Nematocera (Ceratopogonidae, Psychodidae, Simuliidae and

Rev. sci. tech. Off. int. Epiz., 1994 ,13 (4), 1175-1199

Nematocera (Ceratopogonidae, Psychodidae, Simuliidae and Culicidae) and

control methods Y. BRAVERMAN *

Summary: The biology, veterinary importance and control of certain Nematocera are described and discussed.

Cul ico ides spp. (family Ceratopogonidae) transmit the arboviruses of bluetongue (BT), African horse sickness (AHS), bovine ephemeral fever (BEF) and Akabane. Some other arboviruses have been isolated from these species, while fowl pox has been transmitted experimentally by Cu l ico ides . These insects are vectors of the parasitic protozoans Leucocytozoon caulleryi and H a e m o p r o t e u s ne t t ion i s , and the parasitic nematodes O n c h o c e r c a gut turosa , O . g ibsoni and O . cervical is . They also cause recurrent summer hypersensitivity in horses, ponies, donkeys, cattle and sheep.

Farm animals can die as a result of mass attack by Simulium spp., which are also vectors of Leucocytozoon simondi, L. smithi and the filariae O. gutturosa, O. linealis and O. ochengi. Venezuelan equine encephalomyelitis (VEE) and Rift Valley fever (RVF) have been isolated from simuliids, and vesicular stomatitis virus New Jersey strain has been replicated in S imul ium vi t ta tum. Simuliids are well known as vectors of O. volvulus , the cause of human onchocercosis (river blindness).

The family Psychodidae includes the genera P h l e b o t o m u s and Lu tzomyia (subfamily Phlebotominae), vectors of Le i shmania spp. in humans, dogs and other mammals. Vesicular stomatitis virus Indiana strain has been regularly isolated from phlebotomine sandflies.

Mass attack by mosquitoes can also prove fatal to farm animals. Mosquitoes are vectors of the viruses of Akabane, BEF, RVF, Japanese encephalitis, VEE, western equine encephalomyelitis, eastern equine encephalomyelitis and west Nile meningoencephalitis, secondary vectors of AHS and suspected vectors of Israel turkey meningoencephalitis. The viruses of hog cholera, fowl pox and reticuloendotheliosis, the rickettsiae E p e r y t h r o z o o n ovis and E . suis, and the bacterium B o r r e l i a a n s e r i n a are mechanically transmitted by mosquitoes. These insects also induce allergic dermatitis in horses. They transmit several filarial worms of both animals and humans, and are of great medical importance as vectors of major human diseases, including malaria, yellow fever, dengue fever and many more diseases caused by arboviruses.

K E Y W O R D S : An ima l diseases - Culicidae - Culicoides - Disease control -Phlebotomus - Simulium - Vectors.

* The Kimron Veterinary Institute, P.O. Box 12,50250 Beit Dagan, Israel.

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CERATOPOGONIDAE

I N T R O D U C T I O N

T h e f ami ly C e r a t o p o g o n i d a e i n c l u d e s 78 g e n e r a a n d s u b g e n e r a , compr i s ing a p p r o x i m a t e l y 3 ,900 s p e c i e s , b u t in o n l y f o u r g e n e r a a r e f e m a l e s k n o w n t o feed on w a r m - b l o o d e d an imals ( 4 6 , 9 6 , 1 1 6 ) . T h e largest a n d bes t k n o w n genus is Culicoides, the o n l y g e n u s of r e a l v e t e r i n a r y i m p o r t a n c e , w h i c h i n c l u d e s v e c t o r s of i m p o r t a n t p a t h o g e n s to m a m m a l s ( including h u m a n s ) a n d b i rds . S o m e of t h e o t h e r blood-sucking g e n e r a , wh ich will n o t b e discussed h e r e , a r e t r o u b l e s o m e pes t s for h u m a n s . Culicoides compr i se s a p p r o x i m a t e l y 1,000 species , d i s t r ibu ted f rom the t ropics t o t h e subarc t ic and f r o m sea l eve l t o 4,200 m ( in T i b e t ) . Culicoides a r e m o s t c o m m o n l y k n o w n as 'biting m i d g e s ' or 'm idges ' . In t h e A m e r i c a s t h e y a r e k n o w n as ' n o s e e - u m s ' o r ' p u n k i e s ' , and in Aus t r a l i a a n d o t h e r coun t r i e s as ' sandfl ies ' .

