1 0 . THE INSECT FAUNA OF LITTLE CAYMAN
R . R . Askew
L i t t l e Cayman i s seldom mentioneZ i n entoiiiologicali. l i t e r a t u r e . The 1938 Oxford U n i v e r s i t y B i o l o g i c a l E x p e d i t i o n s p e n t t h i r t e e n days or, t h e i s l a n c ? and r e p o r t s on t h e r e s u l t i n q c o l l e c t i o n d e a l w i t h Odona-ta ( F r a s e r , 19431, wa-ter-bugs (Hulgerforc?, 1 9 4 0 ) , N e m o p t e r a
(Banks, 1941)
,
c i c a d a s ( D a v i s , 19391,
C a r a b i d a e ( D a r l i n g t o n , 194'73,
Cerambycidae ( F i s h e r , 1 9 4 1 , 1948)
,
b u t t e r f l i e s ( C a r p e n t e r & Lewis, 1 9 4 3 ) a n d S p h i n g i d a e ( J o r d a n , 1940j , During t h e 19'75 e x p e d i t i o n , i n s e c t s of a l l o r d e r s were s t u d i e d o v e r a p e r i o d o f a b o u t f i v e weeks and many a d d i t i o n s w i l l e v e n t u a l l y be made t o t h e i s l a n d ' s s p e c i e s l i s t . A t p r e s e n t , however, i d e n t i f i c a t i o n of t h e i n s e c t s c o l l e c t e d h a s , w i t h t h e e x c e p t i o n o f t h e b u t t e r f l i e s which have been c o n s i d e r e d s e p a r a t e l y , p r o c e e d e d i n t h e m a j o r i t y o f c a s e s o n l y a s f a r a s t h e f a m i l y l e v e l . A p p l i c a t i o n of f a m i l y names f o r t h e most p a r t f o l l o w s B o r r o r & DeLong ( 1 9 6 6 ) . I n t h i s p a p e r t h e g e n e r a l c h a r a c t e r i s t i c s o f t h e i n s e c t f a u n a a r e d e s c r i b e d .C o l l e c t i n g Methods
A , G e n e r a l c o l l e c t i n g w i t h sweep-net, pond-net, b u t t e r f l y n e t and s e a r c h i n g f o l i a g e , t r e e t r u n k s and on t h e ground. A cone-net a t t a c h e d t o a v e h i c l e was u s e d on one o c c a s i o n . A l s o c o n s i d e r e d a s b e i n g c a u g h t by ' g e n e r a l c o l l e c t i n g ' a r e i n s e c t s found r e s t i n g on w a l l s a d j a c e n t t o o u t s i d e e l e c t r i c l i g h t s a t P i r a t e s ' P o i n t . B . A M a l a i s e t r a p (Model 300 Health-EE-X s u p p l i e d by Entomology
R e s e a r c h I n s t i t u t e , Minnesota) was e r e c t e d on 1 7 t h J u l y a n d o p e r a t e d a l m o s t c o n t i n u o u s l y t o t h e end o f t h e e x p e d i t i o n . I t was s i t u a t e d a t P i r a t e ' s P o i n t , j u s t s o u t h o f t h e l a g o o n and r o a d , i n a g l a d e between b u s h e s o f Conocarpus and o t h e r s h r u b s growing a t t h e b a s e o f t h e n o r t h e r n f a c e o f t h e b e a c h r i d g e . The ground v e g e t a t i o n was dominated by S p o r o b o l u s a n d Ambrosia.
The t r a p was u n b a i t e d ; 70% e t h y l a l c o h o l was u s e d i n t h e c o l l e c t i n g b e a k e r .
A t o l l R e s e a r c h B u l l e t i n No. 241: 97-114, 1980.
C . A Robinson mercury vapour l i g h t t r a p , powered by a p o r t a b l e g e n e r a t o r , was r u n i n t h e grounds o f P i r a t e ' s P o i n t on t h e f o l l o w i n g o c c a s i o n s : 1 4 t h J u l y (20.00-22.00 h o u r s ) , 1 5 t h J u l y
( 2 0 . 0 0 - 2 2 . 0 0 ) , 1 6 t h J u l y ( 2 0 . 0 0 - 2 2 - 0 0 ) , 1 7 t h J u l y (20.00-22.00), 18-19th J u l y ( 2 2 . 0 0 - 4 . 0 0 ) , 19-20th J u l y ( 2 1 . 0 0 - 4 . 0 0 ) , 21-22nd J u l y
( 2 2 . 0 0 - 4 . 0 0 ) , 2 4 t h J u l y ( 2 0 . 0 0 - 2 1 - 3 0 ) , 2 7 t h J u l y (20.00-3.30) and 3 0 t h J u l y (20.30-21.30 h o u r s , when t h e g e n e r a t o r i r r e p a r a b l y b r o k e down). The t r a p was a l s o r u n on 2 8 t h J u l y i n t h e c e n t r a l f o r e s t s o u t h of Sparrowhawk H i l l from 1 8 . 3 0 t o 21.30 h o u r s . Few i n s e c t s a r r i v e d a f t e r 21 .OO h o u r s .
D . O t h e r c o l l e c t i n g methods a t t e m p t e d , w i t h v e r y p o o r r e s u l t s , were t h e u s e of a yellow t r a p , p i t - f a l l t r a p s and e x t r a c t i o n f u n n e l
( c h a r g e d w i t h washed-up t u r t l e g r a s s ) . The Fauna i n General
By t h e methods o u t l i n e d above, a t l e a s t 613 i n s e c t s p e c i e s were c o l l e c t e d . C l o s e r e x a m i n a t i o n of t n e m a t e r i a l w i l l p r o b a b l y r e v e a l f u r t h e r s p e c i e s . R e p r e s e n t a t i v e s of a l l o r d e r s e x c e p t P r o t u r a , P l e c o p t e r a , Embioptera, Z o r a p t e r a , Anoplura, S t r c p s i p t e r a , Mecoptera, T r i c h o p t e r a and S i p h o n a p t e r a were found. Only a few v e r t e b r a t e s were examined f o r e c t o p a r a s i t e s and S i p h o n a p t e r a w i l l undoubtedly be p r e s e n t on t h e i s l a n d . The o t h e r o r d e r s l i s t e d , i f p r e s e n t , s h o u l d have been d e t e c t e d and it can be concluded t h a t t h e y a r e r e p r e s e n t e d on L i t t l e Cayman a t t h e most by a few, r a r e s p e c i e s .
The numbers of s p e c i e s found i n e a c h o r d e r a r e shown i n t a b l e 1 2 . The r a t i o of t h e number o f s p e c i e s (x 100) i n e a c h o r d e r t o t h e number of s p e c i e s r e c o r d e d i n t h e U n i t e d S t a t e s n o r t h o f Mexico ( B o r r o r &
DeLong, 1966) i s g i v e n f o r comparison. Of t h e l a r g e r o r d e r s , t h e L e p i d o p t e r a a p p e a r t o be b e s t r e p r e s e n t e d a l t h o u g h t h e use o f a l i g h t t r a p undoubtedly b i a s e d c o l l e c t i n g i n t h e i r f a v o u r , The t o t a l o f s p e c i e s r e c o r d e d i s a minimun?; many m i c r o l e p i d o p t e r a c a u g h t i n t h e l i g h t and M a l a i s e t r a p s c o u l d n o t be i d e n t i f i e d because o f t h e i r p o o r c o n d i t i o n . C o l e o p t e r a , a l t h o u g h t h e second most numerous o r d e r i n terms of s p e c i e s c a u g h t , i s d i s p r o p o r t i o n a t e l y p o o r l y r e p r e s e n t e d . Among t h e s m a l l e r o r d e r s , Odonata, O r t h o p t e r a and N e u r o p t e r a a r e a l l w e l l - r e p r e s e n t e d . The c u r v e showing t h e numbers of s p e c i e s r e c o r d e d o v e r t h e c o u r s e o f t h e e x p e d i t i o n ( f i g . 4 ) o n l y m o d e r a t e l y l e v e l s o f f , from which i t must be concluded t h a t many more s p e c i e s remain t o be d i s c o v e r e d .
