1982 (Chapter 9) DIEHL Fisiology of Ticks Tick Reproduction = Oogenesis and Oviposition

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C H A P T E R 9 
Tick Reproduction: Oogenesis and Oviposition 
P. A. DIEHL and A. AESCHLIMANN 
Institut de Zoologie, Université de Neuchatel, Neuchatel, Switzerland 
and 
F. D. OBENCHAIN 
International Centre of Insect Physiology and Ecology, P.O. Box 30772, Nairobi, Kenya 
C O N T E N T S 
9.1. Introduction 278 
9.2. Structure of the Female Genital System 280 
9.2.1. The Ovary 280 
9.2.2. The Oviducts, Common Oviduct or Uterus, and Vagina 281 
9.2.3. The Tubular and Lobular Accessory Glands 282 
9.2.4. Gene's Organ and the Porose Areas 282 
9.3. Ovarian Development—Oogenesis 284 
9.3.1. Previtellogenic Development of the Oocyte 284 
9.3.2. Vitellogenic Development of the Oocyte 289 
9.3.2.1. Cytological Aspects of Vitellogenesis 289 
9.3.2.2. Biochemistry of the Yolk 295 
9.3.2.3. Developmental Origins of the Yolk 297 
9.3.2.4. Biochemistry of the Egg-shell 300 
9.3.3. Ovulation and Final Oocyte Maturation in the Genital Tract 300 
9.3.3.1. Cytological Development of the Ovulated Oocyte 301 
9.3.3.2. Syngamy 301 
9.3.3.3. Physiology and Biochemistry of the Ovulated Oocyte 302 
9.4. Oviposition 303 
9.4.1. The Oviposition Process 304 
9.4.2. Composition of Egg-shell Lipids 305 
9.4.3. Developmental Transition—Oocyte to Ovum 306 
9.5. Tick Parasitic and Gonotrophic Strategies 306 
9.5.1. The Argasid Strategy 306 
9.5.2. Evolutionary Modifications of the Argasid Reproductive Strategy 307 
9.5.2.1. Reproductive Diapause 307 
9.5.2.2. Facultative Autogeny 308 
9.5.2.3. Obligatory Autogeny 309 
9.5.3. The Ixodid Strategy 310 
9.6. Critical Variables in the Regulation of Oogenesis and Oviposition 311 
9.6.1. The Impact of Copulation and Insemination 312 
9.6.1.1. Regulation of Ixodid Engorgement Behaviour 312 
9.6.1.2. Regulation of Blood-meal Digestion, Oogenesis, and 
Oviposition 313 
P O T -J 277 
278 P. A. Diehl, A. Aeschlimann and F. D. Obenchain 
9.6.5. Biotic 
9.6.6. Acari« 
9.7. Conclusions 
Acknowledgements 
References 
9.6.3. 
9.6.2. 
9.6.4. 
9.6.1.3. Nature of the Copulation Stimulus and its Mode of Action 
9.6.1.4. Mechanisms Assuring Copulation and Syngamy 
The Impact of the Blood-meal 
9.6.2.1. The Influence of Quantity 
9.6.2.2. The Influence of Quality 
9.6.2.3. The Influence of Host Resistance 
The Impact of Intrinsic Regulatory Mechanisms 
9.6.3.1. Digestion, Respiration, and Synthetic Processes 
9.6.3.2. Putative Mechanisms of Endocrine Control 
9.6.3.3. Neural Control Mechanisms 
9.6.3.4. Female Senescence 
The Impact of Environmental Variables 
9.6.4.1. Photoperiod 
9.6.4.2. Temperature 
9.6.4.3. Water Relations 
9.6.4.4. Radiation 
Biotic Interactions 
Acaricidal Control 
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9 . 1 . I N T R O D U C T I O N 
T h i s c h a p t e r p r o v i d e s a bas i c de sc r ip t i on of the a n a t o m y a n d cyto logy of 
t h e female gen i t a l s y s t e m t o g e t h e r w i t h a d i scuss ion of t h e v a r i o u s p h y s i o -
logical a n d b i o c h e m i c a l a spec t s of tick oogenes is w h i c h o p e r a t e a g a i n s t t he 
f u n d a m e n t a l l y differing b a c k g r o u n d s p r o v i d e d by the d i s t inc t ive g o n o t r o p h i c 
s t ra teg ies of a r g a s i d a n d ixod id t icks. E m p h a s i s is p l aced on the m o r e r ecen t 
l i t e r a t u r e ; m a j o r c o n t r i b u t i o n s p r i o r to t h e ea r ly 1970s a r e d i scussed in t h e 
m o n o g r a p h s of A r t h u r (1962) a n d B a l a s h o v (1972) o r in t he review by O l i v e r 
T i c k s a r e well k n o w n for the i r h igh r e p r o d u c t i v e po t en t i a l ; females of 
l a rge r ixod id species c a n lay u p to 20 ,000 eggs . T h e phys io log ica l a n d 
b i o c h e m i c a l so lu t ions to p r o b l e m s assoc ia ted w i t h t he i n t ak e of t he h u g e 
b l o o d - m e a l a n d its d iges t ion a n d t r a n s f o r m a t i o n in to t h e n u m e r o u s yolk- r ich 
eggs a r e fasc ina t ing , a n d m a n y of these a r e a s h a v e b e e n t r e a t e d in o t h e r 
c h a p t e r s in th is book . Cu t i c l e syn thes i s is r e s u m e d in feeding ixodid females ; 
m u c h a d d i t i o n a l endocu t i c l e is depos i t ed d u r i n g the first few d a y s of feeding. 
T h e e x p a n s i o n of t he cut ic le d u r i n g l a t e r p h a s e s of e n g o r g e m e n t a l lows for 
t h e c o n s i d e r a b l e s t r e t c h i n g n e e d e d to a c c o m m o d a t e t he h u g e b l o o d - m e a l 
( C h a p t e r 1). I n o r d e r to m a x i m i z e t he a m o u n t s of n u t r i e n t s o b t a i n e d , females 
c o n c e n t r a t e t he b l o o d - m e a l by e l im ina t i on of excess w a t e r a n d ions t h r o u g h 
sa l iva ry g l a n d secre t ions ( ixodid t icks) o r t h r o u g h the coxal g l a n d s ( a rgas id 
ticks) ( C h a p t e r 7) . 
T h e b l o o d - m e a l is t h e n d iges t ed in t r ace l lu l a r ly ( C h a p t e r 6 ) ; m o s t of t h e 
b l o o d - m e a l p r o t e i n is t h e n t r a n s f o r m e d in to yolk p ro t e in s by t he g u t cells 
a n d / o r f a t -body cells. T h e p rocess of oogenes is , u l t ima te ly l e a d i n g to t h e 
(1974) . 
Tick Reproduction: Oogenesis and Oviposition 279 
FlG. 9.1. (a) Diagrammatic dorsal and (b) sagittal views of the female genital systems of 
representative ticks from the Argasidae (Ornithodoros moubata), Ixodidae-Prostriata (Ixodes ricinus, 
after Roshdy, 1969, and Graf, 1978a) and Ixodidae-Metastriata (Amblyomma hebraeum (a) after 
El-Said, 1976, and Hyalomma asiaticum (b) after Balashov, 1972). O, ovary; lg, lateral grove; po, 
proximal oviduct; do, distal oviduct; a, ampulla; od, oviduct; u, uterus; co, common oviduct; 
ct, connecting tube; rs, receptaculum seminis; c, cervical vagina; v, vestibular vagina; t, tubular 
accessory glands, 1, lobular accessory gland, vu, vulva. 
A R G A S I D A E : a b 
P R O S T R I A T A : a b 
M E T A S T R I A T A : a b 
280 P. A. Diehl, A. Aeschlimann and F. D. Obenchain 
depos i t i on of eggs , is t h e sub jec t of th is c h a p t e r . T h e e n g o r g e d female tick 
is a v i r t u a l " e g g f ac to ry" w h i c h efficiently t r ans fo rms the c o n c e n t r a t e d 
b l o o d - m e a l cake in to eggs . I t s o p e r a t i o n s p r e s e n t m a n y in t e re s t ing p r o b l e m s , 
n o t on ly to phys io log i s t s a n d b i o c h e m i s t s , b u t a lso to pa ras i to log i s t s . I n d e e d , 
b y c o m p a r i s o n to insec t s , t icks h a v e a n excep t iona l c apac i t y for t r a n s m i t t i n g 
v a r i o u s p a t h o g e n s , s u c h as v i ruses , b a c t e r i a , r i cke t t s iae , a n d p r o t o z o a , to 
the i r p r o g e n y b y w a y of t r a n s o v a r i a l t r a n s m i s s i o n (Burgdor fe r & V a r m a , 
1967; B a l a s h o v , 1972; Burgdor f e r & B r i n t o n , 1975). A t h o r o u g h s t u d y of t he 
cyto logy, phys io logy , a n d b i o c h e m i s t r y of t he oocyte m a y lead to a b e t t e r 
u n d e r s t a n d i n g of h o w tick p a t h o g e n s use t h e t r a n s o v a r i a n r o u t e so 
successfully. 
9.2. S T R U C T U R E O F T H E F E M A L E G E N I T A L SYSTEM 
T h e gen i t a l s y s t e m s of female ixodid a n d a rga s id t icks a r e bas ica l ly s imi l a r 
( rev iewed b y B a l a s h o v , 1972) , cons i s t ing of a n o v a r y w i th p a i r e d ov iduc t s 
w h i c h u l t i m a t e l y j o i n t oge the r as t he c o m m o n ov iduc t o r u t e r u s . A s h o r t 
c o n n e c t i n g t u b e l eads from t h e u t e r u s in to t h e v a g i n a w h i c h is subspec ia l i zed 
in to cerv ica l a n d v e s t i b u l a r r egions (Fig. 9 .1) . After c o p u l a t i o n , a r g a s i d a n d 
p r o s t r i a t e ixod ids (species of Ixodes) s to re t he m a l e p r o d u c t s ( e n d o s p e r m a -
t o p h o r e s c o n t a i n i n g s p e r m , etc.) in t he e n l a r g e d u t e r u s o r in t he e x p a n d e d 
cerv ica l p o r t i o n of t h e v a g i n a , respec t ive ly . M e t a s t r i a t e ixod ids (all g e n e r a 
excep t Ixodes) s to re t h e e n d o s p e r m a t o p h o r e s in a r e c e p t a c u l u m semin i s w h i c h 
is fo rmed pos t e ro -do r sa l l y by a sac- l ike ex tens ion of the cerv ica l p o r t i o n of 
t he v a g i n a . T u b u l a r accessory g l a n d s o p e n in to t he v a g i n a b e t w e e n t h e 
cerv ica l a n d v e s t i b u l a r reg ions . I n feeding ixod ids , t he e p i t h e l i u m of t he 
v e s t i b u l a r v a g i n a deve lops i n to a l o b u l a r accessory g l a n d . 
All female t icks possess a n evers ib le g l a n d u l a r G é n é ' s o r g a n w h i c h o p e n s 
a b o v e the c a p i t u l u m . W i t h t he excep t ion of Ixodes kopsteini ( A n a s t o s et al., 
1973), ixod id females a lso h a v e t w o " p o r o s e a r e a s " , s i t ua t ed o n t h e t e c t u m 
of t h e c a p i t u l u m . T h e s e o r g a n s p l ay a n i m p o r t a n t role in t he p roces s of 
w a t e r p r o o f i n g t h e freshly la id eggs . 
9.2.1 . T h e Ovary 
T h e o v a r y of a newly ecdysed female is a n e longa t ed , t u b u l a r o r g a n , ly ing 
b e h i n d t h e c e n t r a l n e r v e m a s s a n d a b o v e t h e rec ta l sac . F e m a l e Argas 
vespertilionis, a s a n excep t ion , possess p a i r e d ovar ies ( R o s h d y , 1961) . 