B I O L O G Y

A d u l t s (47, 96) (Fig. 1d) m e a s u r e 1.5-5 m m long, wi th a small h e a d b e a r i n g a pair of p r o m i n e n t e y e s a n d a p a i r of r e l a t i v e l y l o n g a n t e n n a e w i t h f i f t een s e g m e n t s . The p l u m o s e a n t e n n a e of t h e m a l e s a r e a u d i t o r y o r g a n s , sens i t ive t o t h e f e m a l e wing-beat t o n e , w h i l e t h e f e m a l e s h a v e n o n - p l u m o s e a n t e n n a e . T h e p r o b o s c i s h a n g s down v e r t i c a l l y f r o m t h e h e a d . I n m a n y s p e c i e s , t h e t h o r a x is d o r s a l l y c o v e r e d w i t h black m a r k i n g s . T h e smal l e l o n g a t e d d e p r e s s i o n s , t e r m e d h u m e r a l p i t s , o n t h e f ron t dorsal p a r t of t h e t h o r a x , a r e t yp i ca l on ly of t h e g e n u s Culicoides. T h e s h o r t a n d relatively b r o a d wings lack scales, bu t in m a n y species a r e cove red with mic roscop ic ha i rs . Typical of Culicoides a n d o t h e r C e r a t o p o g o n i d s is t h e ' r -m c r o s s - v e i n ' . I n m o s t s p e c i e s , the w i n g s h a v e c o n t r a s t i n g d a r k a n d m i l k y w h i t e s p o t s , a n d w h e n a t r e s t t h e w ings are p l a c e d o v e r t h e a b d o m e n l i k e t h e b l a d e s of a c l o s e d p a i r of s c i s so r s . T h e legs are r e l a t ive ly s h o r t . T h e a b d o m e n of t h e f e m a l e h a s a r o u n d e d t ip , whi le t h a t of t h e male b e a r s a s m a l l p a i r of c l a s p e r s . M a l e a d u l t s g e n e r a l l y e m e r g e f r o m p u p a e b e f o r e the f e m a l e s . E m e r g i n g a d u l t s u s u a l l y fly o n l y a few h u n d r e d m e t r e s f r o m t h e i r larval h a b i t a t s , b u t a f l ight r a n g e of 4.0 k m h a s b e e n r e p o r t e d for C. variipennis (55). Culicoides, e spec ia l ly t h e high-f ly ing spec ies (20) , cou ld b e c a r r i e d by a i r s t r e a m s for h u n d r e d s of k i l o m e t r e s (19) . T h e first m a j o r func t ion of t h e a d u l t a f te r e m e r g e n c e is ma t ing , for which (in m a n y species) t he males form a swarm; individuals t h e n leave the s w a r m t o c o p u l a t e in flight wi th ind iv idua l a p p r o a c h i n g f ema les . S w a r m i n g is induced by v a r i o u s l a n d m a r k s s u c h as a b u s h o r t h e m a r g i n of a p o n d , o r e v e n t h e h e a d of an an ima l (27) . O n l y females suck b lood , f rom a var ie ty of m a m m a l i a n ( inc luding human) a n d a v i a n h o s t s . T h e b l o o d m e a l v o l u m e is of t h e o r d e r of 0 .139 µl a n d 0 .410 µl for C. imicola a n d C. zuluensis, r e s p e c t i v e l y ( 1 6 ) . S o m e s p e c i e s h a v e s t r o n g host p re fe rences , whi le o the r s will feed on a wide r r a n g e of hos ts . A u t o g e n o u s species exist, which d o n o t n e e d a b l o o d m e a l t o m a t u r e the i r first ba t ch of eggs (58), b u t all requi re a b l o o d m e a l t o m a t u r e s u b s e q u e n t ba t ches . B o t h sexes feed on na tu ra l ly -occur r ing sugar s o l u t i o n s . T h e b i t i n g ac t i v i t y of m o s t Culicoides s p p . is c r e p u s c u l a r (14 ) and/or n o c t u r n a l , b u t a few species a r e d iu rna l . T h e l eng th a n d n u m b e r of o v a r i a n cycles vary b e t w e e n spec ies , a n d d e p e n d o n t h e a m b i e n t cond i t ions . I n C. grisescens, four ovarian cyc les ( i .e . b l o o d f e e d i n g a n d o v i p o s i t i o n ) h a v e b e e n r e c o r d e d ( 3 6 ) , w h e r e a s three cycles h a v e b e e n o b s e r v e d for C. variipennis variipennis (68) . Such a life s p a n is long e n o u g h for any Culicoides-home p a t h o g e n to r e a c h t h e infec t ive s t age . T h e adu l t life