I n t e r m s o f i n d i v i d u a l s , t h e s u b j e c t i v e i m p r e s s i o n i s t h a t C u l i c i d a e , C o r i x i d a e and Formicidae a r e t h e most abundant groups on t h e i s l a n d ; Aedes taeniorhynchus Wied and a s p e c i e s o f C o r i x i d were e a s i l y t h e two most f r e q u e n t l y e n c o u n t e r e d s p e c i e s .
F a m i l i e s w i t h t h e h i g h e s t numbers o f i n c l u d e d s p e c i e s a r e Noctuidae (45 s p e c i e s ) and P y r a l i d a e (15)
,
F o r m i c i d a e ( 1 9 ) , C i c a d e l l i d a e ( 1 7 ) and S t a p h y l i n i d a e ( 1 5 ) . Within some of t h el a r g e r f a m i l i e s t h e r e i s o f t e n a wide r a n g e o f s p e c i e s ' s i z e .
Table 12. O r d i n a l d i s t r i b u t i o n of s ~ e c i e s of i n s e c t s found on L i t t l e Cayman. Numbers of s p e c i e s from North America n o r t h of Mexico a r e from Borror & DeLong ( 1 9 6 6 ) .
Number of s p e c i e s found i n Order
Collembola Thysanura Ephemeroptera Odonata
O r t h o p t e r a I s o p t e r a Dermaptera Psocoptera
Thysanoptera
Hemiptera H e t e r o p t e r a Hemiptera Homoptera Neuroptera
C o l e o p t e r a Lepidoptera D i p t e r a Hymenoptera
T o t a l
L i t t l e Cayman N . America R a t i o xlOO
2 314 0 . 6
2 5 0 4.0
613 84061 ( i n c l u d i n g 0.7
o r d e r s n o t on L . C . )
L i n e a r measurements of t h e l a r g e s t and s m a l l e s t s p e c i e s w i t h i n a
f a m i l y a r e shown i n t a b l e 1 3 . I n d i v i d u a l s of n e a r a v e r a g e dimensions were s e l e c t e d f o r measurement. Comparable f i g u r e s f o r t h e B r i t i s h f a u n a a r e a l s o i n c l u d e d i n t h e t a b l e a n d , remembering t h a t t h e s e a r e drawn from a g e n e r a l l y much l a r g e r f a u n a , t h e y emphasize t h e o f t e n c o n s i d e r a b l e w i t h i n - f a m i l y s i z e r a n g e of Cayman i n s e c t s . T h i s i s p a r t i c u l a r l y t r u e f o r L e p i d o p t e r a , O r t h o p t e r a , and f o r some f a m i l i e s of C o l e o p t e r a b u t n o t C a r a b i d a e o r S t a p h y l i n i d a e . Large C a r a b i d s and S t a p h y l i n i d s seem t o be a b s e n t and t h i s may be b e c a u s e of e x c l u s i o n by t h e many l a n d c r a b s on L i t t l e Cayman. The r a n g e of s i z e a p p e a r s t o be g r e a t e s t i n e n d o p t e r y g o t e f a m i l i e s ( e x c e p t
D i p t e r a ) . I n t e r r e s t r i a l e x o p t e r y g o t e s p e c i e s , a d u l t s and immature s t a g e s o f t e n have a s i m i l a r b i o l o g y and t h i s may s u p p r e s s t h e
e s t a b l i s h m e n t of s p e c i e s t h a t a r e s m a l l a s a d u l t s .
~ ~ l a r g e s i z e r a n g e 1 . ~ ~ u ~ i t 1 1 i i - 1 f a m i l i e s of Cayr~an irzsec-is i s c o n t r i b u t e d t o by b o t h v e r y s m a l l and v e r y l a r g e s p e c i e s , b u t e s p e c i a l - l y by t h e l a t t e r , I n o r d e r s i n which more t h a n two r e p r e s e n t a t i v e s were f o u n d , t h e D i p t e r a and Hymenoptera a r e t h e o n l y o n e s i n which a B r i t i s h s p e c i e s e x c e e d s i n l i n e a r d i m e n s i o n s t h e l a r g e s t Cayman s p e c i e s o b t a i n e d .
COLLEMBOLA
Neanuridae 1 s p e c i e s Entomobryidae 1 s p e c i e s
The Neanurid, a p i n k i s h - o r a n g e s p e c i e s , o c c u r r e d i n a g g r e g a t i o n s on t h e s u r f a c e o f r a i n - w a t e r i n p i t - f a l l t r a p s . The Entomobryid was f o u n d amongst l i t t e r n e a r S p o t Bay a n d , a p p a r e n t l y t h e same s p e c i e s , i n a c c u m u l a t i o n s o f washed-up t u r t l e g r a s s on t h e s h o r e .
L e p i s m a t i d a e 2 s p e c i e s
B a e t i d a e 1 s p e c i e s
A s u b i m a g i n a l s k i n and a l i v e l a r v a found i n a r a i n - w a t e r p o o l on t h e b l u f f s o u t h of Crawl Bay.
ODONATA
Aeshnidae 1 s p e c i e s L i b e l l u l i d a e 6 s p e c i e s
D r a g o n f l i e s were c o n s p i c u o u s and a b u n d a n t , e s p e c i a l l y n e a r t o t h e b r a c k i s h c o a s t a l l a g o o n s and on t h e Sesuvium marsh i n t h e e a s t . No Zygoptera were n o t e d on L i t t l e Cayman, a l t h o u g h two s p e c i e s were found on Grand Cayman t o g e t h e r w i t h t h r e e s p e c i e s of A n i s o p t e r a n o t e n c o u n t e r e d on t h e s m a l l e r i s l a n d . F r a s e r (1943) r e c o r d s t w e l v e s p e c i e s of Odonata c o l l e c t e d by t h e Oxford U n i v e r s i t y e x p e d i t i o n ( s i x
Table 13. Within-family s i z e ranges o f L i t t l e Cayman and B r i t i s h i n s e c t s .
Dimensions a r e body l e n g t h ( e x c l u d i n g antennae and abdominal appendages) e x c e p t f o r Odonata, Neuroptera and L e p i d o p t e r a where wing expanse i s g i v e n , and S c a r a b a e i d a e f o r which e l y t r a l l e n g t h i s shown.
