1982 (Chapter 1) HACKMAN Fisiology of Ticks The Tick Cuticle

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C H A P T E R 1 
The Tick Cuticle 
R. H. H A C K M A N and B. K. FILSHIE 
Division of Entomology, Commonwealth Scientific and Industrial Research Organization, Canberra, 
Australia 
C O N T E N T S 
1.1. Introduction 1 
1.2. Structure 3 
1.2.1. Morphology of the Cuticle 4 
1.2.1.1. Epicuticle 4 
1.2.1.2. Procuticle, Exocuticle, Mesocuticle, Endocuticle, and 
Subcuticle 8 
1.2.1.3. Pore Canals and Wax Canals 12 
1.2.1.4. Muscle Attachments, Glands, and other Integumental 
Structures 15 
1.2.2. Deposition of the Cuticle 18 
1.2.2.1. Formation of the Epicuticle 19 
1.2.2.2. Formation of the Procuticle 20 
1.2.2.3. Modifications to Cuticle Structure during Feeding 24 
1.3. Cuticular Components 29 
1.3.1. Chitin 29 
1.3.2. Protein 32 
1.3.3. Lipids 34 
1.3.4. Other Components 35 
1.3.5. Sclerotization 36 
1.3.6. Penetration of Acaracides 36 
1.3.7. Water Exchange 36 
1.4. Conclusions 38 
References 39 
1.1. I N T R O D U C T I O N 
In i t i a l d e s c r i p t i o n s of t h e tick cut ic le , w h i c h d a t e from a r o u n d t h e b e g i n n i n g 
of this c e n t u r y , w e r e b a s e d o n h i s t o c h e m i c a l s tud ies u s ing the l ight m i c r o -
scope , b u t in t he las t d e c a d e fu r the r p rog re s s h a s b e e n m a d e in o u r u n d e r -
s t a n d i n g of t he s t r u c t u r e , syn thes i s , a n d c o m p o s i t i o n of t he cut ic le by use 
of n e w e r t e c h n i q u e s s u c h as e l ec t ron m i c r o s c o p y , c h r o m a t o g r a p h y , a n d 
e l ec t rophores i s . L ike o t h e r a r t h r o p o d s , t icks h a v e a n ex t e rna l ske le ton o r 
i n t e g u m e n t w h i c h is skin , ske le ton , a n d , if necessa ry , a food rese rve . T h e 
c u t i c l e is t h a t p a r t of t h e i n t e g u m e n t ex t e rna l to a n d secre ted by the 
1 
2 R. H. Hackman and Β. K. Filshie 
e p i d e r m i s ( the e p i d e r m a l c e l l l a y e r ) , w h i c h is itself s u p p o r t e d on a n 
i n t e r n a l b a s e m e n t m e m b r a n e . I n insec ts t he r e is ev idence w h i c h sugges t s 
t h a t s o m e c u t i c u l a r p ro t e in s m a y n o t b e syn thes i zed by the e p i d e r m a l cells 
b u t a r e t r a n s p o r t e d ac ross t h e m from the h a e m o l y m p h , h a v i n g b e e n syn-
thes ized e l sewhere . H o w e v e r , t i ssue c u l t u r e e x p e r i m e n t s h a v e e s t ab l i shed 
t h a t e p i d e r m a l cells secre te cut ic le . Cu t i c l e is a h e t e r o g e n e o u s , non -ce l l u l a r 
m e m b r a n e , w h i c h is n o t on ly t he e x t e r n a l cover ing b u t e x t e n d s i n to t he 
fore- a n d h i n d - g u t s a n d l ines t h e d u c t s of d e r m a l g l a n d s a n d the t r a c h e a l 
sy s t em. 
T h e cut ic le is n o t un i fo rm over t he en t i r e a n i m a l b u t va r ies f rom h a r d 
sc lero t ized p l a t e s to soft ex tens ib le m e m b r a n e s . T o a l low m o v e m e n t , r igid 
p l a t e s a r e c o n n e c t e d t o g e t h e r by flexible ( i n t e r s egmen ta l ) m e m b r a n e s , w h i c h 
ac t as h i n g e s . I x o d i d ticks a r e referred to as h a r d t i c k s b e c a u s e of the i r 
sc lero t ized ( h a r d e n e d ) c a p i t u l u m , s c u t u m , a p p e n d a g e s , a n d o t h e r sma l l 
a r e a s . O n t h e o t h e r h a n d , a r g a s i d t icks a r e the l e a the ry or s o f t t i c k s b e c a u s e 
sc lero t ized a r e a s a r e re la t ive ly sma l l . T h e cut ic le , be ing a n ex t ene ra l ske le ton , 
d e t e r m i n e s t he m a x i m u m size a n d the s h a p e t h a t a p a r t i c u l a r d e v e l o p m e n t a l 
s t age c a n a t t a i n , a n d fu r the r g r o w t h is poss ib le only by m o u l t i n g , i.e. 
s h e d d i n g t h e cut ic le a n d r e p l a c i n g it by a l a rge r o n e . I x o d i d ticks u n d e r g o 
two m o u l t s in the i r p rog re s s f rom l a r v a e to n y m p h s to a d u l t s . A r g a s i d t icks 
u n d e r g o t h r e e o r m o r e m o u l t s . S o m e species h a v e two n y m p h a l i n s t a r s , 
o t h e r s u p to six o r m o r e . R e s p i r a t i o n in n y m p h a l a n d a d u l t t icks is by w a y 
of t r a c h e a e w h i c h t e r m i n a t e in t he s p i r a c u l a r p l a t e s o n t he sides of t he b o d y . 
L a r v a l t icks , excep t for t hose of s o m e a rga s id species , d o n o t a p p e a r to h a v e 
sp i rac les , a n d it is a s s u m e d t h a t ga seous e x c h a n g e occu r s t h r o u g h the i n t ac t 
cut ic le . 
T h e cut ic le is d i v i d e d in to t w o layers , a th in o u t e r e p i c u t i c l e a n d a th icker 
i n n e r p r o c u t i c l e . T h e ep icu t ic le is c o m p l e x a n d c o n t a i n s severa l l ayers , viz. 
l ip id , p o l y p h e n o l , a n d cu t i cu l in ; in a r g a s i d t icks a c e m e n t l ayer overl ies t h e 
l ipid layer . T h e p r o c u t i c l e is fo rmed of p r o t e i n a n d ch i t in . I t s o u t e r reg ion 
m a y b e sc le ro t ized to form a n e x o c u t i c l e ; in w h i c h case the r e m a i n i n g i n n e r 
reg ion is k n o w n as t he e n d o c u t i c l e . I n s o m e cut ic les t he o u t e r p a r t of t h e 
e n d o c u t i c l e m a y s h o w different s t a i n i n g p r o p e r t i e s from the i n n e r p a r t . T h e 
o u t e r p a r t is t h e n referred to as m e s o c u t i c l e . Mesocu t i c l e is d e s c r i b e d as 
a s t ab i l i zed b u t non-sc le ro t i zed reg ion . T i c k s , in c o m m o n w i t h o t h e r chel i -
ce r a t e s , possess a n e n d o s t e r n i t e o r i n t e r n a l skeleta l s u p p o r t for s o m e p r o s o m a l 
m u s c l e s . C o n t r a r y to ear l i e r c l a ims , C u t l e r a n d R i c h a r d s (1974) r e p o r t t h a t 
t h e e n d o s t e r n i t e does no t c o n t a i n ch i t in ; its c h e m i c a l c o m p o s i t i o n is u n k n o w n . 
W a t e r loss in t icks is a l m o s t exclusively t h r o u g h the cut ic le (Lees , 1946), 
a n d t h e l ip id l ayer of t he ep icu t ic le p l ays a m a j o r role in r e g u l a t i n g t he 
m o v e m e n t of w a t e r . 
Se t ae o r br is t les a r e p r e s e n t on t he cut ic le a n d each is set in a socket o n 
t o p of a c a n a l l e a d i n g f rom a n e p i d e r m a l cell. P o r e c a n a l s e x t e n d t h r o u g h 
The Tick Cuticle 3 
PORE C A N A L FILAMENTS 
OPENING OF DUCT 
OF DERMAL GLAND 
EPICUTICLE 
EXOCUTICLE 
(PIGMENTED LAYER) 
MESOCUTICLE 
CUTICLE 
ENDOCUTICLE 
EPIDERMIS 
BASEMENT MEMBRANE 
OENOCYTE TRICHOGEN C E L L DERMAL GLAND 
(SETA FORMING C E L L ) 
TORMOGEN CELL 
(SOCKET FORMING C E L L ) 
FlG. 1.1. A diagrammatic representation of the arthropod integument. (From Hackman, 1971.) 
t he p rocu t i c l e f rom t h e e p i d e r m i s u p to t h e ep icu t ic le . A n u m b e r of sense 
o r g a n s a n d d e r m a l g l a n d s o p e n o n t o t he surface of t he cut ic le . S o m e se t ae 
a r e t h o u g h t to b e t e m p e r a t u r e sensor s a n d o t h e r s tac t i le sensors . F i g u r e 1.1 
is a d i a g r a m m a t i c r e p r e s e n t a t i o n of t h e a r t h r o p o d i n t e g u m e n t , F ig . 1.2 a n 
e lec t ron m i c r o g r a p h of a t r a n s v e r s e sec t ion of t he i n t e g u m e n t from t h e d o r s a l 
sur face of t h e a l l o s c u t u m of t he n y m p h of Boophilus microplus. F o r r e cen t 
rev iews o n t h e a r t h r o p o d cut ic le , reference c a n be m a d e to H a c k m a n ( 1 9 7 1 , 
1974a) a n d Nevi l le (1975) . References to t he ea r ly w o r k on tick cut ic le a r e 
to b e found in R i c h a r d s (1951) . 
1.2. S T R U C T U R E 
O u r p r e s e n t k n o w l ed g e of tick c u t i c u l a r s t r u c t u r e c o m e s f rom ear l ie r 
s tud ies w i t h t h e l igh t m i c r o s c r o p e c o m b i n e d w i t h a few r ecen t de sc r ip t i ons 
of t he fine s t r u c t u r e f rom t r a n s m i s s i o n a n d s c a n n i n g e lec t ron m i c r o s c o p e 
s tud ie s . By c o m p a r i s o n w i t h insec t cu t ic le , p u b l i s h e d i n fo rma t ion on t h e fine 
s t r u c t u r e of t h e t ick i n t e g u m e n t is s p a r s e i n d e e d . T h e s e few s tud ies i n d i c a t e 
SETA 
4 R. H. Hackman and B. K. Filshie 
t h a t m a n y pa ra l l e l s m a y be d r a w n b e t w e e n insect a n d tick cut ic les . H o w e v e r , 
severa l differences h a v e b e e n d i scovered , p a r t i c u l a r l y in t he s t r u c t u r e a n d 
d e v e l o p m e n t of t he cut ic le of t he a l l o s c u t u m of female ixodid t icks. T h i s 
cut ic le h a s a n e n o r m o u s c a p a c i t y for g r o w t h , e x p a n s i o n , a n d s t r e t c h i n g 
d u r i n g e n g o r g e m e n t of b lood in t h e a d u l t i n s t a r . T h e fol lowing d e s c r i p t i o n 
of t h e s t r u c t u r e of t h e cut ic le c o m b i n e s a rev iew of p u b l i s h e d i n fo rma t ion 
a u g m e n t e d b y s o m e n e w d e s c r i p t i o n s a n d m i c r o g r a p h s of t he cut ic le of t he 
a d u l t female ca t t l e t ick, B. microplus. 