1177

Life cycle of Culicoides (96)

span of s o m e ind iv idua l s m a y e x t e n d t o 70 days (93) , whi le t h e n u m b e r of g e n e r a t i o n s per yea r d e p e n d s o n c l i m a t e a n d s p e c i e s . I n I s r a e l , C. imicola h a s b e e n r e p o r t e d t o produce e igh t g e n e r a t i o n s b e t w e e n Ju ly a n d D e c e m b e r , w i t h e a c h g e n e r a t i o n l as t ing approximately 23 days (18) . Culicoides lay 30-450 eggs d e p e n d i n g o n species , sou rce of blood ( h o s t ) a n d s e a s o n (9 , 4 7 ) . E a c h e g g is 3 5 0 - 5 0 0 µm l o n g a n d is d a r k in c o l o u r (Fig. l a ) . Eggs of m o s t species h a t c h af ter two to n i n e days a t f avourab le t e m p e r a t u r e s ; for e x a m p l e , C. imicola in s u m m e r t a k e s t h r e e d a y s ( 1 8 ) . N o r t h e r n s p e c i e s (e.g. C. grisescens) o v e r w i n t e r a n d h a t c h a f te r s e v e n t o n i n e m o n t h s (79) . E v a s i o n of dryness by aes t iva t ion h a s also b e e n r e c o r d e d (47) . E g g s a r e laid in w e t soil o r any sor t of semi-aquat ic h a b i t a t , e.g. decay ing p l a n t m a t e r i a l (15) . T h e r e a r e four la rva l ins ta rs and the fu l ly-grown la rva (Fig. l b ) is cy l indr ica l , wh i t i sh in c o l o u r a n d a p p r o x i m a t e l y 5-6 m m l o n g . T h i s l a r v a l s t a g e l a s t s l o n g e r t h a n a n y o t h e r s t a g e in t h e Culicoides development cycle. T h e larva h a s a conical h e a d which b e a r s a p a i r of smal l eyes , a pa i r of m i n u t e a n t e n n a e , a n d m a n d i b l e s . T h e r e a r e t h r e e t h o r a c i c a n d n i n e a b d o m i n a l

F i e l

d) Adult

C) PUPA

b) Larva

a) Eggs

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segmen t s ; these lack any a p p e n d a g e s , except tha t t h e last s egmen t t e r m i n a t e s in gill-like s t ruc tures which have an osmoregu la to ry function ( resp i ra t ion be ing cu t aneous ) (47,96). L a r v a e m o v e in a s e r p e n t i n e fashion and feed o n a wide r a n g e of m ic ro -o rgan i sms and decay ing v e g e t a b l e m a t e r i a l . M a n y species h a v e a n a r r o w r a n g e of b reed ing - s i t e types which can b e ident if ied, enab l ing cont ro l m e a s u r e s to b e t a r g e t e d for pa r t i cu la r species. I n w a r m c o u n t r i e s , d e v e l o p m e n t of l a r v a e m a y t a k e 14-25 d a y s ; for C. imicola in s u m m e r , la rva l d e v e l o p m e n t t akes 13-14 days (18, 96) . In t e m p e r a t e r eg ions , l a rvae of m a n y spec ies o v e r w i n t e r a n d t h e r e f o r e r e m a i n as l a rvae for s even m o n t h s . T h e fourth larval ins tar p u p a t e s . T h e p u p a (Fig. 1c) is 2-4 m m long, t h e c e p h a l o t h o r a x b e a r s a pair of b r e a t h i n g t r u m p e t s , t h e a b d o m i n a l s egmen t s a re e q u i p p e d wi th t ube rcu l e s end ing in a fine hair, a n d the last s e g m e n t bea r s a pa i r of horn- l ike p rocesses . T h e p u p a l s tage lasts two to t en days; two days for C. imicola in s u m m e r (18, 96).

V E T E R I N A R Y I M P O R T A N C E

Culicoides a r e b i o l o g i c a l v e c t o r s of s e v e r a l e c o n o m i c a l l y - i m p o r t a n t a rbov i ru se s . B l u e t o n g u e virus ( B T V ) , which main ly causes d isease in s h e e p ( B T V does infect cattle, b u t m o s t i n f e c t i o n s a r e s u b c l i n i c a l ) , o r i g i n a t e d in A f r i c a a n d is n o w p r e s e n t in all z o o g e o g r a p h i c a l r eg ions . T h e d isease can cause very high ra tes of morb id i t y (75%) and m o r t a l i t y (20 -50%) in s u s c e p t i b l e s h e e p ( 1 1 , 47 ) . M e l l o r (61) l is ts s e v e n t e e n species w o r l d - w i d e which cou ld b e infec ted in t h e l a b o r a t o r y or f rom which vi rus was isolated w h e n they w e r e col lec ted from the field; however , only six species w e r e ab le to transmit t h e virus . T h e m o s t i m p o r t a n t conf i rmed vec tors a r e C. variipennis (in N o r t h Amer ica) a n d C. imicola (Africa, t he M i d d l e E a s t and s o u t h e r n E u r o p e ) . C i rcums tan t i a l evidence sugges t s t h a t t h e d i s e a s e cou ld b e s p r e a d o v e r long d i s t ances by w i n d - b o r n e infected vec to rs (19) .