Dimensions (mm. )
of l a r g e s t s p e c i e s Magnitude range
Order Family ( L i t t l e Cayman) L. Cayman B r i t a i n
Odonata L i b e l l u l i d a e 82 1 . 5 1 . 6
O r t h o p t e r a B l a t t i d a e 39 4.6 1 . 7
G r y l l i d a e 15 3 - 3 2.5
h e t e r o p t e r a Miridae
i3omop t e r a C i c a d e l l i d a ~
Neuroptera Myrmeleontidae 118 2 . 1
-
C o l e o p t e r a Carabidae 10 5 . 0 1 2 . 4
S t a p h y l i n i d a e 1 2 6 . 7 11.7
Hydrophilidae 3 8 20.0 20.0
E l a t e r i d a e 2 8 4.7 2.4
Cerambycidae S c a r a b a e i d a e L e p i d o p t e r a Sphingidae
Noctuidae P i e r i d a e H e s p e r i i d a e
D i p t e r a Chloropidae 2 1.8 5.0
Hymenoptera Formicidae (workers) 7.1 5 - 1 4.7
Sphe c i d a e 2 3 5 . 1 7.0
Braconidae 9 6 . 0 9.8
*
s p e c i e s found on Cayman Bracfrom L i t t l e Cayman) a l t h o u g h n o t a l l a r e t h e same a s t h o s e t a k e n i n 1975. The most numerous s p e c i e s , E r y t h r o d i p l a x naeva (Hagen)
,
was found a l l o v e r t h e i s l a n d i n c l u d i n g t h e d r y i n t e r i o r . A l a r g e rP a n t a l a s p e c i e s was a l s o common b u t c o n f i n e d t o t h e v i c i n i t y of c o a s t a l l a g o o n s where l a r g e ' f l o c k s ' were f r e q u e n t l y s e e n hawking u n t i l s u n s e t a t a h e i g h t of a b o u t f i v e m e t r e s .
ORTHOPTERA
A c r i d i d a e 1 s p e c i e s ( C y r t a c a n t h a c r i d i n a e )
T e t t i g o n i i d a e 4 s p e c i e s ( 2 C o n o c e p h a l i n a e , 2 P h a n e r o p t e r i n a e ) G r y l l i d a e 6 s p e c i e s ( 3 M o g o p l i s t i n a e , 2 Oecanthinae,
1 G r y l l i n a e ) Phasmidae 1 s p e c i e s B l a t t i d a e 6 s p e c i e s
The dominance o f t h e t e r r e s t r i a l c r i c k e t s and c o c k r o a c h e s o v e r t h e o t h e r f a m i l i e s may b e r e l a t e d t o t h e abundance o f a r b o r e a l l i z a r d s , The Phasmid and t h e two P h a n e r o p t e r i n a e , a l l t r e e - l i v i n g , were e a c h found o n l y o n c e . The A c r i d i d , a l a r g e s p e c i e s , was w i d e s p r e a d i n a l l s t a g e s . An Oedipodine g r a s s h o p p e r w i t h r e d hindwings was c o l l e c t e d on Cayman S r a c b u t n o t found on L i t t l e Cayman.
ISOPTERA
K a l o t e r m i t i d a e , T e r m i t i d a e , R h i n o t e r m i t i d a e (1 s p e c i e s e a c h ) L i t t l e t i m e was s p e n t i n c o l l e c t i n g t e r m i t e s and more s p e c i e s a r e t o be e x p e c t e d .
DERMAPTERA
L a i d u r i d a e 1 s p e c i e s ( L a b i d u r a r i p a r i a ( p a l l a s ) ) L a b i i d a e 1 s p e c i e s (Baryqerax s p . )
Only t h r e e specimens of e a r w i g were found. The o r d e r h a s n o t h i t h e r t o been r e p o r t e d from t h e Cayman I s l a n d s and t h e Baryqerax
s p e c i e s i s p r o b a b l y u n d e s c r i b e d ( t e s t e A . B r i n d l e ) . P SOCOPTERA
The f o u r s p e c i e s f o u ~ d , r e p r e s e n t e d by o n l y f o u r i n d i v i d u a l s , a r e n o t y e t i d e n t i f i e d t o f a m i l y .
MALLOP HAGA
A s i n g l e b i t i n g l o u s e was t a k e n from a r e d - f o o t e d booby. Few o t h e r b i r d s were examined.
THYSANOPTERA
P h l o e o t h r i p i d a e 1 s p e c i e s Family ? 1 s p e c i e s
No s p e c i a l e f f o r t was made t o l o c a t e t h r i p s and t h e o r d e r i s p r o b a b l y u n d e r - r e p r e s e n t e d i n t h e c o l l e c t i o n s .
HEMIPTERA HETEROPTERA
C o r i x i d a e 2 s p e c i e s N o t o n e c t i d a e 2 V e l i i d a e 1 Anthocoridae 4 Miridae 7 Isome t o p i d a e 1 Reduviidae 2 Nabidae 1 Tincjidae 3 Lygaeidae 4 p y r r h o c o r i & e 3 C o r e i d a e 3 C o r i z i d a c 3 S a l d i d a e 1.
S c u - t e l l e r i d a e 4 Pentatomidae 4
C o r i x i d a e were e x c e e d i n g l y a b u n d a n t , coming t o t h e mercury vapour t r a p i n enormous numbers and o f t e n being s e e n i n t h e b r a c k i s h l a g o o n s . One s p e c i e s dominated t h e c o l l e c t i o n s , b u t more t h a n two s p e c i e s may e v e n t u a l l y be found t o be p r e s e n t . Hungerford (1940) r e c o r d s o n l y one w a t e r bug, Trichocorixa v e r t i c a l i s ( F i e b . ) from L i t t l e Cayman.
Most o f t h e t e r r e s t r i a l s p e c i e s were r a t h e r l o c a l b u t sometimes p l e n t i f u l . One of t h e P y r r h o c o r i d s a g g r e g a t e d i n l a r g e numbers on f a l l e n f r u i t s , and a n o t h e r was common on c u l t i v a t e d bean p l a n t s , HEMIPTERA HOMOPTERA
C i c a d i d a e 1 s p e c i e s Membracidae 1 s p e c i e s C i c a d e l l i d a e 17 T r o p i d u c h i d a e 1
F l a t i d a e 3 Delphacidae 7
C i x i i d a e 4 A c a n a l o n i i d a e 1
Aphididae 1 A l e y r o d i d a e 1
S t r i k i n g f e a t u r e s o f t h e Homopteran f a u n a a r e t h e p a u c i t y of S t e r n o r h y n c h a and t h e a p p a r e n t a b s e n c e of Cercopidae.
NEUROPTERA
M a n t i s p i d a e 1 s p e c i e s Chrysopidae 3 s p e c i e s A s c a l a p h i d a e 1 Myrmeleontidae 4
Neuroptera a r e v e r y w e l l - r e p r e s e n t e d , i n s p i t e of t h e absence of Hemerobiidae. T h i s l a t t e r may be r e l a t e d t o t h e s c a r c i t y of a p h i d s . The a n t - l i o n s were a l l c o l l e c t e d a s a d u l t s a t l i g h t and two s p e c i e s were common. Banks (1941) r e p o r t s t h e p r e s e n c e on
L i t t l e Cayman o f C h r y s o p a t r a n s v e r s a Walker and Myrrneleon i n s e r t u s Hagen o n l y , from m a t e r i a l c o l l e c t e d by t h e 1938 Oxford U n i v e r s i t y e x p e d i t i o n . Both of t h e s e s p e c i e s were found i n 1975. No M a n t i s p i d h a s h i t h e r t o been r e p o r t e d from t h e Cayman I s l a n d s .