1.2.1. Morphology of the Cuticle 
I n c o m m o n w i t h s imi l a r d e s c r i p t i o n s of insect cut ic le , difficulties exist in 
co r r e l a t i ng t h e i n t e r p r e t a t i o n of s t r u c t u r e s seen in t he l ight m i c r o s c o p e w i t h 
those seen a t h i g h e r r e so lu t ion in t he e lec t ron m i c r o s c o p e . T h e s e difficulties 
resu l t f rom t h e different m e t h o d s of p r e p a r a t i o n a n d e x a m i n a t i o n w h i c h a r e 
used w i t h t h e t w o t e c h n i q u e s a n d t h e different w a y s in w h i c h i m a g e s a r e 
fo rmed . F o r i n s t a n c e , different s t a i n i n g m e t h o d s a p p l i e d to paraffin sec t ions 
h a v e a l lowed t h e p rocu t i c l e to be s u b d i v i d e d in to a n u m b e r of l a y e r s — 
exocut ic le , mesocu t i c l e , endocu t i c l e , a n d s u b c u t i c l e — b u t w i t h e lec t ron s t a ins 
these l ayers a r e difficult o r even imposs ib l e to d i s t i ngu i sh from o n e a n o t h e r . 
T h e w a x a n d c e m e n t l ayers , b o t h la rge ly so lub le in l ipid so lvents , a r e no t 
p r e s e r v e d b y t h e n o r m a l m e t h o d s u sed to p r e p a r e cut ic le for t r a n s m i s s i o n 
e lec t ron m i c r o s c o p y . B e c a u s e t h in ( 5 0 - 1 0 0 n m ) sec t ions m u s t be used for 
e lec t ron m i c r o s c o p y , difficulties exist in t he i n t e r p r e t a t i o n of t h r e e - d i m e n -
s iona l s t r u c t u r e s s u c h as t h e s h a p e of p o r e cana l s o r t he d i spos i t ion of fibrous 
e l e m e n t s w i t h i n t h e p rocu t i c l e . 
1.2.1.1 Epicuticle I n a r t h r o p o d s genera l ly , l i gh t -mic roscope s tud ies h a v e d e m -
o n s t r a t e d t he p r e s e n c e of four d i s t inc t l ayers , viz. c e m e n t , w a x , cu t i cu l in , 
a n d p o l y p h e n o l . T h e p r e s e n c e of these layers h a s b e e n inferred from his to -
c h e m i c a l r e a c t i o n s . I n d i v i d u a l l ayers a r e too th in to be resolved s e p a r a t e l y 
by l ight m i c r o s c o p y ( R i c h a r d s & A n d e r s o n , 1942; W i g g l e s w o r t h , 1947; 
R i c h a r d s , 1951) . P o l y p h e n o l s h a v e b e e n d e m o n s t r a t e d by the i r ab i l i ty to 
r e d u c e a m m o n i a c a l si lver n i t r a t e . T h e c u t i c u l i n l a y e r , w h i c h is s u p p o s e d 
to b e a t a n n e d l i p o p r o t e i n c o m p l e x , is def ined by its r e s i s t ance to l ipid 
so lvents s u c h as bo i l ing ch lo ro fo rm, t he l ipid only b e i n g re leased after 
w a r m i n g w i t h p o t a s s i u m c h l o r a t e a n d n i t r i c ac id (Wigg le swor th , 1947) . W a x 
l a y e r s a r e seen on ly in t r a n s v e r s e sec t ions of frozen cut ic le , u s ing l ipid s t a in s 
s u c h as o s m i u m t e t rox ide , o r those of t h e S u d a n series ( R i c h a r d s , 1951) . 
C e m e n t , w h e n p r e s e n t , forms t h e o u t e r m o s t layer , a n d is p r o d u c e d by d e r m a l 
g l a n d sec re t ions p o u r e d o u t o n t o t he cut ic le surface t h r o u g h fine d u c t s shor t ly 
after m o u l t i n g . 
L i g h t - m i c r o s c o p e s tud ie s of ixodid a n d a rga s id t icks h a v e d e m o n s t r a t e d 
all four of these l aye rs . T h e c e m e n t l ayer is p r e s e n t only in a r g a s i d s (Lees , 
The Tick Cuticle 5 
1947; B a l a s h o v , 1968) . N o t h i n g is k n o w n of its s t r u c t u r e o r c o m p o s i t i o n , b u t 
it is a s s u m e d t h a t it h a s a s imi l a r func t ion to t h e h o m o l o g o u s l aye r of insec ts , 
n a m e l y t he p r o t e c t i o n of t h e u n d e r l y i n g w a x layer . T h e c e m e n t l ayer is m o r e 
r e s i s t an t to l ip id so lven ts t h a n is w a x b u t c a n be r e m o v e d w i t h bo i l ing 
ch lo roform ( A r t h u r , 1962) . 
T h e w a t e r p r o o f i n g p r o p e r t i e s of t he cu t ic le lie in t he surface " w a x " layer , 
s i t u a t e d o u t s i d e t h e cu t i cu l in (Lees , 1947) . A l t h o u g h s o m e w o r k h a s b e e n 
ca r r i ed o u t to c h a r a c t e r i z e t h e l ip ids e x t r a c t e d f rom t h e cut ic le (see § 1.3.3), 
t h e loca t ion of t he se l ip ids is n o t k n o w n abso lu t e ly . I t is u sua l ly a s s u m e d 
t h a t t h e y o r i g i n a t e en t i r e ly f rom t h e sur face w a x layer . I t is n o t k n o w n 
w h e t h e r t h e l aye r d e p o s i t e d o n t h e surface of t h e cu t i cu l in is c o m p o s e d 
en t i re ly of l ip id o r w h e t h e r a d d i t i o n a l c o m p o n e n t s a r e p r e s e n t . O n e w o u l d 
n o t n o r m a l l y expec t to find, in sec t ions p r e p a r e d for e lec t ron m i c r o s c o p y , a 
l ayer of w a x in th is pos i t ion , b u t a we l l -p rese rved l ayer is seen d e s p i t e t he 
a p p l i c a t i o n of l ip id so lven ts d u r i n g t h e e m b e d d i n g p r o c e d u r e ( N a t h a n s o n , 
1967) . I n B. microplus t h e l aye r is c lear ly seen in pos t -ecdys ia l cu t ic le of 
n y m p h a n d a d u l t (F igs . 1.2 a n d 1.6). I t is i r r e g u l a r in th i ckness , v a r y i n g 
from 0.1 μpi ι u p to 1 μ ιη o r m o r e , gene ra l ly poor ly s t a ined b u t s o m e t i m e s 
c o n t a i n i n g l a m i n a t e d e l e c t r o n - d e n s e p l a t e s , a r r a n g e d in sma l l c rys ta l l i tes 
w h i c h a r e n o t o r i e n t e d in a n y p re fe r red d i r ec t i on (Fig . 1.6). S imi l a r layers 
a r e a b s e n t in insec t s . 
T h e cu t i cu l in a n d p o l y p h e n o l l aye r s , a s def ined for insec ts by W i g g l e s w o r t h 
(1947) , h a v e b e e e n d e m o n s t r a t e d b y Lees (1947) in severa l ixodid a n d a r g a s i d 
spec ies . B a l a s h o v (1968) r e p o r t e d t h e p r e s e n c e of a m b e r - c o l o u r e d cu t i cu l in 
l ayers in ixod ids a n d a r g a s i d s v a r y i n g b e t w e e n 1 a n d 3 μηι th ick . H o w e v e r , 
th is t h i ckness is g r e a t e r t h a n t h a t of t h e w h o l e ep icu t ic le , as d e t e r m i n e d by 
o t h e r a u t h o r s . Fo l lowing t h e ea r ly a p p l i c a t i o n s of e lec t ron m i c r o s c o p y to 
a r t h r o p o d cut ic le s t r u c t u r e , L o c k e (1957, 1966) re-def ined t h et e r m cu t i cu l in 
to refer to t h e t h i n e l ec t ron d e n s e l aye r of t h e ep icu t ic le of insec ts t h a t is first 
la id d o w n o n t h e sur face of t he e p i d e r m i s a t m o u l t i n g . Locke referred to t h e 
m u c h th i cke r i n t e r n a l l aye r c o m p r i s i n g t h e r e m a i n d e r of t h e ep icu t ic le , as 
t he p r o t e i n e p i c u t i c l e o r t h e d e n s e h o m o g e n e o u s l a y e r . T h e l a t t e r t e r m 
is t he o n e c u r r e n t l y in use . 
F i l sh ie (1970a , b) d e s c r i b e d a n a d d i t i o n a l u n s t a i n e d layer on t h e o u t s i d e 
of t h e cu t i cu l in of insec t s , ca l led t h e o u t e r ep icu t ic le . I n t he r a b b i t t ick 
Haemaphysalis leponspalustris, N a t h a n s o n (1967) d e s c r i b e d four reg ions o r 
l ayers . H i s r eg ions I I , I I I , a n d I V c o r r e s p o n d in pos i t ion to t he o u t e r 
ep icu t ic le , cu t i cu l in , a n d d e n s e h o m o g e n e o u s layers of t h e insec t ep icu t ic le , 
respec t ive ly (F igs . 1.5 a n d 1.6. for B. microplus). F i l sh ie (1976) , in a de t a i l ed 
s t u d y of t h e s t r u c t u r e of t h e ep icu t i c le of t h e a d u l t female of B. microplus, 
found t h e s a m e l aye r s , b u t t h e o u t e r ep icu t ic le a n d t h e d e n s e l ayer b o t h 
c o n t a i n e d a d d i t i o n a l complex i t i e s n o t seen p rev ious ly in o t h e r a r t h r o p o d 
cut ic les . T h e o u t e r ep icu t ic le , w h e n first fo rmed , c o n t a i n s r e g u l a r s t r i a t ions 
6 R. H. Hackman and B. K. Fils hie 
w i t h a p e r i o d of a b o u t 5 n m . T r a v e r s i n g t h e d e n s e layer a r e e lec t ron o p a q u e 
filaments a b o u t 17 n m in d i a m e t e r w i t h a spa t i a l dens i ty of a b o u t 800 p e r 
μ η ι
2
 (Figs . 1.7 a n d 1.9). T h e a b o v e resu l t s w e r e o b t a i n e d by s t a in ing sec t ions 
w i th sal ts of u r a n i u m a n d l ead . If, i n s t ead , sec t ions a r e t r e a t e d w i th 1-2% 
p o t a s s i u m p e r m a n g a n a t e followed by lead c i t r a t e , different e l e m e n t s of t h e 
d e n s e l aye r of t he ep icu t ic le a r e r evea led . I n t r a n s v e r s e sec t ions of t h e d e n s e 
layer , faint s t r i a t ions c a n be seen p e r p e n d i c u l a r to t he c u t i c u l a r sur face (Fig . 
1.8). W h e n the d e n s e l ayer is sec t ioned pa ra l l e l w i t h t he cut ic le surface (Fig . 
1.10), it c a n be seen t h a t t he s t r i a t ions a r e c a u s e d by a c lose -packed a r r a y 
of e lec t ron l u c e n t microf ibr i ls sec t ioned t r ansverse ly . E a c h microf ibr i l is 
a p p r o x i m a t e l y 3 n m in d i a m e t e r a n d n e i g h b o u r i n g microf ibr i ls a r e s p a c e d 
a b o u t 6 n m a p a r t . T h i s is t he first r e p o r t of microf ibr i ls in t he ep icu t ic le of 
a n y a r t h r o p o d , b u t ones s imi l a r in size a n d o r i e n t e d m o r e or less pa ra l l e l to 
the c u t i c u l a r sur face (Nevi l le , 1975), a r e seen in t h e p rocu t i c l e of insec ts (Fig. 
