), Tushemereirwe et al. (2000)
3. Deleafing
Wallace (1938), Vilardebo (1960), Saraiva (1964), Jones (1986), Castrillon (1989, 1991), Mau (1991), Mbwana & Rukazambuga
(1999), Tushemereirwe et al. (2000)
4. Desuckering
Wallace (1938), Nonveiller (1965), Treverrow (1985), Tushemereirwe et al. (2000)
5. Mulch location
Varela (1993), Gold (1998b), Ssennyonga et al. (1999)
6. Deep planting of suckers
Kehe (1985), Seshu Reddy et al. (1993, 1999)
7. Earthing up rhizomes
Swaine (1952), Saraiva (1964), Nonveiller (1965), Kehe (1988)
8. Roguing
Froggatt (1925), Veitch (1929), Saraiva (1964), Nonveiller (1965), Castrillon (1991)
9. Nutrient amendments and promoting plant vigour
Jones (1986), Sponagel et al. (1995), Bosch et al. (1996), Tushemereirwe et al. (2000), Aranzazu et al. (2001)
10. Sanitation (destruction of crop residues)
Froggatt (1924, 1925), Ghesquierre (1925), Pinto (1928), Hargreaves (1940), Harris (1947), Haarer (1964), Nonveiller (1965),
Gordon & Ordish (1966), Simmonds (1966), Firman (1970), de Villiers (1973), PANS (1973), McNutt (1974), Nanne & Klink
(1975), Aranda (1976), Vilardebo (1977), Crooker (1979), Mau (1981), Suplicy Filho & Sampaio (1982), Arroyave (1985),
Dawl (1985), Treverrow (1985, 1993), Greathead et al. (1986), Jones (1986), Kelly(1986), Peasley & Treverrow (1986),
108 C.S. Gold et al.
Table 6. (Continued)
Williams et al. (1986), Cardenas & Arango (1987), Waterhouse & Norris (1987), INIBAP (1988b), Allen (1989), Anonymous
(1989), Pinese (1989), Castrillon (1989, 1991), Mau (1991), Treverrow et al. (1992), Treverrow & Bedding (1993), Treverrow &
Maddox (1993), Varela (1993), Pinese & Piper (1994), Seshu Reddy et al. (1994, 1998), Simon (1994), Stanton (1994), Vittayaruk
et al. (1994), Smith (1995), Sponagel et al. (1995), Bosch et al. (1996), Mestre (1997), Dochez (1998), Gold (1998b), Mbwana &
Rukazambuga (1999), Nkakwa (1999), Aranzazu et al. (2000, 2001), Tushemereirwe et al. (2000)
11. Burying infested plants and rhizomes
Ghesquiere (1924), Simmonds (1966)
Trapping
1. Residues
Knowles & Jepson (1912), Pinto (1928), Sein (1934), Hargreaves (1940), Harris (1947), Wolcott (1948), Cuille (1950),
Yaringano & van der Meer (1975), Mitchell (1980), Arleu & Neto (1984), Arleu et al. (1984), Londono et al. (1991), Anonymous
(1992), Koppenhofer et al. (1994), Masanza (1995), Ndege et al. (1995), Seshu Reddy et al. (1995), LeMaire (1996), Gold (1998),
Ngode (1998), Nkakwa (1999), Tushemereirwe et al. (2000)
2. Residues treated with pesticides
Veitch (1929), Whalley (1957), Bullock & Evers (1962), Sotomayor (1972), Yaringano & van der Meer (1975), Cardenas &
Arango (1986), Treverrow et al. (1992), Cerda et al. (1994), Masanza (1996), Aranzazu et al. (2000, 2001)
3. Residues treated with entomopathogens
Mesquita (1988), Budenberg et al. (1993a), Kaaya et al. (1993), Carballo & Lopez (1994), Contreras (1996), Masanza (1996),
Braimah (1997), Nankinga (1997, 1999), Nankinga & Ogenga-Latigo (1996), Nankinga et al. (1999), Aranzazu et al. (2000, 2001)
4. Residues treated with entomopathogenic nematodes
Schmitt et al. (1992), Treverrow (1994), Aranzazu et al. (2000, 2001)
5. Enhanced trapping with semiochemicals
Budenberg et al. (1993a), Cerda et al. (1994), Ndiege et al. (1996a,b), Jayaraman et al. (1997), Alpizar et al. (1999), Tinzaara et al.
(1999b), Tushemereirwe et al. (2000)
planted fields over extended periods of time. As a result,
the use of clean planting has been widely recognised
and promoted.
Re-infestation remains a critical concern. The period
of protection afforded by the use of clean planting
material will vary by cultivation practice. The most
pronounced effect will occur when clean material is
planted in isolated sites with no recent history of
banana production. For example, Froggatt (1925) advo-
cated the use of clean planting material and recom-
mended against planting near infested stands or in fields
where holdover populations of weevils remained from
prior plantings. Previously infested fields can be rid of
weevils by crop rotation or fallowing (Table 6). If pos-
sible, the old corms should be removed (Seshu Reddy
et al. 1993; Stanton 1994). Data on adult survival in
the absence of food sources suggest this period should
be at least 4–6 months (Froggatt 1924; Peasley &
Treverrow 1986; Pinese 1989; Seshu Reedy et al. 1998)
and possibly up to 24 months (Treverrow 1985).
In some regions, clean, isolated fields may not be
available and the ability to take land out of banana pro-
duction (i.e. crop rotation or fallowing) may be limited.
In Uganda, where highland cooking banana (AAA-EA)
is the preferred staple and an important component of
food security, high population density and land pres-
sure preclude the use of isolated fields (Gold et al.
1999b). As a result, gap filling in infested fields and
planting of new stands proximal to established, infested
banana stands is common. Under such conditions, the
impact of clean planting material will be reduced (Sein
1934; McIntyre et al. 2002).
A number of methods have been proposed for clean-
ing planting material of weevils. These include the
use of tissue culture plantlets; selection of weevil-free
suckers; paring, immersion in cold water, hot water
treatment, and/or heat sterilisation of suckers; and the
use of entomopathogens.
The use of tissue culture plantlets as a means of
banana weevil control has been recommended by
Peasley & Treverrow (1986) and Pone (1994). Unlike
other methods, tissue culture plants are likely to
be 100% free of banana weevils and nematodes at the
time of planting. Once established in the field, it is
unclear whether tissue culture plants are more or less
susceptible to banana weevils than plants grown from
suckers.
Tissue culture material is widely used for com-
mercial banana production in Latin America, Asia,
and Africa for pest and disease control. For exam-
ple, Dochez (1998) found that 77% of surveyed com-
mercial farmers on the south coast of Kwazulu/Natal,
South Africa used tissue culture plantlets. Although
Seshu Reddy et al. (1998) suggest that tissue culture
is beyond the reach of most small-scale farmers in
sub-Saharan Africa, production and dissemination of
Biology and IPM for banana weevil 109
tissue culture plantlets is currently being promoted in
Burundi, Kenya, Rwanda, and Tanzania.
Selection of weevil-free planting material by care-
ful observation of plants in the field has been widely
recommended (Table 6). This entails selecting suckers
from fields with no or low weevil infestation and/or
rejecting suckers that appear to have weevil damage.
However, banana suckers may carry eggs and/or early-
instar larvae, which are not easily detected by visual
observation. In areas where weevil problems are severe,
most farms may be infested and farmers may not be able
to choose clean suckers.
Paring, or removal of the outer surface of the corm,
has also been widely recommended (Table 6). Paring
can expose weevil galleries and allow the farmer to
reject heavily damaged suckers. Removal of all leaf
sheaths and paring of the entire corm will elimi-
nate most weevil eggs and many first-instar larvae.
However, later instar larvae are often deep within the
corm and will not be removed by paring (Hildreth 1962;
Reinecke 1976; Arroyave 1985).
Paring the entire corm normally entails removal of
all the roots. This method has also been recommended
as a means of nematode control (Speijer et al. 1995).
Concerns about viability of pared suckers have been
raised by Hord & Flippin (1956) and Coates (1971).
Although pared suckers may suffer under conditions of
low soil moisture, in Uganda growth of pared suckers
in field trials is usually satisfactory (Gold et al. unpubl.
data).
Ghesquiere (1924, 1925) suggested that submerg-
ing suckers in water for 2 days would kill all weevil
eggs, larvae, and adults. In contrast, Froggatt (1924),
Gettman et al. (1992), and Minost (1992) reported this
method as ineffective. Simmonds (1966) suggested that
soaking required 3 weeks to eliminate weevils, which
was both impractical and would cause loss of plant-
ing material. As a result, this method is rarely recom-
mended.
Hot water treatment to kill weevil eggs and larvae
was first recommended in the 1920s and continues to be
promoted (Table 6). Ordinarily, the corms are pared and
then completely submerged in hot water. Sein (1934)
reported that placing suckers in boiling water for 1 min
killed all weevil eggs and surface larvae, while heat
sterilisation at 43◦C for 8 h eliminated larvae deeper
within the corm. Arroyave (1985) summarised recom-
mendations for hot water treatments in Latin America
(i.e. Hildreth 1962; Barriga & Montoya 1972; Jurado
1974; Castano 1983) in which prescribed temperatures
ranged from 54◦C to 60◦C and submersion times from 8
to 20 min. No data on treatment efficacy were presented
for any of these studies.
The use of some hot water treatment regimes (52◦C
for 27 min or 54–55◦C for 20 min) is also a highly effec-
tive control against banana nematodes (Seshu Reddy
et al. 1993; Prasad & Seshu Reddy 1994; Speijer
et al. 1995). These temperatures have been suggested
for concurrent management of weevils and nematodes
(Seshu Reddy et al. 1993; Prasad & Seshu Reddy
1994).
In Hawaii, Gettman et al. (1992) reported greaterthan 99% mortality of weevil eggs and larvae when
suckers of dessert bananas (AAA) were placed in a
water bath of 43◦C for 3 h. Arroyave (1985) tested
hot water treatments (52–55◦C for 15 min) for clean-
ing plantain suckers in Colombia and found that lar-
vae within the interior of the corm survived. She
attributed this to failure of the heat to penetrate through
the corm and suggested that larger suckers would have
greater larval survival. These larvae would then provide
focal points for re-infestation. Similarly, Peasley &
Treverrow (1986) and Treverrow et al. (1992) report
that hot water baths are not effective at killing larvae
deep within the corm.
Efficacy of paring and hot water treatment in killing
weevil eggs and larvae was also tested in Uganda (Gold
et al. 1998a). Paring removed >90% of weevil eggs but
had little effect on weevil larvae. Mortality of banana
weevil immatures was also recorded after immersion
of infested banana suckers in four hot water regimes:
43◦C for 2 h, 43◦C for 3 h, 54◦C for 20 min, and 60◦C
for 15 min. All hot water treatments resulted in 100%
mortality of eggs. However, only hot water baths of
43◦C for 3 h resulted in high mortality (i.e. 94%) of
weevil larvae. Larval mortality in other treatments was
26–32%. Larval survival was considerably higher in
the central cylinder than in the cortex.
Banana weevils are attracted to cut corms and may
quickly re-infest pared or hot water treated planting
material if these are left in an area exposed to weevils.
Therefore, quick planting of treated material is also
recommended (Table 6). Planting material may also
be protected by pesticide (Rukazambuga 1996), neem
(Musabyiamana 1999) or entomopathogen (Godonou
1999) dips or applications in the planting hole. In
recent years, research has been conducted on micro-
bial control of banana weevil to reduce re-infestation
rates and prolong the benefits of clean planting mate-
rial. Griesbach (1999) initiated research on the use of
endophytes that may be inoculated into tissue culture
plantlets and reduce weevil infestation (see below).
110 C.S. Gold et al.
In Ghana, Godonou (pers. comm.) failed to establish
isolates of B. bassiana as endophytes, but successfully
demonstrated that application of B. bassiana formula-
tions into planting holes could reduce weevil attack of
suckers during the crop establishment phase (Godonou
1999; Godonou et al. 2000).
Field trials in Uganda compared weevil and
nematode populations, plant growth and yield in
(1) untreated suckers (controls); (2) pared corms;
(3) pared and hot water (54◦C for 20 min) treated corms
(Gold et al. 1998b). Weevil numbers were lower in
treated material than in control plots for 11–27 months.
Weevil damage levels in controls were 1.7–3 times
higher than in plots grown from treated planting mate-
rial for the plant crop. However, all treatments dis-
played similar levels of weevil damage in the first
ratoon. Hot water treatment had little advantage over
paring for controlling weevil but afforded excellent
nematode control for the duration of the trial. Plants
grown from treated material had faster maturation
rates and lower levels of plant loss (2–4%) due to pests
than untreated plants (21–34%). Thus, yield per ha was
1.4–2.8 times higher in plots grown from treated than
from untreated material for the first 28 months of the
trials, even though there were no treatment effects on
bunch size.
Farmer adoption of clean planting material tech-
nologies clearly varies from region to region and even
among sites within regions. Where tissue culture is
not available or affordable, selection of clean suckers
should be straightforward. However, many farmers will
reject only the most seriously damaged suckers. Paring
to remove weevil eggs and expose larval damage has
not been widely adopted by farmers in East Africa.
Many farmers believe that suckers will not perform
well following removal of most or all of the root system.
In Tanzania, for example, Taylor (1991) reported that
farmers viewed the recommendation of corm paring
with ‘extreme disbelief’.
Implementation of hot water baths for control of
banana weevils and nematodes requires investment in a
hot water tank and a heating source (e.g. electricity, gas
burner, wood). As a result, adoption by resource-poor
farmers may be limited (c.f. Ssennyonga et al. 1999;
C. Kajumba unpubl. data). Moreover, it is unlikely that
farmers would adopt hot water baths of 3 h, as required
for highly effective weevil control. Additionally, con-
trol of the proper temperature is important because
of the delicate balance between killing pests and
damaging the plant (Castano 1983; Seshu Reddy et al.
1998). Therefore, Gold et al. (1998a) suggested that
paring alone might be adequate for reducing weevils,
although hot water baths would continue to be preferred
for nematode control.
In a survey of farmers in Kisekka subcounty in
Masaka district, Uganda, 77% of farmers tried to select
uninfested suckers, 37% cut out damaged sections of
the corm, while 46% rogued severely infested plants
(Ssennyonga et al. 1999). Few farmers (3%) were
aware of paring and less than 2% regularly did this.
Twelve percent tried to obtain material for cultivars
that they deemed ‘tolerant’ of weevil attack.
In summary, infested planting material provides the
principal entry point of banana weevils and nematodes
into newly planted fields. Use of clean planting mate-
rial reduces initial weevil numbers and, thereby, retards
population build-up. Tissue culture plants offer one
means of assuring pest-free planting material although
production capacity, costs and means of dissemination
are limiting factors in some countries. Alternatively,
paring the corm removes most eggs and exposes
damage of heavily infested plants that may then be
rejected. Hot water treatment (20 min at 55◦C) fur-
ther reduces weevil numbers by killing larvae within
the corm. However, neither paring nor hot water treat-
ment completely eliminates banana weevil. The fact
that Gold et al. (1998b) no differences in infesta-
tion levels between bananas grown from treated and
untreated planting propagules in first ratoon crops
puts into question the use of clean-planting material
in subsistence systems where stands are expected to
last many years. Thus, the use of clean material pro-
vides initial protection to a banana stand, but ulti-
mately needs to be integrated with other weevil control
methods.
2. Cropping systems and crop management
The employment of multiple cropping systems as a
means of controlling banana weevil may be limited.
Mixed cropping systems often result in lower insect
pressure by reducing immigration rates, interfering
with host plant location and increasing emigration
rates (Altieri & Letourneau 1982; Risch et al. 1983).
However, banana weevils are sedentary insects that live
in perennial systems in the presence of an abundant
supply of hosts. Moznette (1920) concluded that the
weevils only move out of overcrowded or depleted
resources, a condition unlikely to occur in banana
plantations.
Cropping systems effects on banana weevil levels
would most likely be through changes in host plant
Biology and IPM for banana weevil 111
quality and/or microclimates (i.e. factors influencing
soil moisture). To date, there is little evidence of effec-
tive natural enemies whose action might be enhanced
by crop diversification in banana stands (c.f. Root 1973)
with the possible exception of myrmicine ants (see
below). At the same time, the banana weevil’s limited
mobility suggests that intercropping will have minimal
effect on banana weevil immigration and emigration
rates or tenure time.
Selection of cropping systems that may discourage
banana weevils include intercropping with insect repel-
lent crops or green manures. Kehe (1985, 1988) sur-
veyed farms in Cote d’Ivoire and found that plantains
mixed with older coffee stands (i.e. >5 years) had low
incidence of weevil attack (mean CI = 6%), while
plantain mixed with younger coffee plants (CI= 91%),
with cacao (CI = 88%) or with annual crops (CI =
79%) all suffered high levels of attack. He postulated
older that coffee plants produced sufficient caffeine to
serve as an effective insecticide or feeding inhibitor.
Kehe (1988) suggested that the caffeine is released into
the soil and is (presumably) absorbed into the plant
where it is effective against weevil larvae. Although,
Sarah (1990) found that spreading coffee mulch at the
base of banana mats had disappointing results, many
farmers in Masaka district, Uganda believe application
of coffee husks does reduce weevil levels (Ssennyonga
et al. 1999). Quantitative studies will be needed to
verify this hypothesis.
In Tanzania, a series of trials on intercropping and
banana weevils failed to produce viable crop mix-
tures that would both reduce weevil damage and pro-
duce satisfactory banana yields (Uronu 1992). Reduced
weevil populations occurred only in mixtures with
sweet potato where the bananas were badly stunted
by intercrop competition. In Uganda, intercrops of
green manures with reported insecticidal properties
(i.e. Canavalia, Mucuna, Tephrosia) had no effect on
either weevil adult numbers or on damage (McIntyre
et al. 2002). Application of Crotalaria as mulch had
no influence on either weevil numbers or damage
(McIntyre et al. unpubl. data). Similarly, Salazar (1999)
found no significant effect of Mucuna on banana weevil
populations in Puerto Rico.
It has often been suggested that banana weevil is a
greater problem in poorly managed stands (see above).
For example, farmers in central Uganda attributed
increasing weevil problems to reduced labour avail-
ability and concomitant reductions in management
attention (Gold et al. 1999a,b). Conversely, higher lev-
els of management might serve to reduce weevil pest
status. For example, Jones (1986) and Sponagel et al.
(1995) suggest that practices encouraging vigorous
banana growth might allow the plant to arrest or tolerate
weevil attack.
Weeding, removal of trash from the base of the mat,
deleafing and desuckering have all been reported as
means of eliminating shelters and hiding places for
weevils or making the environment at the base of the
mat less favourable to ovipositing females (Table 6). In
Kisekka subcounty, Masaka district, Uganda, nearly all
farmers deleafed to reduce wind damage. Two-thirds of
these farmers also reported that they also removed old
leaves to help control weevils; most felt that this method
was moderately to very effective in reducing weevil
damage (Ssennyonga et al. 1999). However, no data
are available in Masaka district or elsewhere to show
the relationship between these forms of crop sanitation
and weevil damage levels.