COLE OPTERA
C i c i n d e l i d a e 2 s p e c i e s D y t i s c i d a e 2
L e p t o d i r i d a e 1 P s e l a p h i d a e 1 C i s i d a e 1 E l a t e r i d a e 5 H e t e r o c e r i d a e 1 Xnizophagidae 2 P h a l s c r i d a e 1 C o c c i n e l l i d a e 6 .qnti~i.cidae 1 Oedemeridae 5 P l o r d e l l i d a e 1 T e n e b r i o n i d a e 1 B o s t r i c h i d a e 2 Cerambycidae 9 B r u c h i d a e 4 P l a t y p o d i d a e 2
C a r a b i d a e 11 s p e c i e s H y d r o p h i l i d a e 9 S t a p h y l i n i d a e 1 5 O r t h o p e r i d a e 1 C l e r i d a e 2 B u p r e s t i d a e 1 D e r o d o n t i d a e 1 S i l v a n i d a e 1 La c h r i d i i d a e 2 C o l y d i i d a e 1 E u y l e n i d a e 1 Meloidae 1 A l l e c u l i d a e 2 Anobiidae 2 S c a r a b a e i d a e 1 0 Chrysomelidae 3 C u r c u l i o n i d a e 6 S c o l y t i d a e 2
Two f a m i l i e s o f t e r r e s t r i a l c a r n i v o r e s , C a r a b i d a e and
S t a p h y l i n i d a e , c o n t a i n t h e h i g h e s t numbers o f b e e t l e s p e c i e s f o u n d . Becker (1975) shows t h a t t h e b e e t l e f a u n a of i s l a n d s t e n d s t o i n c l u d e a h i g h e r p r o p o r t i o n of t e r r e s t r i a l c a r n i v o r e s t h a n d o e s t h e f a u n a of t h e a d j a c e n t m a i n l a n d , and he p o s t u l a t e s t h a t c a r n i v o r o u s b e e t l e s ,
b e i n g more c a t h o l i c i n f o o d r e q u i r e m e n t s t h a n most phytophagous s p e c i e s , a r e more e a s i l y a b l e t o become e s t a b l i s h e d on i s l a n d s . On L i t t l e
Cayman t h e p e r c e n t a g e o f t e r r e s t r i a l c a r n i v o r o u s s p e c i e s ( c o u n t i n g o n l y C i c i n d e l i d a e , C a r a b i d a e , S t a p h y l i n i d a e , C l e r i d a e and C o c c i n e l l i d a e ) i n t h e t o t a l number of phytophagous s p e c i e s ( B u p r e s t i d a e , B o s t r i c h i d a e , Cerambycidae, C h r y s o m e l i d a e , B r u c h i d a e and C u r c u l i o n i d a e o n l y ) p l u s t e r r e s t r i a l c a r n i v o r e s i s 59. C o r r e s p o n d i n g f i g u r e s g i v e n by Becker f o r Jamaica and Cuba a r e 66% and 41% r e s p e c t i v e l y , w h i l s t p e r c e n t a g e s f o r mainland L a t i n America r a n g e o n l y between 21 and 37. A l l C a r a b i d s and S t a p h y l i n i d s found on L i t t l e Cayman a r e f u l l y winged and a l l
s p e c i e s were t a k e n a t l i g h t a t n i g h t . The g e n e r a l l y s m a l l s i z e of t h e s p e c i e s i s d i s c u s s e d above.
Another e c o l o g i c a l g r o u p of b e e t l e s w e l l - r e p r e s e n t e d on L i t t l e Cayman c o m p r i s e s s p e c i e s t h a t f e e d a s l a r v a e i n wood and Cerambycidae a r e e s p e c i a l l y common. B e e t l e b o r i n g s were n o t e d i n s t e m s of
A v i c e n n i a
,
C o n o c a r p u s and R h i z o p h o r a.
LEPIDOPTERA
R h o p a l o c e r a 23 s p e c i e s ( d e t a i l s e l s e w h e r e )
S p h i n g i d a e 11 Noctuidae 45 P e r i c o p i d a e 1 Syntomidae 4
C o s s i d a e 1 Notodontidae 1
A g a r i s t i d a e 1 Psychidae 1 A r c t i i d a e 2 Geometridae 1 3
P y r a l i d a e 15 ' M i c r o l e p i d o p t e r a ' 39 Family ? 1 6
Family i d e n t i f i c a t i o n s of t h e - m o t h s , p a r t i c u l a r l y M i c r o l e p i d o p t e r a , a r e a s y e t i n c o m p l e t e . There a r e p r o b a b l y many more s p e c i e s of t h e s m a l l e r moths t h a n a r e l i s t e d h e r e ; many were c a u g h t i n t h e l i g h t t r a p and have been b a d l y damaged by t h e enormous numbers of a n t s and
C o r i x i d s t h a t were a l s o c a p t u r e d . P r o p e r i n v e s t i g a t i o n of t h e M i c r o l e p i d o p t e r a r e q u i r e s a s p e c i a l i s t a b l e t o s t u d y them f u l l - t i m e .
f e a t u r e of t h e l i g h t t r a p c o l l e c t i o n s was t h e abundance of s m a l l i i l ~ t i l s and of -the l a r g e r S p h i n g i d a e . The i n t e r m e d i a t e s i z e r a n g e
a p p e a r e d -to be u n d e r - r e p r e s e n t e d corr~ppared w i t h samples fro-n! t e n p e r a t e Europe. Most of the Noctuidae a r e s m a l l , b u t a s i n g l e specimen o f t h e v e r y i a r y e A s c a l a p k i o d o r a k a (L, j was found dea.d i n t h e house a t P i r a t e ' s P o i n t , J o r d a n (1940j l i s t s f i v e s p e c i e s of Sphingid from L i t t l e Cayman, a l l of which were t a k e n a g a i n i n 1975 t o g e t h e r w i t h s i x more s p e c i e s .
A number of s p e c i e s c a p t u r e d a t o u t s i d e e l e c t r i c l i g h t s were n o t r e p r e s e n t e d i n t h e l i g h t t r a p samples. Some of t h e s e were among t h e most c o l o u r f u l s p e c i e s found and i n c l u d e d N o r o p s i s h i e r o y l y p h i c a C r . and X a n t h o p a s t i s t i m a i s C r . ( N o c t u i d a e ) .
Two b r i g h t l y c o l o u r e d d a y - f l y i n g s p e c i e s , C o m p o s i a f i d e l i s s i m a B.-S. ( P e r i c o p i d a e ) and U t e t h e i s a s p e c i e s ( A r c t i i d a e )
,
were f r e q u e n t l y s e e n , and a n o t h e r A r c t i i d , C a l i d o t a s t r i g o s a W I k . , was c a p t u r e d b o t h i n t h e l i g h t t r a p and a t t h e house l i g h t s .Psychodidae 1 s p e c i e s Ceratopogonidae 4 S c i a r i d a e 3
S t r a t i o m y i d a e 3 A s i l i d a e 1 T h e r e v i d a e 3
Dolichopodidae 8
O t i t i d a e 7 S e p s i d a e 1 Lonchaeidae 3 D r o s o p h i l i d a e 1 Agromyzidae 3 A s t e i i d a e 1+
S t r e b l i d a e 1 Sarcophagidae 5 Muscidae 3
C u l i c i d a e 6 s p e c i e s Chironomidae 1 Cecidomyiidae 3 Tabanidae 2 Empididae 1 Bombyliidae 6 S y r p h i d a e 4 T e p h r i t i d a e 5 Lauxaniidae 4 Ephydridae 3 C h l o r o p i d a e 9 C l u s i i d a e 1
Hippoboscidae 1
C a l l i p h o r i d a e 2 T a c h i n i d a e 9
I n terms of numbers of i n d i v i d u a l s , t h e C u l i c i d a e i s p r o b a b l y t h e most abundant i n s e c t f a m i l y on t h e i s l a n d . A e d e s t a e n i o r h y n c h u s swarmed everywhere e x c e p t on t h e beaches and i n t h e c e n t r a l f o r e s t . I t was e s p e c i a l l y abundant i n mangroves and a t t h e edges of t h e
b r a c k i s h l a g o o n s , and females would f e e d a t any time of day, sometimes on being d i s t u r b e d from v e g e t a t i o n . Numbers i n c r e a s e d n o t i c e a b l y on 26th J u l y , t h r e e days a f t e r t o r r e n t i a l r a i n . No s p e c i a l e f f o r t was made t o c o l l e c t mosquitoes on L i t t l e Cayman. The Mosquito Research and C o n t r o l U n i t has r e c o r d e d 17 s p e c i e s from L i t t l e Cayman and 29 s p e c i e s from neighbouring Cayman Brac (M.E.C. G i g l i o l i , p e r s . comm.).