T h e o v a r y is a ho l low o r g a n (Figs . 9.2 a n d 9.6) w h o s e l u m e n is s u r r o u n d e d 
b y a t h i n o v a r i a n wal l cons i s t ing of ep i the l ia l cells a n d oogon ia a n d p r i m a r y 
oocytes in v a r i o u s ea r ly s tages of d e v e l o p m e n t . I n unfed a d u l t female Der-
macentor andersoni, h o w e v e r , oogon ia a r e n o longer p r e s e n t ( B r i n t o n & Ol ive r , 
1971a) . A fold o r l o n g i t u d i n a l g roove , r u n n i n g a l o n g the d o r s a l o r a n t e r o -
Tick Reproduction: Oogenesis and Oviposition 281 
d o r s a l sur face of t h e o v a r y (Figs . 9.1 a n d 9 .6) , c o n t a i n s oogon ia a n d p r i m a r y 
oocytes in the i r ear l ies t d e v e l o p m e n t a l s t ages . O u t s i d e t he l o n g i t u d i n a l 
g roove , t h e oocy tes a r e gene ra l l y m o r e a d v a n c e d (Figs . 9.1 a n d 9 .6) , a n d as 
g r o w t h c o n t i n u e s after t h e female beg ins feeding the oocytes p r o t r u d e in to 
t h e h a e m o c o e l g iv ing t h e o v a r y a g rape - l ike a p p e a r a n c e . By this s t age in 
the i r d e v e l o p m e n t t h e oocytes a r e c o n n e c t e d to t he o v a r i a n wal l solely by 
a t h i n s ta lk , t h e funicle , of e l o n g a t e d ep i the l i a l cells (F igs . 9.2, 9.6, a n d 9 .9) . 
T h i s s t a n d s in s h a r p c o n t r a s t to t h e s i t ua t i on in t he o v a r y of insec ts w h e r e 
d e v e l o p i n g oocy tes a r e s u r r o u n d e d by a l aye r of foll icular cells. 
E x t e r n a l l y , a b a s e m e n t l a m i n a forms a b a r r i e r b e t w e e n t h e o v a r i a n t issue 
a n d t h e h a e m o l y m p h (F igs . 9 . 9 - 9 . 1 2 ) . A few m u s c l e fibres a r e a t t a c h e d to 
t he o u t s i d e of t h e b a s e m e n t l a m i n a (Figs . 9.2 a n d 9 .11) , a n d t r a c h e a a n d 
t r acheo le s p e n e t r a t e b e t w e e n t h e cells of t h e o v a r y (Figs . 9.2 a n d 9 .7) . 
9.2.2. T h e Oviducts , C o m m o n Oviduct or Uterus , and Vagina 
A p a i r of t u b u l a r o v i d u c t s r u n fo rward in loops f rom t h e l a t e ra l e n d s of 
t he o v a r y t o w a r d s t h e u t e r u s a n d v a g i n a (Fig . 9 .1) . I n a r g a s i d s , t he p r o x i m a l 
e n d s of t h e o v i d u c t s a r e he l ica l ly twis ted . I n ixod ids , a p o r t i o n of t he d i s ta l 
o v i d u c t is s l ight ly w i d e n e d b u t in a r g a s i d s th is w i d e n e d r e g i o n — t h e 
a m p u l l a — i s m u c h m o r e p r o n o u n c e d . I n m a n y t icks m a t u r e s p e r m accu -
m u l a t e p re fe ren t ia l ly in t h e l u m e n of t h e d i s ta l ov iduc t s a n d in t he a m p u l l a e . 
P h a g o l y s o s o m e s in t h e o v i d u c t cells of th is r eg ion p l ay a role in t he b r e a k d o w n 
of s p e r m , a n d th is p roces s is p a r t i c u l a r l y p r o n o u n c e d in s o m e a rga s id species 
( R o b e t e z , p e r s . c o m m . ) . 
T h e s t r u c t u r e of t h e o v i d u c t a l lows for c o n s i d e r a b l e s t r e t ch i n g d u r i n g t h e 
p a s s a g e of eggs , a n d egg m o v e m e n t is d u e to pe r i s t a l t i c c o n t r a c t i o n s of 
m u s c l e s a t t a c h e d to t h e o u t s i d e of t h e b a s e m e n t l a m i n a . 
Dis ta l ly , t h e o v i d u c t s fuse i n t o a s ingle , u n p a i r e d c o m m o n o v i d u c t o r 
u t e r u s (Fig . 9 .1) . I n a r g a s i d t icks t h e b i lobed u t e r u s forms a l a rge t r i a n g u l a r 
s ac (Fig . 9 .1a) w h i c h s tores e n d o s p e r m a t o p h o r e s a n d i m m a t u r e ( u n c a p a c i -
t a t e d ) s p e r m , b u t a l so as m a n y as severa l d o z e n s of eggs d u r i n g egg- lay ing . 
I n t h e P r o s t r i a t a (Fig . 9 .1b) t h e c o m m o n o v i d u c t is well deve loped b u t it is 
r e d u c e d to a s h o r t , i n c o n s p i c u o u s d u c t in t h e M e t a s t r i a t a (Fig . 9 .1b ) . I n 
b o t h of t he se ixod id g r o u p s t h e s t o r a g e of e n d o s p e r m a t o p h o r e s a n d i m m a t u r e 
s p e r m o c c u r s in o t h e r a r e a s of t h e female gen i t a l t r ac t . 
A s h o r t c o n n e c t i n g t u b e d e s c e n d s f rom t h e u t e r u s i n to t he p r o x i m a l o r 
cerv ica l p o r t i o n of t h e v a g i n a (Fig . 9 .1) . I n a r g a s i d s (Fig . 9 .1a) t he cervica l 
v a g i n a is s h o r t . I n P r o s t r i a t a (Fig . 9 .1b ) , t h e cervica l v a g i n a forms a n 
e n l a r g e d , sac- l ike s t r u c t u r e w h i c h func t ions as a r e c e p t a c u l u m semin i s . I n 
t he M e t a s t r i a t a (F ig . 9 . 1b ) , a s e p a r a t e r e c e p t a c u l u m semin i s is found a b o v e 
t h e u t e r u s ; it o p e n s pos t e ro -do r sa l l y i n t o t h e cerv ica l v a g i n a . I n all t h r ee tick 
g r o u p s t h e v e s t i b u l a r v a g i n a c o n n e c t s t h e cervica l v a g i n a to t h e gen i t a l 
282 P. A. Diehl, A. Aeschlimann and F. D. Obenchain 
a p e r t u r e a n d , t h r o u g h m u s c u l a r ac t ion , p r o l a p s e s d u r i n g the p rocess of 
ov ipos i t ion . I n th is respec t , t he v e s t i b u l a r v a g i n a ac t s as a n ov ipos i to r (Lees 
& B e a m e n t , 1948) . 
T h e v a g i n a ( a n d its accessory g l a n d s ) a n d the t u b e w h i c h c o n n e c t s it to 
the c o m m o n o v i d u c t o r u t e r u s a r e of e c t o d e r m a l or ig in a n d they a r e l ined 
w i t h cu t ic le . T h e o t h e r , m o r e p r o x i m a l p o r t i o n s of t he female gen i t a l t r ac t , 
a r e of m e s o d e r m a l o r ig in . 
9.2.3. T h e Tubular and Lobular Accessory Glands 
T h e p a i r e d t u b u l a r accessory g l a n d s a r e c o m m o n to all t ick spec ies . T h e y 
o p e n i n t o t h e v a g i n a a t t he d o r s a l b o u n d a r i e s of the cervical a n d the v e s t i b u l a r 
p o r t i o n s (Fig . 9 .1) . D u r i n g the ov ipos i t ion pe r iod , t he l u m e n of e ach g l a n d 
b ec o m e s filled w i t h a p ro t e in - r i ch secre t ion w h i c h p r e s u m a b l y coa t s t he egg 
surface d u r i n g its p a s s a g e t h r o u g h the v a g i n a . T h e funct ion of t he secre t ion , 
h o w e v e r , r e m a i n s u n k n o w n . 
T h e l o b u l a r accessory g l a n d s a r e found on ly in ixodid t icks. D u r i n g feeding, 
t he h y p o d e r m i s of t he v e s t i b u l a r v a g i n a (Fig. 9.1a, b) d e t a c h e s from the 
cut ic le a n d b e c o m e s g l a n d u l a r . D u r i n g ovipos i t ion , t he l ip id- r ich secre t ion 
is d i s c h a r g e d , t h r o u g h the cut ic le , i n to t h e l u m e n of t he g l a n d a n d o n t o the 
surface of t h e p a s s i n g egg w h i c h b e c o m e s pa r t i a l l y wa te rp roo fed (Lees & 
B e a m e n t , 1948) . 
9.2.4. Gene's Organ and the Porose Areas 
G é n é ' s o r g a n is s i t u a t e d a t t he a n t e r i o r pole of t he tick, j u s t a b o v e the 
c a p i t u l u m . I t is a n evers ib le t w o - o r four - lobed sac w h i c h e m e r g e s t h r o u g h 
a n a p e r t u r e in t h e c a m e r o s t o m a l fold of ixod ids (Fig. 9.4) o r in t he c a m e r o -
s t o m a l d e p r e s s i o n of a r g a s i d s . His to log ica l ly , it r e semble s t he l o b u l a r acces -
sory g l a n d s ; t h e h y p o d e r m a l cells, d e t a c h e d from the th in cut ic le , d i s c h a r g e 
FlG. 9.2. Section through the ovary of Ornithodoros moubata at the beginning ofvitellogenesis. Large 
oocytes contain a euchromatic nucleus (n) with a vacuolar nucleolus. They are attached 
to the ovarian wall (ow) through a small funicle (f). A few muscle fibres (mf) and tracheae 
(t) are found at the outside of the ovary, ol, lumen of the ovary; HC, haemocoel. Scale = 4 μpiι 
(fromjenni, 1971). 
FlG. 9.3. Ventral view of female Ornithodoros moubata with everted Géné's organ (GO) showing 
the two horns (h). c, capitulum; vu, vulva (courtesy J. E. Germond). Scale = 1 mm. 
FlG. 9.4. Capitulum of female Amblyomma variegatum in dorsal view; arrows point to the porose 
areas on the basis capituli and the camerostomal fold through which the Géné's organ everis. 
Scale = 25 μιτι. (Courtesy E. Hess.) 
FlG. 9.5. Enlarged view of Amblyomma variegatum porose area; arrow points to sensillum trichodium 
of uncertain function. Scale = 4 μpiι . (Courtesy E. Hess.) 
Tick Reproduction: Oogenesis and Oviposition 283 
284 P. A. Diehl, A. Aeschlimann and F. D. Obenchain 
t he i r sec re t ion i n t o t h e l u m e n of t he g l a n d . As i nd iv idua l eggs a r e ov ipos i t ed , 
G é n é ' s o r g a n ever t s (Fig . 9.3) a n d s m e a r s it w i t h a l ip id- r ich sec re t ion . T h i s 
c o m p l e t e s t h e w a t e r p r o o f i n g of t h e egg (Lees & B e a m e n t , 1948; B a l a s h o v , 
1972) . 
T w o p o r o s e a r e a s (Figs . 9.4 a n d 9.5) a r e p r e s e n t o n t h e t e c t u m of t he 
bas i s cap i tu l i of all ixod id females excep t / . kopsteini (Anas to s et al., 1973) . 
As t h e G e n e ' s o r g a n ever t s it covers t h e po rose a r e a s . T h e secre t ions f rom 
the l a rge c a n a l s (Fig . 9.5) of t h e p o r o s e a r e a s a r e t h e n i n c o r p o r a t e d i n t o t h e 
sec re to ry p r o d u c t s of t he G e n e ' s o r g a n w h e r e they a p p e a r to funct ion as 
i n h i b i t o r s of t h e a u t o x i d a t i o n of u n s a t u r a t e d egg w a x l ip ids (A tk inson & 
B i n n i n g t o n , 1973) . 