Recent work has demonstrated that grass mulches
may increase weevil damage by creating a more
favourable environment (i.e. cool. moist conditions)
for adult weevils (Price 1994; Rukazambuga 1996;
Braimah 1997). In Tanzania and Uganda, some farm-
ers mulch away from the base of the mat as a
means of reducing weevil infestations (Varela 1993;
Ssennyonga et al. 1999; Gold et al. 1999d). For exam-
ple, in Kisekka subcounty, 35% of farmers believed
that mulching away from the base of the mat helped
control weevils, while 19% practised this method.
In on-station and on-farm trials, weevil populations
and damage were consistently higher in mulched than
in unmulched plots, while mulch location (i.e. to
or away from the base of the mat) had little effect
on either weevil numbers or damage (Gold et al.
unpubl. data).
Deep planting and earthing up (Table 6) have
been recommended to render the corm inaccessi-
ble to ovipositing females and to prevent high mat.
Seshu Reddy et al. (1993) planted cooking bananas
at depths of 15, 30, 45, and 60 cm in drums and
reported that shallow planted suckers were more prone
to attack, although some weevils were able to find
the deepest planted suckers. The longer-term effects
of deep planting and earthing up are unclear. Abera
(1997) showed that weevils freely oviposit in leaf
sheaths, while Masanza (unpubl. data) found increased
oviposition on buried versus unburied corms dur-
ing dry seasons. In addition, deep planting is likely
to affect oviposition levels in the plant crop only
as the corm will move towards the soil surface in
ratoon crops.
112 C.S. Gold et al.
Roguing of obvious weevil-attacked plants has also
been recommended (Table 6). However, only the most
severely attacked plants can be identified by obvious
external symptoms (c.f. Rukazambuga 1996) and it is
most likely that roguing would have a limited effect on
weevil population and damage levels in the remainder
of the banana stand.
3. Crop sanitation
Following harvest, crop residues may serve as shel-
ters for adults (Gold et al. 1999d) and oviposition sites
for females (Abera 1997). For example, Gold et al.
(1999d) found 25–32% of adult weevils associated
with prostrate (i.e. cut or fallen) residues, while another
10–12% were found in standing stumps.
For some clones, banana weevil damage is much
higher on residues than on growing banana plants. In
Ecuador, Vilardebo (1960) reported that 75–80% of
weevil attack in Gros Michel was directed towards
residues, while most attack in Petite Naine or Robusta
clones was against the growing plant. Under condi-
tions of low weevil pressure in Australian Cavendish
plantations, weevil activity was almost exclusively in
corms of harvested plants (Treverrow et al. 1991).
Treverrow & Bedding (1993) also found that 60% of
the weevils emerged from residues. Ostmark (pers.
comm.) felt that most attack against Cavendish in
Central America came after harvest; therefore, plan-
tations were able to tolerate very high levels of weevils
without suffering yield loss. However, Stanton (1994)
has suggested that heavy attack of old corm can weaken
anchorage and lead to toppling.
The attraction of adult weevils to cut corms makes
residues especially attractive. Rukazambuga (pers.
comm.) found >200 eggs on a single stump of the
susceptible highland cooking cultivar Atwalira. In
Indonesia, extensive oviposition, reflected in large
numbers of early-instar larvae, was observed in corm
disk traps placed directly on the soil (C. Gold pers.
observ.). Moreover, recently harvested Pisang awak
and stumps to be largely weevil-free, while up to
100 larvae per residue were observed on harvested and
cut plants left prostrate on the soil (C. Gold pers. observ.
1997). In Uganda, Gold & Bagabe (1997) reported
negligible damage on recently harvested Kisubi (AB)
in Uganda, but extensive tunneling in its residues.
Heavy attack on residues might also reflect increased
survivourship as compounds conferring resistance in
some clones might break down after harvest. For exam-
ple, Kiggundu found that weevils freely oviposited
on Kisubi yet damage, prior to harvest, was light.
Preferential attack and/or increased larval success on
prostrate residues may result from the exposure of the
true stem to ovipositing weevils, whereas in standing
plants and stumps, the first-instar larvae must often
tunnel through the pseudostem before reaching its
preferred food source.
It is widely believed that destruction of crop residues
(splitting of harvested pseudostems and/or removal
of corms) eliminates adult refuges, food sources, and
breeding sites, lowers overall weevil populations and
reduces damage on standing plants in susceptible
clones (Table 6). While destruction of residues will
kill any eggs and larvae in them, it is also possi-
ble, that the residues may serve as traps that draw
gravid females away from growing bananas (Peasley &
Treverrow 1986; Waterhouse & Norris 1987; Gold
1998a). Treverrow (1985) and Allen (1989) recom-
mend placement of 60-cm lengths of cut pseudostems
in banana stands to lure ovipositing females away from
banana mats. This material quickly dries out, lead-
ing to wastage of any eggs placed in these residues.
Ghesquiere (1924, 1925) suggested destroying or even
burying old stems and corms. Hargreaves (1940) advo-
catedcutting residues at ground level, splitting pseu-
dostems and spreading them as a mulch, covering
corms with compact soil or, if heavily infested, remov-
ing and chopping them. These recommendations are
now widespread (Table 6).
Nevertheless, some farmers and researchers believe
that nutrients and water move from residues to fol-
lowers and that up to 1.5 m of pseudostem should be
left ‘in situ’ (Peasley & Treverrow 1986; Treverrow
et al. 1992; Smith 1995; Sponagel et al. 1995). INIBAP
(1988b) recommended cutting residues at ground level
in East Africa (to prevent weevil larvae moving from
the mother plant to the follower), while leaving residues
at 1 m in West Africa.
The value of sanitation as a means of weevil control
has been disputed. For example, Peasley & Treverrow
(1986) and Treverrow et al. (1992) suggest that crop
hygiene (i.e. sanitation) is the long-term key to weevil
control and that without it all other control measures
are pointless. Nanne & Klink (1975) report that sani-
tation can drastically reduce weevil populations. Jones
(1986) indicated that control is mostly linked to san-
itation. Gold et al. (1997) determine weevil levels on
50 farms in Ntungamo district, Uganda and found that
sanitation had more impact on weevil pest status than
any other agronomic practice, while in Masaka district
Tinzaara et al. (unpubl. data) found lowest levels of
Biology and IPM for banana weevil 113
weevils on farms employing the highest levels of sanita-
tion, In contrast, Jones (1968) suggested that sanitation
requires too much labour, while Ostmark (pers. comm.)
felt that weevils were not serious pests in commercial
plantations to and, therefore, sanitation was worthless
and not worth the effort. Much of this debate is spec-
ulative, based on causal observations, perceptions of
weevil pest status, and beliefs on weevil population
dynamics. Unfortunately, there have been virtually no
data from controlled studies on the role of crop sanita-
tion in weevil population dynamics and related damage.
During the rainy season, Masanza (1999) found that
corms cut 5 cm above the soil surface had twice as many
eggs as when cut at the soil surface and four times
as many eggs as corms cut 5 cm below the soil sur-
face and covered with soil. In contrast, during the dry
season buried corms had three times as many eggs as
corms cut at or above the soil surface. Masanza (1999)
attributed these seasonal differences to shifts in soil
moisture profiles.
Masanza (1999) also looked at attraction and accep-
tance of different types of highland cooking banana
residues in the laboratory. Consistent with the findings
of other researchers, weevils were more attracted to
and oviposited more on corm material than on pseu-
dostems. Surprisingly, the weevils were more attracted
to corms >30 days after harvest than freshly cut corms.
Under field conditions, banana weevils oviposited on
corms up to 120 days after harvest, although females
placed four times as many eggs on fresh corms as those
>30 days old. Eclosion rates were independent of corm
age, although larval/pupal survivourship was greater
and the combined stage duration shorter on fresh corms
(11.5% survivourship; median 38 day duration) than on
14–30 days old corms (7.5%; 43 days) or >30 days old
corms (4.5%; 47 days). Pupal weights were also greater
for larvae reared on fresh corms. Throughout Uganda,
many farmers remove corms many weeks, rather than
immediately, after harvest. Masanza’s (1999) data sug-
gest that removal of fresh corms may be far more
effective in reducing weevil numbers.
In a survey of commercial Cavendish plantations in
the south coast of Kwazulu/Natal, South Africa, all
farmers believed residues served as breeding grounds
for weevils (Dochez 1998). However, only 53% of the
farmers were willing to remove them due to labour
costs and the belief that the residues were beneficial to
the growth of followers.
During rapid rural appraisals at 25 sites in
Uganda, many farmers recognised the theoretical
value of crop sanitation (widely recommended by
extension services), but few practised it because it was
seen as costly and time consuming (Gold et al. 1993). In
a second study, farmers in central Uganda attributed the
recent decline in highland cooking banana productiv-
ity, in part, to increasing damage to banana weevil that
was aggravated by lack of field sanitation (Gold et al.
1999b). The abandonment of field sanitation practices
was related to a relaxation of government by-laws
(held over from the colonial period) and to lower
availability/increasing costs for external labour.
Farmer interviews on crop sanitation practices were
also conducted with farmers in Masaka and Ntungamo
districts, Uganda (Ssennyonga et al. 1999; Masanza
et al. unpubl. data). In both sites, farmers implemented
a wide range of residue management practices rang-
ing from cutting residues a few centimetres below
ground level to up to 1 m above the collar. Cut residues
were mostly left intact, chopped or split and spread as
mulch. Some farmers covered corms with compacted
soil to prevent weevil oviposition, while others cov-
ered corms with leaves in a modified disk on stump trap.
Nevertheless, the majority of farmers implemented low
(i.e. sporadic) levels of sanitation while only a few
systematically destroyed crop residues.
4. Trapping adult weevils
Trapping to monitor weevil populations and the effi-
cacy of different types of traps has been discussed
above. The use of trapping as a means of control-
ling banana weevils has also been recommended by
many workers (Table 6), although this approach has
been controversial (INIBAP 1988a,b; Gold et al. 1993).
Modifications (e.g. addition of chemicals, biopesti-
cides, or semiochemicals) on basic trapping meth-
ods have also been proposed. Jayaraman et al. (1997)
and Alpizar et al. (1999) suggested that mass trap-
ping with semiochemicals could overcome the weevil’s
low fecundity and slow population build-up and lead
to successful control, while Braimah (1997) offered
that the use of pseudostem traps enhanced by semio-
chemicals and combined with other compatible con-
trol methods (e.g. entomopathogens) holds the key to
banana weevil control. In contrast, Mestre (1997) con-
cluded that the weevil is a poor candidate for mass trap-
ping with semiochemicals because it is soil dwelling,
sedentary, and rarely flies.
The effect of trapping on weevil populations will, in
part, reflect the intensity of trapping (trap density and
trapping frequency) and the types of materials used. In
addition, it is likely that trapping in established fields
114 C.S. Gold et al.
will result in a gradual decline in weevil numbers with
a lag time required before effects are manifested in
reduced damage.
Weevil reductions due to trapping have been reported
by Vilardebo (1950), Arleu & Neto (1984), Arleu
et al. (1984), Koppenhofer et al. (1994), Seshu Reddy
et al. (1995), Ndege et al. (1995), Masanza (1995),
Ngode (1998), and Alpizar et al. (1999). However, the
use of trapping as a control of banana weevil has also
been considered ineffective or impractical (Roberts
1955; Braithwaite 1958; Jones 1968; Ostmark 1974;
Jaramillo 1979; Stover & Simmonds 1987; INIBAP
1988b; Gold & Gemmell 1993; Gowen 1995).
Data from controlled field studies are largely
wanting. In Honduras, Roberts et al. (1955) and
Ostmark (1974) report of a 2-year study in which
one million weevils were collected from 16.2 ha of
banana (i.e. 2575 weevils/ha/month), but trap catches
were similar at the beginning and end of the study.
The authors concluded that trapping is ineffective for
weevil control. However, no information was provided
on trap density and weevil population levels so it is hard
to determine what proportion of weevils were being
removed.
In contrast, Yaringamo & van der Meer (1975)
reported a 50% population reduction in Peru from
4 months of corm trapping, but the means by which
this reduction was determined is not clear. In Kenya,
Seshu Reddy et al. (1995) alsofound a 50% reduc-
tion in weevils captured following systematic trapping.
Koppenhofer et al. (1994) ran a series of experiments to
look at the effects of pseudostem trapping (at variable
trap densities reflecting available material) on weevil
numbers. In the first experiment (weekly trapping), trap
captures declined by 33% over an 11-week period. In
a second experiment (weekly trapping), weevil num-
bers collected in traps declined by about 50% in 1 year
in one field, but showed no change in a second field.
In a third trial, marked weevils were released into a
field and populations were estimated using the Lincoln
index. Weevils were collected from traps on a daily
basis for 7 weeks, after which the population was esti-
mated again. During this time period, weevil density
had declined by 59–67% from the original release level.
In all of these studies, comparisons were made with
initial populations and, thus, the trials lacked proper
controls, making the results inconclusive. For exam-
ple, reported weevil reductions in the Seshu Reddy
et al. (1995) study and first two Koppenhofer et al.
(1994) trials were interpreted from trap capture rates,
which may have reflected weather conditions and trap
efficiency (Vilardebo 1973). Similarly, weevil popula-
tion declines of the same magnitude as that reported in
Koppenhofer et al.’s (1994) third trial have been found
for field populations of marked and released weevils in
trials where trapping was not conducted (Rukazambuga
1996; Gold & Night unpubl. data).
Controlled studies to determine the efficacy of
pseudostem trapping in reducing weevil populations
were conducted under farmer conditions in Ntungamo
district, Uganda (Gold et al. 2002b). First, a par-
ticipatory rural appraisal was conducted in which
farmers expressed concern about yield declines in
cooking banana that they attributed primarily to
banana weevil (Okech et al. 1996). Observations
on farmers’ fields confirmed high weevil popula-
tions (estimated through mark and recapture meth-
ods) and damage levels on many farms (Gold et al.
1997). Twenty-seven farms were then stratified on the
basis of weevil population density and divided among
three treatments: (1) researcher-managed trapping (one
trap/mat/month): (2) farmer-managed trapping (trap
intensity at discretion of farmer); and (3) controls
(no trapping). In researcher-managed trapping, weevils
were collected once per month, 3 days after placement
of traps.
Intensive trapping (managed by researchers) resulted
in significantly lower C. sordidus damage after 1 year.
Over the same period, C. sordidus numbers declined
by 61% in farms where trapping was managed by
researchers, 53% where farmers managed trapping and
38% in farms without trapping; however, results var-
ied greatly among farms and, overall, there was no
significant effect of trapping on C. sordidus numbers.
Moreover, there was only a weak relationship between
the number of C. sordidus removed and the change in
population density. Trapping success appeared to be
affected by management levels and immigration from
neighbouring farms.
Recent trapping studies by ICIPE in Kenya found
that a high percentage of weevils could be removed by
continuous intensive trapping (2 traps per mat) over
several months (S. Lux pers. comm.). However, the
amount of material required for such trapping was unre-
alistic. Nevertheless, trap efficacy might be improved
by the use of semiochemicals including pheromones
and plant volatiles, by themselves or used as delivery
systems for entomopathogens.
Adoption of systematic pseudostem trapping
requires discipline and commitment on the part of the
farmer (Nonveiller 1965). Following the completion
of the Ntungamo study, adoption was very low due to
Biology and IPM for banana weevil 115
the resource requirements of this method, even though
most farmers were convinced that trapping could be
beneficial (Gold et al. 2002b). Ndege et al. (1995)
also noted that material and labour requirements might
be beyond the means of many subsistence farmers in
western Tanzania.
In a survey of highland cooking banana grow-
ers in Kisekka subcounty, Masaka District, Uganda,
Ssennyonga et al. (1999) found that 75% and 12%
of farmers knew of disk on stump and pseudostem
trapping, respectively. Yet, only 15% of all farmers
practised systematic disk on stump trapping, while no
farmers implemented pseudostem trapping. In addi-
tion, farmers must have realistic expectations on the
benefits of trapping. During a rapid rural appraisal in
Kabarole district, Uganda, farmers reported that they
tried trapping for a few weeks but abandoned it when
they failed to see immediate improvement (Gold et al.
1993).
The use of enhanced trapping with semiochemicals
could result in higher rates of weevil removal at lower
trap densities and with reduced labour. The commer-
cial company Chemtica International, in Costa Rica,
tested lures with male aggregation pheromones and
found that a formulation, Cosmolure+, (containing
a mixture of the four sordidin isomers plus plant
volatiles) was most attractive to both male and female
banana weevils (C. Oehlschlager pers. comm.). In
Uganda, these lures captured as many as 18 times the
number of weevils/day as conventional pseudostem
traps (Tinzaara et al. 1999a), while in Costa Rica,
Alpizar et al. (1999) reported that pitfall traps with
Cosmolure+ collected 12 times as many weevils as
unbaited sandwich traps. In addition, pseudostem traps
may last for only 3–7 days and require frequent visits to
remove and destroy the weevils (which enter and leave
the traps). By contrast, weevils drown in pheromone
traps, which can remain effective for up to 1 month.
Using interference studies by collecting weevils
from pheromone-baited pitfall traps placed at dif-
ferent distances, Oehlschlager (pers. comm.) deter-
mined that the optimum spacing of traps was 20 m
(by contrast, Alpizar et al. (1999) estimated the
effective attractivity radius of Cosmolure+ traps at
2.5–7.5 m). Based on these results, Chemtica rec-
ommended a density of 4 traps/ha, placed initially
in a single line at 20 m apart, 10 m in from border
(C. Oehlschlager pers. comm.). The traps are replaced
monthly and moved 20 m further into plot giving full
coverage after 9 months. Three assumptions are made:
(1) in 1 month, the traps remove most weevils within
a 20-m radius; (2) the weevils are sedentary and rein-
vasion into areas where traps have already been placed
is negligible; (3) a limited number of weevils emerge
from the bananas in areas where trapping has been
completed.
In a preliminary study to test the first of these
assumptions, Gold and Kagazi (unpubl. data) placed
five Cosmolure+ traps at the base of banana mats (trap
mat) in a heavily infested stand (mat spacing at 3 m).
Weevils were collected from the traps for 1 month, after
which the trap mat and its 8 nearest neighbours were
uprooted and remaining weevils counted. A total of
395 weevils were collected from the traps, 321 weevils
were collected from the base of the five trap mats and
242 weevils from 17 of 40 neighbouring mats. Extrap-
olation suggests a total of 569 weevils on adjacent
mats. This would indicate that the pheromone traps col-
lected only 31% of the weevils within a radius of 3 m.
Nevertheless, the data suggest that many weevils were
attracted by the pheromone lures, as an average of 64
weevils were recovered from the mat adjacent to each
trap compared to 14 weevils at each of the neighbouring
mats.