Of t h e h i g h e r f l i e s , t h e o n l y conspicuous s p e c i e s a r e t h e
Bombyliids. These were t o be seen hovering over v e g e t a t i o n o r r e s t i n g on t h e ground, and t h e y seem t o occupy t h e p l a c e f i l l e d by Syrphidae i n temperate r e g i o n s . Syrphids a r e r a t h e r s c a r c e a l t h o u g h a l a r g e s p e c i e s was f r e q u e n t l y s e e n , e s p e c i a l l y i n t h e i n t e r i o r of t h e i s l a n d , A s p e c i e s of i f i c r o d o n was t a k e n i n some numbers i n t h e Malaise t r a p , b u t n o t observed e l s e w h e r e , A T a b a n u s f l e w around members of t h e p a r t y s t i l l wet a f t e r b a t h i n g i n t h e s e a b u t no o t h e r D i p t e r a were conspicuous i n t h e f i e l d and t h e numbers of s p e c i e s c a p t u r e d i n t h e Malaise t r a p was somewhat unexpected. C h l o r o p i d s , Dolichopodids and T a c h i n i d s were f a m i l i e s r e p r e s e n t e d by most s p e c i e s i n t h e Malaise t r a p . Some of t h e s p e c i e s of Sarcophagidae and T a c h i n i d a e a r e grey and b l a c k f l i e s w i t h r e d d i s h a p i c e s t o t h e i r abdomens, and t h e y s u p e r f i c i a l l y resemble two Sphecid wasps w i t h s i m i l a r c o l o u r a t i o n .
Two s p e c i e s e c t o p a r a s i t i c on v e r t e b r a t e s were found. The
Hippoboscid was c o l l e c t e d i n t h e Malaise t r a p ; t h e S t r e b l i d was t a k e n from a specimen of t h e b a t M a c r o t u s w a t e r h o u s i i Gray.
HYMENOPTERA
Braconidae 11 s p e c i e s Eulophidae 1 0
E n c y r t i d a e 1 Torymidae 5 Eurytomidae 2 Cynipidae 2 S c e l i o n i d a e 3 B e t h y l i d a e 1 M u t i l l i d a e 1 Formicidae 19
Pompilidae 1
Megachilidae 1
H a l i c t i d a e 2
Ichneumonidae 3 s p e c i e s Elasmidae 3
Eupelmidae 1
Pteromalidae 4 C h a l c i d i d a e 1
Ceraphronidae 1
D i a p r i i d a e 1 T i p h i i d a e 1
Rhopalosomatidae 1
Vespidae 1
Sphecidae 8 C o l l e t i d a e 1
Formicidae dominate t h e hymenopterous fauna on L i t t l e Cayman and a r e probably exceeded i n numbers of i n d i v i d u a l s o n l y by C u l i c i d a e and C o r i x i d a e . A l l of t h e wasp s p e c i e s found (Sphecidae, Pompilidae, Vespidae, Rhopalosomatidae, M u t i l l i d a e , T i p h i i d a e ) were f r e q u e n t t o abundant, b u t t h e b e e s ( C o l l e t i d a e , H a l i c t i d a e , Megachilidae) were s c a r c e .
Two Bembicine ( S p h e c i d a e ) wasps were e s p e c i a l l y numerous, t h e l a r g e S t i c t i a s i g n a t a (L.) and a s m a l l e r s p e c i e s . The former i s w i d e s p r e a d on t h e i s l a n d and n e s t s i n c o l o n i e s i n s a n d y ground where d a p p l e d shade i s p r o v i d e d by t r e e s and s h r u b s . The s m a l l e r Bembicine s p e c i e s i s found a r o u n d t h e c o a s t b u t n o t i n t h e i n t e r i o r , a g a i n n e s t i n g i n s a n d y ground b u t u s u a l l y where t h e r e i s no s h a d e .
Of i n t e r e s t i s t h e f a c t t h a t f i v e o f t h e t h i r t e e n wasp s p e c i e s p r o v i s i o n t h e i r n e s t s w i t h c r i c k e t s which a r e w e l l - r e p r e s e n t e d on L i t t l e Cayman. These a r e t h e Rhopalosomatid, a g e n e r a l l y r a r e group b u t one s p e c i e s o f which was t a k e n i n some numbers a t n i g h t i n t h e M a l a i s e t r a p and l i g h t t r a p , and f o u r S p h e c i d s p e c i e s (two L a r r i n i , two C h l o r i o n i n i
-
S p h e x s p . and P r i o n y x s p . ) . Of t h e r e m a i n i n g wasps, t h r e e p r e y upon E n d o p t e r y g o t e l a r v a e ( t h e Vespid (Eumeninae),
M u t i l l i d and T i p h i i d ) , t h r e e upon f l i e s ( t h e two Bembicini and one O x y b e l i n i ) , and two upon s p i d e r s ( t n e P o m p i l i d and S c e l i p h r o n j a m a i c e n s e (F,) ) .The m a j o r i t y o f s p e c i e s o f p a r a s i t i c Hymenoptera was o b t a i n e d w h i l s t s w e e p - n e t t i n g on t h e d i s t u r b e d ground of t h e o l d c o a s t a l
p l a n t a t i o n s . I n g e n e r a l t h e y a r e r a t h e r s c a r c e , a n o p i n i o n r e i n f o r c e d by t h e s m a l l n u v b e r s c a u g h t i n t h e M a l a i s e t r a p . Only B r a c o n i d a e and E u l o p h i d a e were r e p r e s e n t e d by f a i r l y l a r g e numbers o f s p e c i e s , and t h e i r r e l a t i v e l y h i g h f r e q u e n c y i s p r o b a b l y r e l a t e d t o t h e many s p e c i e s of M i c r o l e p i d o p t e r a found on t h e i s l a n d . Ichneumonidae a r e
d i s t i n c t l y s c a r c e and it i s s u g g e s t e d t h a t t h e i r n i c h e on L i t t l e Cayman i s o c c u p i e d b y t h e r a t h e r l a r g e number of T a c h i n i d ( D i p t e r a ) s p e c i e s .
No s p e c i e s o f Symphyta was f o u n d .
Sweep-net samples
E l e v e n samples were c o l l e c t e d w i t h a sweep-net a t v a r i o u s
l o c a l i t i e s and on d i f f e r e n t d a t e s . No a t t e m p t was made t o s t a n d a r d i s e t h e amount of t i m e s p e n t i n c o l l e c t i n g e a c h sample. C a t c h e s were s m a l l . I n s e v e n o f t h e s a m p l e s , Hemiptera H e t e r o p t e r a a r e t h e most numerous g r o u p , i n two Hemiptera Homoptera, and i n one e a c h C o l e o p t e r a and Hymenoptera P a r a s i t i c a .
J a n z e n and Pond (1975) p r e s e n t d a t a from s t a n d a r d i s e d sweep-net s a m p l e s of s e c o n d a r y v e g e t a t i o n i n England and Michigan (U.S.A.).