9 .3 . O V A R I A N D E V E L O P M E N T — O O G E N E S I S 
S ince t h e rev iews of A r t h u r (1962) a n d B a l a s h o v (1972) , a n u m b e r of 
p u b l i c a t i o n s h a v e c o n s i d e r a b l y e n l a r g e d o u r u n d e r s t a n d i n g of tick oogens i s , 
p a r t i c u l a r l y in t e r m s of t h e u l t r a s t r u c t u r e of oocytes d u r i n g vi te l logenesis 
a n d t h e b i o c h e m i s t r y of t h e yolk. T h e s e n e w d e v e l o p m e n t s will be d i scussed 
w i t h i n t h e f r a m e w o r k e s t ab l i shed by B a l a s h o v (1972) in his d e s c r i p t i o n of 
t h e five s t ages of oocy te g r o w t h . 
9.3 .1 . Previte l logenic Deve lopment of the Oocyte 
O o g o n i a first a p p e a r in t h e o v a r i a n p r i m o r d i a of unfed l a rvae (Ba l a shov , 
1972); c o n t i n u e d oogon ia l d iv is ions o c c u r d u r i n g t h e s u b s e q u e n t d e v e l o p -
m e n t a l s t ages of t h e t ick. I n t e r c e l l u l a r b r idges h a v e b e e n o b s e r v e d b e t w e e n 
the o o g o n i a of D. andersoni w h e r e they s e e m to b e i m p o r t a n t for t h e s y n c h r o n -
iza t ion of oogon ia l d e v e l o p m e n t a n d for t h e e x c h a n g e of ce l lu la r m a t e r i a l 
( B r i n t o n , 1971) . 
A l t h o u g h oogon ia l d iv i s ions c o n t i n u e , p r i m a r y oocytes ( B a l a s h o v ' s s t age 
I — t h e p e r i o d of s m a l l c y t o p l a s m i c g r o w t h ) first a p p e a r in fed n y m p h s w h e n 
t h e s m a l l oocy tes i m m e d i a t e l y e n t e r p r o p h a s e of t h e first m a t u r a t i o n d iv is ion 
w i t h o u t in te rk ines i s . T h e pe r iod of sma l l c y t o p l a s m i c g r o w t h e n d s w h e n the 
me io t i c p r o p h a s e is a r r e s t e d in d iak ines i s . T h e me io t i c c h r o m o s o m e s b e c o m e 
invis ib le n e a r t h e e n d of p r o p h a s e I . W h i l e t h e t i m e of c h o m o s o m e d i s so lu t ion 
d e p e n d s o n t h e t ick species , it is neve r l a t e r t h a n ear ly d iak ines i s ( G o r o s h -
c h e n k o , 1960; B a l a s h o v , 1972) . D u r i n g this s t age , t h e v o l u m e of t h e oocy te 
n u c l e u s a n d c y t o p l a s m inc rease on ly s l ight ly . F r e e r i b o s o m e s o c c u p y m o s t 
of t he c y t o p l a s m . I n t e r c e l l u l a r b r idges , first o b s e r v e d b e t w e e n oogon ia , pe rs i s t 
b e t w e e n t h e y o u n g oocytes of D. andersoni, e n s u r i n g the e x c h a n g e of cell 
c o n s t i t u e n t s a n d the i r c o n t i n u e d s y n c h r o n y (Br in ton , 1971). S t age I oocy tes 
Tick Reproduction: Oogenesis and Oviposition 285 
m a y c o n t i n u e the i r d e v e l o p m e n t d u r i n g t h e n y m p h a l m o u l t in s o m e a u t o -
g e n o u s spec ies , b u t in m o s t t icks t h e a c c u m u l a t i n g oocytes h a v e no t e n t e r e d 
s t age I I . 
B a l a s h o v ' s s t age I I , t h e p e r i o d of g r e a t c y t o p l a s m i c g r o w t h in t h e p rev i -
te l logenic oocy te , beg ins w i t h t h e in i t i a t ion of t h e a d u l t b lood m e a l . I t e n d s 
w i t h t h e a p p e a r a n c e of t h e first yolk g r a n u l e s in t he c y t o p l a s m , gene ra l ly a 
few d a y s after t h e female beg ins feeding (Fig . 9 . 6 ( 1 - 7 ) ) . T h e n u c l e u s en l a rges 
c o n s i d e r a b l y d u r i n g th is p e r i o d . T h e c h r o m o s o m e s b e c o m e to ta l ly invis ib le 
a n d a e u c h r o m a t i c " g e r m i n a l ves ic le" deve lops (Figs . 9.2, 9.6, a n d 9 .8) . 
P r o m i n e n t l y v a c u o l a t e d , s ingle (Fig . 9.2) o r m u l t i p l e (Fig . 9.8) nuc leo l i a r e 
fo rmed a n d m a s s e s of r i b o n u c l e o p r o t e i n pa r t i c l e s a r e d e r i v e d from the 
n u c l e u s . T h e s e r i b o s o m a l p r e c u r s o r s g a i n access to t he c y t o p l a s m t h r o u g h 
p o r e s in t h e n u c l e a r m e m b r a n e (Fig . 9 .11) . 
C y t o p l a s m i c v o l u m e inc reases g r ea t l y d u r i n g th is pe r iod a n d t h e oocy te 
beg ins to p r o t r u d e fu r the r i n t o t h e h a e m o c o e l a b o v e t h e surface of t he ova ry , 
FlG. 9.6. Diagrammaticsummary of oogenesis in ovarian cross-section. Younger oocytes (1-3) 
are restricted to the longitudinal groove (LG) while oocytes in advanced vitellogenesis are 
located away from the groove; (1-7) during Balashov's (1972) stage of great cytoplasmic growth 
the nucleus, nucleolus and cytoplasm enlarge greatly and the oocyte protrudes from the ovarian 
wall (OW) to which itis attached by the funicle (F). (8-10) Balashov's stages I I I - I V are the period 
of protein yolk deposition or vitellogenesis. At the end of this development the nuclear membrane 
and nucleolus disappear, the chromosomes condense into a karyo-sphere and (11) ovulation takes 
place. The former point of oocyte attachment to the funicle region is visible as a thinned area on 
the shell. HC, haemocoel; OL, ovarian lumen; S, symbiotes. 
286 P. A. Diehl, A. Aeschlimann and F. D. Obenchain 
FlG. 9.7. Longitudinal groove in the ovary of Amblyomma hebraeum containing small, developing 
oocytes 7 days after the completion of engorgement. Scale = 10 μιτι, (Courtesy E. Hess.) 
FlG. 9.8. Early oocytes in the ovarian wall of unfed Rhipicephalus bursa which is packed with 
symbionts (s). Oocyte nuclei (n) contain 1 or 2 vacuolated nucleoli (nu) and oocyte cytoplasm 
contains ribosomes, endoplasmic reticulum, mitochondria and a few symbiotes. HC, haemocoel. 
Scale = 0.25 μpiι. (From Hecker & Aeschlimann, 1970.) 
to w h i c h it is a t t a c h e d b y t h e funicle (Figs . 9.2, 9.6, 9.9, a n d 9 .11) . F r e e 
r i b o s o m e s a n d p o l y s o m e s a c c u m u l a t e in t he c y t o p l a s m (Fig. 9.10) a l t h o u g h 
the e n d o p l a s m i c r e t i c u l u m is no t p r o m i n e n t d u r i n g this s t age of oocy te 
d e v e l o p m e n t a n d a p p e a r s mos t l y as a diffuse s m o o t h e n d o p l a s m i c r e t i c u l u m . 
A n n u l a t e l a m e l l a e m a y b e p r e s e n t ( A e s c h l i m a n n & H e c k e r , 1970; B r i n t o n 
& Ol ive r , 1971b) a n d t h e n u m b e r of d i c tyosomes inc reases . T o w a r d s t he 
e n d of t h e p h a s e of g r e a t c y t o p l a s m i c g r o w t h , mu l t i ve s i cu l a t ed bod ies m a k e 
FlG. 9.9. Funicle from the ovary of unfed Ornithodoros moubata. A few elongated funicle cells connect 
the oocyte (O) to the ovarian wall. Nuclei (n) and mitochondria (m) are prominent. Basement 
lamina (arrow) separates the ovary from the haemocoel (HC). Scale = 0.25 μpiι. 
FlG. 9.10. Peripheral cytoplasm of an unfed Ornithodoros moubata oocyte in the phase of great 
cytoplasmic growth. The basal lamina (bl, far right of photomicrograph) covers microvilli of the 
oocyte surface and separates the oocyte from the haemocoel. Oocyte cytoplasm contains numerous 
free ribosomes, mitochondria (m), some endoplasmic reticulum (arrows), and lysosome-like 
organelles. Scale = 0.1 μpiι. 
Tick Reproduction: Oogenesis and Oviposition 287 
288 P. A. Diehl, A. Aeschlimann and F. D. Obenchain 
t he i r a p p e a r a n c e . T h e y m a y be de r ived from d i c tyosomes . P r i m a r y a n d 
s e c o n d a r y lysosomes m a y be found (Figs . 9.10 a n d 9.11) b u t the i r role h a s 
no t b e e n s t u d i e d . T h e p r e s e n c e of cell o rgane l l e s a n d s y m b i o n t s in t he 
lysosomes of Ornithodoros moubata sugges t s t h a t t hey t ake p a r t b o t h in t h e 
t u r n o v e r of cell o rgane l l e s a n d in t h e r egu l a t i on of s y m b i o n t infect ion r a t e s 
(Dieh l , u n p u b l i s h e d o b s e r v a t i o n s ) . M a n y m i t o c h o n d r i a a r e a lso p r e s e n t (Fig . 
9 .10) . A t t h e e n d of t h e g r e a t g r o w t h p h a s e , t he surface a r e a of t he ce l lu la r 
m e m b r a n e h a s b e e n g rea t l y e n l a r g e d by the p r o d u c t i o n of n u m e r o u s microvi l l i 
be low t h e t u n i c a p r o p r i a o r b a s e m e n t l a m i n a (Figs . 9.10 a n d 9 .11) , a n d t h e 
e n d o p l a s m i c r e t i c u l u m a n d Golg i reg ions a r e well d e v e l o p e d . T h e oocy te is 
p r e p a r e d for t h e s u b s e q u e n t pe r iod of vi te l logenesis as it c o n t a i n s all of t h e 
r equ i s i t e ce l lu la r o rgane l l e s for a c c u m u l a t i o n of yolk a n d the d e p o s i t i o n of 
t h e egg-shel l . 
Tick Reproduction: Oogenesis and Oviposition 289 
D u r i n g i ts g r o w t h , t h e p r i m a r y oocy te b e c o m e s inc reas ing ly po la r i zed . 
T h e l a rge n u c l e u s is gene ra l l y s i t u a t e d n e a r t h e funicle; r icket ts ia- l ike Wol-
bachia species a c c u m u l a t e a t t h e o p p o s i t e po le of t he oocy te (Figs . 9.6, 9 .8 , 
9 . 1 1 , a n d 9 .17) . 
T h e s e m i c r o - o r g a n i s m s a r e c o n s i d e r e d to b e s y m b i o n t s a n d the i r s t r u c t u r e 
h a s b e e n d e s c r i b e d in severa l t ick species ( R o s h d y , 1964a, b ; H e c k e r et al., 
1968; H e c k e r & A e s c h l i m a n n , 1970; B a l a s h o v , 1972; R e i n h a r d t etal., 1972) . 
B ü c h n e r (1965) p o s t u l a t e d t h a t t hey m a y p r o v i d e t h e tick w i t h v i t a m i n s of 
t h e B - c o m p l e x , b u t t he i r a c t u a l phys io log ica l role h a s n o t b e e n e l u c i d a t e d . 
Symbion t - f r ee Argas arboreus (Su i to r , 1964) s h o w e d n o r e d u c e d v iab i l i ty in 
t h e Fi g e n e r a t i o n . 
9.3.2. Vi te l logenic Deve lopment o f the Oocyte 
T h e v i te l logenic p h a s e s of oocy te g r o w t h beg in w i t h t he a p p e a r a n c e of t he 
first yolk g r a n u l e s a n d e n d w i t h o v u l a t i o n (Fig . 9 . 6 ( 8 - 1 1 ) ) . T h i s p e r i o d of 
d e v e l o p m e n t i n c l u d e s B a l a s h o v ' s s t ages I I I a n d I V (1972) of oocy te g r o w t h . 