Afr ican h o r s e s ickness ( A H S ) ( 4 , 4 7 ) is an acu te or sub-acu te , highly fatal d isease of equ ines , which is enzoo t i c in Africa. Since the t u rn of t h e century, the d isease has spread to t he I n d i a n s u b c o n t i n e n t , t h e M i d d l e E a s t a n d s o u t h e r n E u r o p e . I n t h e s e n e w areas, o u t b r e a k s of t h e d isease h a v e b e e n less f r equen t t h a n in Africa. T h e r e a r e four clinical f o r m s of t h e d i s e a s e , of w h i c h t h e p u l m o n a r y f o r m is t h e m o s t s e v e r e . M o r t a l i t y in s u s c e p t i b l e h o r s e s m a y r e a c h 9 0 % ; m u l e s a r e less a f fec ted a n d d o n k e y s a r e t h e least suscept ib le . It is a s s u m e d tha t t he d isease can exist p e r m a n e n t l y in any a r e a of t he world w h e r e win te r cond i t ions favour survival of the Culicoides vec tors , whi le t h e exis tence of n o n - e q u i n e rese rvo i r hos ts has also b e e n sugges ted as an exp l ana t i on for t he persistence of t he virus t h r o u g h the winter . In add i t ion to t he ro le of an ima l s in t h e in t roduc t ion of t he d i sease , A H S can b e i n t r o d u c e d in to n e w a r ea s by wind or infes ted a i rp l anes . The m o s t e s t a b l i s h e d field v e c t o r of A H S is t h e E t h i o p i a n spec ies C. imicola, bu t recently t he virus has also b e e n iso la ted f rom C. pulicaris and C. obsoletus in Spain (62) .

B o v i n e e p h e m e r a l f e v e r ( B E F ) (47) is a n a r b o v i r a l d i s e a s e of c a t t l e , w h i c h is e n z o o t i c in A f r i c a a n d t h e o r i e n t a l r e g i o n a n d h a s c a u s e d e p i z o o t i c s in A u s t r a l i a . O u t b r e a k s h a v e also b e e n r e c o r d e d in t h e M i d d l e E a s t (99) . T h e d i sease is usual ly not fa ta l o r h a s a v e r y low m o r t a l i t y r a t e , b u t m o r b i d i t y a m o n g s u s c e p t i b l e c a t t l e in an e p i z o o t i c a r e a m a y r e a c h 1 0 0 % . T h e p r i n c i p a l d a m a g e c a u s e d by B E F is d u e to the r educ t ion of milk yield in da i ry he rds , de layed concep t ion a n d abor t ion . T h e vectors are Culicoides a n d m o s q u i t o s p e c i e s . I n A f r i c a , B E F v i r u s h a s b e e n i s o l a t e d from C. coarctatus, C. imicola (10) a n d a m i x e d p o o l of C. kingi a n d C. oxystoma (25) , in A u s t r a l i a f rom C. brevitarsis (88) a n d in J a p a n f rom C. punctatus (45) . R e t r o s p e c t i v e analysis of t he s p r e a d of t h e disease in several cases indica ted tha t B E F was in t roduced by w i n d - b o r n e infected vectors (69 ,74) .

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A k a b a n e d i sease is a n ep izoo t i c a rbov i r a l d i sease which causes abo r t i on , p r e m a t u r e birth, still b i r th , a n d congen i t a l a r th rog rypos i s a n d h y d r a e n c e p h a l y in ca t t le , s h e e p a n d goats. Epizoot ics h a v e b e e n desc r ibed in J a p a n , A u s t r a l i a a n d I s rae l (98) . A k a b a n e h a s also been r e p o r t e d in severa l Af r ican , M i d d l e E a s t e r n a n d S o u t h - E a s t A s i a n c o u n t r i e s and in A r g e n t i n a (3 ) . T h e v e c t o r s a r e Culicoides s p p . a n d m o s q u i t o e s . T h e v i rus h a s been i s o l a t e d f r o m t h e A f r i c a n s p e c i e s C. milnei a n d C. imicola ( 1 0 ) , f r o m t h e Austral ian C. brevitarsis a n d C. wadai ( 3 , 89) a n d f r o m C. oxystoma in J a p a n ( 3 , 51 ) . Evidence for long-d i s t ance , w i n d - b o r n e d ispersa l of infec ted vec to rs has b e e n p r e s e n t e d in Austral ia (70) .