Nevertheless, Alpizar et al. (1999) obtained very
positive results using Chemtica recommendations on
Cosmolure+ trap number and placement in three plan-
tain fields and in one Grand Enano (AAA) stand. In the
plantain systems, weevil capture rates in treated plots
remained at initial levels for 9 months and steadily
decreased thereafter, while trap captures remained
steady in control plots. Over 18 months, damage lev-
els, measured by Vilardebo’s (1973) CI, decreased from
15% to 12% in the treated plots, while increasingfrom
15% to 34% in controls. This resulted in a 25% yield
gain for the first 18 months. Similar results were found
in the Grand Enano field where treated plots had less
damage and a 32% yield advantage.
The use of Cosmolure+ traps is now being tested
in a number of countries in Latin America, as well as
in Uganda, Cameroon, South Africa, India, and else-
where. These studies will demonstrate the efficacy of
the pheromone with different biotypes of the weevil
and in different agro-ecological conditions. Should
pheromones prove effective, however, the use of such
traps will entail resolving logistics related to importa-
tion, distribution, and storage, as well as monitoring
the costs and benefits to farmers.
In Kenya, ICIPE has been working on the use
of kairomone traps made with processed pseu-
dostem material that is then buried in the soil.
High numbers of weevils are attracted to these traps
116 C.S. Gold et al.
(S. Lux pers. comm.). The objective of this trap-
ping system is to create ‘killing nodules’ whereby
weevils are attracted to these traps and then killed
by entomopathogens (e.g. B. bassiana or Metarhizium
anisopliae) applied to the traps. If successfully devel-
oped, such a system would require production and
distribution of an entomopathogen (which might be
mass-produced locally) rather than a pheromone that
would require importation from Costa Rica.
5. Adoption of cultural controls
Implementation of cultural controls of banana weevil
varies by region and may reflect a range of fac-
tors including: (1) susceptibility of the predomi-
nant banana clones; (2) farmer perceptions on the
(potential) severity of weevil problems; (3) farmer
objectives (i.e. subsistence vs. commercial; prophylatic
vs. remedial control strategies); (4) farmer resources
(e.g. labour, finances, equipment), (5) farmer aware-
ness of control methods; (6) extension recommenda-
tions; (7) the ability of the farmer to modify methods
to suit his resources and needs; (8) farmer perceptions
of control efficacy in reducing weevil pest pressure;
(9) access to inputs, e.g. clean planting material
(e.g. tissue culture); (10) the length of time before
beneficial effects might become apparent. For exam-
ple, farmers in Kabarole district, Uganda abandoned
pseudostem trapping because they did not see weevil
reductions in a few weeks time (Gold et al. 1993),
while farmers in Lwengo subcounty, Masaka district
were disappointed with pheromone traps because of
unrealistically high expectations for immediate impact.
In contrast, a majority of farmers in Kisekka subcounty,
Masaka Distict, Uganda said they would be willing to
test a new method for 6 months before deciding upon
its value.
Some prescribed methods like deleafing or crop san-
itation may be practised for agronomic, rather than
pest control purposes. For example, >75% of surveyed
farmers in the Kisekka subcounty study split pseu-
dostems and/or removed stumps (Ssennyonga et al.
1999) which they used as mulch. Of these, less than
half recognised sanitation a possible means of weevil
control. Other farmers removed old corms to give the
mat room to grow, although some felt that corms of
recently harvested plant provided anchorage to the mat.
The intensity with which weevil management practices
were implemented varied considerably among farmers
and often reflected their economic status. Farmers prac-
tising systematic sanitation of banana residues tended
to sell a higher proportion of their crop and have a
higher levels of resources than those who did not.
In areas of Uganda with limited commercial oppor-
tunities for banana, implementation of labour-intensive
cultural controls was limited. In Ntungamo district, for
example, 75% of farmers practised little or no sani-
tation and either left harvested stumps on the mat or,
if cut, left them intact to rot (Masanza 1999). Twenty
percent of farmers carried out sporadic sanitation in
which they would destroy some but not all residues
or would wait until many residues were more than
1 month old. Only 5% of farmers implemented sys-
tematic sanitation in which most residues were fully
destroyed soon after harvest. In addition, most farmers
felt that pseudostem-intensive trapping was not a feasi-
ble control strategy because of its labour and material
requirements (Gold et al. 2001). Similarly, in central
Uganda, few farmers were willing to implement labour-
intensive controls against banana weevil, even though
they perceived this pest as a leading cause of banana
decline (Gold et al. 1999b).
XII. Biological Control with Arthropod
Natural Enemies
Biological control is the combined action of a natu-
ral enemy complex (parasitoids, predators, pathogens),
antagonists or competitors in suppressing the popu-
lation density of a pest to a level lower than would
occur in their absence (Debach 1964; van Driesche &
Bellows 1996). Most often, biological control includes
the successful establishment of natural enemies and
has the advantages that it is ecologically sound, com-
patible with most farming practices (except the use
of pesticides) and requires little or no investment on
the part of the farmer. Some natural enemies may
require periodic augmentative releases to bolster exist-
ing populations or to insure rapid dissemination into
new sites. Otherwise, successful biological control
is permanent and stabilises herbivore populations at
low levels, thereby reducing the risks of outbreaks.
Even partially successful biological control would con-
tribute to IPM of banana weevil since natural ene-
mies are most often compatible with breeding for host
plant resistance and cultural controls (Neuenschwander
1988).
Biological control efforts against banana weevil
have included the use of exotic natural enemies
(classical biological control), endemic natural enemies,
secondary host associations, and microbial control
Biology and IPM for banana weevil 117
(e.g. entomopathogens, endophytes, entomophagous
nematodes). Microbial control agents may require
repeated applications and may be considered as biopes-
ticides, although they lack the toxic side effects
of chemical insecticides. As such, they may entail
repeated application costs on the part of the farmer.
1. Classical biological control
Classical biological control of banana weevil may be
possible. Introduced pests, unimportant in their native
habitats, often reach damaging levels when released
from the control of co-evolved natural enemies. The
banana weevil appears to fit this pattern. Although there
is some belief that the weevil might reach pest status in
parts of Asia, the weevil is generally not considered to
be a serious pest in Asia. Greathead et al. (1986) esti-
mated the chances for a successful classical biological
control programme at 30%.
Therefore, exploration for banana weevil natural
enemies in Asia followed by selection, quaran-
tine and release of suitable species could establish
an herbivore equilibrium below economic thresh-
olds. The first searches for natural enemies in Asia
were undertaken by Muir in 1908 (Froggatt 1925),
Jepson (1914) and Froggatt (1928). They identified
Plaesius javanus Erichson (Coleoptera:Histeridae),
Belonuchus ferrugatus Erichson (Coleoptera: Staphyl-
inidae), Leptochirus unicolor Lepeletier (Coleoptera:
Staphylinidae), Canthartus sp. (Coleoptera:Cucujidae)
and Chrysophila ferruginosa (Wied) (Diptera:
Rhagionidae) as being predacious on the banana
weevil and banana stem weevil Odoiporus longicollis
Oliv. (Coleoptera:Curculionidae). Of these the most
important appeared to be P. javanus whose larvae
and adults both attack banana weevil immatures.
Later searches revealed the presence of other preda-
tors, e.g. Hololepta spp.(Coleoptera:Histeridae) and
Dactylosternum hydrophiloides MacLeay (Coleoptera:
Hydrophilidae) (Table 7a).
The life history of P. javanus has been described by
Jepson (1914), Froggatt (1928), Weddell (1932) and
Barrera & Jimenez (1994). The females place single
eggs under leaves, at the base of plants and on crop
residues.The adults can live up to 14 months, while
the immature stages last 5–6 months. P. javanus is
an opportunistic generalist predator that will feed on
a range of prey. In the laboratory, the adults and larvae
can eat up to 8 and 40 banana weevil larvae per day,
respectively. This predator is most commonly found in
Table 7. Prospects for classical biological control of the banana weevil C. sordidus: Natural
enemies in area of origin and summary of earlier classical biological control attempts
a. Common natural enemies of banana weevil in Southeast Asia
Coleptera
Histeridae Plaesius javanus Erichson
Hyposolenus (Plaesius) laevigatus (Marseul)
Hololepta quadridentata (F.)
Hololepta spp.
Staphylinidae Belonuchius ferrugatus Erichson
Leptochirus unicolor Lepeletier
Silvanidae Cathartus sp.
Hydrophilidae Dactylosternum hydrophiloides MacLeay
Dactylosternum abdominale (F.)
Diptera
Rhagionidae Chrysophila ferruginosus (Wied.)
b. Introductions of natural enemies for the biological control of banana weevil
Insect Attempts Established Location established
Plaesius javanus 27 10 Fiji, Jamaica
Hyposolenus laevigatus 2 2 Cook Island, Dominica
Dactylosternum abdominale 1 0
D. hydrophiloides 4 2 Australia, Jamaica
Hololepta quadridentata 7 1 Saint Vincent
Hololepta spp 3 0
Chrysophylus ferruginous 1 0
Total 45 15
Sources: Gold (1998a), Hasyim & Gold (1999) adapted from Viswanath (1976),
Waterhouse & Norris (1987), Geddes & Iles (1991), Waterhouse (1993).
118 C.S. Gold et al.
deteriorating banana residues and rarely enters weevil
galleries in living plants.
Between 1913 and 1959, 45 attempts were made to
introduce 8 natural enemies from Asia to other banana-
growing regions in the world (Table 7b). P. javanus
was released in Australia, Oceana, Latin America and
Africa. Most commonly, the introductions were done
with small predator consignments and with disregard
for the ecological similarities between source and tar-
get sites. In most cases, the natural enemies have
failed to establish following introduction (Hoyt 1957;
Greathead et al. 1986; Waterhouse & Norris 1987) or,
if established, failed to live up to expectation. Only in
Fiji and Jamaica has there been any suggestion of even
partial control (Greathead et al. 1986; Waterhouse &
Norris 1987).
Although the lack of success in trying to estab-
lish natural enemies introduced from Asia to other
banana-growing regions in the world is discouraging,
additional search efforts would be desirable. These
searches might focus on parasitoids (especially of the
relatively vulnerable egg stage) which might be host-
specific to banana weevil and/or banana stem weevil
(Neuenschwander 1988). Such natural enemies tend to
be more effective biological control agents than oppor-
tunistic predators such as P. javanus. However, egg par-
asitoids are difficult to find and their efficiency may be
influenced by cultural practices (e.g. mulching) which
will influence exposure of oviposition sites.
More recently, searches for natural enemies of
banana weevil were carried out by the International
Institute for Tropical Agriculture (Nigeria) and the
Research Institute for Fruits (Solok, Indonesia) at a
total of 5 sites in Sumatra, Indonesia in 2000 and
2001. More than 19,000 eggs and 1500 larvae were
collected in the field and reared in the laboratory. The
eggs were maintained on filter paper in petri dishes,
while the larvae were reared on heat-sterilised banana
corm material. A phorid fly, (Megaselia sp.) was reared
from several banana weevil larvae, although it is not
clear if this was a parasitoid or saprophage. Otherwise,
no parasitoids emerged from this material (Abera et al.
unpubl. data).
2. Endemic natural enemies
Lists of endemic arthropod natural enemies of
banana weevil have been provided for Latin America
(Mesquita & Alves 1984; Arroyave 1985; Castrillon
1991; Londono et al. 1991; Pena & Duncan 1991;
Schmitt 1993; Garcia et al. 1994; Sponagel et al. 1995;
Goitia & Cerda 1998; Castrillon 2000), Africa
(Koppenhofer 1993b,c, 1994, 1995; Koppenhofer &
Schmutter 1993; Koppenhofer et al. 1992, 1995;
Tinzaara et al. 1999a) and Asia outside the pre-
sumed area of weevil origin (Seshu Reddy et al. 1998;
Padmanaban et al. 2001). Cuille (1950), Simmonds
(1966), Beccari (1967), and Schmitt (1993) also pro-
vide lists of known natural enemies against banana
weevil. Reported natural enemies include nabids,
cydnids, capsids, reduviids, mirids, thrips, rhagion-
ids, sarcophagids, histerids, carabids, hydrophilids,
staphylinids, dermaptera, curculionids, scarabaeids,
tenebrionids, and formicids. Vertebrates reported to
feed on banana weevil adults include the giant toad
Bufo marinus (Dawl 1985), common large arboreal
lizard Anolis cristatelus (Wolcott 1924) rats, bandi-
coots, frogs, birds (Hely et al. 1982) and servals (Gold
et al. pers. observ.). Very little information is available
on the efficacy of these natural enemies. Most appear
to be of little importance.
Koppenhofer et al. (1992) listed 12 preda-
tors of banana weevil in western Kenya. These
included adults of Thyreocephalus interocularis
(Eppelsheim) (Coleoptera:Staphylinidae), Hesperius
sparsior (Bernhauer) (Coleoptera:Staphylinidae),
Charichirus sp. (Coleoptera:Staphylinidae), Hister
niloticus Marseul (Coleoptera:Histeridae), Hololepta
striaditera Marseul (Coleoptera:Histeridae),
D. abdominale (Fabr.) (Coleoptera:Hydrophilidae),
Abacetus optimus Peringuey (Coleoptera:
Carabidae), Eutochia pulla Erichson (Coleoptera:
Tenebrionidae), Labia curvicauda (Motschulsky)
(Coleoptera:Labiidae) and L. borellii Burr (Coleoptera:
Labiidae), Euborellia annulipes (Lucas) (Dermaptera:
Carcinophoridae), and an unidentified histerid. The
origin of D. abdominale is unclear. Koppenhofer &
Schmutterer (1993) described it as indigenous to East
Africa, while Koppenhofer et al. (1995) reported that it
was introduced from Malaysia to other banana-growing
regions of the world. Waterhouse & Norris (1987) list
a single unsuccessful attempt (in Jamaica) with this
species.
Koppenhofer (1994, 1995), Koppenhofer &
Schmutter (1993), and Koppenhofer et al. (1995) did
in depth studies on the bionomics and control potential
of T. interocularis, E. annulipes, adominale. In labo-
ratory experiments, these predators variously searched
corms of living plants and residue pseudostems and
corms (Koppenhofer et al. 1992). Eleven predators
attacked the banana weevil egg stage, ten attacked
the first two larval instars, nine attacked the third and
Biology and IPM for banana weevil 119
fourth instar, while four attacked later stages. The lar-
vae of T. interocularis and D. abominalae were also
predacious on weevil eggs and larvae.
Using high predator densities (i.e. 10–30 adults in
plastic containers, 10–200 adults in cages) under exper-
imental conditions, D. abdominale reduced weevils by
up to 50% in suckers, 39% in stumps, and 40–90% in
residue pseudostems, T. interocularis reduced weevil
densities in spent pseudostems by 42%, while the
other predators were unimportant (Koppenhofer &
Schmutterer 1993; Koppenhofer 1995). However, the
number of natural enemies used in these experiments
well exceeded field densities suggesting that the impact
of these predators in banana stands is likely to be lim-
ited (Koppenhofer & Schmutterer 1993). Field evalu-
ation of natural enemy efficacy was not carried out for
any of these species.
Hargreaves (1940) was the first to suggest that ants
might have potential as biological control agents of
banana weevil in Africa, although no studies were con-
ducted. During the 1970s, Cuban researchers began a
biological control programme using the myrmicine ant
Pheidole megacephala (Hymenoptera:Formicidae)
against sweet potato weevils (Perfecto 1994). Based on
anecdotal reports that plantain stands lasted 15 years
without the application of insecticides and only
2–3 years where chemicals were applied, Roche (1975)
deduced the presence of effective natural enemies
and suggested that Tetramorium guineense (Mayr)
might becapable of suppressing banana weevil pop-
ulations. T. guineense was observed to nest in leaves
and galleries and to keep plants free of weevils and
frass. A programme was then initiated employing
the use of T. guineense and P. megacephala against
the banana weevil. The ants have been observed to
enter crop residues and remove eggs and larvae
(S. Rodriguez pers. comm.). According to Perfecto &
Castineiras (1998), P. megacephala can also reduce
weevil oviposition when they nest near the plant roots.
Roche & Abreu (1982, 1983) began the propa-
gation and dissemination of T. guineense colonies.
Colonies with up to 22 queens and 62,000 workers
and immatures were collected and liberated in new
fields (Perfecto & Castineiras 1998). Ant establish-
ment was followed by the rapid appearance of new
colonies. At the onset of one trial, weevil trap catches
were greater than 10/mat. Liberation of ants on 8%
and 50% of the mats provided total field coverage in
6 and 2 months, respectively (Roche & Abreu 1983).
Eighteen months later, the high colony release rate had
reduced weevil populations by 65%, while trap catches
were 56% lower in the low release rate. By compar-
ison, pesticide applications reduced trap captures by
79%. Based on these results, Roche & Abreu (1983)
recommended releasing ants on 25–30% of the area
for ‘complete control’ in 3–4 months.
The control potential of myrmicine ants has also
been demonstrated by Castineiras & Ponce (1991).
They released 9 and 15 P. megacephala colonies/ha
into plantain plots (separated by 200 m alleys) 6 months
after planting. During the first crop cycle, weevil trap
captures, and damage indices (CI of Vilardebo (1973))
were similar in plots where ants had been released,
in carbofuran treated plots and controls. In the second
cycle, ants reduced weevil trap captures by 54–69%
and damage by 64–66%, with a corresponding yield
increase of 15–22%. The level of control of ants was
similar to that of the pesticide.
Castineiras (1982) studied the diurnal activity and
seasonality of P. megacephala and found the ant for-
aged throughout the day with greater activity during
daytime in winter and greater and during night time in
summer. Similarly, Roche & Perez (1985) found con-
tinuous activity of T. guineense with reduced activity at
high temperatures and greater activity with increasing
relative humidity. Bendicho & Gonzalez (1986) found
lower levels of control with T. guineense in the dry sea-
son, even though ant numbers were higher at that time.
The Cubans have since developed an integrated con-
trol strategy against banana weevil using T. guineense,
P. megacephala, and the entomopathogen B. bassiana
(S. Rodriguez pers. comm.). The ants alone have been
reported to provide 60–70% control (Perfecto 1994),
although the studies have not been well documented
and only few data have been published. Farmers have
reportedly seen the value of these predacious ants
and often place molasses and kitchen scraps around
their banana plants to encourage the ants (Perfecto &
Castineiras 1998). The use of pesticides has been pro-
hibited in areas where biological control programmes
against banana weevil are in operation.
Based on the results gained in Cuba, Greathead
(1986) suggested that ants might have potential
for biological control of banana weevil in Africa.
Waterhouse & Norris (1987) also recognised the poten-
tial of ants for weevil control in Asia and the Pacific
and proposed that they might be evaluated in areas
(e.g. Solomon Islands, Papua New Guinea) where the
weevil is not important.
Walker & Dietz (1979) found four species of
Tetramorium (including T. guineensee) and two
species of Pheidole including (P. megacephala) in the
120 C.S. Gold et al.
Cook Islands. Varela (1993) found 40 species of ants
in a survey of banana stands in four areas in Kagera
district, Tanzania. Pheidole was the most abundant
genus with P. megacephala the dominant species. She
observed P. megacephala nesting on the ground and
in leaf sheaths and found in large numbers in tunnels.