T h e i r c a t c h e s from Michigan a r e shown i n t a b l e 1 4 t o g e t h e r w i t h t h e t o t a l L i t t l e Cayman c a t c h . Although d e t a i l e d c o m p a r i s o n s between t h e two samples c a n n o t be made b e c a u s e of d i f f e r e n c e s i n c o l l e c t i n g
methods, it i s l i k e l y t h a t t h e more marked d i s p a r i t i e s r e f l e c t r e a l d i f f e r e n c e s between t h e two a r e a s . P e r c e n t a g e r e p r e s e n t a t i o n o f
e x o p t e r y g o t e s i s g r e a t e r i n t h e Cayman s a m p l e s ; o f e n d o p t e r y g o t e g r o u p s o n l y Hymenoptera A c u l e a t a and C o l e o p t e r a on L i t t l e Cayman s l i g h t l y e x c e e d t h e i r r e p r e s e n t a t i o n i n t h e Michigan samples. S p e c i e s o f D i p t e r a a r e markedly l e s s w e l l - r e p r e s e n t e d i n t h e Cayman samples.
J a n z e n and Pond compare t h e i r t e m p e r a t e l a t i t u d e s a m p l e s w i t h t h o s e c o l l e c t e d i n a comparable manner i n C o s t a R i c a , a n d draw a t t e n t i o n t o
T a b l e 14. P e r c e n t a g e composition of sweep-net samples from L i t t l e Cayman compared w i t h t h o s e r e p o r t e d by Janzen and Pond
(1975) from Michigan, U . S.A.
O r t h o p t e r a P s o c o p t e r a
Bern. H e t e r o p t e r a Hem, Bornoptera Thysanoptera Neuroptera C o l e o p t e r a Mecopcera L e p i d o p t e r a D i p t e r a
Hym. A c u l e a t a H y m . P a r a s i t i c a
N
L i t t l e Cayman s p e c i e s i n d i v i d u a l s
Michigan
s p e c i e s i n d i v i d u a l s
1 . 6 0 . 8
0 0
7 . 5 1 2 . 1 13-2" 27,E 3
'
many "0 0
3 . 1 5,O
0 . 3 0. L
4.7 0.8
32.7 1 6 . 1
*
Excluding a p h i d st h e preponderance o f O r t h o p t e r a and o t h e r l a r g e e x o p t e r y g o t e s i n t h e t r o p i c a l sample. They s u g g e s t a s a r e a s o n t h e l a c k of s e a s o n a l c o n s t r a i n t s upon growth i n t h e t r o p i c s . The s m a l l e r e x o p t e r y g o t e s
(Homoptera and T h y s a n o p t e r a ) a r e p r o b a b l y b e t t e r r e p r e s e n t e d i n t e m p e r a t e r e g i o n s , a l t h o u g h a p h i d s have been claimed (Janzen, 1973) t o b e a prominent f e a t u r e of t h e i n s e c t f a u n a o f Caribbean i s l a n d s . T h i s i s c e r t a i n l y n o t t h e c a s e on L i t t l e Cayman where t h e p a u c i t y of a p h i d s r e s e m b l e s t h e s i t u a t i o n i n C o s t a R i c a (Janzen & Pond, 1 9 7 5 ) .
Ants a r e r e l a t i v e l y v e r y abundant i n t h e t r o p i c s ; e l e v e n of t h e t w e l v e s p e c i e s of a c u l e a t e Hymenoptera i n t h e sweep-net samples from L i t t l e Cayman a r e a n t s and t h e y comprise a l l b u t one of t h e a c u l e a t e i n d i v i d u a l s swept. I n Michigan o n l y e l e v e n o f t h e t w e n t y - s i x
a c u l e a t e s p e c i e s c o l l e c t e d by Janzen and Pond a r e a n t s .
The abundance o f p a r a s i t i c Hymenoptera i n t e m p e r a t e l a t i t u d e s , compared w i t h t h e i r s t a t u s i n t h e t r o p i c s , i s o f t e n remarked upon.
Although i t was my i m p r e s s i o n t h a t P a r a s i t i c a were s c a r c e on L i t t l e
Cayman, t h e y d i d f e a t u r e q u i t e p r o m i n e n t l y i n t h e sweep-net
c o l l e c t i o n s . I t i s p o s s i b l e , however, t h a t t h e r e was some s a m p l i n g b i a s t o w a r d s t h e i r c o l l e c t i o n .
The e s t i m a t e d s p e c i e s d i v e r s i t y o f t h e L i t t l e Cayman s a m p l e s i s l e s s t h a n t h a t of t h e Michigan s a m p l e s . M a r g a l e f ' s i n d e x o f s p e c i e s d i v e r s i t y i s 2 0 . 8 f o r L i t t l e Cayman and 38.3 f o r Michigan, a l t h o u g h t h e Michigan v a l u e would p r o b a b l y b e lower i f a p h i d s and t h r i p s c o u l d b e i n c l u d e d i n i t s c a l c u l a t i o n . N e v e r t h e l e s s , t h e low v a l u e f o r L i t t l e Cayman i s r a t h e r s u r p r i s i n g and t e n d s t o c o n t r a d i c t t h e g e n e r a l r u l e t h a t t h e d i v e r s i t y o f t r o p i c a l f a u n a s i s g r e a t e r t h a n t h a t of t e m p e r a t e r e g i o n s .
M a l a i s e t r a p samples
The IJlaldlse t r a p was o p e r a t e d f o r e i g h t ! m n - c o n s e c u t ~ v e 24-hour p e r i o d s and f o r f l v e a d d i t i o n a l d a y t i m e ( 6 , 0 0
-
1 6 , 0 0 h o u r s ) p e r i o d s , T o m 1 c a t c h e s o b t a i n e d a r e g i v e n l n t a b l e 1 5 a n d , f o r comparison,d a t a p r e s e n t e d by Matthews tl Matthews (1971) f o r Surinam and Kansas, T h e s e l a t t e r f i g u r e s c a n be compared t o , and be s e e n t o a g r e e c l o s e l y w i t h , t h e 24-hour c a t c h e s p e r c e n t a g e r e p r e s e n t a t i o c o f o r d e r s by
i n d i v i d u a l s on L i t t l e Cayman. The Kansas sample (Marston, 1965) was o b t a i n e d o v e r a l e n g t h of t i m e s i m i l a r t o t h a t f o r t h e L i t t l e Cayman sample, and i t i s i n t e r e s t i n g t h a t t h e t o t a l numbers o f i n s e c t s c a u g h t a t t h e two p l a c e s a r e a l s o f a i r l y c l o s e .
D i p t e r a a r e t y p i c a l l y t h e dominant o r d e r i n M a l a i s e t r a p s a m p l e s , w i t h Hymenoptera g e n e r a l l y o c c u p y i n g t h e second p o s i t i o n (Matthews &
Matthews, 197'1). I n t h e L i t t l e Cayman samples D i p t e r a a r e t h e most a b u n d a n t o r d e r , b u t second p l a c e i s s h a r e d by Hemiptera and
Hymenoptera, r e i n f o r c i n g t h e view s u g g e s t e d by t h e sweep-net samples t h a t c e r t a i n Remiptera a r e p a r t i c u l a r l y w e l l - r e p r e s e n t e d on L i t t l e Cayman. The Surinam sample i n c l u d e s few Hemiptera.