Other a rbov i ruses caus ing t h e fol lowing d iseases of ve t e r ina ry i m p o r t a n c e h a v e b e e n isolated f r o m Culicoides s p p . , a l t h o u g h Culicoides a r e n o t c o n s i d e r e d as v e c t o r s : Cr imean-Congo h a e m o r r h a g i c fever (22) , Rift Valley fever (54) , I s rae l t u r k e y m e n i n g o encephalitis (17) , V e n e z u e l a n e q u i n e e n c e p h a l o m y e l i t i s (115) a n d ves icu la r s toma t i t i s New Je rsey (50) . O t h e r a r b o v i r u s e s h a v e a lso b e e n i so l a t ed f r o m Culicoides spp . , b u t are apparent ly w i t h o u t i m p o r t a n c e in an ima l hea l t h .

Fowl pox v i rus , wh ich is n o t a n a r b o v i r u s , h a s b e e n e x p e r i m e n t a l l y t r a n s m i t t e d b y C. arakawae f rom infec ted t o suscept ib le ch ickens s even days pos t - infec t ion (34) .

Leucocytozoon caulleryi, a p r o t o z o a n pa ra s i t i c d i s ea se of b i rd s wh ich affects b l o o d and t issue cel ls of i n t e r n a l o r g a n s , is f r e q u e n t l y f o u n d in ch icks in S o u t h - E a s t A s i a . Infect ions o c c u r f r e q u e n t l y in J a p a n a n d h a v e a l s o b e e n r e p o r t e d f r o m s o u t h e r n California ( 6 3 , 7 2 ) . T h e vec to r s a r e C. arakawae, C. circumscriptus a n d C. odibilis; t h e parasite can also d e v e l o p in b o v i n e feeders of the C. schultzei g r o u p (65 ,66 ) .

Haemoproteus nettionis is a p a r a s i t e of d u c k s . I n f e c t i o n s a r e c h a r a c t e r i s e d by schizogony in v i s c e r a l e n d o t h e l i a l ce l l s , g a m e t o c y t e d e v e l o p m e n t in c i r c u l a t o r y erythrocytes, a n d p r e s e n c e of g ranu le s of p i g m e n t in in fec ted e ry th rocy te s . Th i s pa ra s i t e has b e e n r e p o r t e d in t r o p i c a l a n d t e m p e r a t e a r e a s ( 1 0 3 ) . T h e v e c t o r in C a n a d a is C. downesi (31).

Culicoides s p p . t r a n s m i t s e v e r a l o t h e r p r o t o z o a n p a r a s i t e s of w i ld b i r d s a n d mammals.

Nine species in t h e filarial g e n u s Onchocerca h a v e b e e n r e c o r d e d in cat t le a n d w a t e r buffalo. Losses t o t h e beef i ndus t ry occu r b e c a u s e f ree w o r m s cause ugly b l e m i s h e s to the carcass , a n d e n c a p s u l a t e d a d u l t w o r m s in n o d u l e s h a v e t o b e t r i m m e d f r o m t h e carcass (47 ,78) . T h e vec tors of O. gutturosa a r e C. nubeculosus a n d C. kingi, whi le t hose of 0. gibsoni a r e C. pungens, C. shortii, C. orientalis, C. oxystoma a n d t h e c e r a t o p o g o n i d Lasiohelea townsvillensis (56) .

F o u r Onchocerca s p p . h a v e b e e n r e c o r d e d in e q u i n e s : t h r e e in h o r s e s a n d o n e in donkeys. Onchocerca cervicalis, wh ich causes severa l pa tho log ica l s y m p t o m s in h o r s e s , is t ransmit ted by C. nubeculosus a n d C. variipennis, a n d can also d e v e l o p in C. obsoletus and C. parroti (47, 56) . Culicoides arubae is a su spec t ed biological vec to r of Onchocerca sp. in horses in t h e U n i t e d S ta te s of A m e r i c a ( U S A ) (115).

R e c u r r e n t s u m m e r h y p e r s e n s i t i v i t y ( 2 9 , 1 2 0 ) , t h e m o s t w i d e l y - r e c o g n i s e d f o r m of insect hypersens i t iv i ty in f a r m a n i m a l s , h a s b e e n r e p o r t e d in v a r i o u s p l aces , i nc lud ing Australia, C a n a d a , I s rae l , J a p a n a n d t h e U S A . Skin les ions in ho r ses a n d p o n i e s caused by Culicoides b i t e s h a v e b e e n r e p o r t e d in A u s t r a l i a , w h e r e t h e i n f e c t i o n r a t e w a s 32-60% (85) . R e c e n t l y , Culicoides h y p e r s e n s i t i v i t y h a s b e e n r e p o r t e d in ca t t l e , s h e e p and donkeys (120).