1.4). I t is u sua l ly a s s u m e d t h a t the u n s t a i n e d microf ibr i ls of a r t h r o p o d 
p rocu t i c l e s a r e c o m p o s e d of ch i t in a n d t h a t the d e n s e m a t r i x m a t e r i a l is 
p r o t e i n ( R u d a l l , 1967) . A p a r t from the a b o v e s t r u c t u r a l ev idence t h e r e is 
n o n e to sugges t t h a t ch i t in is p r e s e n t in t he ep icut ic le of t icks. A l t h o u g h t h e r e 
h a v e b e e n i so la ted r e p o r t s of ch i t in in t he ep icut ic le of o t h e r a r t h r o p o d s 
( K r i s h n a n et al., 1955) these h a v e b e e n s h o w n to be incor rec t ( K e n n a u g h , 
1959), t he c h i t i n - c o n t a i n i n g l ayer h a v i n g b e e n w r o n g l y identif ied as p a r t of 
t he ep icu t ic le . N e v e r t h e l e s s , it is i n t e r e s t ing t h a t t h e microf ibr i ls of t he 
ep icu t ic le a n d t h e p rocu t i c l e of B. microplus a r e of t he s a m e d i a m e t e r . 
A fu r the r s t r u c t u r a l f ea tu re , a p p a r e n t l y p e c u l i a r to t he tick ep icu t ic le , is 
a t u b u l a r n e t w o r k a t t he in ter face b e t w e e n the d e n s e l ayer a n d the p rocu t i c l e 
(Fi lshie , 1976) . I n d i v i d u a l t u b u l e s a r e a p p r o x i m a t e l y 15 n m in d i a m e t e r . 
T h e y i n t e r c o n n e c t w i t h o n e a n o t h e r a n d follow closely t he i r r e g u l a r profile 
of t he i n n e r face of t he d e n s e l ayer (Figs . 1.5, 1.6, 1.7, a n d 1.10). I n gene ra l , 
t he fea tures p e c u l i a r to t h e ep icu t ic le of B. microplus d e s c r i b e d a b o v e — d e n s e 
filaments, microf ibr i l s , a n d t h e t u b u l a r n e t w o r k — a r e m o s t easi ly d i s t in -
g u i s h e d in t h e cut ic le of e i the r t he p h a r a t e a d u l t o r t he ear ly pos t -ecdys ia l 
FIG. 1.2. Transverse section of the cuticle of the alloscutum of an engorged nymph. Inner 
endocuticle (inner) is distinctly lamellate. Outer endocuticle (outer) is not lamellate but bundles 
of microfibrils (arrows) tend to occur in the same orientation at regular spacings through the 
thickness of the outer endocuticle, with a period approximately the same as the lamellar spacing 
of the inner endocuticle. Epicuticle, epi; pore canals, pc; "wax" layer, w. Scale = 2.5 μηι. 
FIG. 1.3. High magnification of the inner endocuticle of the cuticle shown in Fig. 1.2, including 
one complete lamella. The microfibrils show the hélicoïdal packing typical of other arthropod 
cuticles with microfibrils cut in cross-section (xs) between the dense laminae, where microfibrils 
are oriented parallel to the section plane (Is). Scale = 25 μηι. 
FlG. 1.4. Higher magnification of portion of Fig. 1.3 showing individual, unstained microfibrils 
cut in cross-section (arrows) surrounded by electron-dense granular material. Scale = 100 μpiι. 
The Tick Cuticle 7 
8 R. H. Hackman and B. K. Filshie 
a d u l t female ( c o m p a r e F igs . 1.5, 1.6, 1.7, a n d 1.10). A p p a r e n t l y , c h e m i c a l 
c h a n g e s t h a t t ake p l a c e after m o u l t i n g r e n d e r t he ep icut ic le less r eac t ive to 
e lec t ron s t a in s , so t h a t t h e s e p a r a t e c o m p o n e n t s , p a r t i c u l a r l y t h e m i c r o -
fibrillar s t r u c t u r e , c a n n o t b e c lear ly d i s t i n g u i s h e d . T h e ep icu t ic le of n y m p h s 
oïHyalomma asiaticum h a s b e e n s t ud i ed by A m o s o v a (1975) . I t s fine s t r u c t u r e 
is essent ia l ly i den t i ca l to t h a t of B. microplus. 
1.2.1.2. Procuticle, Exocuticle, Mesocuticle, Endocuticle, and Subcuticle T h e t e r m s 
p rocu t i c l e , exocut ic le , mesocu t i c l e , a n d endocu t i c l e all a p p l y to t h e c h i t i n -
p r o t e i n l ayers b e n e a t h t he ep icu t ic le of a r t h r o p o d s . R i c h a r d s (1951) first 
def ined t h e p rocu t i c l e as t he o r ig ina l , undi f fe ren t ia ted , non-sc le ro t i zed 
c h i t i n - p r o t e i n m a t e r i a l sec re ted by the e p i d e r m i s . As m e n t i o n e d in t he 
i n t r o d u c t i o n to this c h a p t e r , t he o u t e r p a r t s of t h e p rocu t i c l e over c e r t a in 
reg ions of t h e exoske le ton m a y b e c o m e sc lerot ized fol lowing ecdys is . T h i s 
o u t e r p a r t is t h e n k n o w n as t he exocut ic le a n d the i n n e r soft cut ic le sec re ted 
after ecdysis is k n o w n as t h e endocu t i c l e . F r e q u e n t l y , t he reg ion b e t w e e n 
exocut ic le a n d e n d o c u t i c l e s t a ins differently a n d h a s b e e n ca l led t he m e s o -cut ic le . T h e t h i n l aye r i m m e d i a t e l y ou t s i de t h e e p i d e r m i s , p r e s u m a b l y con-
t a i n i n g t h e u n p o l y m e r i z e d p r e c u r s o r s of t he c h i t i n - p r o t e i n c o m p l e x , a l so 
s t a ins differently from t h e res t a n d w a s r ecogn ized by S c h m i d t (1956) as a 
s e p a r a t e layer , t h e subcu t i c l e . 
I n p r e v i o u s l i t e r a t u r e on t h e tick cut ic le , t he t e rmino logy a p p l i e d to these 
layers is ve ry confused. Lees (1947) refers to exocut ic le as sc lero t ized e n d o -
cut ic le a n d to endocu t i c l e as non-sc le ro t i zed endocu t i c l e , b u t in a s u b s e q u e n t 
p a p e r (Lees , 1952) h e refers to t h e s a m e layers as o u t e r endocu t i c l e a n d i n n e r 
endocu t i c l e , respec t ive ly . N a t h a n s o n (1967, 1970) , Bead le s et aL (1973) , a n d 
B e a d l e (1974) cor rec t ly use t h e t e rmino logy of R i c h a r d s (1951) for t h e 
sc lero t ized r eg ions , b u t t hey use t h e t e r m exocut ic le incor rec t ly to refer to 
t he o u t e r e n d o c u t i c l e of soft cut ic le . B a l a s h o v (1968) refers to a l ayer of p a r t l y 
sc lero t ized mesocu t i c l e in t he a l l o s c u t u m cut ic le of ixodid t icks. T h i s cut ic le 
m u s t u n d e r g o c o n s i d e r a b l e s t r e t c h i n g d u r i n g feeding (see §1 .2 .2 .3) , a p rocess 
t h a t cou ld n o t o c c u r in even a p a r t l y sc lero t ized cut ic le . T h i s confusion 
ind ica t e s t h e des i rab i l i ty of a d o p t i n g a s t a n d a r d t e rmino logy . W e sugges t 
t h a t t h e o n e p r o p o s e d by R i c h a r d s (1951) be used . 
I n t h e a r g a s i d o r soft t icks, B a l a s h o v (1968) r e p o r t s t h a t t he ex tens ib le 
b o d y cut ic les of different species h a v e different surface s t r u c t u r e s , a l t h o u g h 
i n t e r n a l s t r u c t u r e s a r e s imi l a r b e t w e e n species . T h e surface m a y be folded 
FlGS. 1.5 and 1.6. Transverse sections of the outer part of the cuticle of the alloscutum of a 
partially fed adult. The epicuticular layers consist of an outermost wax layer (w) which 
sometimes has a lamellated substructure (Fig. 1.6), the cuticulin (c) and outer epicuticle (oe) 
(detail seen in higher magnification insert to Fig. 1.6), the dense layer (d), and tubular network 
(tn) at interface of dense layer and outer endocuticle (outer). Arrows indicate junction of pore 
canals (pc) with wax canals (wc) which pass through the epicuticle as far as the outer epicuticle. 
Figure 1.5, scale = ΙΟμpiι; Fig. 1.6, scale = 25 μpiι (insert X5). 
The Tick Cuticle 9 
10 R. H. Hackman and Β. K. Filshie 
or t u b e r c u l a t e in unfed t icks, t h e folds t e n d i n g to flatten in s o m e reg ions 
u p o n e n g o r g e m e n t . T h e endocu t i c l e a p p e a r s to b e n o n - l a m e l l a t e t h r o u g h o u t 
its en t i r e th ickness ( 1 5 - 3 0 μpiι in adu l t s ) excep t for a n a r r o w reg ion 1-3 μ ιη 
th ick on t h e i n n e r b o r d e r . T h e c a p i t u l u m a n d legs of a r g a s i d species a r e 
fo rmed of h a r d cut ic le (Ba la shov , 1968). I n these reg ions , t he cut ic le is 
comple t e ly sc le ro t ized , cons i s t ing en t i re ly of exocut ic le a n d ep icu t ic le . A t h i n 
endocu t i c l e is p r e s e n t in s o m e o t h e r sc lero t ized a r e a s such as t h e d o r s a l a n d 
s p i r a c u l a r p l a t e s . T h e a r t i c u l a t e d cut ic le in a r g a s i d s is c o m p o s e d en t i re ly of 
endocu t i c l e ( a n d ep icu t i c l e ) , 2 0 - 3 0 μ ιη th ick, w i t h a very d i s t inc t l a m e l l a t e 
s t r u c t u r e ( B a l a s h o v , 1968) . T h e r e h a v e b e e n n o fine s t r u c t u r a l s tud ies of 
a r g a s i d t ick cu t ic le . I n t h e ixodid t icks , sc lero t ized cut ic le occu r s over t h e 
c a p i t u l u m , s c u t u m , a p p e n d a g e s , a n a l va lves , m a l e v e n t r a l p l a t e s , a n d severa l 
o t h e r s m a l l sc ler i tes . A c c o r d i n g to B a l a s h o v (1968) , t he p rocu t i c l e b e c o m e s 
en t i re ly sc lero t ized a n d , a l t h o u g h l ame l l ae a r e n o t seen in t he l ight m i c r o -
scope , t he r e su l t i ng exocut ic le is h igh ly b i ré f r ingent . Bead l e (1974) e x a m i n e d 
the sc lero t ized cut ic les of B. microplus a n d Boophilus decoloratus w i th t h e e lec t ron 
m i c r o s c o p e . I n t he a d u l t , t h e cut ic le th ickness r a n g e d b e t w e e n 3 - 6 μ ιη ove r 
m o s t a r e a s b u t r e a c h e d u p to 10 μ ιη in s o m e reg ions of t h e m o u t h p a r t s a n d 
a p p e n d a g e s . L a m e l l a e o r fibrous l a m i n a e w e r e no t reso lved . 
T h e i n t e r s e g m e n t a l cu t ic le of Boophilus is 3 - 5 μιτι th ick a n d is c o m p o s e d 
of 5—8 l a m e l l a e exh ib i t i ng a finer, fibrous p a r a b o l i c p a t t e r n (Bead le , 1974). 
T h e reg ion of t he cut ic le of ixod id t icks t h a t h a s rece ived m o s t a t t e n t i o n 
is t h a t of t h e a l l o s c u t u m of t h e female . T h i s cut ic le h a s t he p e c u l i a r c a p a c i t y 
of e x p a n s i o n a n d s t r e t c h i n g d u r i n g b lood - suck ing . T h e fol lowing species h a v e 
b e e n e x a m i n e d : Ixodes ricinus (Lees , 1947, 1952), Boophilus annulatus (= B. 
calcaratus) a n d Hyalomma detritum (Tsv i l eneva & M a s h a n s k y , 1965) , Hae-
maphysalis le pons palustris ( N a t h a n s o n , 1967, 1970) , Amblyomma americanum 
(Bead les et al., 1973) , Β. decoloratus a n d B. microplus (Bead le , 1974) , a n d 
Hyalomma asiaticum ( A m o s o v a , 1975) . T h e a l l o s c u t u m of t he l a r v a e a n d 
n y m p h s of ixod ids a lso h a s l imi ted c a p a c i t y for s t r e t c h i n g (Ba l a shov , 1968; 
Bead l e , 1974) . 