In Uganda, Gold & Nemeye (unpubl. data) surveyed
banana stands in 5 sites and found 35 species of ants
including T. sericeiventre, P. megacephala, and five
other species of Pheidole.
Most of the literature is unclear whether these ants
will enter galleries in living plants (which are ordinar-
ily filled with latex) or only in crop residues. However,
Bendicho & Gonzalez (1986) noted that the small
size of T. guineense allows penetration into larval gal-
leries. In one laboratory experiment, Bendicho (1987)
inserted banana weevil larvae into planted corms and
later observed T. guineense workers enter the galleries
and remove larvae. Abera (pers. comm.) has observed
Pheidole spp. removing eggs and larvae from pseu-
dostems in laboratory studies. Gold (pers. observ.) also
observed small, unidentified (probably myrmicine)
ants in weevil galleries in plants at the time of harvest.
In Venezuela, Goitia & Cerda (1998) found
15 species of ants (eight myrmicinae, one pseudomyr-
micine, two dolochoderinae, three ponerilnae, and one
ecitononae) in a 5-year-old banana plantation. The
most common of these were Azteca foreli, Ectatomma
ruidum, Wasmannia auropunctata, and Odontomachus
baueri. Of these, W. auropunctata and E. ruidum were
considered potential predators of the weevil. However,
it was not confirmed if either of these species do, in
fact, predate on weevil immatures.
Traore (1995) surveyed plantain systems in Benin,
Cote d’Ivoire and Nigeria for possible egg parasitoids
using yellow pan traps. He found a wide range of egg
parasitoids belonging to 12 genera, of which Mymar
Curtis, Lymaenon Hal, and Anagrus Haliday were most
common. However, he was unable to find any indi-
cations of parasitism of banana weevil eggs collected
from plants, placed in the field in infested suckers,
or attached to yellow cards. Similarly, Koppenhofer
(1993c) and Abera (unpubl. data) were unable to detect
egg parasitism in Kenya and Uganda, respectively.
3. Secondary host association
Neuenschwander (1988) suggested that natural ene-
mies of closely related hosts offer the promise for
efficient secondary associations with banana weevil.
Traore (1995) investigated the possible use of the
mymarid egg parasitoid Anaphes victus Huber against
banana weevil in Benin. A. victus is an important par-
asitoid of weevil eggs in the Americas. This parasitoid
was selected for study because it searches near the soil
level, is habitat rather than species specific and because
it effectively suppresses populations of carrot weevil
(Listronotus oregonensis (LeConte)) (Boivin 1993).
Traore’s study tested two A. victus biotypes (Quebec
and Texas) reared from carrot weevil eggs.
In the laboratory, A. victus readily accepted banana
weevil eggs with 60% parasitism by the Quebec bio-
type and 35% by the Texas biotype. However, par-
asitoid emergence was negligible (2% and 0% from
the Quebec and Texas biotypes, respectively) (Traore
1995). In contrast, A. victus immatures successfully
emerged from water hyacinth weevil, Neochetina
eichhorniae Warner, demonstrating that the parasitoid
could successfully complete its development within
a new host. Traore (1995) attributed these disparate
results to differences in host egg size. Banana weevil
eggs were considerably larger than those of carrot
or water hyacinth weevils. Larvae of A. victus failed
to consume all of the banana weevil egg contents
with decomposition of unconsumed material contribut-
ing to pupal failure. Most of the few parasitoids that
successfully reached the adult stage then failed to
emerge through the relatively thicker chorion of banana
weevil eggs.
XIII. Microbial Control
Research on microbial control of banana weevil
is still in its early stages. Microbial agents
tested against the weevil include entomopathogenic
fungi (e.g. B. bassiana and M. anisopliae), ento-
mopathogenic nematodes (e.g. Steinernema spp. and
Heterorhabditis spp.) and endophytes (e.g. non-
pathogenic Fusarium spp.). Entomopathogenicfungi
and nematodes are most often used to kill adult weevils,
while endophytes target the immature stages. Although
a number of strains have shown promise in the labo-
ratory and in preliminary field studies, efficient and
economically viable mass production and delivery sys-
tems still need to be developed, while the performance
of microbial control agents against banana weevil
under different agro-ecological conditions is not well
understood.
Epizootics of entomopathogenic fungi or nema-
todes in nature are uncommon, while natural infection
rates of banana weevil tend to be quite low. Only in a
Biology and IPM for banana weevil 121
few sites have entomopathogens been reported to estab-
lish following applications in banana fields. Without
adequate establishment, entomopathogens will require
repeated applications as a biopesticide. This will entail
continued production, distribution and storage costs
that will be passed on to the farmer.
1. Entomopathogenic fungi
a. Research protocols and strain selection
Nankinga (1994, 1997) noted that species in the ‘fungi
imperfecti’ may survive as saprophytes making them
better candidates as biological control agents than
fungi that are obligate parasites. Two genera within
this group, Beauveria and Metarhizium, are widely
distributed and have been reported from hundreds of
insect hosts. The most common species are B. bassiana,
B. brongniartii, and M. anisopliae.
B. bassiana and M. anisopliae have gained consider-
able attention as biological control agents for weevils
and other agricultural pests (Ferron 1981). These are
especially important for controlling cryptic insects,
such as banana weevil, which are not accessible to
arthropod natural enemies. The ability of the ento-
mopathogen to survive and infect soil-dwelling insects
is a primary determinant of efficacy under field condi-
tions. Pathogen viability can range from days to years,
depending on ecological conditions and the applica-
tion method used. Different strains of B. bassiana and
M. anisopliae have distinct ecological requirements
(e.g. temperature, humidity, and soil pH) which deter-
mine the environmental conditions under which they
are most effective.
The conidia of Beauveria and Metarhizium enter the
insect through its spiracles or digestive system or by
producing extracellular proteolytic, chitinolytic, and
lipolytic enzymes which facilitate penetration through
the insect’s cuticle (Nankinga 1999). B. bassiana can
also adhere to the cuticle and penetrate the integument
through a germ tube (Godonou 1999). The fungi can
kill the insect through direct attack on the insect’s nutri-
ents or through toxic metabolites (Nankinga 1997).
For example, in banana weevil, Kaaya et al. (1993)
observed that chains of B. bassiana or M. anisopliae
hyphae invade the haemocoel and muscle tissues and
destroy tracheal taenidia and fat bodies. Dead insects
kept in moist environment quickly developed surface
growth of mycelia. B. bassiana can invade the haemo-
coel where it produces a toxin, beauvericin, that reduces
competition with bacteria and weakens the immune
system (Hamill et al. 1969). Strain virulence is often
related to toxin production (Ferron 1981). After killing
their hosts, the fungus can live saprophytically.
Pathogenicity studies on banana weevil have
been done in disperse locations (Africa, Australia,
Latin America) against populations of weevils that
may represent distinct biotypes (c.f. Ochieng 2002).
Pathogenicity of fungal isolates may be affected by:
(1) the source of the isolate (Brenes & Carballo 1994);
(2) the method of culturing (Altre & Vandenberg
2001); (3) spore dose (Nankinga 1994; Godonou 1999);
(4) temperature and relative humidity (Fargues & Luz
2000; Arthurs & Thomas 2001); (5) formulation and
mode of application (Nankinga 1994; Godonou 1999;
Godonou et al. 2000). Under field conditions, fun-
gal efficacy may also be affected by factors influenc-
ing soil moisture (e.g. soil type, precipitation patterns,
mulch). For example, Nankinga (1999) suggested that
mulching might prolong the life of the fungus, but also
noted that an increase in soil moisture might lead
to more rapid degradation of B. bassiana by other
soil microorganisms. Pena et al. (1993) and Traore
(1995) found higher rates of infected weevils when
B. bassiana was applied to sterilised soil than when
applied to non-sterile soil, further suggesting the
antagonistic action of other soil organisms. Nankinga
(1999) suggests that microbial degradation of ento-
mopathogens may be more pronounced in high organic
soils than in clay soils. In general, more inoculum is
required for the control of soil-borne insects (Godonou
1999).
Research protocols for the development of a micro-
bial control programme of banana weevil include
a series of steps starting at isolation and screening
of candidate strains to the development of econom-
ical and effective field delivery systems (Godonou
1999). Efficient mass production systems are critical
for programmes that will depend on augmentative
or inundative releases. Candidate strains of micro-
bial agents are often selected from existing collec-
tions, from dead weevils found in the field or by
Galleria bait methods to obtain fungi in soils in
banana plantations (Castineiras et al. 1990; Brenes &
Carballo 1994; Nankinga 1994, 1999). For exam-
ple, B. bassiana strains screened against banana
weevil have been isolated from hemiptera, lepidoptera,
coleoptera (including banana weevil and other weevils)
and hymenoptera (i.e. ants). Although B. bassiana
isolates are usually most pathogenic to the orig-
inal or related hosts (Nankinga 1999), some of
the best performing strains had been isolated from
non-coleopterans (Brenes & Carballo 1994).
122 C.S. Gold et al.
Strains effecting high kill rates in the laboratory need
to be characterised to determine sporulation rates, their
potential for mass production on a range of substrates,
and spore viability following storage and performance
under different ecological conditions. Further testing
will then evaluate candidate strains for field effi-
cacy at different fungal concentrations, under differ-
ent formulations and for a range of delivery systems.
Ultimately, the capacity to deliver entomopathogens
to farmers, costs of application, and the level of con-
trol will determine the feasibility of a microbial control
method.
Most research on entomopathogens and banana
weevil has focused on levels of adult mortality in the
laboratory, in pot trials and/or in small pilot field stud-
ies. While many of these studies show promise, little
work has been done in larger trials or at the farmer level
to show the true potential of microbial control agents.
This makes it difficult to interpret and integrate the
body of literature that has been developed on the effi-
cacy of different strains and application formulations
concentrations and rates.
Entomopathogenic fungi have been tested against
banana weevil since the 1970s (Ayala & Monzon
1977; Delattre & Jean-Bart 1978). Since then, numer-
ous laboratory studies conducted in many different
banana-growing regions have demonstrated high lev-
els of mortality to a large number of strains (Table 8).
Additional research has been conducted on strain
selection, mass production on a range of substrates
(e.g. maize, rice), spore viability and storage, formula-
tions (powders, water solutions, mineral oils) and shelf
life, doses, application methods, and mortality rates
after varying time intervals. Few studies have addressed
delivery systems and efficacy under field conditions.
The use of entomopathogens against banana weevil has
been reviewed by Nankinga et al. (1999).
b. Natural infection in banana fields
In Brazil, Mesquita et al. (1981) assessed field infec-
tion levels of both banana weevil and Metamasius
hemipterus collected in pseudostem traps over
9 months. Monthly infection rates were not differenti-
ated by species and ranged from 1–7% with an overall
mean of 3%. De Souza et al. (1981) foundfield infec-
tion to average 1–2%, with a peak of 8%. Infection
rates were negatively correlated (−0.35 to −0.44) with
weevil population levels. Batista Filho et al. (1992)
found 9% infection of banana weevils by B. amorpha
in pseudostem traps in a Prata stand and no infection in
an adjacent Nanica plot. In Cuba, Gomes (1985) found
<1% field-collected weevils infected by B. bassiana,
while in Colombian surveys, Van den Enden & Garcia
(1984) found only five infected adults and two infected
immatures.
In Florida, Pena et al. (1993) reported 6% natural
infection of banana weevils by B. bassiana in one study.
In a second field, weekly assessment of weevils in pseu-
dostem traps showed infection rates to range 4–34%;
mortality of >10% occurred in 4 of 38 sampling peri-
ods (Pena et al. 1995). Many additional dead weevils
infected with B. bassiana were found adhering to the
underside of fallen banana pseudostems and corms.
In this study, infection rates tended to rise following
increases in weevil population levels.
In Uganda, Nankinga (1994) isolated B. bassiana
or M. anisopliae (using Galleria larvae) from 29 and
3 samples, respectively, out of 37 soil samples taken
from banana stands in total of 24 sites. However, Gold
(pers. observ.) and Nankinga (unpubl. data) found natu-
ral infection to be 0–3% among hundreds of thousands
of weevils collected in pseuodstem traps and among
tens of thousands of these weevils maintained in the
laboratory.
In a survey of the Department of Risaralda,
Colombia, Castrillon (2000) found B. bassiana in 6
of 9 municipalities with an incidence of 0–11% (mean
4%) infection of weevils collected in pseudostem traps
and maintained for 15 days in the laboratory.
c. Spore production, formulations, and viability
Methods for mass production and delivery of ento-
mopathogens have been reviewed by Nankinga (1999)
and Godonou (1999). Production systems included
liquid fermentation, solid substrates, and diphasic
methods. Substrates offering large surface areas for
fungal sporulation are normally preferable. In addi-
tion to choice of substrate, moisture content, balance
of nutrients, pH, and aeration may also affect conidial
or spore production (Godonou 1999). Pathogen appli-
cations can be made in dry state using solid substrate
carriers, as wettable powders, dusts, baits or granules,
or in oil- or water-based liquid sprays. Formulations
are also important in stabilising the pathogen, improv-
ing efficacy in field and providing an economic and
easily usable form of active ingredient with long
shelf life (Godonou 1999). Nankinga (1999) found
maize to be the best solid substrate as it was associ-
ated with high sporulation, low contamination, >95%
germination and 60–100% infectivity of weevils in
14 days. Oil may provide greater adhesiveness to cuti-
cle, increase the number of conidia reaching the insect’s
Biology and IPM for banana weevil 123
intersegmental membranes, enhance protection against
ultraviolet light and desiccation, and cause higher mor-
tality at lower doses (Prior et al. 1988; Nankinga 1999).
However, oil-based formulations are more costly than
other formulations.
Batista Filho et al. (1987) reported 75% viability
of B. bassiana and M. anisopliae spores inoculated
into solid rice and 85% viability in liquid substrates.
Nankinga (1994) compared spore production among
different B. bassiana isolates and found that some did
better at ambient temperatures, while others performed
better at higher temperatures. She also found spore
viability for up to 2 years. Ferreira (1995) estimated
spore viability for four strains of B. bassiana to be
75–95%. Godonou (1999) and Godonou et al. (2000)
used the number and weight of conidia per unit sub-
strate and conidial viability, to complement virulence
levels, in selection of candidate strains for further test-
ing. Conidia obtained from rice and oil palm kernel
cake substrates displayed 98% viability.
d. Mortality rates for adults
Numerous strains of entomopathogens have been
screened against banana weevil in the Americas and
Africa, employing a range of formulations, spore
concentrations, and application methods. Mortality
of weevils exposed to many strains often reached
90–100% (Table 8).
In Cuba, Ayala & Monzon (1977) found 50–70%
mortality of weevils 33 days after being released in
cages at the base of banana mats treated with 4, 8, 12,
or 16 g of B. bassiana (2×105 spores/mg). Castineiras
et al. (1990) evaluated 17 strains of B. bassiana (mostly
from lepidoptera) and 11 strains of M. anisopliae
(including three from banana weevil) for efficacy
against banana weevil following 1 min dips in water
suspensions (2×108 spores/ml). After 30 days, mortal-
ity ranged 15–58% and only one strain of each species
effected mortality of >50%.
In Guadeloupe, Delattre & Jean-Bart (1978)
screened six strains of B. bassiana, two strains of
B. brongniartii, five strains of M. anisopliae, and one
strain of Nomuraea rileyi against banana weevil in the
laboratory using impregnated filter paper. Three strains
each of B. bassiana and M. anisopliae caused mortality
reaching 60–100% after 90 days. The remaining strains
of B. bassiana and M. anisopliae and the tested isolates
of B. brongniartii and N. rileyi were all ineffective. In
container experiments, spores or conidia applied to the
loamy soil resulted in 0–15% mortality, while spores
applied to clay caused 52–54% weevil mortality.
In the West Indies, Khan & Gangapersad (2001)
found LD50 and LT50 values of 4.57 × 107 spores/ml
and 10 days, respectively for B. bassiana, 5.13 ×
107 spores/ml and 21 days for M. anisopliae, and
4.92 × 108 spores/ml and 32 days for M. flavoviridae.
In Brazil, Gomes (1985) applied a single strain of
B. bassiana in a spore suspension (powder) at a con-
centration of (2 × 109 spores/mg). Direct immersion
of weevils resulted in mortality of 22%, while applica-
tions to pseudostem traps and soil resulted in mortality
of 16% and 34%, respectively.
In laboratory studies, Batista Filho et al. (1987)
reported weevil mortality to B. bassiana and
M. anisopliae to be 85% and 93%, respectively, in rice-
based substrates and 97% and 56%, respectively, in
liquid formulations. After 16 days, Batista Filho et al.
(1994) found 38% and 78–100% mortality of weevils
in pseudostem traps treated with B. bassiana alone and
as a homogenised rice paste + mineral oil formula-
tion. In another experiment, Batista Filho et al. (1995a)
observed 70% and 98% mortality when weevils were
exposed to rice substrate and mineral oil formulations
of B. bassiana, respectively. The proportion of weevils
showing fungal symptoms was similar (60%) in the
two formulations. However, a mineral-based formula-
tion caused more rapid mortality (e.g. 88% at 8 days)
than the rice substrate (14%).
Busoli et al. (1989) tested two strains each of
B. bassiana (isolated from a pyralid and a scarab) and
of M. anisopliae (isolated from a scarab and a cer-
copid). The fungi were produced on rice and applied
topically as a powder with 1000 or 2000 spores per
insect. The two doses of B. bassiana caused mortality
of 32% and 80%, respectively at 10 days and 61% and
99% mortality at 33 days. In comparison, the two doses
of M. anisopliae caused mortality of 15% and 68%,
respectively at 10 days and 47% and 79% mortality at
33 days.
In Florida, Pena et al. (1993) tested three isolates
of B. bassiana against banana weevil. Mortality of
>40% was achieved with 107 or 108 spores/g soil.
Virulence was greater on sterile soils than on non-
sterile soils. Water-saturated soils had significantly
higher levels of weevil mortality (>35%) than dry
soils (10%).
In Costa Rica, Brenes & Carballo (1994) screened
24 isolates of B. bassiana (from hemiptera, lepidoptera,
ants and other weevils) by shaking the insects in coni-
dial powder. The six most promising isolates were
selected for further testing. Mortality of weevils dipped
in water suspensions containing 1 × 109 spores/ml
Ta
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126 C.S. Gold et al.
ranged 73–100% with a LT50 of 7–10 days. Using
a range of spore concentrations, an CL90 of 2.67 ×
109 spores/ml was calculated for the most promis-
ing isolate. Carballo & de Lopez (1994) then found
31–63% adult mortality when B. bassiana conidial
powder or spores on rice substrate were applied to
pseudostem traps.