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C O N T R O L

C o n t r o l a g a i n s t n u i s a n c e spec ies is r e g u l a r l y a p p l i e d in t o u r i s t - f r e q u e n t e d coasts, e.g. t h e C a r i b b e a n i s lands , F l o r i d a a n d A u s t r a l i a ( 1 , 57) , b u t n o t for t h e p r o t e c t i o n of f a r m a n i m a l s . T h e r e is n o p r a c t i c a l e x p e r i e n c e of insec t i c ida l c o n t r o l of a d u l t s in the field by w h o l e - b o d y sprays o r any o t h e r m e t h o d . In Aus t ra l i a , it has b e e n sugges ted that ive rmec t in b e u s e d as a sys temic insect ic ide in cat t le ; 9 9 % mor ta l i t y of C. brevitarsis was a c h i e v e d w i t h i n 10 d a y s fo l lowing t r e a t m e n t . S u c h t r e a t m e n t c o u l d r e d u c e t h e local p o p u l a t i o n and r e t a r d t he sp r ead of b l u e t o n g u e viruses. A n add i t iona l a d v a n t a g e of this t r e a t m e n t is t h a t t h e d u n g of i v e r m e c t i n - t r e a t e d ca t t l e is la rv ic ida l for Culicoides spp. for u p t o 28 d a y s (113 ) . A r a n g e of r e c o m m e n d e d m e t h o d s for c o n t r o l of a d u l t s was pub l i shed in 1989 (13). T h e killing of l a rvae is p rac t icab le main ly in a reas w h e r e the re is a l i m i t e d n u m b e r of l a rva l d e v e l o p m e n t s i t e s , b u t it is a l so use fu l t o p r o t e c t special ins ta l la t ions such as i n semina t ion cen t res by cont ro l l ing t he b r e e d i n g sites wi th in 2-4 km of t he ins ta l la t ion. Effect ive killing of C. variipennis l a rvae has b e e n ach ieved wi th a 5% g r a n u l a r f o r m u l a t i o n of t e m p h o s ( 4 1 ; R .F . H o l b r o o k , p e r s o n a l c o m m u n i c a t i o n ) . For con t ro l l ing C. imicola a n d o t h e r species b r e e d i n g in heavy o rgan ic m a t t e r si tes, the use of a 2 % g r a n u l a t e d p r e p a r a t i o n of t h e insec t g r o w t h r e g u l a t o r c y r o m a z i n e h a s been sugges ted (13).

SIMULIIDAE


T h e family S imu l i i dae inc ludes m o r e t h a n 1,270 spec ies in t w e l v e g e n e r a , of which the genus Simulium ( compr i s ing m o r e t h a n 1,000 species) is t he m o s t i m p o r t a n t . Flies of this family a r e c o m m o n l y n a m e d blackflies. In add i t ion to Simulium, t h r e e o t h e r genera ( n a m e l y Prosimulium, Austrosimulium a n d Cnephia) a l so c o n t a i n b i t i n g species . Simulium spec ie s occu r w o r l d - w i d e e x c e p t in N e w Z e a l a n d , H a w a i i a n d a n u m b e r of o t h e r small i s lands. T h e grea tes t n u m b e r of species (366) occurs in t he Pa lea rc t i c region. T h e r e a r e m a n y species complexes (46, 96).

B I O L O G Y

T h e adu l t blackfly (46 ,96 ) (Fig. 2d) is 1.5-4 m m long, wi th a s tou t b o d y (usual ly black in co lour ) a n d a h u m p e d tho rax . T h e h e a d has a pai r of large c o m p o u n d eyes (separa ted in females a n d j o i n e d in ma le s ) , shor t , s tou t a n t e n n a e wi th e leven dist inct s egmen t s and n o l ong ha i r s , a n d pa lp s wi th five s e g m e n t s wh ich a r e l onge r t h a n t h e s h o r t proboscis . M o u t h p a r t s d o n o t p e n e t r a t e d e e p l y i n t o t h e h o s t t i s s u e a n d b l ack f l i e s c a n n o t bite t h r o u g h c lo thes . T h e co lour less wings a r e s h o r t a n d b r o a d , w i t h o u t scales o r l ong hairs; at res t , t h e wings lay ove r t h e b o d y like a c losed pa i r of scissors. T h e a b d o m e n is short a n d squa t , wi th i n c o n s p i c u o u s geni ta l ia . T h e life cycle inc ludes t h e egg s t age , be tween six a n d n ine larval ins tars , p u p a a n d adul t . M a t i n g involves t h e a t t r ac t i on of females to m a l e swarms , which fo rm over visual m a r k e r s n e a r t he b r e e d i n g site. Blackfl ies of both sexes feed o n p l an t ju ices a n d na tu ra l l y -occu r r ing sugary subs t ances ; on ly t h e females t a k e b l o o d m e a l s , of a v o l u m e of a p p r o x i m a t e l y 1.08-3.26 µl (37) . B lackf l i e s a r e pool f eede r s a n d b l o o d feeding t akes a p p r o x i m a t e l y 4-5 m i n (114). M o s t species s e e m to be o r n i t h o p h i l i c ( 1 1 7 ) . B i t i n g is r e s t r i c t e d t o d a y l i g h t h o u r s a n d m a n y s p e c i e s seem p a r t i c u l a r l y ac t i ve o n c l o u d y a n d o v e r c a s t d a y s . Blackf l i es s e l d o m a t t a c k i n d o o r s or e v e n in veh ic les . H o s t d e t e c t i o n is by c h e m i c a l cues a n d visual o r i e n t a t i o n . B r o w n or