From t h e daytime c a t c h of 900 i n s e c t s i n 60 h o u r s i t c a n b e e s t i m a t e d t h a t t h e 24-hour c a t c h e s o f 2149 i n s e c t s a r e composed of a p p r o x i m a t e l y t w i c e a s many i n s e c t s c a u g h t d u r i n g d a y l i g h t t h a n a t n i g h t . D i f f e r e n c e s i n p e r c e n t a g e r e p r e s e n t a t i o n between t h e 12-hour and 24-hour c a t c h e s c o n c e r n e s p e c i a l l y D i p t e r a , w i t h Nematocera, p a r t i c u l a r l y C u l i c i d a e , b e i n g more a c t i v e a t n i g h t and o t h e r f l i e s b e i n g c a u g h t m o s t l y d u r i n g d a y t i m e . A c u l e a t e Hymenoptera a r e a l s o r e l a t i v e l y most f r e q u e n t i n t h e d a y t i m e c a t c h , b u t t h e l a r g e r
p e r c e n t a g e s o f L e p i d o p t e r a , C o l e o p t e r a and O r t h o p t e r a i n t h e 24-hour c a t c h e s i n d i c a t e t h a t t h e y , l i k e t h e Nematocera, a r e p r e d o m i n a n t l y n o c t u r n a l l y a c t i v e .
On 2 0 t h J u l y t h e M a l a i s e t r a p was e m p t i e d a t 6.00 a.m. a n d t h e n c e e v e r y two h o u r s u n t i l 6 . 0 0 p.m. The g r e a t e s t number of D i p t e r a was o b t a i n e d i n t h e pre-noon p e r i o d w i t h a d e p r e s s i o n i n numbers d u r i n g m i d - a f t e r n o o n . T h i s p a r a l l e l s t h e f l y i n g a c t i v i t y o f b u t t e r f l i e s d i s c u s s e d e l s e w h e r e . C o n v e r s e l y , Hymenoptera a t t a i n maximum a c t i v i t y i n m i d - a f t e r n o o n , u s u a l l y t h e h o t t e s t t i m e o f day.
T a b l e 15. P e r c e n t a g e c o m p o s i t i o n o f M a l a i s e t r a p samples from L i t t l e Cayman, and from Surinam and Kansas (Matthews & Matthews, 1 9 7 1 ) .
L i t t l e Cayman Surinam Kansas
24 h r . p e r i o d s 1 2 h r . ( d a y ) p e r i o d s
Odonata
s p p . i n d s . s p p . i n d s .
-
P- -
0 . 6 0 . 1 0 0
i n d i v i d u a l s
<o*
1 0 . 1O r t h o p t e r a 2.9 0 . 8 1 . 0 0 . 1 1 . 7 0 . 5
Dermaptera 0 . 6 0 . 1 0 0 0 0
P s o c o p t e r a 0 . 6 < O * l 1 . 0 0 . 1 0 . 1 0
I i e t e r o p t e r s 1 . 8 0 . 1 2 . 9 0 . 4 )
Hornopt e r a 7 . 6 1 2 , 2 6 . 7 6 . 0 )
N e u r o p t e r a 0 . 6 0 . 1 0 0
C o l e o p t e r a 1 7 . 6 4.8 9 . 6 1 . 3
D i p t . Nematocera 5 . 9 35.9 3.8 3 , 2 )
I 5 8 . 0 6 6 . 3
Hym. P a r a s i t i c a 4.7 0 . 5 3.8 0 . 6 )
) 1 9 . 0 1 2 . 3
Hym. A c u l e a t a 1 0 . 0 1 1 . 8 1 3 . 5 1 7 . 1 )
L e p i d o p t e r a 1 6 . 5 9 . 0 9.6 2.6 1 4 . 0 4.8
M a r g a l e f ' s i n d e x o f s p e c i e s d i v e r s i t y i s 2 2 - 0 f o r t h e 24-hour samples and 1 5 . 1 f o r t h e daytime samples.
Mercury vapour l i g h t t r a p samples ( ~ a c r o l e p i d o p t e r a )
Data on t h e numbers of s p e c i e s and i n d i v i d u a l s of M a c r o l e p i d o p t e r a c a u g h t i n t h e same t y p e of t r a p a s t h a t used on L i t t l e Cayman a r e
a v a i l a b l e f o r a n E n g l i s h s i t e (Woodchester P a r k , G l o u c e s t e r s h i r e )
.
On L i t t l e Cayman, 457 i n d i v i d u a l s of M a c r o l e p i d o p t e r a b e l o n g i n g t o 66 s p e c i e s were c a u g h t a t P i r a t e ' s P o i n t o v e r a p e r i o d of t e n n i g h t s (37 h o u r s ) . The s p e c i e s d i v e r s i t y v a l u e s a r e 10.6 ( M a r g a l e f ) and 2023
( W i l l i a m s ) . These a r e g r e a t e r t h a n t h o s e o b t a i n i n g i n any y e a r a t Woodchester P a r k where t r a p s were o p e r a t e d i n p e r i o d s d u r i n g J u n e o r J u l y ( t a b l e 1 6 ) . The E n g l i s h samples r e s u l t e d from a l l - n i g h t
c o l l e c t i o n s , whereas t h e L i t t l e Cayman samples were b i a s e d t o w a r d s moths f l y i n g i n t h e e a r l y p a r t of t h e n i g h t . T h i s b i a s would
p r o b a b l y d e p r e s s t h e s p e c i e s d i v e r s i t y i n d i c e s f o r L i t t l e Cayman and
T a b l e 16. Comparison of l i g h t t r a p c a t c h e s of M a c r o l e p i d o p t e r a on L i t t l e Cayman and a t Woodchester P a r k , G l o u c e s t e r s h i r e , England.
Numbers o f E s t i m a t e s of s p e c i e s d i v e r s i t y spp. i n d s . m o t h s / t r a p / h r . Williams Margalef - -
Woodchester 1968 73 2783 107 1425 9 . 1
L i t t l e Cayman 1975 66 45 7 12 2W3
-
1 0 . 6t h e f i g u r e s may be t a k e n t o i n d i c a t e a t r u l y h i g h e r d i v e r s i t y of M a c r o l e p i d o p t e r a on L i t t l e Cayman. On L i t t l e Cayman moths were c a p t u r e d a t t h e low r a t e of o n l y t w e l v e an h o u r , and t h i s compares u n f a v o u r a b l y w i t h t h e r a t e of c a p t u r e a t t h e E n g l i s h s i t e , a l t h o u g h comparisons of t h e s e f i g u r e s a r e o f d o u b t f u l v a l u e because s o many v a r i a b l e f a c t o r s a r e i n v o l v e d .
The s i n g l e n i g h t ' s t r a p p i n g i n t h e c e n t r a l f o r e s t s o u t h of Sparrowhawk H i l l y i e l d e d 90 M a c r o l e p i d o p t e r a of 25 s p e c i e s . T h i s i s t o o s m a l l a sample t o g i v e a r e l i a b l e d i v e r s i t y e s t i m a t e , b u t i t i s i n t e r e s t i n g t h a t e i g h t of t h e s p e c i e s were n o t c a u g h t a t P i r a t e ' s P o i n t . These a r e s p e c i e s b e l o n g i n g t o f a m i l i e s o t h e r t h a n S p h i n g i d a e and Noctuidae; a l l S p h i n g i d s and Noctuids c a u g h t i n t h e c e n t r a l f o r e s t were found a l s o a t P i r a t e s s P o i n t , p e r h a p s a d e m o n s t r a t i o n o f t h e
s t r o n g - f l y i n g , d i s p e r s i v e f l i g h t - a c t i v i t y i n t h e s e two f a m i l i e s . Comparison of c o l l e c t i n g methods
The numbers o f s p e c i e s c a u g h t by g e n e r a l c o l l e c t i n g ( a s d e f i n e d on page 9 7 ) , t h e M a l a i s e t r a p and t h e l i g h t t r a p a r e shown i n t a b l e 17.