F igu re s 1.2-1.4 s h o w t r a n s v e r s e sec t ions of t he a l l o s c u t u m cut ic le of t h e 
e n g o r g e d n y m p h of B. microplus. T w o reg ions c a n be seen in e lec t ron 
m i c r o g r a p h s — a d i s t inc t ly l a m e l l a t e i n n e r endocu t i c l e a n d a n o n - l a m e l l a t e 
o u t e r endocu t i c l e (Fig . 1.2). T h e i n n e r endocu t i c l e is c o m p o s e d of 6 or 7 
FIGS. 1 . 7 - 1 . 1 0 . The epicuticle of the alloscutum of an early post-moult adult, sectioned and 
stained in different ways to reveal different substructures. Figures 1.7 and 1.8 are transverse 
sections; Figs. 1.9 and 1 . 1 0 are sections parallel with the cuticle surface. Figure 1.7 and 1.9 are 
stained with uranyl acetate and lead citrate; Figs. 1.8 and 1 . 1 0 are stained with potassium 
permanganate and lead citrate. Faint vertical striations in the dense layer (d) of Fig. 1.7 are 
the dense filaments (df) seen in Fig. 1.8 (outlined area shown at high magnification in insert) 
are microfibrils seen in cross-ection in Fig. 1 . 1 0 (higher magnification in insert). Cuticulin, c; 
pore canals, pc; tubular network, tn; wax canals, wc. All figures to same magnification; 
scale = 25 μpiι (inserts X2.5). 
The Tick Cuticle 
12 R. H. Hackman and Β. Κ. Filshie 
l ame l l ae s p a c e d a b o u t 0.7 μpiι a p a r t w i t h a s u b s t r u c t u r e of he l ico ida l ly p a c k e d 
shee t s of microf ibr i l s (Fig . 1.3). Microf ibr i l s a r e re la t ively e lec t ron lucen t , 
a b o u t 3 n m in d i a m e t e r a n d s u r r o u n d e d by g r a n u l a r e lec t ron d e n s e m a t e r i a l 
(Fig . 1.4). I n insec ts a n d o t h e r a r t h r o p o d s , w h e r e s imi la r m i c r o f i b r i l / m a t r i x 
sy s t ems h a v e b e e n o b s e r v e d , it is t h o u g h t t h a t t he microf ibr i l is c o m p o s e dof ch i t in a n d t h e m a t r i x of p r o t e i n (Nevi l le , 1975) . S imi l a r fibrous m a t e r i a l , 
w i t h a microf ibr i l l a r s u b s t r u c t u r e , is a lso p r e s e n t in t he o u t e r endocu t i c l e 
(Fig . 1.2), b u t i n s t e a d of fo rming a c o n t i n u o u s , he l ico ida l ly a r r a n g e d sys t em, 
it is b r o k e n u p in to sma l l b u n d l e s o r fibrils. W i t h i n e a c h fibril, t he microf ibr i ls 
a r e o r i e n t e d pa ra l l e l to o n e a n o t h e r , b u t fibrillar o r i e n t a t i o n w i t h i n t he o u t e r 
e n d o c u t i c l e is n o t c o n s t a n t . H o w e v e r , t h e r e is ev idence t h a t fibrillar o r ien-
t a t i on va r i e s sys t emat i ca l ly ; l ong i tud ina l l y sec t ioned fibrils o c c u r a t r e g u l a r 
s p a c i n g s t h r o u g h the o u t e r endocu t i c l e ( a r r o w s in F ig . 1.2), t he spac ings 
b e i n g of t h e s a m e o r d e r as t h e l a m e l l a r s p a c i n g of t h e i n n e r endocu t i c l e . T h e 
s p a c e b e t w e e n fibrils in t h e o u t e r endocu t i c l e is filled w i t h a m o r p h o u s , 
g r a n u l a r , re la t ive ly poor ly s t a i n i n g m a t e r i a l . T o w a r d s t he surface , t he con-
c e n t r a t i o n s of fibrils to a m o r p h o u s m a t e r i a l a n d the size of i n d i v i d u a l fibrils 
dec r ea se s m a r k e d l y . I n t he o u t e r m o s t 2 o r 3 μιτι, n o fibrils a r e vis ible a t low 
magn i f i ca t ions (Fig . 1.2). 
T h e r e a r e s o m e differences in s t r u c t u r e b e t w e e n the cut ic le of t he a l lo-
s c u t u m of t h e n y m p h a n d the female of B. microplus. I n t he female , m a x i m u m 
cut ic le t h i ckness is r e a c h e d w h e n the t ick is a b o u t 4.5 m m long (see §1 .2 .2) . 
M i c r o g r a p h s of t r a n s v e r s e sec t ions of th is cut ic le a r e s h o w n in F igs . 1.14, 
1.16, a n d 1.17. Subd iv i s i on of t h e endocu t i c l e in to i n n e r a n d o u t e r l ayers is 
m o r e m a r k e d t h a n in t h e n y m p h . T h e i n n e r endocu t i c l e ( to ta l th ickness 
18 μιτι) is m a d e u p of a n u m b e r of d i s t inc t l ame l l ae , e a c h a b o u t 2 μιτι th ick 
(Fig. 1.14), b u t t h e s u b s t r u c t u r e of these l a m e l l a e is different from t h a t of 
t he n y m p h . A t h i g h magn i f i ca t ion (Fig . 1.17) it c a n b e seen t h a t a b o u t 5 0 % 
of t he v o l u m e of t he i n n e r endocu t i c l e of t he a d u l t female is m a d e u p of 
a m o r p h o u s m a t e r i a l of m e d i u m e lec t ron dens i ty . S o m e fibrils w i th a m i c r o -
fibrillar s u b s t r u c t u r e a r e a lso p r e s e n t , t he r e m a i n d e r of the v o l u m e b e i n g 
o c c u p i e d b y t h e a n a s t o m o s i n g p o r e c a n a l n e t w o r k (d i scussed b e l o w ) . S o m e , 
if no t al l , of t h e fibrous m a t e r i a l a p p e a r s to lie w i th in t he p o r e c a n a l s , a 
s i t ua t i on t h a t h a s n o t b e e n r e c o r d e d in o t h e r a r t h r o p o d cut ic les . T h e n o n -
l a m e l l a t e o u t e r endocu t i c l e ( to ta l th i ckness a b o u t 20 μpiι) is c o m p o s e d a l m o s t 
en t i re ly of a m o r p h o u s m a t e r i a l w h i c h is c o n t i n u o u s from t h e i n n e r e n d o -
cut ic le . A sma l l a m o u n t of fibrous m a t e r i a l is p r e s e n t , a n d this is a g a i n seen 
la rge ly w i t h i n t h e p o r e c a n a l sy s t em (Fig . 1.16). Lees (1952) r e p o r t e d t h a t 
b o t h t h e i n n e r a n d o u t e r e n d o c u t i d e s of I. ricinus females w e r e l ame l l a t e , t h e 
o u t e r l a m e l l a e b e i n g t h e m o r e dense ly p a c k e d . I n c o n t r a s t , w i t h t he e lec t ron 
m i c r o s c o p e , b o t h w e a n d B e a d l e (1974) d e t e c t e d l a m e l l a e on ly in t h e i n n e r 
e n d o c u t i c l e of B. microplus. 
1.2.1.3. Pore Canals and Wax Canals I n m o s t a r t h r o p o d cut ic les a s y s t e m of fine 
The Tick Cuticle 13 
c h a n n e l s pas ses t h r o u g h t h e en t i r e cu t ic le , poss ib ly e s t ab l i sh ing c o n n e c t i o n s 
b e t w e e n t h e e p i d e r m i s , t h e severa l l ayers of t he cut ic le , a n d the surface . 
U s u a l l y t he c h a n n e l s in t h e e n d o c u t i c l e a n d exocut ic le (whe re s u c h a s u b -
div is ion exists) a r e s imi l a r in s t r u c t u r e . A t t h e in ter face w i th t he ep icu t ic le , 
h o w e v e r , t he c h a n n e l s s o m e t i m e s b e c o m e finer a n d f requent ly b r a n c h d is ta l ly 
(Locke , 1961) . T h e c h a n n e l s in e n d o - a n d e x o c u t i d e s a r e k n o w n as p o r e 
c a n a l s . T h e finer c h a n n e l s t h r o u g h t h e ep icu t ic le h a v e b e e n cal led w a x 
c a n a l s b e c a u s e t hey a r e s u p p o s e d l y invo lved in w a x secre t ion in s o m e insec ts 
(Locke , 1960, 1965) . P o r e c a n a l s a r e re la t ive ly l a rge s t r u c t u r e s a n d a r e easi ly 
reso lved in t h e l ight m i c r o s c o p e , b u t w a x c a n a l s c a n on ly be seen in t he 
e lec t ron m i c r o s c o p e . 
I n t he unfed female t ick (/. ricinus) t h e d e n s i t y of p o r e c a n a l s h a s b e e n 
e s t i m a t e d to be g r e a t e r t h a n 1,400,000 m m
- 2
, o r in excess of 60 p e r e p i d e r m a l 
cell (Lees , 1952) . T h e p o r e c a n a l s y s t e m m a y b e d e l i n e a t e d w i t h t h e r a p i d 
Golg i s t a i n i n g m e t h o d (ch rom-s i lve r ) a n d ce r t a in reg ions s t a in w i t h h a e -
m a t o x y l i n . I f frozen sec t ions a r e a l lowed to d r y , c e r t a in reg ions m a y b e c o m e 
filled w i t h a i r , i n d i c a t i n g t h a t t he c a n a l s w e r e p rev ious ly fluid-filled. I n th ick 
sec t ions t hey a p p e a r to b e a r r a n g e d in b u n d l e s , e a c h of w h i c h m a y c o r r e s p o n d 
to a n u n d e r l y i n g e p i d e r m a l cell. D u r i n g ear ly feeding, t h e p o r e c a n a l s b e c o m e 
m o r e wide ly s p a c e d a n d d i s t e n d e d w i t h i n t h e o u t e r endocu t i c l e a n d exceed-
ingly b r a n c h e d d is ta l ly , w h e r e they a p p e a r to e n d b l ind ly b e n e a t h t he 
ep icu t ic le . W i t h i n t h e i n n e r endocu t i c l e , Lees (1952) h a s r e p o r t e d t h a t t h e 
p o r e c a n a l s b e c o m e progress ive ly filled w i t h solid m a t e r i a l . A r t h u r (1962) , 
h o w e v e r , a r g u e d t h a t t h e c a n a l s m u s t r e m a i n o p e n if, as Lees sugges ted , 
g r o w t h of t h e o u t e r l ayers of t h e cu t ic le is to p r o c e e d u p to t h e t i m e of final 
e n g o r g e m e n t (see §1 .2 .2 .3 ) . T s v i l e n e v a a n d M a s h a n s k y (1965) o b s e r v e d t h a t , 
in H. detritum, t h e d i s t i nc t l a m i n a t i o n in t h e i n n e r endocu t i c l e , a l t h o u g h 
a s soc i a t ed w i t h t h e p r e s e n c e of fibrous cut ic le , w a s m a i n l y c a u s e d by l a t e ra l 
b r a n c h i n g of p o r e c a n a l s . B a l a s h o v (1968) a lso r e p o r t e d ramif ica t ion of t he 
c a n a l s y s t e m in t h e i n n e r e n d o c u t i c l e of / . ricinus a n d a lack of p o r e c a n a l s 
in t he a r t i c u l a t i o n cu t ic le . 