E n g o r g e m e n t a n d m a t i n g a r e u s u a l p r e r e q u i s i t e s for c o m p l e t e v i te l logenesis , 
b u t u n d e r c e r t a i n c i r c u m s t a n c e s d i s cus sed in l a t e r sec t ions of th is c h a p t e r 
unfed o r u n m a t e d females m a y m a t u r e eggs . 
93.2.1. Cytological Aspects of Vitellogenesis T h e e u c h r o m a t i c oocy te n u c l e u s , a n d 
its v a c u o l a t e d n u c l e o l u s , c o n t i n u e s to e n l a r g e w i t h t he onse t of v i te l logenes is . 
T h e d i a m e t e r of t h e nuc l eo lu s m a y r e a c h 2 5 - 3 0 μpiι in Argas persicus o r 
FlG. 9.11. Diagram of cytological changes in the tick oocyte during vitellogenesis (Ornithodoros 
moubata: Aeschlimann & Hecker, 1969; Jenni, 1971; Rhipicephalus bursa: Hecker & Aeschlimann, 
1970; Amblyomma hebraeum: Diehl, unpublished). Interdigitating microvilli link the oocyte to the 
funicle (F ) on the ovarian wall (OW). Numerous microtubules in the funicle cells may serve 
as cytoskeletal supports. Some muscle cells (M), tracheae and tracheoles (T) are attached to 
the basement lamina (BL) which separates the ovary from the haemocoel (HC). OL, ovarian 
lumen. The oocyte nucleus contains a vacuolated nucleolus (1), from which masses (2) of 
ribonucleoprotein particles (presumably ribosomal precursors) detach. They accumulate in 
the cytoplasm as free ribosomes or polysomes (3) after passage through nuclear pores. Yolk 
material synthesized in the endoplasmic reticulum (ER; 4, 5) is packed into small vesicles which 
may detach from the ER(9) or from the Golgi apparatus (6). Other coated vesicles detaching 
from the microvilli-rich cell membrane (7) internalize exogenous yolk precursors from the 
haemolymph. These vesicles (8), possibly from different sources, fuse to form larger vacuoles 
(10) or multivesicular bodies (11). Repeated fusion of vesicles and dissolution of membranes 
in the multivesicular bodies leads to formation of large yolk granules (12). Triglyceride-rich lipid 
inclusions (13) andglycogen (14) also accumulate between the yolk granules. Other vesicles 
containing shell precursors detach from the Golgi apparatus ( 15) and fuse with the cell membrane 
(16). The material polymerizes in the extracellular space between the microvilli. As shell devel-
opmen proceeds the microvilli retract and continuous addition of shell material (17) leads to the 
formation of a homogeneous egg shell (18). Less shell material is deposited in the funicle region 
(19). There is also evidence that some material, possibly elaborated by the funicle cells, may 
be pinocytosed by the oocyte (20). L, primary and secondary lysosomes; M, mitochondria, S, 
symbionts. 
P. A. Diehl, A. Aeschlimann and F. D. Obenchain 290 
Tick Reproduction: Oogenesis and Oviposition 291 
4 0 - 4 5 μpiι in Ixodes ricinus ( B a l a s h o v , 1972). D u r i n g this g r o w t h p h a s e t he 
nuc l eo lus c o n t i n u e s to p r o d u c e l a rge q u a n t i t i e s of r i b o s o m a l p r e c u r s o r s (Fig. 
9 .11) . M e m b r a n e - l i m i t e d yolk g r a n u l e s beg in to a p p e a r in the c y t o p l a s m 
wi th t he onse t of v i te l logenes is ( B a l a s h o v ' s s t age I I I of oocy te g r o w t h ) . T h e 
yolk a p p e a r s to o r i g i n a t e from b o t h i n t r ace l l u l a r a n d ex t r ace l lu l a r sources 
(Figs . 9.11 a n d 9 .12; A e s c h l i m a n n & H e c k e r , 1967, 1969; D ieh l , 1970; B r i n t o n 
& O l i v e r 1971b; J e n n i , 1971) . Ves ic les a n d mu l t i ve s i cu l a r bod ies , de r ived 
from e n d o p l a s m i c r e t i c u l u m a n d d i c t y o s o m e s , fuse i n to l a rge r vacuo les (Figs . 
9 . 1 1 - 9 . 1 3 ) . I n D. andersoni, m i t o c h o n d r i a a r e a lso t h o u g h t to c o n t r i b u t e to 
yolk f o r m a t i o n ( B r i n t o n & O l i v e r 1971b) . Yolk m a t e r i a l of ex t r ace l lu l a r 
or ig in is i n t e r n a l i z e d in m i c r o p i n o c y t o t i c vesicles (Figs . 9.11 a n d 9.12) o r in 
m i c r o p i n o c y t o t i c t u b e s a s soc i a t ed w i t h m e m b r a n e - l i m i t e d reservoi rs (B r in ton 
& Ol ive r , 1971b) . T h e s e vesicles s u b s e q u e n t l y fuse w i th each o t h e r o r w i t h 
m u l t i v e s i c u l a r bod ies ; t he m u l t i v e s i c u l a r bod ies g r a d u a l l y lose the i r i n t e r n a l 
m e m b r a n e s (Figs . 9 .11 -9 .13 ) a n d , t h r o u g h r e p e a t e d fusions, a r e t r a n s f o r m e d 
in to l a rge h o m o g e n e o u s yolk g r a n u l e s (F igs . 9.11 a n d 9 .12) . U s i n g h i s to -
c h e m i c a l t e c h n i q u e s , D i e h l (1970) d e m o n s t r a t e d t h a t the yolk g r a n u l e s of 
0. moubata a r e c o m p o s e d of h a e m o - g l y c o - l i p o p r o t e i n s . 
As v i te l logenes is is c o m p l e t e d a t t he e n d of B a l a s h o v ' s g r o w t h s t age I I I 
(1972) , t h e oocy te of 0. moubata, for e x a m p l e , is p a c k e d w i t h l a rge yolk 
g r a n u l e s w i t h d i a m e t e r s u p to 80 μpiι (Dieh l , 1970). T h e g rea t ly e n l a r g e d 
oocy te r e a c h e s a final d i a m e t e r of a b o u t 6 0 0 - 8 0 0 μpiι in A. persicus, 700 μpiι 
in / . ricinus ( B a l a s h o v , 1972) , o r u p to 1200 μpiι in 0. moubata (Dieh l , 1970). 
B e t w e e n t h e yolk g r a n u l e s , g lycogen a n d t r ig lycer ide- r ich l ipid inc lus ions 
h a v e a c c u m u l a t e d in t h e c y t o p l a s m (Figs . 9.11 a n d 9.16; D ieh l , 1970; J e n n i , 
1971) . 
T h e i n t e r d i g i t a t i n g microvi l l i of t h e oocy te a n d the funicle cells a t t a c h t he 
oocy te to t h e o v a r i a n e p i t h e l i u m (Figs . 9.11 a n d 9.14) t h r o u g h o u t t he first 
4 s t ages of oocy te g r o w t h . I n th is r e spec t t he role of t he funicle cells a p p e a r s 
to b e essent ia l ly m e c h a n i c a l as s h o w n by the n u m e r o u s m i c r o t u b u l i w h i c h 
a r e p r e s e n t in t he i r c y t o p l a s m (Fig . 9 .14) . T h e funicle cells m a y a lso syn thes i ze 
s o m e u n k n o w n m a t e r i a l a n d t r a n s p o r t it to t h e oocy te (Fig. 9.11 ; A e s c h l i m a n n 
FlG. 9.12. Periphery of Amblyomma hebraeum oocyte during vitellogenesis and egg-shell (es) 
deposition. Small coated vesicles containing internalized vitellogenin detach from cell membrane 
(arrows) and fuse to form larger vesicles (v). Repeated fusion leads to the production of 
electron-dense homogeneous yolk granules (y), g, golgi apparatus; m, mitochondria. Scale = 
0.05 μpiι. 
FlG. 9.13. Periphery of Rhipicephalus bursa oocyte during vitellogenesis showing cell membrane 
and microvilli (mv). Microtubules (mt), endoplasmic reticulum (er), and multivesiculated 
bodies (mvb) are visible. The mvb appear to transform into larger vesicles and into yolk granules 
through fusion with dissolution of vesicle membranes. Scale = 0.02 μpiι. (Hecker & Aeschlimann, 
1970). 
P. A. Diehl, A. Aeschlimann and F. D. Obenchain 292 
Tick Reproduction: Oogenesis and Oviposition 293 
FlG. 9.16. Oocyte of Ornithodoros moubata during vitellogenesis showing accumulation of yolk 
granules (y), lipid inclusions (i) and glycogen (gl), er, endoplasmic reticulum, g, Golgi apparatus; 
m, mitochondria. Scale = 0.1 μηι (Aeschlimann & Hecker, 1967.) 
FlG. 9.17. External view by scanning electron microscopy of incomplete egg shell of Ornithodoros 
moubata after removal of basement lamina revealing coalescing patches of egg-shell (es) and 
protruding microvilli. Scale = 0.2 μpiι. (Courtesy I. Rebetez.) 
FlG. 9.14. Region of attachment of Ornithodoros moubata oocyte (O) to the funicle cells (f) showing 
the numerous interdigitating microvilli. Electron-dense deposits of unknown function and an 
incomplete egg-shell (es) are found in the extracellular space between the microvilli. Pinocytotic 
vesicles (arrows) may transport material into the oocyte or they could represent vesicles releasing 
shell precursors. The funicle cells are densely packed with microtubules which may serve as 
cytoskeletal supports. (Hecker & Aeschlimann, 1970.) 
FlG. 9.15. Rickettsia-like symbionts ( Wolbachia sp.) in an oocyte of Rhipicephalus bursa. The dividing 
symbiont (s) contains numerous ribosomes and strands of fibrous material which may be DNA. 
cm, cell membrane; cw, cell wall; arrows indicate plane of division. Scale = 0.025 μpiι. (Hecker 
& Aeschlimann, 1970.) 
294 P. A. Diehl, A. Aeschlimann and F. D. Obenchain 
& H e c k e r , 1967) . H o w e v e r , the i r c o n t r i b u t i o n to t he yolk, in q u a n t i t a t i v e 
t e r m s a t leas t , m u s t b e ve ry sma l l . 
Egg-she l l syn thes i s beg ins d u r i n g B a l a s h o v ' s s t age I I I of oocy te deve l -
o p m e n t a n d it is c o m p l e t e d d u r i n g s t age I V . M o s t a u t h o r s h a v e a g r e e d t h a t 
t he d e v e l o p i n g egg-shel l is syn thes i zed by the oocy te itself. Ves ic les , de r ived 
from e n d o p l a s m i c r e t i c u l u m a n d d i c t y o s o m e s , a p p e a r to fuse w i t h t h e cell 
m e m b r a n e . T h e c o n t e n t s of t h e vesicles a r e d i s c h a r g e d in to t h e ex t r ace l lu l a r 
s p a c e be low t h e b a s e m e n t l a m i n a w h e r e they p o l y m e r i z e to form p a t c h e s of 
egg-shel l a r o u n d t h e microvi l l i (F igs . 9.11 a n d 9 .12) . I n a d v a n c e d oocytes , 
t he microvi l l i b e c o m e fewer a n d r e t r a c t (Fig. 9 .17) , a n d the r e m a i n i n g spaces 
a r e c losed b y t h e a d d i t i o n of n e w p r e c u r s o r m a t e r i a l . A t t he e n d of B a l a s h o v ' s 
s t age I V of oocy te g r o w t h , t h e shell of 0. moubata, for e x a m p l e , is a un i fo rm 
layer 2 - 4 μ ιη in th i ckness . 