Most s p e c i e s were c a u g h t by g e n e r a l c o l l e c t i n g , f e w e s t i n t h e M a l a i s e t r a p . The M a l a i s e t r a p , however, c a u g h t c o n s i d e r a b l y more D i p t e r a t h a n were t a k e n by e i t h e r of t h e o t h e r two methods, w h i l s t most s p e c i e s of b o t h C o l e o p t e r a and L e p i d o p t e r a w e r e c a p t u r e d i n t h e l i g h t t r a p . G e n e r a l c o l l e c t i n g y i e l d e d most s p e c i e s o f t h e o t h e r g r o u p s . The h i g h numbers of C o l e o p t e r a and Hemiptera t a k e n i n t h e l i g h t t r a p a r e
noteworthy and may b e r e l a t e d t o a h i g h i n c i d e n c e o f n o c t u r n a l a c t i v i t y i n t h e s e o r d e r s . Hemiptera, a t l e a s t , a r e g e n e r a l l y c o n s i d e r e d a s p r e d o m i n a n t l y d i u r n a l i n s e c t s . M a l a i s e t r a p samples a l s o s u g g e s t t h a t many i n s e c t s on L i t t l e Cayman a r e n o c t u r n a l . The o b v i o u s e x p l a n a t i o n i s t h e h i g h d e n s i t y of d a y - a c t i v e l i z a r d s on t h e i s l a n d .
S i n c e t h e M a l a i s e t r a p was o p e r a t e d o n l y a t P i r a t e s ' P o i n t , and t h e l i g h t t r a p m o s t l y a t t h i s s i t e , i t i s n o t s u r p r i s i n g t h a t s e v e n t y - f o u r p e r c e n t o f s p e c i e s found on L i t t l e Cayman were t a k e n a t P i r a t e ' s P o i n t . F o r t y - n i n e p e r c e n t were found e l s e w h e r e on t h e i s l a n d , twenty- t h r e e p e r c e n t b e i n g c a p t u r e d a t b o t h P i r a t e ' s P o i n t and e l s e w h e r e .
D i s c u s s i o n
The s i z e of t h e i n s e c t f a u n a o f L i t t l e Cayman i s p r o b a b l y i n a c c o r d w i t h t h e a r e a of t h e i s l a n d . B r a c k i s h l a g o o n s occupy a c o n s i d e r a b l e p a r t of t h e i s l a n d and i n s e c t s a b l e t o d e v e l o p i n t h e i r w a t e r s comprise a major e l e m e n t i n t h e entomofauna. C u l i c i d a e , C o r i x i d a e and Odonata may be c i t e d i n t h i s r e s p e c t . Of t e r r e s t r i a l g r o u p s , a t t e n t i o n h a s been drawn a l r e a d y t o t h e abundance of most g r o u p s of e x o p t e r y g o t e i n s e c t s , O r t h o p t e r a t e n d e d t o o c c u r i n t h e u i ? d i s t . u b e d i n t e r i o r of t h e i s l a n d , b u t t h e insj o r i t y of Hemipteira were found a r o u n d t h e c o a s t and many may w e l l owe t h e i r p r e s e n c e on L i t t l e Cayman t o t h e a f f e c t man h a s had on t h e c o a s t a l . v e g e t a t i o n , Many e n d o p t e r y g o t e s p e c i e s a l s o were fousld o n l y on t h e d i s t u r b e d ground of t h e c o a s t a l s t r i p ; t h i s i s t r u e e s p e c i a l l y f o r p a r a s i t i c Hymenoptera. C o l e o p t e r a and D i p t e r a were w i d e s p r e a d b u t , a l t h o u g h q u i t e r i c h i n s p e c i e s a n d f a m i l i e s , w i t h t h e e x c e p t i o n of mosquitoes seemingly i n r e l a t i v e l y low numbers. T h i s a p p a r e n t l y h i g h d i v e r s i t y i s e x p e c t e d i n a t r o p i c a l r e g i o n a l t h o u g h i t c a n be q u a n t i t a t i v e l y shown o n l y f o r M a c r o l e p i d o p t e r a . S p e c i e s d i v e r s i t y i n M a l a i s e t r a p and sweep-net samples i s n o t h i g h .
Two b i o t i c f e a t u r e s of L i t t l e Cayman p r o b a b l y have an u n u s u a l l y s t r o n g i n f l u e n c e on t h e entomofauna. These a r e t h e abundance of l a n d c r a b s and a r b o r e a l l i z a r d s , t h e p o s s i b l e e f f e c t s of which a r e
d i s c u s s e d above.
On s p e c i f i c i d e n t i f i c a t i o n s s o f a r made, i t a p p e a r s t h a t L i t t l e Cayman s h a r e s much of i t s i n s e c t f a u n a w i t h Cuba and Jamaica. The
seemingly low i n c i d e n c e of endemism i s p r o b a b l y a p r o d u c t of a r e l a t i v e l y s h o r t s e a d i s t a n c e ( a b o u t 200 km.) s e p a r a t i n g L i t t l e Cayman from Cuba and Jamaica, t o g e t h e r w i t h a h i g h i n c i d e n c e of v e r y s t r o n g winds i n t h e r e g i o n . Only a v e r y few f l i g h t l e s s s p e c i e s were found.
Three a r e a s on L i t t l e Cayman a r e of s p e c i a l i n t e r e s t i n
s u p p o r t i n g s p e c i e s n o t found e l s e w h e r e and i n h a v i n g a n a p p a r e n t l y unmodified f l o r a . These a r e a s a r e t h e c e n t r a l f o r e s t s o u t h o f
Sparrowhawk H i l l , t h e Sesuvium marsh a t t h e e a s t e r n e n d of ' t h e i s l a n d , and t h e i n t e r i o r s c r u b a d j a c e n t t o t h e n o r t h s h o r e t r a c k a b o u t one k i l o m e t r e n o r t h of Blossom V i l l a g e . I t i s i n t h e s e a r e a s t h a t endemic s p e c i e s a r e most l i k e l y t o o c c u r .
T a b l e 1 7 . Numbers of s ~ e c i e s c a u a h t bv d i f f e r e n t methods on L i t t l e Cayman.
F i g u r e s i n p a r e n t h e s e s show t h e numbers of s p e c i e s c a u g h t o n l y by t h e method i n d i c a t e d , and t h e p e r c e n t a g e s a r e of t h e number of s p e c i e s c a u g h t by each method o u t of t h e t o t a l number of s p e c i e s found on t h e i s l a n d b e l o n g i n g t o t h e group.
General c o l l e c t i n g Malaise t r a p L i g h t t r a p s p e c i e s
A p t e r y g o t a , E x o p t e r y g o t a ( e x c l , Hemiptera)
H e t e r o p t e r a Hornoptera Neuroptera C o l e o p t e r a L e p i d o p t e r a D i p t e v a Hymenoptera
s p e c i e s % s p e c i e s %
Acknowledgements
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Matthews, R.W. & Matthews, J . R . 1971. The M a l a i s e t r a p : i t s u t i l i t y and p o t e n t i a l f o r sampling i n s e c t p o p u l a t i o n s . Michigan Entomol. 4 : 117-122.
N u m b e r o f s p e c i e s 0
0 I 0 0 I I-
F+ (D 0 -. -< (D
3-
3 - u
,-+
3
PI
2
F i g u r e 24. The p r o g r e s s i o n of i n s e c t s p e c i e s r e c o r d e d on L i t t l e Cayman by d a t e s . F u l l c i r c l e s s i g n i f y d a t e s on which h a l f t h e f i n a l t o t a l of s p e c i e s i n each group were found.
The l i g h t t r a p was f i r s t o p e r a t e d on 1 4 J u l y , t h e Malaise t r a p on 16 J u l y , and t h e main c e n t r a l f o r e s t c o l l e c t i o n s were made on 28 J u l y