M o r e de t a i l o n p o r e c a n a l s t r u c t u r e h a s b e e n p r o v i d e d by e lec t ron m i c r o -
scopy , b u t i n f o r m a t i o n o n t h e t h r e e - d i m e n s i o n a l s t r u c t u r e of t he sys t em 
( b r a n c h i n g , a n a s t o m o s i n g , twis t ing , etc .) is h i n d e r e d by the inab i l i ty to 
e x a m i n e th ick sec t ions o r w h o l e m o u n t s b y th is te c h n i q u e . H o w e v e r , finer 
c a n a l s a n d t h e c o n t e n t of c a n a l s c a n be e x a m i n e d a t h i g h e r r eso lu t ion . 
N a t h a n s o n (1967) e x a m i n e d t h e p o r e c a n a l s of H. le pons palustris w i t h t h e 
e lec t ron m i c r o s c o p e . T h e y a r e m o r e n u m e r o u s in sc lerot ized a r e a s of t he 
cut ic le w h e r e the i r m o r p h o l o g y is s imi l a r to those of Galleria a n d Tenebrio 
(Locke , 1961) . T h e y a r e 0 . 2 - 0 . 4 μpiι in d i a m e t e r in t he endocu t i c l e a n d 
c o n t a i n filaments 2 0 - 3 0 n m in d i a m e t e r . I n t h e exocut ic le t h e c o n t e n t s a r e 
less c lear ly d e l i n e a t e d a n d c a n a l s b r a n c h so t h a t they a r e a b o u t t h r e e t imes 
m o r e n u m e r o u s a t t h e e p i c u t i c u l a r b o r d e r . I n t he cut ic le of t he a l l o s c u t u m 
14 R. H. Hackman and B. K. Filshie 
of H. leporispalus tris p o r e c a n a l s a r e less n u m e r o u s a n d t h i n n e r ( 0 . 1 5 -
0.3 μpi ι ) . T h e y m a y c o n t a i n un i formly d i spe r se fibrous m a t e r i a l 
o r a n e lec t ron o p a q u e core . F i l a m e n t s of d i a m e t e r 15 -20 n m h a v e b e e n 
o b s e r v e d in t he l u m e n of c a n a l s of t h e i n n e r endocu t i c l e , a n d these filaments 
a p p e a r to p a s s i n t o t he c y t o p l a s m p r o p e r of t he u n d e r l y i n g e p i d e r m a l cell. 
I n t h e sc lero t ized cut ic les of l a rva l B. decoloratus a n d B. microplus p o r e c a n a l s 
a r e a b o u t 0.15 μηι a t t he i r w ides t a n d c o n t a i n d e n s e g r a n u l a r m a t e r i a l 
t h r o u g h o u t . N e a r e r the i r j u n c t i o n w i th t h e e p i d e r m i s , t he m a t e r i a l is m o r e 
obv ious ly of c y t o p l a s m i c or ig in (Bead le , 1974). I n t he l a rva l non-sc le ro t i zed 
cut ic le of t h e s a m e species , t h e r e a r e l a rge n u m b e r s of c ana l s in t he i n n e r 
endocu t i c l e w h i c h fuse to p r o d u c e l a rge p o r o u s a r e a s in t he o u t e r endocu t i c l e . 
F igu re s 1.2 a n d 1 .14-1 .17 i l lus t ra te t he fine s t r u c t u r e of the p o r e cana l s 
of B. microplus. I n t he i n n e r endocu t i c l e of t he e n g o r g e d n y m p h (Fig . 1.2) 
t he r e a r e l a rge c a n a l s u p to 0.6 μ ιη in d i a m e t e r t r a v e r s i n g the l a m e l l a e w i t h 
s o m e l a t e ra l b r a n c h i n g . If these a r e real ly p o r e c a n a l s , they a r e s o m e w h a t 
l a rge r t h a n p rev ious ly r e p o r t e d . H o w e v e r , th is cut ic le w a s t a k e n from a t ick 
a t a p o l y s i s ( w h e n the e p i d e r m i s r e t r a c t s from t h e cut ic le a t t he b e g i n n i n g 
of t he a d u l t m o u l t ) , so it is poss ib le t h a t m o u l t i n g fluid m a y h a v e a l r e a d y 
b e g u n d iges t ion of t h e i n n e r l a m e l l a e of t he cut ic le . I n the o u t e r endocu t i c l e 
the p o r e c a n a l s a r e n a r r o w e r , b r a n c h e d , a n d o r i en t ed a t d ive r se ang les to 
t he cut ic le sur face . T h e l a t t e r is t he resu l t of s t r e t c h i n g of t he cut ic le d u r i n g 
the final feeding p e r i o d of t h e in s t a r . A s imi la r effect h a s been o b s e r v e d in 
t he o u t e r endocu t i c l e of t h e a d u l t (Fig . 1.15). 
B r a n c h i n g a n d a n a s t o m o s i n g of p o r e c a n a l s is m u c h m o r e p r o n o u n c e d in 
t he i n n e r e n d o c u t i c l e of t he pa r t i a l l y fed a d u l t (Fig. 1.14). A t h igh m a g n i -
fication (Fig . 1.17) profiles of t he c a n a l sys t em a r e l imi ted by a m e m b r a n e 
w h i c h h a s g r e a t e r e lec t ron dens i t y t h a n e i the r t he g r a n u l a r c o n t e n t s o r t h e 
a m o r p h o u s in te r s t i t i a l m a t e r i a l . T h i s m e m b r a n e c a n b e t r a ced b a c k to its 
con t i nu i t y w i t h t h e p l a s m a m e m b r a n e of t he e p i d e r m a l surface , b u t t h e 
typ ica l t r i l a m i n a r s t r u c t u r e of t he e p i d e r m a l m e m b r a n e c a n n o t b e reso lved 
in t he m o r e d i s t a l r eg ions of t he p o r e c a n a l s . As m e n t i o n e d in t h e p r e v i o u s 
sec t ion , t he p o r e c a n a l s d o a p p e a r to c o n t a i n microf ibr i ls of t he c h i t i n - p r o t e i n 
c o m p l e x , l e n d i n g s o m e s u p p o r t to L e e s ' (1952) o b s e r v a t i o n t h a t t h e p o r e 
c a n a l s of t h e i n n e r endocu t i c l e o f / , ricinus b e c o m e fully " c h i t i n i z e d " . P o r e 
cana l s of i n n e r a n d o u t e r e n d o c u t i d e s a r e c o n t i n u o u s b u t a r e far less n u m e r o u s 
or b r a n c h e d in t h e o u t e r l aye r (Fig . 1.14). A t h i g h e r magn i f i ca t ions (Fig. 
1.15) t hey a r e seen to c o n t a i n g r a n u l a r m a t e r i a l a n d a r e b o r d e r e d b y a n 
e l ec t ron -dense m e m b r a n e s imi l a r to those of t h e i n n e r endocu t i c l e . 
W a x c a n a l s a r e c lear ly reso lved in e lec t ron m i c r o g r a p h s , t he e lec t ron 
dens i t y of the i r c o n t e n t s d e p e n d i n g o n the d e v e l o p m e n t a l s t age of t he t ick 
a n d t h e t ype of s t a in a p p l i e d to sec t ions . I n p re -ecdys ia l a l l o s c u t u m cut ic le 
of a d u l t females t he w a x c a n a l s c o n t a i n a c e n t r a l e l ec t ron -dense filament 
a b o u t 25 n m in d i a m e t e r w h i c h is r evea led by s t a in ing w i th u r a n y l a c e t a t e 
The Tick Cuticle 15 
a n d l ead c i t r a t e (Fig . 1.9), b u t in t h e s a m e cut ic le , t he c o n t e n t s of t h e w a x 
c a n a l s a p p e a r to b e r e m o v e d if sec t ions a r e ox id ized w i th p o t a s s i u m per -
m a n g a n a t e p r i o r to s t a i n i n g w i t h l ead c i t r a t e (Figs . 1.8 a n d 1.10). T h e spa t i a l 
dens i t y of t h e w a x c a n a l s , a s m e a s u r e d f rom sec t ions pa ra l l e l to t he cut ic le 
surface , is a b o u t 10 μ pi ι
- 2
. W a x c a n a l s a n d p o r e cana l s j o i n a t t he in ter face 
b e t w e e n e n d o c u t i c l e a n d ep icu t i c le (F igs . 1 .5-1.7) , b u t t he t u b u l a r n e t w o r k 
a lso found a t th is in te r face does n o t i n t e r c o n n e c t w i t h t he p o r e c a n a l / w a x 
c a n a l s y s t e m (Fi l sh ie , 1976) . T h e w a x c a n a l s p e n e t r a t e b o t h t he d e n s e layer 
of t he ep icu t i c le a n d t h e i n n e r l aye r of t h e cu t i cu l in . D u r i n g l a t e r s tages of 
feeding t h e c o n t e n t s of t h e w a x c a n a l s b e c o m e less r eac t ive to e lec t ron s t a i n i n g 
(F ig . 1.6). 
I t c a n b e seen , t h e n , t h a t t h e p o r e c a n a l / w a x c a n a l sy s t em of t h e tick does 
p r o v i d e a n effective l ink b e t w e e n t h e ep icu t ic le a n d the surface w a x layer 
a n d t h a t b r a n c h e s of p o r e c a n a l s p a s s t h r o u g h a n d b e t w e e n e n d o c u t i c u l a r 
l aye rs . T h e d e n s i t y of w a x c a n a l s (10 m m
- 2
) in B. microplus ep icu t ic le o b t a i n e d 
from e lec t ron m i c r o s c o p y a p p r o x i m a t e s t h e dens i t y of p o r e c a n a l s in t he 
o u t e r e n d o c u t i c l e of t h e unfed female of / , ricinus (1.4 μ ι τ Γ
2
) as c a l cu l a t ed by 
Lees (1952) f rom l ight m i c r o s c o p y . T h e b r a n c h i n g of p o r e c a n a l s be low the 
ep icu t ic le o b s e r v e d b y Lees m a y a c c o u n t for t h e a c t u a l difference in t h e t w o 
f igures. T h e poss ib le roles of p o r e c a n a l s a n d w a x cana l s in t he fo rma t ionof t h e cu t ic le a n d t h e c h a n g e s t h a t o c c u r d u r i n g b lood suck ing will be 
d i scussed in t h e fol lowing sec t ions . 
1.2.1.4. Muscle Attachments, Glands, and other Integumental Structures A n u m b e r 
of different spec ia l ized cells , g r o u p of cells, o r c u t i c u l a r s t r u c t u r e s a r e p r e s e n t 
w i t h i n t h e t ick i n t e g u m e n t . T h e m o s t o b v i o u s of these a r e t h e v a r i o u s sensory 
s t r u c t u r e s , w h i c h a r e a r e a s of cu t ic le modif ied in to h a i r s , pegs , p i t s , e tc . , a n d 
s u p p l i e d w i t h d e n d r i t i c n e r v e e n d i n g s f rom cells usua l ly loca ted w i t h i n o r 
j u s t b e n e a t h t h e e p i d e r m a l cell l ayer . T h e s t r u c t u r e a n d funct ion of these 
sense o r g a n s is d i scussed s e p a r a t e l y in C h a p t e r 3 . 