Contreras (1996) screened five strains of B. bassiana
in the laboratory in oil-based formulations and found
65–95% weevil mortality in 15 days, with an LT50 of
2.5–8 days. Carballo (1998) tested water-based and oil-
based formulations of B. bassiana. Oil formulations of
>20% without fungi caused high levels of mortality
in the weevil, while weevil mortality was negligible
in solutions with 10% oil. Using a 15% oil solution,
Carballo (1998) found mortality to range from 10% at
1 × 107 spores/ml to 97% at 5 × 108/ml.
In Colombia, Garcia et al. (1994) applieda rice
paste formulation of B. bassiana to pseudostem traps
biweekly for a 10-month period. Weevil infection,
assessed 8 days after application, averaged 39%.
In Kenya, Kaaya et al. (1993) reported four strains
of B. bassiana and one strain of M. anisoplae to
cause 90–100% mortality of third-instar larvae. The
B. bassiana isolates killed 60–98% of adult weevils
with LT50 ranging from 8 to 25 days; in contrast, the
M. anisoplae killed only 28% of the adults.
In Benin, Traore (1995) found 50% adult mortal-
ity in the laboratory at 1.1 × 107 spores/ml for one
exotic strain each of B. bassiana and M. anisopliae.
In contrast, soil applications required doses of 1.5 ×
108 spores/ml for M. anisopliae and 2.9×108 spores/ml
for B. bassiana to achieve 50% mortality.
In Ghana, Godonou (1999) evaluated adult weevil
mortality following applications of different formula-
tions of B. bassiana to pots containing plantain sword
suckers or by coating suckers. A groundnut oil plus
kerosene formulation and conidial powder induced the
highest rates of mortality (often >80%) immediately
after application. However, a formulation utilising oil
palm kernel cake also induced substantial of mortality,
while enhancing fungal multiplication and displaying
the greatest level of field persistence. Oil palm kernel
cake had the added advantage of being a readily avail-
able waste product, while other widely tested substrates
(e.g. groundnut, rice, maize) are valuable food crops.
In Uganda, Nankinga (1994) allowed weevils to
walk on PDA cultures and found five isolates of
B. bassiana produced >96% mortality after 21 days,
while one B. bassiana and one M. anisopliae isolate
each caused only 40% mortality. Topical applications
of the same isolates in water suspensions produced
73–100% mortality for five B. bassiana isolates,
22% for one B. bassiana isolate, and 30% for the
M. anisopliae isolate. Nankinga (1994) also found mor-
tality rates to be directly related to spore dose for
three strains of B. bassiana. Higher doses killed almost
all weevils, while females were more susceptible than
males to lower doses of the pathogen. Topical applica-
tions by dispersion or immersion caused much higher
rates of mortality than spraying pathogen solutions on
to soil or pseudostem traps.
In a followup study, Nankinga et al. (1996)
screened 15 strains of B. bassiana, one strain each
of B. brongnatii and B. stephanoderis, nine strains of
M. anisopliae, and two strains of M. flavoviride using an
aqueous solution with 6×109 spores/ml. After 30 days,
14 B. bassiana strains averaged 87% infection (one
strain was ineffective), M. anisopliae strains averaged
79% infection, M. flavoviride strains averaged 16%
infection, the single strain of B. brongnatii caused 85%
infection and the single strain of B. stephoderis killed
only 3% of the weevils.
Nankinga (1999) evaluated a further 31 iso-
lates of B. bassiana, 17 of M. anisopliae, two of
M. flavoviride, and one of B. brongniartii. Eighteen
isolates gave >70% mortality when weevils were
exposed to 3-week-old sporulating cultures. When
weevils were exposed to 3–4 ml spore suspension with
3 × 1011 spores/ml for 2 h, 22 isolates caused 70–90%
mortality. However, when weevils were inoculated with
1 ml of a water suspension of the same dose, no isolate
gave more than 60% mortality. Nankinga (1999) then
selected candidate isolates on the basis of pathogenicity
towards the weevil and growth and sporulation rates.
Although it is difficult to compare the results of
different studies because of the wide range of con-
ditions and methods used, several conclusions can be
reached. There was wide variability in the efficacy of
different strains in killing banana weevils. The most
effective strains were capable of causing high mortal-
ity in the laboratory at lower spore concentrations and
in shorter periods of time. In general, promising iso-
lates of B. bassiana were more effective than those of
M. anisopliae (Delattre & Jean-Bart 1978; Batista Filho
et al. 1987; Mesquita 1988; Busoli et al. 1989; Kaaya
et al. 1993; Nankinga 1994). However, Castineiras &
Ponce (1991) found a mean mortality of 14% for 17 iso-
lates of B. bassiana compared 27% for 11 isolates of
M. anisopliae, while Traore (1995) found a single iso-
late of M. anisopliae to be more virulent than his isolate
of B. bassiana.
Biology and IPM for banana weevil 127
Results from several studies (Delattre & Jean-Bart
1978; Pena & Duncan 1991; Kaaya et al. 1993;
Nankinga & Ogenga-Latigo 1996) suggest that indige-
nous isolates might perform better than exotic strains.
Topical application tended to produce higher lev-
els of mortality than fungal applications to substrates
(e.g. soil, traps) where weevils reside. However, field
delivery systems will have to rely on applications
to substrates or in areas where weevils might be
aggregated by semiochemicals.
e. Mortality to immatures
Van Enden & Garcia (1984), Kaaya et al. (1993), Pena
et al. (1993), Nankinga (1994, 1999), and Godonou
(1999) reported mortality of weevil immatures to
entomopathogens. During field surveys in Colombia,
Van Enden & Garcia (1984) observed a single larva and
one pupa infected by B. bassiana, suggesting that the
fungus can enter banana plants but that effects on imma-
ture populations may be minimal. In the laboratory,
Kaaya et al. (1993) found >90% mortality of third-
instar banana weevil larvae within 9 days of exposure
for each of the four B. bassiana and one M. anisopliae
isolates tested. LT50 times ranged from 3 to 4 days.
Assays of the same isolates on adults produced lower
levels of mortality and LT50 times of 8–22 days.
Pena et al. (1993) allowed weevil oviposition
on suckers that were then immersed in aqueous
B. bassiana suspensions and planted in pots. The per-
centage of larvae infected with B. bassiana in treated
plants was 43% after 11 days and 13% after 26 days.
At 26 days after treatment, larval mortality was 3% in
controls and 13% after 26 days. Pena (unpubl. data)
found that B. bassiana injected into a plant could move
about 30 cm.
In Uganda, dusting suckers with B. bassiana spores
resulted in infection of 41% of the eggs and 19% of
first-instar larvae, while planting suckers in soil treated
with B. bassiana also led to a low level of larval infec-
tion (Nankinga 1994, 1997). In Ghana, soaking of corm
and pseudostem pieces in water formulations resulted
in up to 46% egg failure and 27% larval mortality, com-
pared to 5% and 1% in controls, respectively (Godonou
1999).
Kaaya et al. (1993) isolated the bacteria Serratia
maraescens from dead larvae in a colony of banana
weevil. Third-instar larvae were found to be very
susceptible (mortality >90%) to concentrations of
1 × 108 bacteria/ml, but adults were not affected
by cultures with 1 × 109 bacterial/ml. Traore et al.
(unpubl. data) screened a wide range of isolates of
Bacillus thurgingensis, but found none effective in
killing banana weevil larvae.
f. Field trials and delivery systems
In Guadeloupe, Delattre & Jean-Bart (1978) sprayed
spores of B. bassiana at the base of banana mats in
concentrations of 2.2 × 1010 spores/ml in a plot of
Poyo (AAA) and 5 × 105–1 × 1011 spores/ml in a plot
of Yangambi-Km5. None of the applications had any
effect on banana weevil density.
In a field trial in Brazil, Mesquita (1988) applied
B. bassiana to pseudostem traps (120/ha) by immers-
ing them in spore solutions with concentrations ranging
from 8×107 to 6.48×108 spores/ml. Twenty-four appli-
cations were made at 2-week intervals, with weevils
collected 15 days later and assessed for infection. A low
infection rate, averaging 5%, was attributed to reduced
spore viability under field conditions.
Batista Filho et al. (1991) screened five strains
of B. bassiana and made three applications of the
most virulent in rice paste (50 ml per trap with 1 ×
109 spores/ml) to pseudostem traps in a 1-ha stand and
compared trap catches to an adjacent 1-ha control. They
found 61% fewer adults and 91% fewer larvae in treated
traps.However, in two other trials, Batista Filho et al.
(1995b, 1996) found <20% control following periodic
applications of oil-based formulations of B. bassiana
spores/ml to pseudostem traps.
In Costa Rica, Contreras (1996) studied the effects
of B. bassiana under field conditions with 600 m2 plots
(126 plants). In half of the plots, B. bassiana was
applied in two formulations (oil emulsion and rice sub-
strate) to disk on stump traps, while in the other plots the
entomopathogen was applied to pseudostem traps. The
disk on stump traps captured 3–4 times as many weevils
as plots with pseudostem traps and, therefore, may be
more appropriate for disseminating entomopathogens.
Immediately following application, the proportion of
infected weevils was highest where oil formulations
were applied (72%) than for the rice-based formula-
tion (48%) or controls (7%). In contrast, 8 days after
application, mortality was higher for the rice-based for-
mulation (55%) than the oil formulation (28%) (the
figures we present here are estimated from graphs).
In Colombia, Castrillon (2000) applied B. bassiana
and M. anisopliae to disk on stump traps in both rice-
based substrates (15 g/trap) and in water suspension
(15 cc/trap) through aspersion at each of 18 sites (one
high and one low elevation site in each of nine munci-
palities). Other treatments included a control, a rice
substrate control (i.e. without entomopathogens) and
128 C.S. Gold et al.
lorsban. Traps were evaluated weekly for 8 weeks,
with weevils transported to the laboratory for isola-
tion of pathogens. Application of entomopathogens
in rice-based substrates resulted in 16% (site mean
range 4–34%) infection for B. bassiana and 16% (range
0–42%) for M. anisopliae (i.e. sites weighted equally).
In contrast, applications by aspersion resulted in only
6% and 5% infection for B. bassiana and M. anisopliae,
respectively. Surprisingly, up to 6% B. bassiana infec-
tion was found in treatments where this pathogen had
not been applied, while infection of M. anisopliae in
other treatments was negligible. These data suggest
the either possibility of greater movement of weevils
infected with B. bassiana than those infected with
M. anisopliae or the existence of B. bassiana-infected
weevils in the population prior to evaluation.
In Ghana, Godonou et al. (2000) conducted field
studies to field efficacy and the spread of the
B. bassiana following release of laboratory-infected
weevils. In the first experiment, 20 weevils were
released at the base of recently planted plantain suckers
that had been: (1) protected by application of 60 g of oil
palm kernel cake containing 109 conidia/g; (2) coated
with conidial powder containing 6 × 1010 conidia prior
to planting; (3) planted without fungal application
(controls). After 28 days, the suckers were uprooted
and the number of weevils counted. A weevil recovery
rate of 23% with 30% infection was found on suckers
coated with conidial powder, compared to 31% recov-
ery and 24% infection on suckers protected by oil palm
kernel cake substrates and 50% recovery and no infec-
tion on controls. Godonou et al. (2000) estimated 76%
mortality in the two B. bassiana treatments, compared
to 1% in controls.
In a second experiment, Godonou et al. (2000)
applied the same treatments to suckers planted among
mature plantain plants in an established field. Weevils
were trapped at the base of the suckers for 2 months,
after which they were uprooted. Suckers protected with
B. bassiana in oil palm kernel cake substrates had
the highest mortality of trapped weevils (42%), low-
est percentage of attacked plants (6%), fewest number
of larvae (6), and no dead suckers. In contrast, suck-
ers coated with conidial powder had 6% dead weevils
in traps, 25% attack of plants, 17% plant death, and
26 larvae. Controls displayed similar levels of attack as
those treated with conidial powder. From these results,
Godonou et al. (2000) concluded that suckers could
be protected at the critical stages of plant establish-
ment by applications of conidial powder on an oil
palm kernel cake substrate. Under field conditions,
the fungus increased until the substrate was exhausted,
providing extended protection.
In Uganda, Nankinga (1999) first tested traps in pots
as a potential delivery systems for B. bassiana using
maize culture, oil suspension and water suspension.
Weevils were released, recaptured after 5 days and
maintained for 21 days. Maize culture produced a mor-
tality of 83% in 21 days, compared to 47% in water sus-
pension. The oil formulation killed 100% of the weevils
although only 60% showed signs of infection.
The same treatments were then applied to disk on
stump and pseudostem traps under field conditions.
After 5 days, weevils were collected from traps and
maintained in the laboratory for 21 days. Infection
rates were 50–60% for traps treated with maize cul-
ture, 55–61% for traps treated with oil suspension,
23–44% for traps treated with water suspension, and
0% in oil and water controls. Moreover, captures were
lower in traps treated with maize culture and oil sus-
pension than for those treated with water suspension
or controls. Pathogenicity decreased in treated soils
after 2 weeks, although 15% of weevils collected from
treated soils showed signs of infection 5 months after
treatment.
Nankinga (1999) applied 500 g of maize culture
(2.65 × 108 spores/g) to the topsoil around banana
mats in small (i.e. eight mats) plots covered with grass
mulch. Weevil levels were then compared to plots in
which no fungi were applied. Four weeks after appli-
cation, 48% of collected weevils in treated plots were
infected. Moreover, 20% of weevils collected in treated
plots 5 months after treatment were infected. However,
the treatment did not reduce weevil trap captures over
a 7-month period suggesting migration across small
plots.
In a second experiment, weevil populations were
monitored with pseudostem traps for 8 months in
plots that received two B. bassiana applications. Mean
weevil counts were lowest in plots treated with maize
formulation (40 trapped weevils per plot) followed by
plots receiving soil formulation (54), oil formulation
(68), and controls (81). The incidence of field mortality
of weevils observed in traps was low with a maximum
of 5% and often under 1%. Peak mortality reached 15%
in plots treated with maize formulation and 13% in soil
formulation. Maize-based formulations also tended to
reduce weevil damage levels in the central cylinder
and cortex. Although the maize formulation showed
the potential of field level control, the application rate
(250–500 kg/ha; 1×1014–2×1015 spores/ha) employed
in this study was not economically viable.
Biology and IPM for banana weevil 129
Sublethal effects of entomopathogens against insect
adults may lead to reduced fecundity or egg sterility
(Nankinga 1999). For example, Nankinga (1999) found
that application of B. bassiana to the soil in pots led to
a 56% infection of adults and a 73% reduction in egg
number. In another experiment, where suckers were
treated with B. bassiana, egg eclosion was 39% less
than in controls. In addition, infected adults can trans-
mit both B. bassiana and M. anisopliae to eggs (and
subsequent larvae) (Nankinga & Ogenga-Latigo 1996).
Disk on stump and pseudostem traps may aggre-
gate weevils at delivery sites for entomopathogens
(Kaaya et al. 1993; Contreras 1996; Nankinga 1999).
Budenberg et al. (1993a) further suggested that semio-
chemicals might increase weevil attractiveness of
entomopathogen-baited traps. This would require a
modification of the current pheromone-based pitfall
trap design such that the weevils become infected
rather than drown. Such a method would be advan-
tageous over standard pitfall trapping only if infected
adults were able to transmit the pathogen to other
weevils. Currently, IITA, Uganda NARO, and ICIPE
are also trying to develop a delivery system for
entomopathogens using a kairomone-based trapping
system.
g. Transmission among weevilsNankinga (1994) exposed adult weevils to B. bassiana-
infected weevils. Transmission rates were higher from
dead weevils than from live infected weevils. For exam-
ple, a single dead weevil could infect 70% of exposed
weevils, while a living weevil infected 28%. If unin-
fected weevils were exposed to three dead or three
infected live weevils, infection rates increased to 98%
and 70%, respectively. Schoeman & Schoeman (1999)
mixed uninfected weevils with weevils inoculated with
B. bassiana spore-suspensions. After 44 days, all of
the exposed weevils were dead and showed signs of
mycosis, while 24% of the uninoculated weevils were
also dead with signs of mycosis. However, transmission
rates among weevils in field situations, where weevil
density is relatively low, remains unclear.
2. Endophytes
A wide variety of endophytic fungi have been isolated
from nearly all examined plants (ranging from grasses
to trees) and plant tissues (Carroll 1991). Many of these
have developed mutualistic relationships with plants
and some act as antagonists to pests and diseases. Endo-
phytes may be classified as constitutive or inducible
mutualists; the former occur throughout the life of their
hosts, while the latter remain in a latent state until
stimulated by pest attack (Carroll 1991). The preva-
lent mode of action appears to be through the pro-
duction of metabolites that act as oviposition repel-
lents, toxins or feeding deterrents. Plant physiological
and ecological factors may influence endophyte effi-
cacy. Endophytes can enhance resistance to specialist
herbivores that have evolved mechanisms to circum-
vent the plant’s normal defences (Carroll 1991; Breen
1994).
Research is currently being undertaken at IITA
in Uganda, in collaboration with the University of
Bonn, for the development of a biological control
programme using endophytes against banana weevil.
Research protocols include: (1) isolation and identi-
fication of endophytes from banana corms and pseu-
dostems; (2) screening against banana weevil eggs
and larvae; (3) determination of mechanisms by which
promising strains kill weevil immatures; (4) reinocula-
tion into banana tissue culture plantlets and/or banana
suckers; (5) determination of distribution, prevalence,
and persistence of promising endophytes within banana
plants; (6) efficacy studies in pot and field trials for a
range of clones and under different ecological condi-
tions; (7) developing markers or vegetative compati-
bility groups (VCG) to identify strains of endophytes;
(8) pathogenicity testing of promising strains in banana
and other crops.
Griesbach (1999) obtained 200 isolates from a
total of recently harvested 64 plants on 21 farms
in Ntungamo district, Uganda. Samples were taken
from five highland cooking bananas (AAA-EA), one
highland brewing banana (AAA-EA) and the exotic
clone Kayinja (ABB). Spore suspensions of 12 iso-
lates (8 Fusarium spp., three Acremonium spp., one
Geotrichium sp.) caused 80–100% mortality in weevil
eggs, while 74 additional isolates caused 60–79% mor-
tality. Further work was restricted to the 12 most
promising isolates. Testing of mycotoxins (rather
than direct colonisation) produced 30–88% mor-
tality for the Fusarium isolates and 16–24% for
Acremonium. Screening against banana weevil larvae
gave 0–48% mortality with the best two strains being
F. cf concentricum (48%) and F. oxysporum (32%).
It is possible that endophytes might induce resistance
in banana plants to pests, although initial studies on
induced effects against banana nematodes produced
negative results (Niere 2001).
130 C.S. Gold et al.
Griesbach (1999) was able to successfully inocu-
late tissue culture plants with endophytes. Colonisation
rates were 39–73% colonisation for Fusarium,
0–26% colonisation for Acromonimum, and 0% for
Geotrichium. For the best Fusarium strains, inoculation
success was 38% for Valery (AAA), 44% for Kayinja,
73% for Nabusa (AAA-EA), and 88% for Gros Michel
(AAA). Within three highland cooking clones, the best
Fusarium strains, colonisation rates were 12% in root
tips, 39% in root bases, 48% in corms, and 3% in pseu-
dostems. By contrast, there was only 3% establish-
ment of inoculated endophytes in pared or hot water
treated suckers. Preliminary pot trials on the effects
of inoculated endophytes on weevil damage in tis-
sue culture plants produced promising but inconsistent
results.