1181

a) Eggs

b) Larva in last instar

c) Cocoon with pupa

d) Adult

F I G . 2

Life cycle of Simuli idae (44,96)

1182

b lack eggs a r e laid in b a t c h e s of 150-600 on objects which a re in o r n e a r r u n n i n g water, o r d i rec t ly i n to t h e wate r . T h e egg is 100-400 u m long a n d is t r i a n g u l a r ovo id in shape (Fig. 2 a ) . A l l p r e i m a g i n a l s t ages of t he life cycle occur in r u n n i n g wa te r . S o m e species p r o d u c e d o r m a n t eggs t o a v o i d t h e a d v e r s e c o n d i t i o n s of s u m m e r o r w i n t e r ; in the t r o p i c s , t h e e g g s t a g e t a k e s o n e t o f o u r d a y s . T h e m a t u r e l a r v a of t h e l a s t i n s t a r is 5-13 m m long ; th i s usua l ly h a s a b lack h e a d w i t h a p r o m i n e n t p a i r of f e e d i n g brushes (Fig. 2b) . L a r v a e of m o s t species a r e fi l ter-feeders a n d c o n s u m e a lgae a n d de t r i tus . They c a n n o t eas i ly d i s c r i m i n a t e b e t w e e n types of pa r t i c les a n d swal low e v e r y t h i n g within a c e r t a i n size r a n g e , w h i c h r e n d e r s t h e m v u l n e r a b l e t o i n sec t i c ide s in t h e f o r m of tiny pe l l e t s (117) . T h e b o d y of t h e l a rva is s l ight ly s w o l l e n b e h i n d t h e h e a d a n d distinctly swol len t o w a r d s t h e r e a r end . T h e r e c t u m bea r s finger-like gills dorsally. T h e p ro leg - a s m a l l v e n t r a l p s e u d o p o d b e l o w t h e h e a d , a r m e d w i t h a s m a l l c i r c l e of h o o k l e t s -c o - o p e r a t e s wi th a pos t e r i o r h o o k circlet in larval m o v e m e n t . T h e h o o k circlet and the p ro l eg a l t e rna te ly gr ip a smal l si lken pad , which is adhesively depos i t ed on t h e substrate b y t h e s a l i va ry g l a n d . T h e d e v e l o p m e n t of w h o l e l a rva l i n s t a r s m a y t a k e o n e to two weeks , d e p e n d i n g on species and t e m p e r a t u r e , bu t in species wi th ove rwin t e r i ng larvae, l a rva l d e v e l o p m e n t m a y t a k e seve ra l m o n t h s . M a t u r e l a r v a e u s e t h e silk p r o d u c e d by t h e s a l i va ry g l a n d s t o sp in a p r o t e c t i v e b r o w n i s h c o c o o n (F ig . 2 c ) , w h i c h is s tuck to s u b m e r g e d vege ta t ion , rocks o r o t h e r objects . T h e larva p u p a t e s ins ide the c o c o o n and b r e a t h e s t h r o u g h a pa i r of gills which e x t e n d ou t s ide . In t ropica l a n d sub- t rop ica l areas, t h e p u p a l s tage lasts for two to six days a n d a p p e a r s t o b e i n d e p e n d e n t of t empera tu re . In m a n y species , mass e m e r g e n c e of t h o u s a n d s of adul t s occurs . A d u l t s of m o s t species live for t w o to t h r e e w e e k s , b u t individuals m a y live for u p t o t h r e e m o n t h s . T h e entire life cyc le f r o m egg t o a d u l t c a n t a k e less t h a n t w o w e e k s , d e p e n d i n g o n s p e c i e s and t e m p e r a t u r e . A d u l t s can fly u p t o 200 k m (109) a n d wi th w i n d a s s i s t a n c e can travel m a n y h u n d r e d s of k i l ome t r e s ( 2 3 , 4 6 , 8 0 ) .