T h e egg-shel l of t ickslacks a d i s t inc t m ic ropy l e . H o w e v e r , less egg-shel l 
m a t e r i a l is d e p o s i t e d in t h e oocy te - fun ic le a t t a c h m e n t reg ion , a n d this reg ion 
is vis ible as a n e l o n g a t e d , sha l low g roove in t he shell of r ecen t ly o v u l a t e d 
oocytes of 0. moubata (Dieh l , 1970) . O n the o t h e r h a n d , a mic ropy le - l ike 
r eg ion h a s occas iona l ly b e e n seen in l igh t -mic roscop ica l sec t ions of D. andersoni 
ovar ies ( B r i n t o n & Ol ive r , 1971b) . 
T h e b a s e m e n t l a m i n a a n d the d e v e l o p i n g egg-shel l form m e c h a n i c a l b a r -
r iers w h i c h s e p a r a t e t he oocy te from the h a e m o l y m p h . I t is likely t h a t these 
b a r r i e r s m a y p r o t e c t t h e oocy te to a ce r t a in ex t en t a g a i n s t i n v a d i n g p a t h o g e n s . 
T h e n e a r l y c o m p l e t e a n d fully fo rmed egg-shel ls s e e m to be ser ious obs tac le s 
to p a t h o g e n invas ion . M o r z a r i a et al. (1977) r e p o r t e d t h a t merozo i t e s of 
Babesia major c a n p e n e t r a t e t h e b a s e m e n t l a m i n a of Haemaphysalis punctata 
ovar ies w i t h t h e a id of a spec ia l p e n e t r a t i n g a p p a r a t u s , b u t t he egg-shel l of 
a d v a n c e d oocy tes s eems to p r e v e n t invas ion . T h i s seems a lso to be t he case 
for Borrelia duttoni; o lde r oocytes in 0. moubata cou ld n o t be infected by t h e 
sp i roche te s ( A e s c h l i m a n n , 1958) . Coxiella burneti a n d Rickettsia rickettsi c an 
on ly i n v a d e the y o u n g e r oocytes of Hyalomma asiaticum (Ba la shov , 1972) a n d 
D. andersoni (Burgdor fe r & B r i n t o n , 1975) , respec t ive ly . I t w o u l d a p p e a r t h a t 
m a n y of t he m i c r o - o r g a n i s m s w h i c h a r e t r a n s m i t t e d t r ansova r i l y h a v e evolved 
m e c h a n i s m s for t h e p e n e t r a t i o n of t he b a s e m e n t l a m i n a b u t few, if a n y , c a n 
p e n e t r a t e t h e nea r ly c o n t i n u o u s egg-shel l . O n the o t h e r h a n d , t he b a s e m e n t 
l a m i n a a n d egg-shel l r e m a i n p e r m e a b l e , even to l a rge molecu le s s u c h as 
h a e m o g l o b i n (Lees & B e a m e n t , 1948) , yolk p r o t e i n s , a n d poss ib ly t he egg-
shell p r e c u r s o r s , w h i c h m a y be t a k e n u p from the h a e m o l y m p h t h r o u g h 
m i c r o p i n o c y tosis . 
T o w a r d s t h e e n d of egg-shel l depos i t i on , t he n u c l e u s beg ins to sh r i nk a n d 
t h e nuc l eo lus g r a d u a l l y loses its ba soph i l i a . T h e n u c l e a r m e m b r a n e a n d the 
nuc l eo lus d issolve a n d , a c c o r d i n g to G o r o s h c h e n k o (1965) , t h e c h r o m o s o m e s 
c o n d e n s e i n t o a d e n s e k a r y o s p h e r e (Fig . 9 .6) . T h e oocy te h a s c o m p l e t e d m o s t 
of i ts d e v e l o p m e n t in B a l a s h o v ' s s t age I V of g r o w t h a n d is r e a d y for o v u l a t i o n . 
Tick Reproduction: Oogenesis and Oviposition 295 
T h e oocy tes of t h e t ick o v a r y h a v e n o t d e v e l o p e d s y n c h r o n o u s l y d u r i n g 
vi te l logenesis ; oocy tes of ve ry different d e v e l o p m e n t a l s tages c a n be e n c o u n -
te red a t a n y o n e t i m e . I n i xod ids , t he l e s s - a d v a n c e d oocytes a r e genera l ly 
found in t h e l o n g i t u d i n a l g roove ; t he m o s t a d v a n c e d a r e fa r thes t from the 
g roove (Figs . 9.1 a n d 9 .7) . T h i s m e c h a n i s m e n s u r e s t h a t t he pe r iod of 
v i te l logenes is , o v u l a t i o n , a n d ov ipos i t ion in t he t ick is p r o l o n g e d over severa l 
d a y s o r weeks . T h i s p r o l o n g a t i o n h a s s o m e def ini te a d v a n t a g e s ; t he ex t r a -
ce l lu la r s o u r c e of yolk m a t e r i a l is p r e s u m a b l y n o t ab le to syn thes ize a n d 
e x p o r t t h e p r e c u r s o r s of t h e yolk a t a r a t e w h i c h cou ld a l low vi te l logenesis 
to t a k e p l a c e in all oocy tes a t t h e s a m e t ime . M o r e o v e r , in v iew of t he 
r e s t r i c t ed s p a c e w i t h i n t h e gen i t a l d u c t s a n d the t i m e - c o n s u m i n g r e q u i r e m e n t 
for i n d i v i d u a l h a n d l i n g of eggs d u r i n g the i r wa t e rp roo f ing by the G é n é ' s 
o r g a n , th is m i n i m a l p r o l o n g a t i o n of v i te l logenesis a n d ovu l a t i on m u s t be 
select ively a d v a n t a g e o u s to efficient p r o d u c t i o n of l a rge egg b a t c h e s a n d , 
therefore , to t h e i n c r e a s e d p r o b a b i l i t y of t ick p o p u l a t i o n surv iva l . 
9.3.2.2 Biochemistry of the Yolk C a r b o h y d r a t e s a p p e a r to be s to red in t he 
d e v e l o p i n g oocy te as g lycogen . G l y c o g e n h a s b e e n d e m o n s t r a t e d in 0. moubata 
oocytes b y c y t o c h e m i c a l t e c h n i q u e s a t b o t h t h e l ight a n d e lec t ron m i c r o -
scopica l levels (F igs . 9.12 a n d 9.16; D ieh l , 1970; J e n n i , 1971). B o u n d c a r b o -
h y d r a t e s r e s i s t an t to d i a s t a s e t r e a t m e n t a r e a lso assoc ia ted w i t h yolk p r o t e i n s . 
S tud ie s on egg l ip ids h a v e d e m o n s t r a t e d t h e p r e s e n c e of p h o s p h o l i p i d s , 
free fat ty ac id s , m o n o - , d i - a n d t r ig lycer ides , s terols a n d s teryl es ters in A. 
arboreus a n d A. persicus ( M a r o u n , 1972), in D. andersoni (Boc tor & K a m e l , 
1976) , in Boophilus microplus ( C h e r r y , 1976) , a n d in 0. moubata (Dieh l , 1970). 
T h e c h a i n l e n g t h of free fat ty ac ids in t h e eggs of A. arboreus a n d A. persicus 
r a n g e f rom Cio to C20. P a l m i t i c , s t ea r ic , a n d oleic ac id p r e d o m i n a t e , b u t 
o d d - n u m b e r e d free fat ty ac ids m i g h t a lso be p r e s e n t ( M a r o u n , 1972). Lyso -
lec i th in , s p h i n g o m y e l i n , l ec i th in , a n d c e p h a l i n a r e t he m a i n p h o s p h o l i p i d s , 
as d e t e r m i n e d b y t h i n - l a y e r c h r o m a t o g r a p h y , in t he eggs of 0. moubata (Dieh l , 
1970) . 
I n B. microplus a b o u t 1.5 m g of to ta l choles te ro l is p r e s e n t p e r g r a m of 
eggs; n e a r l y o n e - t h i r d of t h e cho les te ro l inges ted by the female is t r ans fe r red 
to t h e eggs ( C h e r r y , 1976) . T i c k s , like insec ts , a p p a r e n t l y r e q u i r e a n ex t r a -
n e o u s s o u r c e of s terols as they s e e m to b e i n c a p a b l e of syn thes i z ing the 
s te ro id ske le ton ( M a r o u n & K a m a l , 1976) . T h e yolk supp l ies t he e m b r y o s 
a n d d e v e l o p i n g l a r v a e w i t h t h e s terols neces sa ry for the i r d e v e l o p m e n t . 
H i s t o c h e m i c a l m e t h o d s s h o w e d t h a t t h e t r ig lycer ides of 0. moubata eggs 
a r e loca l ized in s m a l l i nc lus ions b e t w e e n t h e l a rge yolk g r a n u l e s (Fig . 9 .16) . 
T h e yolk g r a n u l e s a lso c o n t a i n e d p h o s p h o l i p i d s , s te ro ls , a n d p r o b a b l y s o m e 
t r ig lycer ides (Dieh l , 1970) . I n D. andersoni, p h o s p h o l i p i d s , d i - a n d t r ig lycer-
ides , cho les te ro l a n d choles te ry l es ters a r e a s soc ia t ed w i th t he p r o t e i n a c e o u s 
yolk g r a n u l e s (Boc to r & K a m e l , 1976) . 
E x t r a c t s f rom w h o l e eggs c o n t a i n b o t h yolk l ip ids a n d l ip ids from the 
296 P. A. Diehl, A. Aeschlimann and F. D. Obenchain 
w a t e r p r o o f i n g surface layer . F o r t he p r e s e n t d i scuss ion , s tud ies of s u c h 
ex t r ac t s h a v e l imi t ed v a l u e . E x t r a c t s of who le eggs of D.andersoni c o n t a i n e d 
mos t ly p a l m i t i c , s t ea r i c , oleic, a n d l inoleic ac id ; a n un ident i f ied s a t u r a t e d 
t r i ca rboxy l i c fat ty ac id c o n t a i n i n g a m e t h y l b r a n c h a n d two v ic ina l ca rboxy l i c 
ac id g r o u p s w a s a lso p r e s e n t (Sh imi et al., 1974). T h e m a j o r p h o s p h o l i p i d 
classes f rom w h o l e egg ex t r ac t s of D. andersoni a n d A. arboreus w e r e lysolec i th in , 
s p h i n g o m y e l i n , l ec i th in , a n d p h o s p h a t i d y l e t h a n o l a m i n e . M i n o r classes w e r e 
p h o s p h a t i d y l i n o s i t o l , d i p h o s p h a t i d y l g l y c e r o l , a n d p h o s p h a t i d i c ac id ( H u s -
sein & K a m a l , 1977) . 
Severa l a u t h o r s h a v e s t u d i e d t he p r o t e i n s of tick egg-yolk g r a n u l e s ( B r e m -
ner , 1959; Riek , 1959; D ieh l , 1970; T a t c h e l l , 1971; Boc to r & K a m e l , 1976; 
A r a m a n , 1979) , a n d t h e s e p a r a t i o n of severa l p ro t e in s by e l ec t rophore t i c a n d 
gel filtration t e c h n i q u e s h a v e b e e n r e p o r t e d . Yo lk - s to rage p r o t e i n s , t he so-
ca l led l ipovi te l l ins o r vi tel l ine, h a v e b e e n found in all s u c h s tud i e s . I n 0. 
moubata, for e x a m p l e , t he m a j o r egg p r o t e i n cons t i t u t e s 9 0 - 9 5 % of all p r o t e i n s 
p r e s e n t in t he yolk (Dieh l , 1970) . Boc to r a n d K a m e l identif ied o n e m a j o r 
p r o t e i n b a n d by gel e l ec t rophores i s f rom ex t r ac t s of D. andersoni eggs , b u t 
they o b t a i n e d t w o f ract ions w h e n th is m a t e r i a l w a s c h r o m a t o g r a p h e d o n 
D E A E - c e l l u l o s e . A n e x p l a n a t i o n for the i r findings ( a n d for t he ve ry h i g h 
e s t i m a t e d m o l e c u l a r we igh t s w h i c h they o b t a i n e d ) c o m e from a r ecen t s t u d y 
of t h e egg p r o t e i n s of Rhipicephalus appendiculatus ( V u n d l a , W h i t e h e a d & 
O b e n c h a i n , 1980, I C I P E A n n u a l R e p o r t , u n p u b l i s h e d ) . 