T i c k s , l ike insec ts , possess d e r m a l g l a n d s , w h i c h o c c u r t h r o u g h o u t t h e 
e p i d e r m a l l ayer . I n insec t s , t h e d e r m a l g l a n d s a r e s u p p o s e d to p r o d u c e t h e 
c e m e n t l aye r ove r t h e sur face of t h e w a x l aye r ( W i g g l e s w o r t h , 1947) , a n d 
th is is co r r e l a t ed w i t h t he i r w i d e d i s p e r s a l over t h e b o d y surface . I n t h e b u g 
Rhodnius t h e t y p e Β g l a n d s a r e c o m p o s e d of four cells: (1) t h e sec re to ry cell; 
(2) t h e s accu l e - fo rming cell; (3) t h e d u c t - f o r m i n g cell; a n d (4) a cell w h i c h 
s u r r o u n d s t h e o t h e r t h r e e (La i Fook , 1970) . T h e g l a n d cell lies w i t h i n t he 
e p i d e r m a l l aye r a n d its sec re t ions p a s s i n t o t he saccu le ( w h e n p r e s e n t ) a n d 
t h e n v ia a fine d u c t to a n o p e n i n g o n the cut ic le surface . S c a n n i n g e lec t ron 
m i c r o g r a p h s h a v e conf i rmed t h e p r e s e n c e of d e r m a l g l a n d o p e n i n g s o n the 
cut ic le sur face (Scheie et al., 1968) . T h e r e is ev idence t h a t t he sec re to ry 
ac t iv i ty of d e r m a l g l a n d s in insec ts is n o t r e s t r i c t ed to t h e t i m e of ecdysis o r 
j u s t after ecdys is w h e n t h e c e m e n t l aye r is b e i n g d e p o s i t e d . I n Tenebrio, 
D e l a c h a m b r e (1973) found t h a t t h e g l a n d s still s h o w e d s o m e ac t iv i ty in o lde r 
16 R. H. Hackman and B. K. Fils hie 
a d u l t s a t a t i m e w h e n o n e w o u l d h a v e expec t ed t h a t a d d i t i o n a l c e m e n t w a s 
no t r e q u i r e d for p r o t e c t i o n of t he w a x layer . 
A r g a s i d t icks possess a c e m e n t l aye r a n d ixod ids d o no t , b u t b o t h g r o u p s 
h a v e d e r m a l g l a n d s . I n t h e a r g a s i d Ornithodoros moubata, t he d e r m a l g l a n d s 
p a s s t h r o u g h t w o cycles of ac t iv i ty : j u s t before secre t ion of m o u l t i n g fluid 
a n d a few h o u r s after m o u l t i n g d u r i n g secre t ion of t he c e m e n t l ayer (Lees , 
1947) . T h e n y m p h a l g l a n d s of Dermacentor andersoni a r e of t w o types ; l a rge 
( t y p e A ) a n d s m a l l ( t y p e B ) cells. D u r i n g t h e n y m p h - a d u l t m o u l t , a t h i rd , 
m u l t i - n u c l e a t e g l a n d ( t y p e C) is fo rmed from nuc le i of t ype Β cells. Ixodes 
nanus possess on ly sma l l , t ype Β g l a n d s (Lees , 1947). 
I n ixod ids , Lees (1947) found t h a t t he d e r m a l g l a n d s secre te a th ick yel low 
" g r e a s e " w h i c h s lowly s p r e a d s over t h e cut ic le surface o r collects a r o u n d t h e 
d u c t o p e n i n g s . D i s c h a r g e of th is secre t ion occu r s on ly after full e n g o r g e m e n t 
b u t m a y n o t o c c u r in all d e v e l o p m e n t a l s t ages . Ixodes ricinus l a r v a e a n d 
n y m p h s d o n o t d i s c h a r g e , b u t t he egg- lay ing female does . I n D. andersoni, 
on t h e o t h e r h a n d , g r ea se is sec re ted f rom d e r m a l g l a n d s in t he e n g o r g e d 
n y m p h . 
T h e females of B. microplus secre te a c lear fluid from the d e r m a l g l a n d s 
w h e n h a n d l e d ( K . C . B i n n i n g t o n , pe r . c o m m . ) . D e r m a l g l a n d s , fo rming a 
l y r e - s h a p e d p a t t e r n in t h e v e n t r o - l a t e r a l h y p o d e r m i s of l a r v a e a n d n y m p h s 
of t he A u s t r a l i a n p a r a l y s i s t ick Ixodes holocyclus secre te cop ious a m o u n t s of 
a c r e a m y e x u d a t e d u r i n g the pe r iod b e t w e e n apolys is a n d ecdysis a n d the 
e x u d a t e r e m a i n s o n t h e e x u v i u m in a p a t t e r n reflect ing t h a t of t h e g l a n d s 
(B. F . S t o n e & K . C . B i n n i n g t o n , p e r s . c o m m . ) D e r m a l g l a n d s of e n g o r g e d 
n y m p h s a n d a d u l t s of / . holocyclus a l so secre te a p i n k fluid w h i c h c o n t a i n s a 
pa ra lys i s toxin h a v i n g s imi l a r p r o p e r t i e s to those of t he toxin found in its 
sa l iva ( K o c h , 1967; B . M . D o u b e & Β . V . G o o d g e r , u n p u b l i s h e d d a t a ) . 
C l ea r ly , t he d e r m a l g l a n d secre t ions m a y h a v e different roles to p l a y in 
different tick species a n d a t different d e v e l o p m e n t a l s t ages w i t h i n t he s a m e 
species . M u c h m o r e w o r k is r e q u i r e d in o r d e r to d e t e r m i n e t he c o m p o s i t i o n 
a n d func t ion of these v a r i o u s sec re t ions . 
T h e p o r o s e a r e a s a r e loca ted on the b a s i s c a p i t u l u m of female ixod id 
t icks. T h e cu t ic le in these reg ions is d e p r e s s e d s l ight ly a n d pe r fo ra t ed w i t h 
n u m e r o u s po re s . Ea r l i e r a u t h o r s t h o u g h t t h a t t h e fine d u c t s l e a d i n g f rom the 
po re s w e r e i n n e r v a t e d (see A r t h u r , 1962). C o n s e q u e n t l y , t h e p o r o s e a r e a s 
w e r e t h o u g h t to be sense o r g a n s un t i l r ecen t ly . F e l d m a n - M u h s a m a n d H a v i v i 
(1960) a n d F e l m a n - M u h s a m (1963) d e m o n s t r a t e d t h a t t h e d u c t s led to 
sec re to ry g l a n d s a n d sugges t ed t h a t t h e secre t ion w a s a l u b r i c a n t w h i c h 
c o m b i n e d w i t h t h e sec re t ion of G e n e ' s o r g a n ( the egg -wax ing o r g a n — s e e 
C h a p t e r 9 ) . A t k i n s o n a n d B i n n i n g t o n (1973) select ively d e s t r o y e d t h e p o r o s e 
a r e a s of B. microplus a n d s h o w e d t h a t th is t r e a t m e n t h a d n o d e m o n s t r a b l e 
effect on t h e size a n d h a t c h a b i l i t y of s u b s e q u e n t e g g - b a t c h e s . By ana lys i s of 
egg -waxes from t r e a t e d a n d u n t r e a t e d t icks they s h o w e d , h o w e v e r , t h a t 
The Tick Cuticle 17 
a n t i o x i d a n t w h i c h o r ig ina t e s f rom t h e sec re t ions of t he p o r o s e a r e a s (see § 
1.3.3) i nh ib i t s t h e a u t o x i d a t i o n of s t e ro ids in t he egg-waxes . 
I x o d i d t icks possess a c o x a l g l a n d w h i c h is c o n n e c t e d v ia a d u c t to t h e 
exuvia l s p a c e a n d s h o w s m a x i m u m ac t iv i ty d u r i n g m o u l t i n g ( B i n n i n g t o n , 
1975). H i s t o c h e m i c a l tes ts d e m o n s t r a t e d a n o n - e n z y m i c t y r o s i n e - c o n t a i n i n g 
p r o t e i n w i t h i n t h e ac t ive g l a n d . B i n n i n g t o n sugges ted a poss ib le role for t h e 
g l a n d in h a r d e n i n g of t h e cu t ic le . A r g a s i d t icks a lso possess a n accessory 
coxal g l a n d . T h e d u c t s , un l ike those of ixod ids , a r e c o n n e c t e d first to t h e 
d u c t of t h e o s m o r e g u l a t o r y coxal o r g a n w h i c h in t u r n passes to t he ex te r io r 
(Lees , 1946) . 
T h e d o r s o v e n t r a l m u s c l e s of t h e a l l o s c u t u m of ixod id t icks a r e a r r a n g e d 
r o u g h l y in l o n g i t u d i n a l r o w s b u t t h e r e is n o modi f ica t ion to t h e surface 
p a t t e r n excep t for t h e p r e s e n c e of long , sha l low fur rows o r g rooves (Lees , 
1947) . I n a r g a s i d s t h e b o u n d a r y of t h e in se r t ion of e a c h m u s c l e b u n d l e is 
c lear ly d e l i n e a t e d a n d enc loses a n u m b e r of p o l y g o n a l un i t s e a c h r e p r e s e n t i n g 
t h e in se r t ions of i n d i v i d u a l fibres (Lees , 1947) . A c c o r d i n g to B a l a s h o v (1968) , 
t h e a r g a s i d cu t ic le is sc le ro t ized in these a r e a s . T h e s t r u c t u r e of m u s c l e 
a t t a c h m e n t s in ixod id n y m p h s a n d a d u l t s h a s b e e n s t u d i e d by Y a l v a c (1939) 
w i t h t h e l igh t m i c r o s c o p e . H e s h o w e d t h a t t he m u s c l e of n y m p h s is a t t a c h e d 
to a t endon - l i ke s t r u c t u r e w h i c h a p p e a r s to p a s s b e t w e e n e p i d e r m a l cells 
a n d t h r o u g h t h e cu t ic le to j o i n w i t h t h e ep icu t ic le . I n t he a d u l t , howeve r , 
t h e t e n d o n s a r e n o t v is ib le in t h e cu t ic le . Resu l t s of e lec t ron m i c r o s c o p y h a v e 
s h o w n t h a t al l a r t h r o p o d s h a v e a c h a r a c t e r i s t i c t y p e of a t t a c h m e n t w h i c h , 
b e c a u s e of i ts s t r u c t u r e , c a n b e u n m a d e a n d r e m a d e a t e a c h m o u l t . T h e 
t e n d o n s , o r t o n o f i b r i l l a e a s t hey a r e s o m e t i m e s ca l led , a r e no t c o n t i n u o u s 
f rom the i r p o i n t of a t t a c h m e n t a t t h e m u s c l e cell to the i r t e r m i n a t i o n w i t h i n 
t h e cu t ic le , b u t a r e m a d e u p of t w o sets of fibrils; p r o x i m a l l y of b u n d l e s of 
m i c r o t u b u l e s r u n n i n g t r a n s v e r s e l y t h r o u g h t h e e p i d e r m a l cells, a n d d is ta l ly 
of d e n s e rod l ike tonof ibr i l lae w i t h i n t h e cu t ic le (see Nevi l le , 1975, for s u m m a r y 
of s t r u c t u r e in i n sec t s ) . M u s c l e filaments a n d m i c r o t u b u l e s a r e a n c h o r e d to 
t h e i n t e r n a l faces of m u s c l e cells a n d e p i d e r m a l cells respec t ive ly b y s t r u c t u r e s 
k n o w n as h e m i d e s m o s o m e s . T h e in t e r ce l lu l a r s p a c e c o n t a i n s a cemen t - l i ke 
m a t e r i a l . T h e ea r l i e r o b s e r v a t i o n s of l igh t mic roscop i s t s t h a t t e n d o n s (or 
tonofibr i ls) p a s s b e t w e e n e p i d e r m a l cells (Ya lvac , 1939) a r e incor rec t . All 
e l ec t ron m i c r o s c o p i c o b s e r v a t i o n s m a d e to d a t e s h o w t h a t tonof ibr i l la r s t r uc -
t u r e in a r t h r o p o d s is as d e s c r i b e d a b o v e . E x a m i n a t i o n of t he a t t a c h m e n t in 
B. microplus h a s s h o w n t h a t i ts fine s t r u c t u r e follows t h e g e n e r a l p a t t e r n 
(Fi lsh ie , u n p u b l i s h e d ) . 