3. Entomopathogenic nematodes
The use of entomopathogenic nematodes for insect
control and, specifically, against banana weevil has
been reviewed by Treverrow et al. (1991), Parnitzki
(1992), and Schmitt (1993). The most commonly
used species are within the genera Steinernema and
Heterorhabditis. These have received wide attention as
biological control agents because of wide host range,
ability to kill host rapidly, and no adverse effects on
environment (Schmitt 1993).
The infective stage locates its host by detect-
ing excretory products, temperature gradients, etc.
(Schmitt 1993). Five species of Xenorhabdus bacteria
are mutualistically associated with Steinernema while
Photorhabdus spp. is associated with Heterorhabditis.
Infective juvenile nematodes enter through natu-
ral orifices (Steinernema) or interskeletal membrane
(Heterorhabditis) (Treverrow et al. 1991). After enter-
ing the host, the nematodes penetrate mechanically into
the haemocoel and release Xenorhabdus which causes
septicaemia and insect death within 1–2 days (Schmitt
1993).
Entomopathogenic nematodes have a non-feeding
stage that can survive in the soil for extended peri-
ods. Soil temperature, soil moisture, and soil types are
important abiotic factors which affect these nematode
survival and performance (Schmitt 1993). Parnitzki
(1992) suggested that sensitivity to drought, high tem-
peratures, and ultraviolet light are also limiting factors
in the efficacy of entomopathogenic nematodes.
In surveys in Brazil, Schmitt (1993) found ento-
mopathogenic nematodes to be widespread. However,
naturally occurring mortality of banana weevils to
entomopathogenic nematodes was low and, as with
entomopathogenic fungi, viable delivery systems are
an important consideration.
Entomopathogenic nematodes (Steinernema spp.
and Heterorhabditis spp.) have been tested against
banana weevils in Australia and the Pacific (Treverrow
et al. 1991; Parnitzki 1992; Treverrow & Bedding
1991; Treverrow 1993, 1994), the Caribbean (Laumond
et al. 1979; Kermarrec & Mauleon 1975, 1989;
Figueroa 1990), Florida (Pena et al. 1993) and Brazil
(Schmitt 1993). Entomopathogenic nematodes may
be more effective against banana weevil larvae than
against weevil adults (Figueroa 1990; Kermarrec
et al. 1993; Pena & Duncan 1991; Treverrow 1994).
For example, Figueroa (1990) reported Steinernema
feltiae, S. glaseri, and S. bibionis caused 13–66%
mortality of late-instar larvae in laboratory assays
and 100% mortality and a 70% reduction in weevil
galleries in potted plants. Pena et al. (1993) found
47–89% mortality of weevil larvae compared to 45%
on weevil adults. Larval mortality in greenhouse
tests was 37%. Treverrow et al. (1991) found ento-
mopathogenic nematodes applied to crosscuts in resid-
ual corms were equally effective against small and large
larvae.
However, the cryptic habitat of weevil larvae within
living plants makes delivery against these stages diffi-
cult (Treverrow 1994). For example, Treverrow et al.
(1991) and Treverrow & Bedding (1993) found spray-
ing of entomopathogenic nematodes onto corms inef-
fective against larvae as there were few entry points
and the holes made by adults were quickly blocked by
callus tissue. In addition, it is difficult to know which
plants are infected with larvae, such that applications
can not be restricted to plants or plots with high weevil
numbers.
Therefore, Parnitzki (1992) and Treverrow (1993,
1994) recommended that applications of ento-
mopathogenic nematodes should target adult weevils.
Parnitzki (1992) screened 30 strains of Steinernema
and Heterorhabditis against banana weeviladults in
Tonga and Australia and found that the most effective
strains differed between the two sites. This suggests
either strain–environment interactions or the presence
of weevil biotypes. Parnitzki (1992) recommended that
strains should be screened locally before implementing
a programme using entomopathogenic nematodes. In
Tonga, Parnitzki (1992) felt that only one Steinernema
and three Heterorhabditis offered potential. Several
other strains were able to locate the weevil but were
unable to overcome the host’s defences.
Biology and IPM for banana weevil 131
The development of a delivery system had to con-
sider a number of factors. First, infection of adult
weevils was limited by difficulties the nematodes expe-
rienced in entering the host (Treverrow & Bedding
1993). In laboratory tests, the first spiracle appeared
to offer the best entry point, but this site is secluded by
the insect’s elytra. Second, infection required at least
several days of exposure to the nematodes, with max-
imum efficacy attained with 7–14 days exposure. This
meant that an ideal delivery system would retain weevil
adults at the exposure site.
Ground sprays were considered in that they are
not limited by the availability of certain plant stages
or residues, but these required high nematode den-
sities and persistence was limited (Treverrow 1994).
In contrast, the efficacy of applications could also be
increased if adults could be aggregated and retained
at delivery sites (i.e. by attraction to traps). In Brazil,
for example, Schmitt et al. (1992) baited pseudostem
and disk on stump with S. feltiae and compared these
to ground applications. At 7, 14, and 21 days, mor-
tality was higher on pseudostem traps (51, 40, 40%,
respectively) and disk on stump traps (70, 51, 32%)
than following soil applications (58, 24, 25%).
In Tonga, Parnitzki (1992) applied entomopathogenic
nematodes to cuts in corm stumps (left at 0.5 m) shortly
after harvest. Although weevil adults were attracted to
such sites, mortality was low (i.e. 20%) and there was
no reduction in damage levels.
Treverrow et al. (1992) and Treverrow & Bedding
(1993) developed a delivery system for ento-
mopathogenic nematodes capitalizing on the weevil’s
attraction to cut corms and damaged plants. Initially,
the made two holes in the residual corm or split it par-
allel to the ground (Treverrow 1993). This was later
revised to the use of two conical shaped cuts in residual
corms. These cuts attracted adult weevils and provided
thigmotactic stimuli that encouraged them to remain at
the infection sites. The holes also buffered the delivery
site against temperature extremes and provided excel-
lent conditions (high humidity, moderate temperatures,
protection against ultraviolet light) for nematode per-
sistence. The nematodes were released at a density of
250,000 per hole in a formulation including a poly-
acrylic gel (to reduce water build-up and incidence of
nematode drowning) with an adjuvant of 1% paraffin oil
(to encourage the weevils to raise their elytra, expos-
ing the first spiracle for nematode entry). The nema-
todes persisted for up to 50 days and attacked both
adults and larvae (Treverrow et al. 1991; Treverrow
1994). At moderate weevil infestation levels, nematode
baits performed as well or better than insecticides
(Treverrow 1993; Treverrow & Bedding 1993), but
were not as effective as pesticides in heavily infested
fields (Treverrow 1994). However, controls based on
entomopathogenic nematodes were not economically
competitive with pesticides (Treverrow 1993, 1994).
In contrast to the positive results obtained by
Treverrow, Smith (1995) reported injection of ento-
mopathogenic nematodes into cuts from the pseu-
dostem to the corm in mature plants and residues gave
no benefit over the control. Whereas he was unable to
apply a gel, he attributed the lack of control to larval
drowning. However, in later trials in which the gel was
added to the application formulation, he again found
no benefit. Moreover, he noted that the system was not
attractive to farmers.
XIV. Host Plant Resistance
The literature on the susceptibility of Musa clones
to banana weevil attack is largely fragmentary with
highly variable and often contradictory findings
(Pavis & Lemaire 1997; Kiggundu et al. 1999).
Most often, reported results reflect comparisons
among a small number of clones used in field tri-
als (Sen & Prasad 1953; Hord & Flippin 1956;
Moreira 1971; Oliveira et al. 1976; Mitchell 1978;
Zem et al. 1978; Haddad et al. 1979; Viswanath
1981; Ittyeipe 1986; Irizarry et al. 1988; Kehe 1988;
Bakyalire 1992; Batista Filho et al. 1992; Minost 1992;
Pavis 1993; Seshu Reddy & Lubega 1993; Speijer
et al. 1993; Davide 1994; Pone 1994; Stanton 1994;
Vittayaruk et al. 1994; Abera 1997; Mestre & Rhino
1997; Silva & Fancelli 1998).
Fogain & Price (1994), Ortiz et al. (1995), Rajamony
et al. (1993, 1994, 1995), Anitha et al. (1996) and
Kiggundu (2000) conducted screening trials to identify
existing clones displaying resistance to banana weevil.
These results have been reviewed by Pavis & Lemaire
(1997), Kiggundu et al. (1999), and Kiggundu (2000).
The variability in susceptibility reported by differ-
ent authors for closely related clones, or even across
genome groups may reflect differences in sampling
methods for assessing weevil damage. In field sur-
veys, for example, Gold et al. (1994a) and Bosch et al.
(1996) found different trends when comparing damage
to the corm surface, the outer cortex and the central
cylinder. In Ugandan surveys, plantains (AAB) and
highland bananas (AAA-EA) appeared more suscepti-
ble to banana weevil attack than other genome groups
132 C.S. Gold et al.
(Gold et al. 1994a). For example, both plantains and
highland bananas displayed high levels of attack on the
corm surface with considerable penetration into cortex
and central cylinder. In contrast, weevil attack of Gros
Michel (AAA) was restricted to the corm surface and
cortex with limited penetration into the central cylin-
der. Other introduced beer (AB, ABB), cooking (ABB),
and dessert clones (AB) were relatively resistant with
little surface damage and virtually no penetration into
the corm.
In the Kagera region of Tanzania where banana
weevil damage is often severe, Bosch et al. (1996)
found high levels of surface corm damage in endemic
highland cooking bananas (AAA-EA) as well as exotic
AAA, AB, and ABB clones. However, only the high-
land group sustained high levels of weevil penetra-
tion into the cortex and cylinder. Ogenga-Latigo &
Bakyalire (1993) found that Ndiizi (AB) had similar
levels of surface damage to that of highland cooking
banana, but only 16% as much internal damage.
Unfortunately, some researchers have assessed
weevil damage to the corm surface, while others have
estimated damage to the interior of the corm, making
results difficult to interpret and compare. For exam-
ple, in a screening trial in Uganda, Kiggundu (2000)
found that Nsowe (AAA-EA) scored highest among
highland banana clones in damage to the corm surface
but lowest in internal corm damage. Pavis & Lemaire
(1997) and Mestre (1997) noted the need for standard
screening methods and reference cultivars. Kiggundu
(2000) recommended the use of total cross section dam-
age (c.f. Gold et al. 1994a) as this measure had a high
level of heritability and was well correlated with other
indices of weevil damage. In contrast, Rukazambuga
et al. (1998) suggested the use of damage to the central
cylinder as this damage appeared to have the greatest
impact on plant growth and yield.
Variable findings from studies conducted in dif-
ferent locations may also reflect ecological differ-
ences or genetic variability (i.e. biotypes) among
weevils (Pavis & Lemaire 1997; Kiggundu et al. 1999).
However, some general trends do appear.
1. Resistance across genome groups
Of the two wild progenitors of edible bananas,
M. acuminata (AA) has been reported as more suscepti-
ble to banana weevils than M. balbisiana (BB) (Saraiva
1964;Simmonds 1966; Vilardebo 1973; Mesquita et al.
1984). However, both of these diploids escaped attack
in a screening trial in Cameroon (Fogain & Price 1994).
Mesquita et al. (1984) further suggested that genetic
contribution from M. balbisiana in naturally derived
or bred hybrids conferred higher levels of resistance to
weevils.
Nevertheless, plantains (AAB) are generally con-
sidered the most susceptible Musa genome group to
banana weevil attack and much more susceptible than
most AAA dessert bananas (Ghesquiere 1925; Pinto
1928; Simmonds 1966; Haddad et al. 1979; Mesquita
et al. 1984; Ittyeipe 1986; Jones 1986; Pavis 1988;
Bakyalire 1992; Seshu Reddy & Lubega 1993; Speijer
et al. 1993; Fogain & Price 1994; Gold et al. 1994a;
Price 1994; Sponagel et al. 1995; Pavis & Lemaire
1997). In India, however, Viswanath (1981) reported
plantains as resistant to banana weevil.
Highland cooking bananas (AAA-EA) are also con-
sidered highly susceptible to banana weevil (Sikora
et al. 1989; Bakyalire 1992; Gold et al. 1994a; Bosch
et al. 1996; Rukazambuga et al. 1998). Reports on sus-
ceptibility of AAA dessert bananas (e.g. Gros Michel,
Cavendish, Williams, Valery) have ranged from resis-
tant to susceptible (Zem et al. 1978; Viswanath 1981;
Mesquita et al. 1984; Mesquita & Caldas 1986;
Fogain & Price 1994; Gold et al. 1994a; Stanton
1994; Sponagel et al. 1995; Bosch et al. 1996). Ostmark
(pers. comm.) and Sponagel et al. (1995) suggest that in
AAA dessert bananas weevils favour crop residues over
developing plants and are thus unimportant. In contrast,
Viljoen (pers. comm.) reported serious banana weevil
problems on Cavendish bananas on the southeastern
coast of South Africa.
Ortiz et al. (1995) reported that wild diploids were
generally more resistant than polyploids. AB and ABB
bananas are often considered among the most resis-
tant Musa clones to banana weevil (Hord & Flippin
1956; Mesquita et al. 1984; Mesquita & Caldas 1986;
Seshu Reddy & Lubega 1993; Gold et al. 1994a;
Musabyimana 1995; Ortiz et al. 1995; Bosch et al.
1996; Abera 1997). Haddad et al. (1979) found
ABB clones to be intermediate in susceptibility to
banana weevil between plantains and dessert bananas,
while Viswanath (1981) found ABB bananas to be
susceptible.
Limited information is available on susceptibility of
tetraploids to banana weevil. Ittyeipe (1986) reported
AAAA clones to be the most susceptible to weevil
attack, while Viswanath (1981) found larval success
greatest on AABB bananas.
In germplasm collections in Cameroon and Nigeria,
ensete appeared to be highly susceptible to banana
weevil (Pavis & Lemaire 1997; C. Gold pers. observ.).
Biology and IPM for banana weevil 133
However, in Ethiopia, where the crop is most widely
grown, ensete largely escapes attack because most
production is above the weevil’s upper elevational
threshold (M. Bogale et al. unpubl. data).
Kiggundu (2000) conducted a screening trial in
Uganda with 45 clones including representatives from
all five clonal groups of East African highland bananas
(c.f. Karamura 1998), plantains, exotic cooking, and
brewing (ABB), dessert (AAA), diploids (AA, AB)
and hybrids. Cross section damage (c.f. Gold et al.
1994b) ranged from 0% to 11%. Plantains and highland
bananas appeared most susceptible followed by ABBs,
hybrids, ABs, AAAs, and AAs (Table 9). Cluster anal-
ysis suggested that 19 clones were highly suscepti-
ble to weevil attack (mean damage 8%), 17 clones
were intermediate in susceptibility (4%) and 9 clones
were resistant (1%) (Table 10a).
In India, Rajamony et al. (1993, 1994, 1995) and
Anitha et al. (1996) screened 87 clones (including
7 AA, 7 AB, 18 AAA, 27 AAB, and 28 ABB) col-
lected from 13 localities. Weevil damage was ranked
0–4 (although the scoring method was not clearly
described). Considerable variability was found within
each genome group with lowest damage in the AB
bananas and limited differences among the other
groups. In this study, there was little relationship
between susceptibility to banana weevil and to banana
nematodes.
In summary, the data suggest that plantains (AAB)
and highland cooking banana (AAA-EA) are most sus-
ceptible to banana weevil attack. Diploids, other AAA
(e.g. dessert) bananas and AB and ABB bananas appear
Table 9. Means (±standard error) banana weevil damage by
genome groups of Musa in Uganda
Genome Musa type Mean total Range of
group weevil total weevil
damage damage
AAB Plantains 7.8 7.5–8.1
AAA-EA East African 5.9 2.7–9.9
highland
bananas
ABB Kayinja 3.3 2.3–4.1
Bluggoe
Hybrids Plantain derived 6.6 6.3–7.9
Banana derived 0.2 0.1–0.2
AB Ndiizi, Kisubi 2.4 1.0–3.1
AAA Yangambi-km5, 1.8 0.4–4.0
Cavendish,
Gross Michel
AA Wild banana 0.2 0.2
Calcutta-4
Source: Kiggundu (2000).
to be less susceptible, although considerable variability
has been reported from different studies.
2. Clonal resistance
In screening trials in Cameroon (Fogain & Price 1994)
and Nigeria (Ortiz et al. 1995), all plantain clones
appeared susceptible to banana weevil. In contrast,
Chavarria-Carvajal (1998) evaluated 8 plantain clones
and found the Common dwarf variety and a Lacknau
clone to have less than 20% of the damage occur-
ring in Sin Florescencia and Rhino Horn plantains.
Irizarry et al. (1988) and Fogain & Price (1994)
also found Lacknau clones less susceptible than other
plantains.
In Uganda, field survey data suggested differences
in susceptibility to banana weevil attack among high-
land banana clones (Gold et al. 1994a). Atwalira
(=Nassaba) and Kisansa displayed weevil damage
scores 2–3 times higher than those for Mbwazirume
and Nakyetengu, while the degree of penetration
into the central cylinder was greatest for Nakitembe,
Namwezi, and Musakala. However, these results
were biased by clonal distribution. For example,
Mbwazirume was quite common on farms in regions
with high levels of management and commercial objec-
tives (e.g. Masaka, Mbarara districts). In contrast,
Atwalira was often grown on small farms with lim-
ited inputs (e.g. Luwero). Moreover, Atwalira primarily
occurred in 3 sites, all of which supported high levels of
weevil damage. Further analysis, employing Z values
(i.e. standard scores) (Zar 1984) to eliminate site dif-
ferences, showed Atwalira to have only slightly above
average levels of damage in the sites where it occurred
(Gold et al. unpubl. data).
Kiggundu’s (2000) screening trial included 26
highland bananas among the 45 evaluated clones.
Damage scores within the highland banana group
ranged from 3% to 10%. Cluster analysis of all
clones suggested that 15 highland clones were sus-
ceptible, while 11 were intermediate in susceptibil-
ity (Table 10a). However, analysis of only the high-
land group suggested that 7 clones were highly sus-
ceptible to weevil attack (mean damage 9%), 13
clones were intermediate in susceptibility (6%) and
6 clones were resistant (4%) (Table 10b). Of the
most popular and widespread clones, Mbwazirume and
Nakyetengu appeared relatively resistant. One brew-
ing clone was considered susceptible, three were inter-
mediate in susceptibility and two appeared relatively
resistant.