F r e s h l y h a t c h e d eggs of R. appendiculatus w e r e h o m o g e n i z e d in p h o s p h a t e 
buffer (0.02 M w i t h 0.2 M N a C l , p H 7.0) a n d s e p a r a t e d by gel filtration on 
S e p h a r o s e C L 6 B on a 1.6 X 80 c m c o l u m n . Six m a j o r p ro t e in s w e r e o b s e r v e d 
w i t h m o l e c u l a r we igh t s of 2.1 x 10
6
, 5.1 X 10
5
, 1.06 X 10
5
, 22 ,000, 14,000, 
a n d less t h a n 12,000, respec t ive ly . A h a e m e - m o i e t y w a s a s soc ia t ed w i t h t he 
two l a rge r p r o t e i n s on ly , a n d in those f ract ions t h e ra t ios of p r o t e i n to h a e m e 
w e r e iden t i ca l . V u n d l a , W h i t e h e a d , a n d O b e n c h a i n ( u n p u b l i s h e d ) a lso 
s h o w e d t h a t t h e r a t i o of t h e l a rge p r o t e i n to t he sma l l p r o t e i n w a s 
c o n c e n t r a t i o n - d e p e n d e n t a n d a t low p r o t e i n c o n c e n t r a t i o n s t he sma l l h a e -
m o p r o t e i n w i t h M W = 5.1 X 10
5
 p r e d o m i n a t e d . T h e y a lso s h o w e d t h a t t he 
t e n d e n c y of th is p r o t e i n to u n d e r g o se l f -aggregat ion w a s a c c e n t u a t e d w h e n 
the ionic s t r e n g t h of t h e buffer so lu t ion w a s lowered be low t h a t of phys io log ica l 
sa l ine . T h e y c o n c l u d e d t h a t t h e l a rge h a e m o p r o t e i n in the i r ex t r ac t s of R. 
appendiculatus eggs w a s a t e t r a m e r of t h e sma l l h a e m o p r o t e i n w h i c h is, 
therefore , n a t i v e vi te l l in . R e p o r t s of h a e m o p r o t e i n s w i th m o l e c u l a r we igh t s 
on t h e o r d e r of severa l mi l l ion d a l t o n s (Boc to r & K a m e l , 1976) from t h e 
eggs of D. andersoni r e su l t f rom the use of low ionic s t r e n g t h buffers w h i c h 
l eads to t he f o r m a t i o n of m u l t i p l e a g g r e g a t e s of t he na t i ve vi tel l in . 
Yolk p r o t e i n s c o n t a i n i n g i ron , r e p o r t e d l y in t h e form of h a e m e - d e r i v a t i v e s 
o r i g i n a t i n g as b y - p r o d u c t s of h a e m o l o g l o b i n d iges t ion , w e r e first d e t e c t e d by 
W i g g l e s w o r t h (1943) in 0. moubata a n d / . ricinus eggs . B r e m n e r ident if ied t h e 
Tick Reproduction: Oogenesis and Oviposition 297 
p r o s t h e t i c g r o u p as p r o t o h a e m i n a n d s h o w e d t h a t 5 % of inges ted i ron p a s s e d 
in to t h e eggs of B. microplus wh i l e K i t a o k a (1961) o b t a i n e d e s t ima te s o n t he 
o r d e r of 1 0 % . A r a m a n (1979) r e p o r t e d t h a t a p p r o x i m a t e l y 6 % of inges ted 
i ron is t r ans fe r r ed to t h e eggs of Rhipicephalus sanguineus. T h e h a e m e - m o i e t y 
c a n b e q u a n t i t a t i v e l y d i s soc ia t ed from its a p o p r o t e i n in t he p r e s e n c e of 8 M 
u r e a , a s s h o w n by gel filtration on S e p h a r o s e C L - 6 B of R. appendiculatus 
h a e m o p r o t e i n s ( V u n d l a , W h i t e h e a d & O b e n c h a i n , u n p u b l i s h e d ) , a n d this 
shows t h a t t h e h a e m e is n o n - c o v a l e n t l y b o u n d to t he a p o p r o t e i n . T h e s e 
h a e m e - d e r i v a t i v e s h a v e n o d o c u m e n t e d phys io log ica l role; they a c c u m u l a t e 
in t h e g u t a n d g u t l u m e n of t h e d e v e l o p i n g e m b r y o d u r i n g yolk d iges t ion 
a n d m a y m e r e l y se rve as a p i g m e n t i n g a g e n t w h i c h camouf lages t h e eggs 
after ov ipos i t ion . 
H i s t o c h e m i c a l s t ud i e s o n 0. moubata sugges t ed t h a t t he yolk p r o t e i n s w e r e 
h a e m o - g l y c o - l i p o p r o t e i n s (Dieh l , 1970) a n d s u c h c o m p o u n d s w e r e a lso 
r e p o r t e d f rom t h e eggs of D. andersoni (Boc to r & K a m e l , 1976) , Hyalomma 
dromedani (Bassa l & H e f n a w y , 1972) , a n d R. sanguineus ( A r a m a n , 1979). 
T a t c h e l l (1971) d i d n o t test for l ip ids w h e n h e d e s c r i b e d the p r o t e i n c o m p l e x 
from B. microplus eggs as a h a e m o - g l y c o p r o t e i n . T h e vitel l ine from the eggs 
of D. andersoni h a v e b e e n s t u d i e d in s o m e de ta i l (Boc to r & K a m e l , 1976); 
c a r b o h y d r a t e c o n t e n t v a r i e d from 4 . 5 % to 4 . 7 5 % a n d a m i n o s u g a r s w e r e 
p r e s e n t . M a j o r a s soc i a t ed l ip ids w e r e s h o w n to i n c l u d e p h o s p h o l i p i d s , d ig -
lycer ides , t r ig lycer ides , cho les te ro l , a n d cho lys te ry l es te rs . M a j o r c o m p o n e n t 
a m i n o ac ids i n c l u d e d ty ros ine , lys ine , g l u t a m i c ac id , t h r e o n i n e , a n d va l ine . 
Ana lys i s of t h e t w o h a e m o p r o t e i n s f rom R. appendiculatus eggs by isoelectr ic 
focusing o n a p H 3 .5 -9 .5 g r a d i e n t s h o w e d t h a t t h e m a t e r i a l pur i f ied by gel 
filtration w a s a s ingle species w i t h a n isoelect r ic p o i n t of pi = 6 .5; s o m e 
m i c r o h e t e r o g e n e i t y w a s n o t e d in t h e s a m p l e , w h i c h w a s a t t r i b u t e d to t he 
d ive rs i ty of b o u n d c a r b o h y d r a t e s a n d l ip ids . W h e n the vi tel l in w a s sub jec ted 
to S D S - P A G E it w a s fu r the r s h o w n t h a t t h e m o n o m e r ( M W = 5.1 X 10
5
) 
a n d t e t r a m e r ( M W = 2.1 X 10
6
) w e r e c o m p o s e d of iden t i ca l p r o t e i n - s u b u n i t 
c h a i n s w i t h m o l e c u l a r w e i g h t s in t h r e e size r a n g e s (97,000, 87 ,000 , a n d 
46 ,000 d a l t o n s ) . 
9.3.2.3. Developmental Ongins of the Yolk T h e g lycogena n d t r ig lycer ide yolk 
inc lus ions a r e p r o b a b l y syn thes i zed b y t h e oocy te itself, b u t b i o c h e m i c a l 
p roo f is l ack ing . Cy to log i ca l i nves t iga t ions sugges t t h a t p r o t e i n c o m p o n e n t s 
of t h e oocy te o r i g i n a t e b o t h f rom e n d o g e n o u s a n d exogenous sources . A n 
e n d o g e n o u s o r i n t r a c e l l u l a r sou rce of yolk p r o t e i n s w a s sugges t ed by the 
i n c o r p o r a t i o n of
 1 4
C - l a b e l l e d a m i n o ac ids i n t o p r o t e i n s w h i c h b e h a v e d elec-
t r o p h o r e t i c a l l y like vi tel l ine w h e n t h e ovar i e s of R. sanguineus w e r e m a i n t a i n e d 
in vitro ( A r a m a n , 1979) . Stil l , a n e x o g e n o u s sou rce of vi tel l ine h a s b e e n m o r e 
extens ive ly d o c u m e n t e d . T r y p a n b l u e (Dieh l , 1970), fluorescein-labelled 
h a e m o l y m p h p r o t e i n s ( T a t c h e l l , 1971) , r a d i o a c t i v e h a e m o l y m p h p r o t e i n s 
( J e n n i , 1971) , a n d l a rge p r o t e i n s s u c h as h a e m o g l o b i n (Lees & B e a m e n t , 
298 P. A. Diehl, A. Aeschlimann and F. D. Obenchain 
1948) a r e r ead i ly i n c o r p o r a t e d in to d e v e l o p i n g oocytes , d e m o n s t r a t i n g the i r 
c a p a c i t y to t ake u p e x o g e n o u s p ro t e in s t h r o u g h the p e r m e a b l e b a s e m e n t 
l a m i n a a n d the d e v e l o p i n g egg-shel l . 
H a e m o - g l y c o - l i p o p r o t e i n s c a n be d e m o n s t r a t e d in t he female h a e m o l y m p h 
d u r i n g d iges t ion w h e r e they a r e e l ec t rophore t i ca l ly a n d i m m u n o l o g i c a l l y 
s imi l a r to t h e egg vitel l ine (Dieh l , 1970; A r a m a n , 1979). M o r e o v e r , V u n d l a , 
W h i t e h e a d , a n d O b e n c h a i n ( u n p u b l i s h e d ) used isoelectr ic focusing to s h o w 
t h a t h a e m o p r o t e i n s a p p e a r i n g in t he h a e m o l y m p h of recen t ly e n g o r g e d 
females , b u t a b s e n t in t he h a e m o l y m p h of m a l e s , w a s iden t i ca l to t he vi tel l in 
of R. appendiculatus. D e s p i t e t h e p r e s e n c e of c o n t r a d i c t o r y r e p o r t s on v a r i o u s 
differences in t h e e l ec t ropho re t i c mobi l i t i es o r i m m u n o l o g i c a l iden t i t i e s of 
t ick vi tel l in a n d h a e m o l y m p h p ro t e in s ( T a t c h e l l , 1971; Boc to r & K a m e l , 
1976; D u c o m m u n , u n p u b l i s h e d o b s e r v a t i o n s on 0. moubata), it n o w a p p e a r s 
unl ike ly t h a t v i te l logenins o c c u r r i n g in t he h a e m o l y m p h a r e s t r u c t u r a l l y 
a l t e r ed before the i r i n c o r p o r a t i o n in to t he tick egg a l t h o u g h such p roces s ing 
takes p l a c e in s o m e insec ts ( E n g e l m a n n , 1978; K o e p p e & O f e n g a n d , 1976) . 
T h e si te of e x o g e n o u s v i te l logenin syn thes i s in ixodid ticks a p p e a r s to be 
t he fa t -body . F a t - b o d y cells of R. sanguineus ( b u t n o t m i d g u t cel ls) , after in 
vitro i n c u b a t i o n w i t h
 1 4
C - a m i n o ac ids , re leased labe l led p ro t e in s w h i c h h a d 
s imi l a r e l e c t r o p h o r e t i c mobi l i t i e s to h a e m o l y m p h v i te l logenin ( A r a m a n , 
1979) . T h e ex tens ive d e v e l o p m e n t of ixodid fa t -body d u r i n g a n d after feeding 
s u p p o r t s t h e v iew t h a t it is ac t ive in v i te l logenin syn thes i s ( O b e n c h a i n & 
Ol ive r , 1973) a n d t h e u l t r a s t r u c t u r e of Amblyomma hebraeum a n d 0. moubata 
a d u l t f a t -body (Figs . 9 .18-9 .19) shows t h a t these cells a r e well e n d o w e d w i t h 
the neces sa ry o rgane l l e s for p r o d u c t i o n a n d expo r t of p ro t e in - r i ch sec re t ions . 