T h e s t r u c t u r e of sp i rac les in t icks h a s b e e n s t u d i e d b y a n u m b e r of a u t h o r s 
( N u t t a l l et al., 1908; M e l l a n b y , 1935; B r o w n i n g , 1954a, b ; A r t h u r , 1956, 
1962; H i n ton , 1967; Woo l l ey , 1972; R o s h d y & H e f n a w y , 1973; R o s h d y , 
1974) . I n B. microplus ( H i n t o n , 1967) t h e l a r v a lacks sp i rac les , b u t in b o t h 
t he n y m p h a n d a d u l t t h e sp i r ac l e cons is t s of a c r i b r i f o r m p l a t e s imi l a r in 
18 R. H. Hackman and Β. K. Filshie 
ex t e rna l s t r u c t u r e to t h a t of bee t le l a r v a e of t h e family S c a r a b a e i d a e . I n t he 
a d u l t t he r e a r e a b o u t 35—40 surface po re s , e ach b e i n g a n ova l o r c i r cu l a r 
ho le a b o u t 2 μpiι w i d e , a r r a n g e d p e r i p h e r a l l y a r o u n d a l a rge cen t r a l s t r u c t u r e 
cal led t h e o s t i u m . Ea r l i e r a u t h o r s ( B r o w n i n g , 1954a, b ; A r t h u r , 1956, 1962) 
sugges t ed t h a t t h e o s t i u m w a s t he func t iona l sp i rac le . T h i s w a s d i s p u t e d b y 
H i n t o n (1967) , w h o c l a i m e d the o s t i u m w a s a co l lapsed ecdys ia l t u b e for 
ex t r ac t i on of t he n y m p h a l t r a c h e a l s y s t e m d u r i n g t h e n y m p h - a d u l t ecdys is . 
S u b s e q u e n t l y R o s h d y a n d H e f n a w y (1973) s h o w e d t h a t in t he sp i rac le of 
n y m p h a l Haemaphysalis longicornis t h e o s t i u m is c o n n e c t e d to t he t r a c h e a l 
sy s t em via a n a t r i a l c h a m b e r w i t h a va lve c a p a b l e of o p e n i n g a n d c los ing 
the sp i rac le . R o s h d y (1974) a lso s h o w e d t h a t t he p e r i p h e r a l po re s a r e con-
nec t ed by n a r r o w d u c t s to u n d e r l y i n g t e g u m e n t a l g l a n d s a n d c o n c l u d e d t h a t 
they d i d n o t func t ion as ae ropy le s , as p r o p o s e d b y H i n t o n (1967) . T h e 
fo rma t ion of t h e sp i rac le in a d u l t H. longicornis h a s b e e n d e s c r i b e d by R o s h d y 
(1974) . T h e r ecen t o b s e r v a t i o n s of R u d o l p h a n d K n ü l l e (1978) o n Amblyomma 
variegatum a p p e a r to s u p p o r t t he i n t e r p r e t a t i o n of H i n t o n , whi le s t ress ing the 
role of t h e a t r i a l va lve in t h e r e g u l a t i o n of gas e x c h a n g e b e t w e e n t h e t r a c h e a l 
s y s t e m a n d the a t m o s p h e r e (see §2 .2 .3) . 
1.2.2. Deposi t ion of the Cuticle 
T h e life-cycle of all a r t h r o p o d s is d iv ided in to a n u m b e r of d i sc re t e s tages 
o r i n s t a r s s e p a r a t e d by pe r iods of m o u l t i n g , w h e n the cut ic le of t he p r ev ious 
i n s t a r is shed a n d a n e w o n e fo rmed by the u n d e r l y i n g l ayer of e p i d e r m a l 
cells. I n c r e a s e in body-s ize is a ch i eved in two w a y s . I n those a r e a s w h e r e t h e 
p o s t - m o u l t cu t ic le is h a r d e n e d or sc lero t ized , e x p a n s i o n to a c c o m m o d a t e th is 
i nc rea se m u s t o c c u r i m m e d i a t e l y before h a r d e n i n g , i.e. u sua l ly in t he 1-2 
h o u r s t h a t succeed ecdysis ( s h e d d i n g of t he p r e v i o u s cu t ic le ) . E x p a n s i o n 
u n d e r these c i r c u m s t a n c e s u sua l ly is b r o u g h t a b o u t by a t e m p o r a r y inc rease 
in h a e m o l y m p h p r e s s u r e w h i c h in t u r n is a ch i eved by a c o m b i n a t i o n of 
m u s c l e c o n t r a c t i o n a n d a i r swa l lowing (Cot t re l l , 1964). G r o w t h in those 
p a r t s of t he b o d y enc losed by sc lero t ized cut ic le occu r s , therefore , in a series 
of d i sc re te i n c r e m e n t s b r o u g h t a b o u t b y p o s t - m o u l t e x p a n s i o n a n d h a r d e n i n g 
of t h e cut ic le . O n the o t h e r h a n d , m a n y p a r t s of t he cut ic le r e m a i n soft, 
u n t a n n e d , a n d flexible t h r o u g h o u t t he ins t a r , a n d g r o w t h c a n b e ach i eved 
d u r i n g the i n t e r m o u l t pe r iod by g r a d u a l e x p a n s i o n in surface a r e a of t he 
cut ic le . D u r i n g the final feeding s tages in s o m e t icks, v o l u m e inc rease is so 
r a p i d t h a t it c a n n o t be a c c o m m o d a t e d by c o n c o m i t a n t cut ic le g r o w t h , a n d 
c o n s i d e r a b l e s t r e t c h i n g of t h e cut ic le occu r s in a d d i t i o n to a n ear l ie r g r o w t h 
p h a s e . A l t h o u g h t h e i n n e r l aye r of u n ta n n e d cut ic le ( the p rocu t i c le ) is c a p a b l e 
of s t r e t ch ing , t he ep icu t ic le is a l w a y s found to be inex tens ib le even t h o u g h 
it r e m a i n s flexible. I n those i n s t ances w h e r e inc rease in body-s ize occu r s 
d u r i n g a n in s t a r , t h e ep icu t ic le is ini t ia l ly folded, t h e surface b e c o m i n g 
The Tick Cuticle 19 
progress ive ly s m o o t h e d w i t h g r o w t h . C o n s e q u e n t l y , in i t ia l depos i t i on of t he 
severa l l ayers of t h e cu t ic le is i n t i m a t e l y r e l a t ed to s u b s e q u e n t r e q u i r e m e n t s 
for g r o w t h , l o c o m o t i o n , a n d a d a p t a t i o n to t he e n v i r o n m e n t of t he ins t a r . 
1.2.2.1 Formation of the Epicuticle As d i scussed in §1 .2 .1 .1 , t he layers t h a t 
c o m p r i s e t h e ep icu t i c le a r e — f r o m t h e ou t s ide : c e m e n t , w a x , cu t i cu l in , a n d 
d e n s e layer . C h r o n o l o g i c a l l y , h o w e v e r , t h e l ayers a r e n o t sec re ted in t h a t 
o rde r . T h e first l aye r to be d e p o s i t e d is t h e cu t i cu l in . I t beg ins to a p p e a r 
shor t ly after t h e e p i d e r m i s r e t r a c t s f rom the p r e v i o u s cut ic le ( the p rocess 
k n o w n as apolys is ) a t t he b e g i n n i n g of t h e m o u l t . C u t i c u l i n fo rma t ion h a s 
b e e n s t u d i e d in de t a i l in a n insec t b y Locke (1966) a n d m o r e recen t ly in t h e 
a l l o s c u t u m of B. microplus b y Fi l sh ie (1976) . I n m o s t r e spec t s , t he secre to ry 
m e c h a n i s m s a r e i den t i ca l . S m a l l a r e a s of t h e cu t i cu l in m e m b r a n e a p p e a r 
ini t ia l ly as c a p s ove r t he t ips of s m a l l p ro jec t ions o r microvi l l i of t he ap ica l 
p l a s m a m e m b r a n e of t he e p i d e r m a l cells. As secre t ion p r o c e e d s , these c a p s 
b e c o m e progress ive ly l a r g e r in sur face a r e a un t i l n e i g h b o u r i n g a r e a s fuse to 
form a c o n t i n u o u s layer . T h e p l a s m a m e m b r a n e a t t he t ips of microvi l l i 
c o n t a i n s local ized d e n s e a r e a s ( p l a s m a m e m b r a n e p l a q u e s ) a n d it is t h o u g h t 
t h a t p r e c u r s o r s of t h e cu t i cu l in p a s s t h r o u g h t h e m e m b r a n e in these a r e a s 
(Locke , 1966) . M a n y sma l l , d e n s e vesicles a r e a lso seen in the ap ica l cy to-
p l a s m of t h e cells a t th is t i m e a n d s o m e a p p e a r to j o i n w i th t he m e m b r a n e 
a n d d i s c h a r g e the i r c o n t e n t s i n to t h e exuv ia l space . D u r i n g the cu t i cu l in 
fo rma t ion , m o u l t i n g fluid is p r e s u m a b l y b e i n g secre ted as well . T h e d e n s e 
vesicles m a y , therefore , b e a s soc i a t ed w i t h e i the r cu t i cu l in o r m o u l t i n g fluid 
p r o d u c t i o n ; it is n o t poss ib le to d i s t i n g u i s h t h e s e p a r a t e secre tory m e c h a n i s m s 
on m o r p h o l o g i c a l g r o u n d s . 
T o a l low for a n a p p r o x i m a t e l y ninefold i nc rea se in t he surface a r e a of t he 
female a l l o s c u t u m d u r i n g s u b s e q u e n t feeding, t he ep icu t ic le is ini t ia l ly fo rmed 
in l a rge excess so t h a t it is t h r o w n i n t o d e e p , r e g u l a r folds (Fig. 1.13). Fi lshie 
(1976) n o t e d t h a t c o n s i d e r a b l e g r o w t h of t h e cu t i cu l in occu r s even after t h e 
l ayer forms a c o n t i n u o u s shee t , th is e x p a n s i o n p r o b a b l y t ak ing p l ace b y 
i n t u s s u s c e p t i o n of a d d i t i o n a l m a t e r i a l a t si tes w i t h i n t h e a l r e a d y c o n t i n u o u s 
m e m b r a n e . F i g u r e 1.11 s h o w s t h e cu t i cu l in l ayer as a c o n t i n u o u s m e m b r a n e , 
b u t t h e folds a r e on ly a b o u t 2 μpiι d e e p , w h e r e a s the i r final d e p t h is a b o u t 
5 μpiι (Fig . 1.12). 
As t h e cu t i cu l in deve lops , t h e e p i d e r m i s t e n d s to r e t r a c t from w i t h i n t he 
folds, l e av ing long , b r a n c h e d microvi l l i (Fig . 1.11). T h e d e n s e layer of t he 
ep icu t ic le t h e n beg ins to form b e n e a t h t he cu t i cu l in a n d d e n s e e p i c u t i c u l a r 
filaments a r e seen j o i n i n g t h e surface of microvi l l i w i th t he cu t i cu l in . T h e 
e p i c u t i c u l a r filaments form t h e d e n s e c e n t r a l core of t he w a x cana l s in t h e 
ful ly-formed ep icu t ic le (Fi lsh ie , 1976) . A t e n u o u s ecdys ia l m e m b r a n e of 
u n k n o w n func t ion covers t h e surface of e p i c u t i c u l a r folds (Fig. 1.11). 
L i t t l e is k n o w n r e g a r d i n g t h e sec re t ion of t he w a x layer in insec ts o r t icks. 