134 C.S. Gold et al.
Table 10a. Three banana-weevil susceptibility response groups derived from cluster analysis
of 45 Musa cultivars in a screening trial in IITA Sendusu Farm, Namulonge, Uganda
Resistant (Cluster 1) Intermediate (Cluster 2) Susceptible (Cluster 3)
Name Total Name Total Name Total
damage damage damage
TMPx15108-6 2.0 Nakamali 6.4 TMPx7152-2 10.7
Cavendish 1.7 Enshenyi 5.5 Kibuzi 10.1
TMBx612-74 1.4 Kabula 5.4 Ndiibwabalangira 9.9
Kisubi 1.0 Siira 5.2 Endiirira 9.2
Yangambi-Km5 0.3 Nandigobe 5.2 Nakawere 8.8
TMB2x8075-7 0.3 Mutangendo 4.9 Obino l’Ewai 8.3
Calcutta-4 0.2 Bukumu 4.9 TMPx5511-2 7.9
TMB2x7197-2 0.1 Nakyetengu 4.1 Namafura 7.7
TMB2x6142-1 0.1 Bluggoe 4.0 Atwalira 7.7
Bogoya 3.7 Namwezi 7.6
Nsowe 3.3 Naminwe 7.6
Mbwazirume 3.1 Gonja 7.3
Nalukira 3.1 TMPx7002-1 6.8
Tereza 3.0 Musakala 6.5
Ndiizi 2.9 Nakabululu 6.4
Kayinja 2.4 Shombobureku 6.4
FHIA03 2.2Nakitembe 6.2
Bagandeseza 6.1
Kisansa 5.8
Source: Kiggundu (2000).
Table 10b. Three response groups derived from cluster analysis
of EAHB cultivars in a screening trial in IITA Sendusu Farm,
Namulonge, Uganda (∗ = brewing types)
Resistant Intermediate Susceptible
Mbwazirume Bagandesesa∗ Atwalira
Nakyetengu Enshenyi Endiirira∗
Mutangendo Kabula∗ Kibuzi
Nsowe∗ Kisansa Naminwe
Nalukira∗ Bukumu Nakawere
Tereza Musakala Ndiibwabalangira
Nakabulu Namafura
Nakamali
Nakitembe
Namwezi
Nandigobe
Shombobureku∗
Siira
Source: Kiggundu (2000).
3. Mechanisms conferring resistance
Successful attack of bananas by banana weevils
involves host plant location, host plant acceptance
(oviposition), and host plant suitability (larval survival,
developmental rate, and fitness). Host plant resis-
tance may affect any of these processes. Most com-
monly host plant resistance mechanisms have been
attributed to antixenosis (non-preference), antibiosis
and/or host plant tolerance (Painter 1951). For banana
weevil, available data suggest that antibiosis is the
most important factor conferring host plant resistance,
while antixenosis is of little importance. Little has been
reported on host plant tolerance to banana weevil attack
as such work would require yield loss studies over
several crop cycles.
a. Antixenosis
Antixenosis suggests that resistant clones avoid pest
attack by reducing rates of host plant location
(i.e. attraction) and/or host plant acceptance; the com-
bined effects of these two processes would be reduced
oviposition. Pavis & Lemaire (1997) suggested that
antixenotic factors may also deter adult feeding.
Rwekika (1996) and Rwekika et al. (2002) found
the phenolic glucoside salicin an attractant to banana
weevils and suggested that it served as a feeding stim-
ulant for adults. He further noted that salacin and
glucose were present in higher levels in susceptible
highland banana (AAA-EA) clones than in resistant
clones such as Ndiizi (AB), Pisang awak (ABB), and
Kivuvu (ABB). Gowen (1995) reported all clones to
be susceptible to banana weevil attack and suggested
that differences in damage levels reflected differences
in weevil attraction.
The data on host plant attraction to susceptible and
resistant clones is equivocal. In laboratory choice tests,
Biology and IPM for banana weevil 135
Mesquita et al. (1984) found clonal preferences for
adult feeding which differed from those for oviposition,
suggesting different levels of host plant acceptance.
Minost (1992) found that Burmanica (AA) was most
attractive to adult weevils followed by Pisang awak
(ABB), Borneo (AA) and French Clair (AAB), while
Petit Naine (AAA), and Rose (AA) were much less
attractive. However, clonal attraction was not related to
weevil damage: Burmanica had low levels of periph-
eral damage, Petit Naine had intermediate damage,
while Pisang awak and French Clair had high dam-
age. Sumani (1997) also found attraction to pseu-
dostems and corms in choice chambers did not reflect
host plant susceptibility. Minost (1992) concluded that
resistance mechanisms must be related to oviposi-
tion and larval development rather than to host plant
attraction.
In contrast, Budenberg et al. (1993b) reported that
females were equally attracted to cut corms and
volatiles from resistant and susceptible cultivars. He
suggested that host plant attraction was related to adult
feeding and not selection of oviposition sites. However,
adults were more commonly observed feeding on rot-
ting banana tissue (e.g. residues, decaying leaves).
Pavis & Minost (1993) also found similar levels of
attractivity to resistant and susceptible clones.
In field studies, Musabyimana (1995) observed dif-
ferential attraction (based on trap capture rates at the
base of the mat) among clones; However, trap captures
were not related to subsequent damage. In a screening
trial in Uganda, Kiggundu (2000) found some differ-
ence in trap captures among clones, but that many of the
resistant exotic clones and hybrids had high numbers
of weevils, while some of the more susceptible high-
land cooking clones (e.g. Atwalira) had low capture
rates. As a result, there was no relationship between trap
catches and subsequent damage. Abera (1997) found
similar trap captures at the base of mats of the resistant
clone Pisang awak (ABB) as for 5 susceptible highland
banana (AAA-EA) clones.
Little work has been done on host plant accep-
tance. Abera (1997) and Abera et al. (1999) found
field oviposition on Kayinja (ABB) to be similar to that
on highland banana clones, even though the latter dis-
played much higher levels of weevil damage. Kiggundu
(2000) looked at oviposition on resistant and suscepti-
ble clones in both choice and no-choice experiments.
There was very little mean separation and the lower
levels of oviposition occurred on clones (Atwalira,
Nakyetengu, Muvubu) that were not considered
resistant.
In summary, the banana weevil is a relatively seden-
tary insect living in perennial systems with an abun-
dance of host plants. It is unclear to what extent weevils
are preferentially attracted to one clone over another.
Data on movement patterns suggest that some weevils
may spend extended periods of time at the base of a sin-
gle mat, while less than 40% of the weevils moved more
than 10 m in 7 weeks (Gold et al. 1999d). Kiggundu
(2000) suggested that it is unrealistic to think that
banana weevils might walk far looking for a suitable
host. Most likely, tenure time at the base of any given
mat is more related to environmental factors such as
soil moisture.
Although some authors suggest that resistant clones
have feeding deterrents (Pavis & Lemaire 1997) or lim-
ited quantities of feeding stimulants (Rwekika 1996),
there is little evidence to suggest that adult feeding is
an immediate prerequisite for oviposition. The weevil
can live for extended periods of time without feeding
and can move freely from preferred feeding sources
(e.g. decaying residues) to oviposition sites. Available
data indicate that the weevil will freely oviposit on
both susceptible and resistant clones, suggesting that
antibiosis plays a more important role in host plant
resistance (Abera 1997; Kiggundu 2000).
b. Antibiosis
Antibiotic factors are those which negatively influence
larval performance (i.e. poorer survivourship, slower
development rates, reduced fitness). These factors may
include physical (e.g. sticky sap and latex, corm hard-
ness), antifeedants, toxic secondary plant substances
and nutritional deficiencies.
In a mixed cultivar trial, Abera (1997) found weevil
damage to the interior of the corm to be 5–25 times
higher in 5 highland banana clones (3 cooking and
2 brewing) than in Pisang awak. Banana weevil attrac-
tion and oviposition on Kayinja was similar to that on
the highland bananas, while larval survivourship was
estimated as 10–23 times higher in highland bananas
than in Kayinja. From these data, Abera (1997) con-
cluded that antibiosis explained why Kayinja was rel-
atively resistant to banana weevil.
Mesquita & Alves (1983), Mesquita et al. (1984),
and Mesquita & Caldas (1986) found that banana
weevil immatures developed faster and had fewer
ecdyses on some clones than on others. In three studies,
the larval period ranged 22–29, 25–32, and 35–44 days,
depending on clone. Banana clone also influenced
the duration of the pupal stage and pupal weights in
some but not all of the trials. Lemaire (1996) reported
136 C.S. Gold et al.
slower larval development and higher larval mortality
on the resistant clone Yangambi-Km5. Silva & Fancelli
(1998) also reported the influence of clone on larval
developmental period.
Kiggundu (2000) found the length of the larval
period ranged 29–40 days for weevils reared on differ-
ent clones. Two resistant clones, FHIA-03 and Kayinja,
increased larval developmental time. Eclosion rates
were similar among clones. Larval mortality ranged 5–
100% with highest levels occurring in resistant clones
such as Kayinja (100%) and Kabula (AAA-EA) (90%).Larvae reared on Mbwazirume (AAA-EA), FHIA-
03, Ndiizi (AB), Yangambi-Km5 (AAA) also had
high mortality rates. Within the East African highland
group, larval mortality on the more resistant brew-
ing clones tended to be higher than on the cooking
bananas. Corm extracts from Kayinja applied to sus-
ceptible corm material had little impact on eclosion, but
severely inhibited larval feeding, while extracts from
other clones did not.
Pavis & Minost (1993) found a negative correla-
tion (r = −0.47) between corm hardness and infes-
tation rate and hypothesised mechanical resistance
to oviposition or larval development. Ortiz et al.
(1995) assessed 5 plantains cultivars, 2 AAA dessert,
Calcutta 4 (AA), Bluggoe (ABB), Fougamou (ABB)
plus 97 euploid hybrids for corm hardness in transverse
and longitudinal sections within 1 h after collection.
All plantains were equally susceptible to the weevil,
while significant differences were found among the
euploid hybrids for weevil levels and corm hardness;
phenotypic correlations were not significant between
corm hardness and weevil damage scores in segregat-
ing progenies suggesting other resistance mechanisms
may be more important. Kiggundu (2000) also found
no phenotypic relationship between corm hardness and
weevil damage.
Kiggundu (2000) screened extracts of 15 clones from
3 weevil response levels, using high performance liquid
chromatography. The chromatograms displayed peaks
on resistant AB or ABB clones not found on susceptible
clones or resistant AAA clones (i.e. Yangambi-km5 and
Cavendish). The data suggest that an antibiotic mecha-
nism (e.g. toxic compound) is present in cultivars with
the B genome, while resistant AA or AAA bananas
may have other mechanisms of resistance.
Methanol extracts from fresh corm of two cultivars,
Kayinja (resistant) and Atwalira (AAA-EA, suscepti-
ble), were then bioassayed for their effect on weevil
larvae. Application of the Kayinja extract to nutrient
media resulted in a significantly lower developmental
rate and higher mortality of early-instar larvae, than that
resulting from the Atwalira extract (Kiggundu et al.
unpubl. data). A bioassay-guided separation process
of the Kayinja extract was then undertaken using chro-
matographic techniques; 2 of the 16 fractions obtained
were found to be very active against weevil larvae. To
date, however, the compounds responsible for activity
against banana weevil have not been identified.
c. Tolerance
Tolerance suggests that the host plant can sustain
high levels of insect damage without yield reduction.
Cuille & Vilardebo (1963) suggested that Gros Michel
(AAA) was resistant because the large size of the corm
conferred tolerance to weevil attack. Kiggundu (2000)
also suggested that corm can reduce the proportion of
damaged tissue. Pavis (1993) suggested that the vigor-
ous growth of Pisang awak allowed it to tolerate moder-
ate levels of attack. However, no studies have compared
damage thresholds and related yield losses for different
Musa clones.
4. Breeding for resistance
To date, there have been no attempts to breed bananas
or plantains for resistance to banana weevil. Breeding
for resistance depends upon sound knowledge of resis-
tance mechanisms, resistance markers and the genetics
of resistance (Kiggundu et al. 1999). As a foundation, it
is important to determine if there are useful sources of
resistance within the available germplasm. Kiggundu
(2000) observed that the wild diploid Calcutta-4 and
the clones Yangambi-Km5 and FHIA-03 showed high
levels of resistance and might be exploited in breed-
ing programmes. Lemaire (1996) and Mestre & Rhino
(1997) also found Yangambi-Km5 to be highly resis-
tant to banana weevil. Calcutta-4 has already been suc-
cessfully used in conventional breeding programmes
in Nigeria and Uganda, while the male/female fertil-
ity of Yangambi-Km5 and FHIA-03 still need to be
determined (Kiggundu 2000).
Alternatively, breeding for resistance to banana
weevil can employ the use of biotechnological tools
to identify and introduce resistant genes into plantains
or highland banana plants. Such studies could seek to
identify candidate genes from within and without the
Musa genome and through currently available transfor-
mation systems, study the expression of such genes in
banana. This type of research could also include both
Biology and IPM for banana weevil 137
damage-induced gene expression (i.e. in known resis-
tant Musa cultivars) and enzyme (amylase and pro-
tease) inhibitor gene expression using foreign genes
of plant origin.
XV. Botanicals
Walangululu et al. (1993) reported that Tephrosia
leaf powder reduced weevil attraction to treated baits.
However, no follow up studies to these preliminary
results have been reported. In contrast, McIntyre et al.
(2002) found that intercropping and mulching with
T. vogelii had no effect on either weevil adult popula-
tion size or weevil damage to highland cooking banana.
In Kenya, Musabyimana (1999) and Musabyimana
et al. (2001) conducted a systematic and detailed study
on the effects of neem (Azadirachta indica) seed deriva-
tives on banana weevil adult activity , success of imma-
tures and resulting damage. This research, including
both laboratory and field trials, employed different for-
mulations of neem seed powder (NSP), neem kernel
powder (NKP), neem cake (NC), and neem oil (NO).
These formulations were derived from ripe fruits from
coastal Kenya which were then dried for 3–4 days to
13% moisture content. The azadirachtin content was
determined as 4000 ppm for NSP, 5500 ppm for NKP,
5800 ppm for NC, and 850 ppm for NO. Musabyiamana
(1999) and Musabyimana et al. (2001) reported the
following results:
Adult settling: In laboratory choice and no-choice
experiments, treatment of corm pieces
(cv Nakyetengu, AAA-EA) with NSP and NO greatly
reduced the settling response of adults at 48–84 h after
application. The strength of this response was dose
dependent. For example, in a choice experiment, 53%
of the weevils settled on controls compared to 11% on
2.5% NO formulation and 6% on 5% NO formulation.
Oviposition and hatchability: Oviposition was 3–10
times greater on controls than on treated corm. Hatch-
ability of inserted eggs in controls (41%) was 3–20
times treater than on treated material.
Larval feeding: Third-instar larvae took longer to
locate feeding sites and initiate feeding on neem-treated
corm disks than on water-treated controls. Many of
the larvae quickly ceased feeding on treated mate-
rial. Larvae took 18 min to penetrate the control discs
and caused 75% damage (using a modification of
Vilardebo’s (1973) CI) compared to disks treated with
NSP (55 min; 19%); NKP (162 min; 15%); NC (25 min;
22%); NO (34 min, 7%).
Larval growth: After 4 and 14 days, respectively, mor-
tality of second-instar larvae was statistically similar on
controls (17%; 17%) than on treated material (25–40%;
40–60%). However, larval weight was 297 mg in con-
trols, 188 mg in NC, and 61–81 mg in other treatments.
Population build-up and damage: Three months after
release of weevils at the base of bananas planted in
drums, populations were 54–270% higher in controls
than where NC or NSP had been integrated into the
soil. In additional drum experiments, weevil damage
in controls was greater than in neem-treated materi-
als, even though adult populations were similar among
treatments.
Phytotoxicity: NKP and NO appeared toxic to the
banana plants and may have interfered with nutri-
ent and water uptake. NSP and NC displayed phyto-
toxic effects only at application rates >100 g/plant.
Phytotoxicity levels may have been affected by soil
type and azadirachtin content (found to be high in the
NC used in these trials).
Application methods, frequency, rates: Direct appli-
cation of NC and NSP to the soil was much more
cost-effective than applications of aqueous solutions.
Overall, NSP appeared to be the preferred deriva-
tive as it was easier to produce and had better
effects. From these results, Musabyimana (1999)rec-
ommended application rates was 60–100 kg/ha once
every 4 months.
Field trials: In field trials at 3 sites, applications of
NC and NSP (1) contributed to higher sucker establish-
ment; (2) had little impact on adult numbers; (3) pro-
vided major reductions in weevil damage; (4) reduced
nematode damage; and (5) contributed to yield advan-
tages of up to 50% across 2 crop cycles. However, only
high application rates reduced weevil damage at the
site where weevil damage was most heavy. This appli-
cation rate also resulted in phytotoxicity problems and
loss of the ratoon crop.
Musabyimana’s (1999) results suggest that neem
derivatives can reduce weevil damage by interfering
with each stage of attack: (1) fewer adults will locate
or remain at the host plant; (2) females locating the host
plant will have reduced oviposition; (3) eclosion rates
138 C.S. Gold et al.
will be reduced; (4) an antifeedant effect will delay
and reduce larval feeding; and (5) larval fitness will
be reduced. The influence of neem applications on lar-
val success suggest that neem derivatives also have a
systemic effect.
In laboratory studies in Cameroon, Messiaen
(2000, 2002) had results consistent with those of
Musabyimana (1999): Neem had a repellent effect
on adults and reduced oviposition levels and eclosion
rates. Braimah (1997) found that potted soil which
had previously supported neem plants were repellent
to weevils. Silva & Fancelli (1998) also found neem
to be a repellent to adults but provided little detail.
In addition, Messiaen (2000, 2002) reported that neem
affected fertility of female weevils.
However, in field studies, Messiaen et al. (2000) and
Messiaen (2002) found limited advantage in weevil
control from applications of neem dips (i.e. aqueous
solution of concentrated NSP) and no benefits from
granular applications of NSP (30–100 g/plant). Neem
treatments did not have any effect on weevil adult pop-
ulations in either of two trials. However, neem dips
reduced sucker mortality by 73–85% and total plant
mortality by 50%. Neem dips also reduced damage in
one trial by 70% but had no effect on weevil damage
in a second trial. In contrast, had no effect on plant
mortality or weevil damage.
From his results in Kenya, Musabyimana (1999)
concluded that NSP and NC soil applications are effec-
tive enough to do away with paring and hot water
treatment of suckers to be used as planting material.
His data suggest that extended protection under field
conditions is possible. However, the largely negative
results obtained by Messiaen et al. (2000) and Messiaen
(2002) in Cameroon were inconsistent with those of
Musabyimana (1999) and show that it would be useful
to conduct further studies at additional sites. In addi-
tion, the availability of neem products, their economic
viability and their acceptance by farmers in different
banana production systems needs to be determined.