F i g u r e 9.20 d e m o n s t r a t e s by ind i r ec t i m m u n o f l u o r e s c e n c e the affinity of the 
ce l lu la r c o n s t i t u e n t s of t h e fa t -body from a female R. appendiculatus 2 d a y s 
after t he c o m p l e t i o n of e n g o r g e m e n t for a n a n t i s e r u m ra i sed in r a b b i t s after 
in ject ion of t h e pur i f ied vi tel l in f rom tick eggs . M i d g u t t issues d id no t r e ac t 
w i t h t h e a n t i b o d y p r e p a r a t i o n , a n d the a p p r o p r i a t e con t ro l s for au tof luor -
escence a n d r eac t i on to n o r m a l r a b b i t s e r u m w e r e all nega t ive ( O b e n c h a i n , 
D h a d i a l l a & A h m e d , u n p u b l i s h e d o b s e r v a t i o n s ) . O n the o t h e r h a n d , a u t o -
r a d i o g r a p h i c a l d a t a f rom 0. moubata sugges t t h a t m i d g u t cells syn thes ize a t 
least s o m e of t he e x o g e n o u s v i te l logenins ( J e n n i , 1971) in a rgas id t icks; t he 
FlG. 9.18. Trophocytic fat-body cell of female Amblyomma hebraeum during vitellogenesis showing 
extensive development of rough endoplasmic reticulum and with lipid (1) and glycogen (arrows) 
inclusions. Scale = 0.2 μηι. (Hecker & Aeschlimann, 1970.) 
FlG. 9.19. Trophocytic fat-body cell of female Ornithodoros moubata showing the similarities of its 
development during vitellogenesis to that of ixodid fat-body. Scale = 0.05 μpiι. 
FlG. 9.20. Fat-body strand of female Rhipicephalus appendiculatus during period of active vitel-
logenesis with demonstration by indirect immunofluorescence of cytoplasmic affinity for 
rabbit-raised antisera to purified egg vitellin (Obenchain, Dhadialla & Ahmed, unpublished). 
Scale = 40 μpiι. 
Tick Reproduction: Oogenesis and Oviposition 299 
300 P. A. Diehl, A. Aeschlimann and F. D. Obenchain 
s e e m i n g c o n t r a d i c t i o n s of t hese o b s e r v a t i o n s r e m a i n to be conf i rmed by 
b i o c h e m i c a l t e c h n i q u e s . 
9.3.2.4. Biochemistry of the Egg-shell V e r y l i t t le i n fo rma t ion exists o n t h e c h e m -
is t ry of t h e egg-shel l . H i s t o c h e m i c a l (Dieh l , 1970) a n d b i o c h e m i c a l t e c h n i q u e s 
h a v e b e e n used (Lees & B e a m e n t , 1948) to d e m o n s t r a t e the p r o t e i n a c e o u s 
n a t u r e of t h e egg-shel l of 0. moubata. N o m u c o p o l y s a c c h a r i d e s , c a r b o h y d r a t e s , 
o r l ip ids w e r e d e t e c t e d . T h e shell of eggs r e a d y for ovu l a t i on is soft a n d m a y 
be c o n s i d e r a b l y s t r e t c h e d , b u t t he shells of recen t ly ov ipos i t ed eggs a r e r ig id . 
T h e egg-shel l of R. sanguineus is a lso c o m p o s e d m a i n l y of p r o t e i n s a n d 
p e r h a p s of s o m e s m a l l s c a t t e r e d a r e a s of ch i t in ( J a skosk i & But l e r , 1971). 
T h e a m i n o ac id s , lys ine , a r g i n i n e , a s p a r t i c ac id , se r ine , g lyc ine , g l u t a m i c 
ac id , a l a n i n e , t h r e o n i n e , va l ine , ty ros ine , i so leuc ine , l euc ine , a n d t r y p t o p h a n e 
w e r e ident i f ied b y t h in - l aye r c h r o m a t o g r a p h y . T h e p r e s e n c e of ch i t in w a s 
r evea led b y t h e d i s p u t e d c h i t o s a n tes t . G l u c o s a m i n e cou ld n o t be d e t e c t e d ; 
therefore , t h e p r e s e n c e of ch i t in in t h e egg-shel l r e m a i n s doub t fu l . 
T h e m e c h a n i s m of p o l y m e r i z a t i o n of t he p r o t e i n p r e c u r s o r s a n d t h e n a t u r e 
of t h e l inks b e t w e e n t h e shell p r o t e i n s r e m a i n u n k n o w n . P r e l i m i n a r y tests 
in 0. moubata s h o w e d t h a t h y d r o g e n b o n d i n g a n d d i s u l p h i d e b r idges w e r e 
a p p a r e n t l y n o t i m p o r t a n t ; t he l inks s e e m to b e ve ry s t ab l e (Dieh l , u n p u b l i s h e d 
o b s e r v a t i o ns ) . J u s t before ovu l a t i on , a n i n c o m p l e t e l ayer of r e d u c i n g g r a n u l e s 
of u n k n o w n c h e m i c a l n a t u r e a p p e a r s o n t h e ou t s i d e of t he egg-shel l of 0. 
moubata (Lees & B e a m e n t , 1948); i ts s ignif icance is u n k n o w n . 
B a s e d on cyto logica l o b s e r v a t i o n s , m o s t w o r k e r s bel ieve t h a t t h e shell is 
p r o d u c e d en t i re ly b y the oocy te . H o w e v e r , J e n n i (1971) d e d u c e d from e q u i v o -
cal a u t o r a d i o g r a p h i c a l d a t a t h a t h a e m o l y m p h p r o t e i n s serve as egg-shel l 
p r e c u r s o r s . B i o c h e m i c a l e x p e r i m e n t s a r e n e e d e d to a n s w e r th is q u e s t i o n . 
9.3.3. Ovulat ion and Final Oocyte Maturation in the Genital Tract 
I f p r o p e r l y fert i l ized, e n g o r g e d female t icks usua l ly beg in to o v u l a t e w i t h i n 
1-2 weeks after t h e s t a r t of feeding. By th is t i m e , v i te l logenesis a n d egg-shel l 
f o rma t ion h a v e b e e n c o m p l e t e d in t h e m o s t a d v a n c e d p o p u l a t i o n of d e v e l o p i n g 
oocytes a n d they a r e r e a d y for o v u l a t i o n . T h e a c t u a l p rocess of o v u l a t i o n h a s 
neve r b e e n o b s e r v e d ; it m u s t therefore b e a r a p i d even t . M o s t a u t h o r s a s s u m e 
t h a t o v u l a t i o n o c c u r s as t h e resu l t of i n c r e a s i n g p r e s s u r e exe r t ed b y t h e 
g r o w i n g oocy te o n t h e b a s e m e n t l a m i n a w h i c h forces t h e oocy te i n t o t h e 
o v a r i a n l u m e n . A l t e rna t ive ly , t he p rocess m a y be t r iggered by a m e c h a n i s m 
w h i c h r e d u c e s t h e i n t e r ce l lu l a r a d h e s i o n of t h e funicle cells j u s t p r i o r to 
o v u l a t i o n . T h i s w o u l d p r o v i d e a m o r e sub t l e form of con t ro l for t h e t i m i n g 
of o v u l a t i o n . I n t h e a b s e n c e of e x p e r i m e n t a l d a t a , d i scuss ions o n t h e m e c h -
a n i s m of o v u l a t i o n a r e en t i re ly specu la t ive . 
Fo l lowing o v u l a t i o n , pe r i s t a l t i c m o v e m e n t s of t he o v a r y a n d o v i d u c t s 
Tick Reproduction: Oogenesis and Oviposition 301 
t r a n s p o r t t h e eggs t o w a r d s t h e l ower p a r t s of t h e ov iduc t s a n d in to t he u t e r u s . 
T h e m e c h a n i s m con t ro l l i ng t h e c o n t r a c t i o n of musc le s involved in this 
t r a n s p o r t is u n k n o w n ; per i s ta l s i s m a y b e u n d e r n e r v o u s a n d / o r h o r m o n a l 
con t ro l . 
As o v u l a t i o n c o n t i n u e s , oocy tes a c c u m u l a t e in t h e l u m e n of t he o v a r y or 
of t h e u t e r u s , a n d these reg ions c a n b e c o m e g rea t l y d i s t e n d e d . I n t he ov iduc t s , 
h o w e v e r , t h e oocy tes t e n d to b e a l i gned o n e b e h i n d the o t h e r in a s t r ing-
of-pear ls f o r m a t i o n . 
9.3.3.1. Cytological Development of the Ovulated Oocyte W i t h the excep t ion of t he 
n u c l e a r r eg ion , t h e cy to logy of t h e o v u l a t e d oocy te does no t c h a n g e no t i ceab ly 
d u r i n g t h e p a s s a g e of t h e gen i t a l d u c t s . T h e c y t o p l a s m wi th t he yolk c o m -
p o n e n t s a n d t h e h o m o g e n e o u s egg-shel l of oocytes a p p e a r s imi la r before a n d 
after o v u l a t i o n . A p p a r e n t l y , t h e po l a r i t y of t h e oocy te is m a i n t a i n e d . T h e 
r icket t s ia - l ike s y m b i o n t s r e m a i n a s s e m b l e d a t t h e oocy te p e r i p h e r y oppos i t e 
t h e n u c l e a r r eg ion (Dieh l , 1970) . 
I n 0. moubata t h e p r e v i o u s pos i t ion of a t t a c h m e n t of t he oocy te to t he 
funicle cells r e m a i n vis ible as a s l ight d e p r e s s i o n in t he shell of o v u l a t e d eggs . 
I n D. andersoni a n d o t h e r Dermacentor species this a r e a h a s b e e n o b s e r v e d in 
l i gh t -mic roscop ic sec t ions a n d in w h o l e m o u n t s a n d h a s b e e n ca l led t he 
m i c r o p y l a r r eg ion ( B r i n t o n & Ol ive r , 1971b) . I t is n o t k n o w n , howeve r , if 
th i s t h i n n e d shel l r eg ion a c t u a l l y ac t s as a m i c r o p y l e faci l i ta t ing s p e r m 
p e n e t r a t i o n ; in insec ts fer t i l iza t ion o c c u r s t h r o u g h a t h in shell r eg ion or 
t h r o u g h m i c r o p y l a r c a n a l s (cf. W i g g l e s w o r t h , 1972) . 
Cy to log ica l c h a n g e s a r e vis ible w i t h i n t h e n u c l e a r reg ion of t he o v u l a t e d 
oocy te . C o n d e n s e d c h r o m o s o m e s w e r e o b s e r v e d in oocytes from the lower 
o v i d u c t o r u t e r u s of 0. moubata) th is c o n d e n s a t i o n m a y be t h e express ion of 
a r e s u m e d first m a t u r a t i o n d iv i s ion (Dieh l , 1970) . A c c o r d i n g to G o r o s h c h e n k o 
(1965) a n d B a l a s h o v (1972) , t he first m a t u r a t i o n divis ion is r e s u m e d a n d 
c o m p l e t e d on ly after t h e fer t i l izat ion of t h e p r i m a r y oocyte w h i c h t akes p l ace 
in t h e lower ( a m p u l l a t e ) p a r t s of t h e o v i d u c t . S e c o n d a r y oocytes a r e t h u s 
fo rmed on ly after t h e p a s s a g e of t h e a m p u l l a t e o v i d u c t reg ion . 
9.3.3.2. Syngamy R e p r o d u c t i o n in t icks is mos t l y b i sexua l a l t h o u g h s o m e tick 
species s u c h as Haemaphysalis longicornis h a v e p a r t h e n o g e n e t i c races whi le 
o t h e r s s u c h as Amblyomma rotundatum a p p e a r to be to ta l ly p a r t h e n o g e n i c (see 
rev iew of O l ive r , 1971; C h a p t e r 8 ) . I n t h e b i s exua l species , s y n g a m y or t he 
p e n e t r a t i o n of t he oocy te by t h e s p e r m takes p l ace w i t h i n t he female gen i t a l 
t r ac t . T h e a c t u a l s i te of s y n g a m y , h o w e v e r , is still a p o i n t of c o n t e n t i o n . 