W i g g l e s w o r t h (1947) d e m o n s t r a t e d t h a t in Rhodnius t he wa t e rp roo f ing layers 
20 R. H. Hackman and B. K. Filshie 
a r e d e p o s i t e d o n t h e surface of t he cu t i cu l in shor t ly after ecdys is . I n a s imi l a r 
series of e x p e r i m e n t s o n severa l species of t icks, Lees (1947) s h o w e d t h a t t he 
cut ic le b e c a m e essent ia l ly w a t e r p r o o f m u c h ear l ier , t h a t is shor t ly after 
c o m p l e t i o n of t h e cu t i cu l in l ayer a n d before ecdysis . I n 0. moubata c e r t a i n 
a r e a s over m u s c l e in se r t ions , s o m e of t he s te l la te folds a n d tube rc l e s of t he 
ep icu t ic le a n d t ips of br is t les r e m a i n u n w a t e r p r o o f e d for s o m e t i m e after 
c o m p l e t i o n of t h e cu t i cu l in , t hose over t he m u s c l e inse r t ions un t i l shor t ly 
before ecdys is . I n / . ricinus a n d D. andersoni t he re is a n i r r e g u l a r d i s t r i b u t i o n 
of sma l l p a t c h e s t h a t r e m a i n n o n - w a t e r p r o o f un t i l th is t ime . Lees p o s t u l a t e d 
t h a t a b s o r p t i o n of m o u l t i n g fluid p r i o r to ecdysis p r o b a b l y occu r s in those 
reg ions t h a t h a p p e n n o t to b e w a t e r p r o o f e d . 
By a b r a d i n g t h e surface of pos t -ecdys ia l cut ic le a n d t h e n o b s e r v i n g the 
recovery p roces s , Lees (1947) w a s ab l e to s h o w t h a t w a x secre t ion is n o t 
r e l a t ed to t h e d i s t r i b u t i o n of d e r m a l g l a n d o p e n i n g s , a n d h e c o n c l u d e d t h a t 
the w a x l aye r is sec re ted b y the e p i d e r m i s t h r o u g h the p o r e c a n a l s . I n 0. 
moubata, c o m p l e t e r ecovery f rom a b r a s i o n takes a b o u t 3 d a y s . W a x secre t ion 
ceases after r ecovery in ixod ids , b u t c o n t i n u e s u p un t i l t he fol lowing m o u l t 
in Ornithodoros, t he c e m e n t l ayer fail ing to re -cover t he r e p a i r e d a r e a . 
As m e n t i o n e d p rev ious ly , t h e " w a x " l ayer seen in p o s t m o u l t cut ic les of B. 
microplus (F ig . 1.6) c a n n o t be c o m p o s e d of s imp le l ip ids , as these w o u l d b e 
e x t r a c t e d d u r i n g p r e p a r a t i o n for e lec t ron mic roscopy . N o t h i n g is k n o w n of 
t he d e p o s i t i o n of th is l aye r seen in t he e lec t ron m i c r o s c o p e , excep t t h a t it is 
no t la id d o w n before ecdysis a n d is therefore no t r e l a t ed to t h e ini t ia l 
w a t e r p r o o f i n g l aye r d i scove red b y Lees (1947) in / . ricinus. 
1.2.2.2 Formation of the Procuticle T h e p rocu t i c l e in t icks is c o m p o s e d of ch i t in 
a n d p r o t e i n b u t t he p r o p o r t i o n of ch i t in is m u c h lower t h a n in insects—cf. 
1 1 . 6 % ch i t in in unfed Hyalomma dromedarii (Basa l & H e f n a w y , 1972) w i t h 
4 4 . 2 % ch i t in in Calliphora vicina l a rval cut ic le ( H a c k m a n & G o l d b e r g , 1977) . 
I n t he l ight of these o b s e r v a t i o n s it is n o t s u r p r i s i n g t h a t t he fibrillar 
FIG. 1.11. Newly forming epicuticle of the adult female alloscutum. Cuticulin layer (c) forms 
a continuous covering over microvillar extensions (mv) of the plasma membrane, but folds of 
the epicuticle are yet to become deeper by further expansion of the cuticulin (compare with 
fully formed epicuticle of Fig. 1.12). Tips of the folds of cuticulin are covered with an ecdysial 
membrane (ed.). Junctions between epidermal cells (cj) occur about every second fold. The 
apical cytoplasm contains numerous small dense vesicles (dv), mitochondria (m), and rough 
endoplasmic reticulum (er) and occasional large, dense cytolysomes (cl). Scale = 2.5 μpiι. 
FIG. 1.12. Transverse section of the cuticle of the alloscutum of an unfed adult. Note the regular 
deep folds of the epicuticle (epi) and the outer endocuticle (outer) which is clearly lamellate 
throughout its thickness. A dense subcuticle (sub) can be seen and pore canals (pc) run vertically 
through the cuticle. Epidermal cells are very large, contain large nuclei (n) with prominent 
nucleoli. Scale = 1.0 μpiι. 
FIG. 1.13. Scanning electron micrograph of the alloscutum of an unfed adult showing the regular, 
parallel, zigzag folds in the epicuticle. Scale = 0.5 μpiι. 
The Tick Cuticle 
22 R. H. Hackman and B. K. Filshie 
c o m p o n e n t of t ick cut ic les is difficult to de tec t in the e lec t ron m i c r o s c o p e . 
D u r i n g p rocu t i c l e secre t ion in insec ts , ch i t in microf ibr i ls , s u r r o u n d e d by a n 
e l ec t ron -dense l ayer p r e s u m e d to be p ro t e in , h a v e been seen c lear ly c o m i n g 
from the t ips of p l a s m a m e m b r a n e microvi l l i (Fi lshie , 1970b) . S imi l a r i m a g e s 
h a v e n o t b e e n o b t a i n e d w i t h t icks. A l t h o u g h microvi l l i a r e p r e s e n t o n t he 
ap ica l surfaces of e p i d e r m a l cells ( N a t h a n s o n , 1967, 1970; Bead le , 1974) , 
microf ibr i ls a r e n o t seen in t he l ayer of cut ic le ( sub-cut ic le ) ad j acen t to t he 
e x t e r n a l face of t he cell (Figs . 1.12 a n d 1.14). T h e c o m p l i c a t e d s h a p e of t he 
ap ica l p l a s m a m e m b r a n e a n d its occas iona l i n t ru s ions i n to t he i n n e r l a m e l l a e 
of t he p rocu t i c l e , led N a t h a n s o n (1967, 1970) to sugges t t h a t t he t icks ' 
p rocu t i c l e m a y b e fo rmed by success ive i n c o r p o r a t i o n of t he en t i r e b o r d e r 
a r e a i n to t h e cu t ic le . T h e p rocess w o u l d t h e n be a n i n t r ace l l u l a r r a t h e r t h a n 
a sec re to ry o n e . T h i s h y p o t h e s i s is no t s u p p o r t e d by B e a d l e (1974) . 
D u r i n g ea r ly p rocu t i c l e f o rma t ion in B. microplus t he cut ic le of t he a l lo-
s c u t u m is l a m e l l a t e ove r its en t i r e th ickness excep t for t he reg ions ins ide 
surface folds. E a c h l ame l l a is ca. 0.6 μηι th ick (Fig. 1.12). E v e n us ing p o t a s -
s i u m p e r m a n g a n a t e a n d led c i t r a t e s t a i n i n g of sec t ions for e lec t ron m i c r o -
scopy , as r e c o m m e n d e d by Nevi l le a n d L u k e (1969) for insect cut ic les , 
microf ibr i ls c a n n o t be seen in t he tick cut ic le a t th is s t age . P r o c u t i c u l a r 
m a t e r i a l s eems to be la id d o w n ini t ia l ly in a very c o m p a c t form. If m i c r o -
fibrillar m a t e r i a l is p r e s e n t , it is no t c o n t r a s t e d b e c a u s e of the lack of s t a i n i n g 
of the in te r s t i t i a l m a t r i x . 
N a t h a n s o n (1967) found n u m e r o u s re la t ively l a rge , e l ec t ron -dense g r a n u l e s 
in t he e p i d e r m a l cells of b o t h sc lerot ized a n d unsc le ro t i zed cut ic le of H. 
le pons palustris a n d sugges t ed they m a y c o n t a i n c u t i c u l a r p r e c u r s o r s . H o w e v e r , 
his p u b l i s h e d m i c r o g r a p h s of these g r a n u l e s b e a r a s t r o n g r e s e m b l a n c e to 
those of p i g m e n t g r a n u l e s seen in insect e p i d e r m a l cells (see, for e x a m p l e , 
F i l sh ie et al., 1975) . F u r t h e r o b s e r v a t i o n s on k n o w n p i g m e n t e d a r e a s of t icks 
need to b e c a r r i e d o u t to clarify this o b s e r v a t i o n . 
I n n e r e n d o c u t i c l e of t h e n y m p h of B. microplus is of t he u s u a l he l icoidal ly 
a r r a n g e d fibrous p a t t e r n seen in insec ts (Figs . 1.2-1.4 a n d see §1 .2 .1 .2) . I n 
FlG. 1.14. Transverse section through the alloscutum cuticle of an adult at the end of the growth 
phase, when the cuticle is approximately at its maximum thickness (in this case 45 μpiι). The 
inner endocuticle (inner) is clearly lamellate and the outer endocuticle (outer), clearly non-
lamellate. Pore canals (pc) of the inner endocuticle are extremely numerous, branched and 
anastomosed, whereas in the outer endocuticle they are less branched and far less numerous. 
Epicuticle, epi; subcuticle, sub. Scale = 1.0 μιη. 
FlG. 1.15. Transverse section of the fully stretched alloscutum cuticle after final engorgement. 
The stretching causes the thickness to be reduced to about half that at the end of the growth 
phase (Fig. 1.14). Pore canals of the inner endocuticle appear to have closed up so that the 
lamellate appearance is no longer seen. The junction between inner and outer endocuticles is 
also indistinct but is probably in the region of the dotted line. Pore canals (pc) of both the inner 
and outer endocuticles are extremely deformed by the stretching. The epidermal layer beneath 
the cuticle is still intact and the cells appear healthy. Scale = 1.0 μιη. 
The Tick Cuticle 23 
24 R. H. Hackman and Β. K. Filshie 
t he a l l o s c u t u m of a d u l t s , howeve r , microf ibr i ls a r e seen m a i n l y w i t h i n p o r e 
cana l s (F igs . 1.14, 1.16, a n d 1.17). Lees (1952) r e p o r t e d t h a t p o r e c a n a l s of 
/. ricinus b e c o m e progress ive ly ch i t in ized a n d t h a t fibrillar m a t e r i a l c a n be 
seen r u n n i n g t r ansve r se ly t h r o u g h the cells from the nuc l eus to t h e ap i ca l 
b o r d e r , a n d poss ib ly i n to p o r e c a n a l s . T h e s e o b s e r v a t i o n s sugges t t h a t ch i t in 
in t icks m a y be fo rmed as a n i n t r ace l l u l a r m a t e r i a l (if t he in te r io r s p a c e of 
p o r e c a n a l s c a n b e cons ide r ed to be i n t r ace l l u l a r as a n a l t e r n a t i v e to its 
ex t r ace l l u l a r sec re t ion) as in insec ts . T h i s p h e n o m e n o n h a s no t b e e n r e p o r t e d 
in o t h e r a r t h r o p o d s . 
1.2.2.3. Modifications to Cuticle Structure during Feeding A r t h r o p o d e c t o p a r a s i t e s , 
in g e n e r a l , a r e c a p a b l e of i nges t ing l a rge q u a n t i t i e s of fluid a n d a r e a n a t o m -
ically a d a p t e d in o n e w a y or a n o t h e r to a c c o m m o d a t e inc reases in b o d y -
v o l u m e over o n e o r m o r e o r d e r s of m a g n i t u d e . I n s o m e in s t ances , for e x a m p l e , 
t he b l o o d - s u c k i n g r eduv i id R. prolixus, t h e b lood m e a l is t a k e n in a s h o r t 
t i m e a n d m a y a m o u n t to t en t imes t h e pre- feed ing we igh t of t he insec t 
( W i g g l e s w o r t h , 1933) . I n o t h e r i n s t ances , s u c h as in t he a d u l t female t icks 
of t h e family I x o d i d a e , b o d y - w e i g h t d u r i n g the final i n s t a r m a y inc rease by 
u p to 100 t imes o r m o r e d u r i n g the p r o l o n g e d pe r iod of hos t a t t a c h m e n t . I n 
t e r m s of cut ic le g r o w t h , t h e pe