XVI. Pesticides
Chemical pesticides for control of banana weevil may
be applied to protect planting material (through dipping
of suckers or applications in planting holes), periodi-
cally applied at the base of the mat after crop establish-
ment, and/or applied to pseudostem traps to increase
trap catches. Since the first recommendation in 1907
for the use of chemicals to control banana weevil,
there have been numerous studies on the relative
efficacy of different insecticides under different for-
mulations and application rates, persistence, and the
appearance of insecticide resistance in banana weevils.
Chemicals remain an important part of banana weevil
control although costs often make them prohibitive for
subsistence farmers.
The early use of non-synthetic pesticides against
banana weevil has been reviewed by Viswanath (1976).
Gravier (1907) recommended immersing suckers in
Bordeau mixture. During the next 20 years, a range of
chemicals, including sodium arsenite, mercuric chlo-
ride, lead arsenate, Paris green, calcium arsenate, and
borax were tested against the weevil. Of these Paris
green and sodium arsenite were deemed the most effec-
tive (Froggatt 1924, 1925; Veitch 1929; Sein 1934;
Weddell 1945).
In 1951, the use of chemicals gained further impor-
tance with the advent of synthetic insecticides that
largely replaced labour-demanding cultural controls
such as trapping or sanitation (Braithwaite 1958;
Vilardebo 1984; Simon 1994). As with many other
pests, the introduction of chemicals in the 1950s was
greeted with optimism. Braithwaite (1958) suggested
that eradication of the banana weevil might be achieved
with aldrin and dieldrin.
Since the introduction of synthetic insecticides, a
wide range of chemicals, encompassing all of the
major classes, have been tested and recommended
as effective for the control of banana weevil (reviewed,
in part, by Sponagel et al. (1995) and Seshu Reddy
et al. (1998)). These have include aldicarb, aldrin, ben-
diocarb, cadusafos, carbaryl, carbofuran, carbosulfan,
chlordane, chlorfenvinphos, chlorpyrifos, chlotecore,
cyfluthrin, DDT, diclorvos, dieldrin, dimethoate, disul-
foton, ekadrin, endosulfan, endrin, EPN, ethoprop,
fensulfothion, fenthion, fipronil, HCH, heptachlor,
isazofos, isofenphos, kepone, lindane, mephos-
folan, monocrotophos, omethoate, oxamyl, parathion,
phenamiphos, phorate, pirimiphos-ethyl, profenofos,
propoxur, prothiophos, tebupirimphos, triazophos, and
trichlorphon. Some of these chemicals (e.g. isazophos,
oxamyl, phenamiphos) served primarily as nematicides
but also provided good control against banana weevil
(Robalino et al. 1983; Bujulu et al. 1986). Recommen-
dations include sucker drenches, and applications to
planting holes, the base of the mat and to pseudostem
traps. Many previously recommended chemicals have
since been banned or otherwise fallen out of favour
for high levels of mammalian toxicity, environmental
concerns, and/or the development of resistance.
Biology and IPM for banana weevil 139
Chemical pesticides tend to be more regularly
used in commercial plantations, while insecticide use
is much less for low-resource, subsistence growers.
During rapid rural appraisals at 25 sites in Uganda in
1991, for example, few farmers reported use of chem-
ical insecticides in banana fields (Gold et al. 1993).
Most farmers claimed that they could not afford, had
no access to or no information on how to use insecti-
cides. At seven sites, a majority of farmers expressed a
desire to apply chemicals against banana weevil, if they
were subsidised or made more affordable. Many farm-
ers found the use of insecticides against banana weevil
appealing because chemicals require little labour, are
fast-acting and appear to be a reliable means of con-
trol. In contrast, farmers had more limited confidence
in cultural control methods which require labour inputs
and for which results might not be apparent for many
months.
In a commercial growing region of Masaka dis-
trict, Uganda an estimated 30–40% of the farmers in
Masaka regularly used pesticides (70% carbofuran) to
control banana weevil (Gold et al. 1999a). Elsewhere
in the district, however, less than 30% of farmers
applied chemicals (mostly carbofuran) against the
weevil (Ssennyonga et al. 1999). An equal propor-
tion of farmers had abandoned the use of insec-
ticides, primarily because of cost. Those farmers
who continued to use insecticides tended to be
commercial farmers and in the upper economic strata
of the community. Most of those who used carbo-
furan reported it to be very effective at controlling
weevils.
Insecticide resistance in banana weevil has been doc-
umented in Australia (Kelly 1966; Vilardebo 1967;
Swaine & Corcoran 1973; Edge 1974; Shanahan &
Goodyer 1974; Edge et al. 1975; Wright 1977; Swaine
et al. 1980; Collins et al. 1991), Latin America
(Sotomayor 1972; Foreman 1976; Mitchell 1978;
Mello et al. 1979; Sampaio et al. 1982) and Africa
(Bujulu et al. 1983; Gold et al. 1999a) for a range
of chemicals including cyclodienes (aldrin, BHC,
heptachlor, dieldrin), organophosphates (chlorpyrifos,
ethoprophos,pirimiphos-ethyl, and prothiophos) and
carbamates (carbofuran). Cross-resistance has also
been demonstrated (Edge 1974; Collins et al. 1991).
Castrillon (2000) suggests that in concert with the
development of resistance, pesticides upset natural
control by endemic natural enemies, leading to greater
weevil pressure. Sengooba (1986) and Sebasigari &
Stover (1988) attributed weevil outbreaks in Uganda
to the development of resistance to dieldrin.
Roberts (1958) attributed outbreaks of another
banana weevil, M. hemipterus, to applications of dield-
rin which he believed eliminated natural enemies,
including ants. In Uganda and Tanzania, outbreaks
of banana weevil in the mid-1980s were attributed to
pest resurgence following development of resistance to
dieldrin (Sengooba 1986; Sebasigari & Stover 1988;
Taylor 1991; Gold et al. 1999a) leading to loss of
confidence in chemical control by some farmers.
XVII. Summary and Conclusions
Bananas and plantains are important cash and sub-
sistence food crops throughout the tropics and sub-
tropics. Banana is a genetically diverse crop with
numerous clones (including diploids, triploids, and
tetraploids) that may be grown under highly dis-
parate cropping and management systems. Banana is
grown from sea level to >2000 masl. Production sys-
tems range from low-input kitchen gardens and small
stands to intensive, large-scale commercial banana
plantations serving export markets in Europe and North
America. Small-scale production is often extremely
important in the livelihoods of many third-world farm-
ers. In Africa, Latin America, and Asia, a wide vari-
ety of clones (including dessert, cooking, roasting, and
brewing types) serve local markets and contribute to
the food security of the rural poor. The highland cook-
ing banana is the primary staple in the East African
Great Lakes region, while plantains are important foods
throughout West Africa and Latin America.
The banana weevil is the most important insect pest
on bananas and plantains. Studies of banana weevil
began in the early 1900s, although most research has
been conducted since 1980. Much of the information
on the weevil has been published in theses, proceedings
and reports. In some cases, it is hard to separate con-
clusions and recommendations based on the author’s
direct observations and experiences, as opposed to reit-
eration of what has already been written elsewhere.
Recommendations to farmers have often been based on
casual field observations, suppositions and hypotheses
that have not been supported by scientific evidence.
Research findings are often hard to interpret. In
Uganda, for example, damage levels showed only a
weak relationship with adult densities, while popu-
lation shifts did not relate well with the number of
weevils removed through systematic trapping. Surveys
in Uganda have demonstrated wide variability in
weevil populations and damage on adjacent farms
140 C.S. Gold et al.
in similar environments, suggesting that management
has a strong influence on weevil pest status. Analysis
of data, however, did not provide clear relationships
between most management parameters and damage
although the most important factor appeared to be crop
sanitation (Gold et al. 1997, unpubl. data).
Data collected from different sites are often contra-
dictory. The weevil has been variously reported to be
most active in the dry season, the wet season or dis-
play activity patterns independent of weather factors.
Variability in larval developmental rates has also been
reported by different researchers working at proximal
sites. Studies on cultivar susceptibility have also pro-
duced variable results; reports of weevil pest status
on Cavendish, for example, range from unimportant
to very serious. The inconsistency in research find-
ings across studies may reflect differences in banana
clones, management and production systems, agro-
ecological conditions, weevil biotypes, and research
methodologies.
Nevertheless, certain aspects of the banana weevil’s
biology appear clear. The banana weevil is charac-
terised by nocturnal activity, long life span, limited
mobility, low fecundity, and slow population growth.
The sex ratio is 1 : 1. The adults are free living and most
often associated with banana mats and cut residues.
Flight is rare or uncommon and movement by crawl-
ing is limited. Dissemination is primarily through the
movement of infested planting material. The weevil
is attracted to their hosts over short distances by
volatiles. Cut corms, including recently detached suck-
ers used as planting material, are especially attrac-
tive. Males produce an aggregation pheromone that is
responded to by both sexes.
The adults often live more than 1 year, but pro-
duce only a few eggs per week. Oviposition is in
the corm or lower pseudostem. The immature stages
are passed within the host plant, mostly in the corm.
Developmental periods in degree-days have been deter-
mined for the different immature stages. Under ambient
conditions, the egg stage lasts 1 week, the larval stage
about 1 month and the pupal stage 1 week. Population
build-up is slow. The weevil displays only weak den-
sity dependence effects, suggesting that high mortal-
ity to the immatures acts as a brake to population
growth.
Highland banana and plantains are particularly sus-
ceptible to banana weevil damage. In East Africa,
weevil attack has led to accelerated yield declines in
much of the region and the replacement of highland
bananas with exotic brewing bananas that are resistant
to this pest. Severe weevil problems may also appear
in certain regions on clones commonly perceived as
resistant (e.g. Cavendish in South Africa), suggest-
ing that environment may also play a role in deter-
mining weevil. Data on yield loss to banana weevil
are limited. It is clear, however, that weevil problems
become increasingly severe in ratoon crops, although
the weevil can sometimes be a serious problem in newly
planted stands. The weevil may extend the length of
the crop cycle, cause reductions in bunch weight and
contribute to plant loss through toppling and snapping.
Mat die-out and shortened plantation life have also been
attributed to weevil attack.
The weevil’s biology creates sampling problems and
makes its control difficult. Most commonly, weevils
are monitored by trapping adults, mark and recapture
methods, and damage assessment to harvested or dead
plants. A range of sampling methods have been pro-
posed to assess damage, of which the most impor-
tant have been the CI (Vilardebo 1973), PCI (Mitchell
1980), and cross section estimates of damage to the
central cylinder and cortex (Gold et al. 1994b). All
of these require destructive sampling and are often
subjective, making comparisons between studies dif-
ficult. Estimates of damage to the central cylinder and,
possibly cortex, may best reflect the impact of the
weevil on plant growth and yield (Rukazambuga 1996).
Establishing agreed upon sampling protocols should be
a high priority among banana weevil researchers.
Research results suggest that no single method will
bring about complete control of the banana weevil and
that there is no ‘silver bullet’ waiting to be found.
Therefore, a broad IPM strategy appears to be the best
approach to addressing banana weevil problems. This
includes cultural control, biological and microbial con-
trol, host plant resistance, the use of botanicals, and
chemical control. Adoption of different components is
likely to be affected by the farmer’s perception of the
importance of the weevil and his level of resources.
Cultural controls of banana weevil have been widely
promoted and are available to most farmers. The most
important of these methods are the use of clean plant-
ing material, crop sanitation and agronomic meth-
ods to improve plant vigour and tolerance to weevil
attack, neem, and trapping. A combination of these
methods is likely to provide at least partial control
of banana weevil. However, all of these methods have
costs and adoption by resource-poorsubsistence farm-
ers is often limited. Moreover, few controlled studies
have been undertaken to demonstrate the benefits of
these methods.
Biology and IPM for banana weevil 141
The use of clean planting material is important in
excluding banana weevils and other pests from newly
planted banana stands. Tissue culture plantlets are rou-
tinely used in commercial banana production through-
out the world and are being promoted for subsistence
farmers in some countries. Access to tissue culture
and associated costs are limiting factors for dissemi-
nation of this technology. Other methods (e.g. paring,
hot water treatment) of cleaning planting propagules
are also available where access to tissue culture mate-
rial is not possible. Paring requires little labour on
the part of the farmer. In contrast, hot water treat-
ment is often good in theory but very difficult in prac-
tice because of material requirements. Moreover, under
conditions of land pressure, many banana stands are
planted in or proximal to previously infested fields. In
such cases, re-infestation is an important concern and
the use of clean planting material is not a long-term
solution to the banana weevil problem.
Crop sanitation and agronomic practices to pro-
mote plant vigour and tolerance to weevil attack
appear to be common-sense approaches to the weevil
problem. These methods are widely recommended
although few data are available to show that they
reduce weevil pressure. Although the employment of
high standards of agronomic practices in maintaning
stand productivity can not be disputed, their role in
banana weevil control is not clear. In an on-station
trial, Rukazambuga et al. (2002) demonstrated greater
yield losses (tonnes/ha) in vigorously-growing banana
than in stressed systems, while McIntyre et al. (2002)
concluded that weevil and nematode-infestation in
established banana fields impeded uptake of nutri-
ent amendments. Musabyiamana (1999) successfully
reduced banana weevils through applications of neem.
Further testing on the use of neem against banana
weevil should be undertaken.
Trapping of banana weevils with pseudostem traps
and disk-on-stump traps has been widely promoted,
although the overall benefit of trapping has been con-
troversial. Gold et al. (2002b) demonstrated through
farmer-participatory research trials that although sys-
tematic pseudostem trapping reduced banana weevil
populations on most farms, subsequent farmer adop-
tion was low due to labour and material requirements.
Enhanced trapping with synthetic pheromone lures
and kairomones is rightfully a priority for current
study.
Between 1912 and 1938, researchers explored
the prospects for classical biological control of
banana weevil. Generalist, opportunistic predators
were collected in Indonesia and released in the Pacific,
Africa, and Latin America. These predators either
did not establish or failed to bring about control
(Waterhouse & Norris 1987). Recent searches for
banana weevil parasitoids in Indonesia had nega-
tive results. Additional searches in India, the centre
of origin of weevil-susceptible plantains, are prob-
ably warranted. Biological control using ants may
be possible (Roche & Abreu 1982, 1983), but the
efficacy of other endemic predators seems limited
(Koppenhofer & Schmutterer 1993).
Microbial control may offer promise for the con-
trol of banana weevil. Numerous strains of B. bassiana
and M. anisopliae have been demonstrated to kill
high percentages (i.e. >95%) of banana weevils when
applied topically to adults in the laboratory. To date,
research has focused on (1) surveys of naturally occur-
ring infections; (2) pathogenicity studies comparing
strains, spore concentrations, formulations and modes
of application; (3) fungal production on different sub-
strates; and (4) a limited amount of field testing on fun-
gal persistence and population suppression (Godonou
1999; Nankinga 1999). Entomopathogenic nematodes
have also been shown to be cause high levels of mor-
tality banana weevils in both the laboratory and field
(Treverrow et al. 1991; Schmitt et al. 1992). Current
research priorities should include the development of
economic mass production and delivery systems and
evaluation of fungal performance and efficacy under
different agro-ecological conditions. Unless these are
developed, the use of entomopathogenic fungi and
nematodes as biopesticides will either be beyond the
means of most farmers or not competitive with the costs
of chemical insecticides.
The use of endophytes for control of banana weevil
may also be possible (Griesbach 1999), although
research in this area is still in its relative infancy.
Breeding efforts in banana have focused on develop-
ing resistance to nematodes and diseases. To date, there
have been no attempts to breed for resistance to banana
weevil. More recently, however, there has been increas-
ing recognition of the importance of banana weevil
as a worldwide problem (Anonymous 2000). At the
same time, there have been advances in both conven-
tional and non-conventional breeding of banana that
may offer exciting opportunities for developing weevil-
resistant hybrids. Screening trials have demonstrated
the availability of many clones, including Calcutta-4,
Yangambi-km5, and FHIA-03, that are resistant to
the banana weevil and might be utilised in breeding
programmes. Antibiosis appears to be predominant
142 C.S. Gold et al.
mechanism conferring resistance to weevils within
Musa germplasm.
Biotechnological approaches, including genetic
transformation, might facilitate the development of
weevil-resistant clones that retain many of the locally
desirable fruit characteristics. For example, it may be
possible to identify candidate genes from within and
without the Musa genome and through currently avail-
able transformation systems, study the expression of
such genes in banana. This could include both damage-
induced gene expression (i.e. in known resistant Musa
cultivars) and enzyme (amylase and protease) inhibitor
gene expression, using foreign genes of plant origin.
In summary, available cultural controls may con-
tribute to suppressing populations of banana weevil,
but are unlikely to offer complete control in stands of
highly susceptible germplasm or regions where pest
pressure is high. Chemicals often offer complete con-
trol, but their costs, the development of weevil resis-
tance against all classes of insecticides and ecological
side effects mitigate against the use of chemical control
as a long-term strategy.
The way forward appears to be through the improved
management in small farmer systems, the refinement
of microbial control mass production and delivery sys-
tems and the development of both conventional and
non-conventional breeding for host-plant resistance.
Further studies on the use of some endemic natural ene-
mies (e.g. myrmicine ants), the use of semiochemical-
based trapping systems and botanicals, such as neem,
also appear to be warranted.
Acknowledgements
We thank Caroline Nankinga (NARO, Uganda),
Andrew Kiggundu (NARO, Uganda) and two anony-
mous reviewers for their critical comments on earlier
drafts of this paper. We are grateful to the follow-
ing people for their personal communications and the
use of unpublished data: Agnes Abera (IITA-ESARC,
Kampala, Uganda), Ignace Godonou (CABI, Nairobi),
Ahsol Hasyim (Research Institute for Fruits, Solok,
Indonesia), Godfrey Kagezi (IITA-ESARC), Slawomir
Lux (ICIPE, Nairobi, Kenya), Michael Masanza
(IITA-ESARC), Beverly McIntyre (formerly NARO,
Uganda), Gertrude Night (IITA-ESARC), Vincent
Ochieng (ICIPE), Cam Oehlschlager (Chemtica,
International, San Jose, Costa Rica), Suleman Okech
(IITA-ESARC), Eugene Ostmark (formerly FHIA,
La Lima, Honduras), S. Rodriguez (INIVIT, Santa
Clara, Cuba), Daniel Rukazambuga, (formerly Ministry
of Agriculture, Tanzania), K.V. Seshu Reddy (ICIPE),
Henry Ssali (NARO, Uganda), William Tinzaara
(NARO, Uganda), Lancine Traore (formerly IITA
and Katholiecke University, Leuven), Altus Viljoen(University of Pretoria, South Africa). We also
wish to acknowledge the support of Wilberforce
Tushemereirwe (NARO, Uganda), the late Paul
Speijer (IITA-ESARC), Peter Neuenschwander (IITA,
Cotonou), John Lynam (Rockefeller Foundation,
Nairobi), Andrew Kerr and Luis Navarro (IDRC,
Nairobi) and the University of Florida Tropical
Research and Education Center for their support and
encouragement in carrying out our own research on
banana weevils. We thank Claudine Picq (INIBAP,
Montpellier) for her assistance in obtaining hard to
retrieve literature.
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