Severa l a u t h o r s be l ieve t h a t s y n g a m y o c c u r s w i t h i n t h e o v a r y b u t the i r d a t a 
a r e n o t c o n v i n c i n g . A s n o t e d a b o v e , B r i n t o n & O l i v e r (1971b) d e s c r i b e d the 
p r e s e n c e of a mic ropy le - l ike a p e r t u r e in t h e d e v e l o p i n g egg-shel l of D. 
andersoni. T h e y p r o p o s e d t h a t fer t i l iza t ion o c c u r r e d in t h e o v a r y w h e n t h e t ip 
of t h e s p e r m b e c a m e a t t a c h e d to th is a p e r t u r e , fol lowing w h i c h the s p e r m 
n u c l e u s w a s be l i eved to b e re l eased i n t o t h e egg. 
302 P. A. Diehl, A. Aeschlimann and F. D. Obenchain 
O n t h e o t h e r h a n d , G o r o s h c h e n k o (1965) a n d B a l a s h o v (1972) r e p o r t t h a t 
s y n g a m y takes p l a c e in t h e lower p a r t s of t he ov iduc t s . M a t u r e s p e r m 
a c c u m u l a t e preferen t ia l ly in t h e lower t h i r d of t h e ov iduc t s ( I x o d i d a e ) o r in 
t h e a m p u l l a e ( A r g a s i d a e ) . O n mic roscop i c e x a m i n a t i o n , m o s t of these s p e r m 
cells a p p e a r to b e a t t a c h e d to t h e o v i d u c t cells by the i r l a rge r a n t e r i o r p a r t ; 
the i r pos t e r i o r e n d , c o n t a i n i n g the n u c l e u s a n d a n ac rosome- l ike reg ion , 
p r o t r u d e s i n to t h e l u m e n . W i t h i n t h e a r g a s i d o v i d u c t m a n y of these s p e r m 
a r e p h a g o c y t i z e d a n d b r o k e n d o w n by p h a g o l y s o s o m e s w i t h i n t he cells of 
the a m p u l l a e (Rebe t ez , pe r s . c o m m . ) . T h e R u s s i a n a u t h o r s bel ieve t h a t 
as t h e o v u l a t e d oocy te d e s c e n d s i n to th is lower reg ion of the o v i d u c t t h e 
a c r o s o m e reg ion of o n e of t h e ava i l ab l e s p e r m dissolves a p o r t i o n of t h e 
p r o t e i n a c e o u s egg-shel l a n d re leases its n u c l e u s i n to t he oocy te . T h e l a rge 
b o d y of t h e s p e r m , h o w e v e r , r e m a i n s on the ou t s ide . T h e m a l e p r o n u c l e u s 
t h e n t akes u p a c e n t r a l pos i t ion in t h e oocy te . T h e p e n e t r a t i o n of t he oocy te 
b y t h e s p e r m n u c l e u s t r iggers t h e r e s u m p t i o n of t he first oocy te m a t u r a t i o n 
d iv is ion . T h e r e su l t i ng s e c o n d a r y oocy te p r o c e e d s to t he s e c o n d a r y m a t u r -
a t i o n d iv is ion , b u t t h e fusion of m a l e a n d female p r o n u c l e i occu r s on ly after 
ov ipos i t ion . 
U n f o r t u n a t e l y , t h e o r ig ina l d a t a of G o r o s h c h e n k o (1965) o n w h i c h th is 
d e s c r i p t i o n of s y n g a m y is b a s e d d o no t a p p e a r to be ava i l ab l e . T h u s , t he 
p r o b l e m of s y n g a m y in t icks c lear ly dese rves a careful r e e x a m i n a t i o n . 
9.3.3.3. Physiology and Biochemistry of the Ovulated Oocyte I n 0. moubata t he v o l u m e 
of t h e oocy te inc reases c o n s i d e r a b l y ( u p to 8 9 % ) after i ts p a s s a g e t h r o u g h 
t h e a m p u l l a d u e to t h e a b s o r p t i o n of w a t e r (Lees & B e a m e n t , 1948; D ieh l , 
1970) . T h i s p h e n o m e n o n a lso a p p e a r s to o c c u r in o t h e r t icks i n c l u d i n g 
a r g a s i d a n d ixod id species (Dieh l , u n p u b l i s h e d o b s e r v a t i o n s ) . A c o n s i d e r a b l e 
m o v e m e n t of w a t e r m u s t o c c u r from t h e h a e m o l y m p h , t h r o u g h the cells of 
t h e lower ov iduc t , a n d i n t o t he o v i d u c t l u m e n in o r d e r to satisfy t he w a t e r 
so rp t ion r e q u i r e m e n t s of t he oocy tes . A t p r e s e n t , w e d o n o t k n o w if t he 
p rocess of w a t e r u p t a k e b y t h e oocy te is pass ive o r ac t ive . I n a n y case , t he 
final w a t e r c o n t e n t a n d , therefore , t he final oocy te v o l u m e is a t t a i n e d in t h e 
lower o v i d u c t s ; th is a d a p t a t i o n m i n i m i z e s t he p r o b l e m of l imi ted s p a c e w i t h i n 
t h e o v a r y a n d t h e u p p e r o v i d u c t s w h i c h m u s t receive a n d s to re l a rge n u m b e r s 
of freshly o v u l a t e d oocy tes . 
T h e egg-shel l of freshly o v u l a t e d oocytes is soft a n d ex tens ib le . C o n c o m -
i t an t ly w i t h t h e p rocess of w a t e r u p t a k e a n d v o l u m e t r i c inc rease , t h e egg-
shel l b e c o m e s progress ive ly h a r d e n e d d u r i n g the oocytes p a s s a g e t h r o u g h 
the lower o v i d u c t . By the t i m e it r e a c h e s t h e u t e r u s t he egg-shel l is r igid a n d 
h a s l i t t le e las t ic i ty (Lees & B e a m e n t , 1948; D ieh l , 1970) . T h e c h e m i c a l a n d 
phys i ca l ba se s of th is h a r d e n i n g p rocess r e m a i n u n e x p l o r e d ; egg-shel l p ro t e in s 
m a y b e c o m e c h a n g e d t h r o u g h the ac t ion of c ross- l ink ing or t a n n i n g a g e n t s 
w h i c h cou ld be p r o d u c e d e i the r by t he oocy te itself o r as a secre t ion of t h e 
o v i d u c t ep i the l i a l cells o r t u b u l a r accessory g l a n d s . I n a n y case , t h e p e r m e -
Tick Reproduction: Oogenesis and Oviposition 303 
abi l i ty p r o p e r t i e s of t h e h a r d e n e d shell a p p e a r u n c h a n g e d ; oocytes a r e ve ry 
p e r m e a b l e even to l a rge p r o t e i n s (Lees & B e a m e n t , 1948). 
As t h e p roces s of w a t e r u p t a k e a n d shel l h a r d e n i n g beg in after t h e p a s s a g e 
of t h e a m p u l l a , it is t e m p t i n g to s p e c u l a t e t h a t s y n g a m y m a y t r igger these 
even t s . T h a t t y p e of c a u s a l r e l a t i o n s h i p w o u l d e n s u r e t h a t s y n g a m y occu r s 
before shel l h a r d e n i n g beg ins a s it s h o u l d b e eas ie r for t he s p e r m to p e n e t r a t e 
t h e flexible r a t h e r t h a n t h e h a r d e n e d egg-shel l . T h i s a t t r a c t i v e h y p o t h e s i s 
s e e m s r a t h e r un l ike ly in l igh t of o t h e r o b s e r v a t i o n s . T h e ov ipos i t ion of 
s eeming ly perfect b u t n o n - v i a b l e eggs b y e x p e r i m e n t a l l y m a n i p u l a t e d 0. 
moubata v i rg in females ( rev iewed be low in §9.5) a p p a r e n t l y speaks a g a i n s t 
s u c h a con t ro l b y s y n g a m y . M o r e o v e r , p a r t i a l l y e n g o r g e d u n m a t e d D. var-
iabilis ( O b e n c h a i n , L e a h y & Ol ive r , u n p u b l i s h e d ) a n d R. appendiculatus 
females ( O b e n c h a i n & D h a d i a l l a , u n p u b l i s h e d ) lay eggs w h e n the i r fed 
we igh t s exceeded a cr i t ica l t h r e s h o l d ( a p p r o x i m a t e l y 10 t imes the i r unfed 
we igh t ) a n d these eggs u n d e r g o a d v a n c e d a n d , r a re ly , c o m p l e t e e m b r y o n i c 
d e v e l o p m e n t . T h e r e f o r e , t h e con t ro l of egg-shel l h a r d e n i n g is p r o b a b l y 
exe r t ed b y sec re t ions of t h e lower ov iduc t s a n d / o r by t h e i n d e p e n d e n t 
d e v e l o p m e n t of t h e oocy te itself. 
T h e cells of t h e a r g a s i d u t e r u s a n d t h e cerv ica l v a g i n a of p r o s t r i a t e ixod ids 
b e c o m e filled w i t h sec re t ions w h i c h a r e r e l eased in to t he l u m e n d u r i n g th is 
s t age of r e p r o d u c t i v e d e v e l o p m e n t . T h e funct ions of these sec re t ions a r e 
u n k n o w n b u t t h e y m a y b e m o r e i m p o r t a n t for t h e v iabi l i ty of t h e s p e r m 
t h a n for oocy te d e v e l o p m e n t . T h e spec ia l ized r e c e p t a c u l u m semin i s of 
m e t a s t r i a t e ixod id t icks is a l so filled w i t h sec re to ry p r o d u c t s re leased f rom 
s imi l a r cells . T h e i r sec re t ions a r e m o r e likely to b e involved in t h e d i s so lu t ion 
of t h e s p e r m a t o p h o r e wal l o r in t he n u t r i t i o n or c a p a c i t a t i o n of t he s p e r m 
( C h a p t e r 8 ) . 
9 . 4 . O V I P O S I T I O N 
H u n g r y o r d e t a c h e d i n c o m p l e t e l y e n g o r g e d ixodid females w h o s e fed 
w e i g h t s h a v e n o t r e a c h e d t h e t h r e s h o l d for ov ipos i t ion ( O b e n c h a i n , L e a h y 
& Ol ive r , u n p u b l i s h e d ) a r e ve ry m o b i l e a n d s h o w the typ ica l hos t - seek ing 
b e h a v i o u r . Fu l ly e n g o r g e d females h a v e lost th is b e h a v i o u r ; they usua l ly 
b e c o m e pos i t ive ly g e o t r o p i c a n d nega t ive ly p h o t o t a c t i c a n d a l m o s t a l w a y s 
h i d e in she l t e r ed p l aces w h e r e ov ipos i t ion will t ake p l ace (Ba la shov , 1972). 
R a p i d l y feeding a r g a s i d females s h o w s imi l a r b e h a v i o u r a l c h a n g e s , b u t the i r 
hos t - seek ing b e h a v i o u r c a n b e c o m e r e a c t i v a t e d if m a t i n g h a s n o t o c c u r r e d 
w i t h i n a c e r t a i n t i m e f r ame o r if t h e p r e v i o u s m e a l w a s i n a d e q u a t e for 
v i te l logenes is to t a k e p l a c e . 
D e p e n d i n g o n t h e t ick species a n d o n e n v i r o n m e n t a l cond i t i ons , t h e r ep le te 
m a t e d female gene ra l l y beg ins to lay eggs after a p re -ov ipos i t ion pe r iod 
l a s t ing f rom 1 o r 2 d a y s u p to severa l weeks . T h e v a r i a b l e l eng th of t he 
304 P. A. Diehl, A. Aeschlimann and F. D. Obenchain 
pre -ov ipos i t ion p e r i o d is m a i n l y d e t e r m i n e d by t e m p