In n o r t h e r n a n d t e m p e r a t e a r ea s , blackfl ies a r e seve re pes t s of fa rm an imals . Cattle k i l led by t he se insects in t h e Vosges in F r a n c e h a v e b e e n e s t i m a t e d t o h a v e suffered an ave rage of 25,000 bi tes , a n d in o n e case 55,000 bi tes (73). D e a t h a n d illness in cat t le and swine , a n d i l lness in ho r ses , h a v e b e e n r e c o r d e d in G e r m a n y a n d e l s e w h e r e (38, 52). In a d d i t i o n t o b l o o d suck ing , blackfl ies inject a vasoac t ive h i s t a m i n e which s t imula tes an acute toxic reac t ion , causing pathological effects in farm animals (8). A n i m a l s a r e at high risk w h e n first m o v e d to pas tu re , as immuni ty at tha t t ime is at t he lowest level. T h e milk yield of dairy cat t le subjected t o heavy blackfly a t tack may fall by 20 -40% (114). Blackflies a re the vectors of mos t species of Leucocytozoon, which a re haemoparas i t i c pro tozoa . Of n o t e d e c o n o m i c i m p o r t a n c e a r e L. simondi ( a pa r a s i t e of wi ld a n d d o m e s t i c ducks and geese in E u r o p e , N o r t h A m e r i c a and Sou th -Eas t As ia ) and L. smithi (a t u rkey parasite in E u r o p e and N o r t h A m e r i c a ) (47). Leucocytozoon infections a p p e a r to b e m o r e severe in d o m e s t i c spec i e s t h a n in wi ld s p e c i e s , a n d d e a t h s a r e m o s t c o m m o n in y o u n g birds. Simuliids a re impor t an t vectors of filaroid parasi tes of domes t ic animals in m a n y parts of t he wor ld . T h e s e flies t r ansmi t several Onchocerca species (e.g. O. gutturosa, O. linealis and O. ochengi) to catt le and also O. volvulus ( the cause of h u m a n onchocercosis or 'river b l i n d n e s s ' ) t o h u m a n s . A l t h o u g h s imu l i i d s a r e n o t k n o w n to b e i n v o l v e d in the t r ansmiss ion of a rbov i ruses , infect ion a n d rep l ica t ion of ves icular s tomat i t i s virus New J e r s e y s t r a i n h a s b e e n r e p o r t e d f r o m Simulium vittatum ( 5 ) , a n d f o u r i so l a t i ons of V e n e z u e l a n e q u i n e e n c e p h a l o m y e l i t i s v i rus h a v e b e e n r e p o r t e d in C o l o m b i a (90). In S o u t h Africa, Rift Valley fever virus has b e e n iso la ted f rom simuli ids (111).

1183

C O N T R O L

A n efficient w a y to r e d u c e b lackf ly p o p u l a t i o n s is by a p p l i c a t i o n of insec t i c ides t o breeding p l ace s of t h e i n sec t s t o kil l t h e l a r v a e . T h e in sec t i c ides a r e a p p l i e d t o a few selected s i tes o n w a t e r c o u r s e s for 15-30 m i n a n d a r e c a r r i e d d o w n s t r e a m , k i l l ing t h e simuliid l a rvae over long s t r e t ches of water . I n l a rge r iver sys tems , insect ic ide is app l i ed using a i r p l a n e s o r h e l i c o p t e r s ( 9 6 ) . R e p e a t e d t r e a t m e n t s a r e n e c e s s a r y , as g r a v i d females f r o m u n t r e a t e d a r e a s r e c o l o n i s e t h e t r e a t e d a r e a . L a r g e - s c a l e c o n t r o l p rogrammes a r e v e r y e x p e n s i v e a n d a r e s e l d o m c o n d u c t e d t o p r o t e c t a n i m a l s a l o n e (115). M a n i p u l a t i v e eco log ica l m e t h o d s , such as t h e b u i l d i n g of d a m s in s t r e a m s a n d rivers, can p r e v e n t t h e b r e e d i n g of c e r t a i n p e s t s p e c i e s ( 5 2 ) . T h e o r g a n o c h l o r i n e s d i ch lo rod ipheny l t r i ch lo roe thane ( D D T ) a n d m e t h o x y c h l o r h a v e g iven g o o d resu l t s in controlling s imul i id l a rvae ( 3 0 , 1 0 6 ) . In Wes t Af r i ca , t h e o r g a n o p h o s p h a t e insec t i c ide temphos h a s b e e n s a t i s f a c t o r i l y u s e d . M o r e r e c e n t l y , t h e b a c t e r i u m Bacillus thuringiensis var . israelensis ( B T I ) w a s i n t r o d u c e d for l a r v a l c o n t r o l ( 2 1 , 64 , 1 1 5 ) . BTI has t he a d v a n t a g e of hav ing little effect o n o t h e r aqua t i c insects . A s blackfly a t t acks are often c o n c e n t r a t e d a t t h e ea r s o r bel ly m i d l i n e , r e p e l l e n t o r insec t ic ida l sp rays a r e most effective w h e n a p p l i e d t o t h e s e s i tes (115) . A n i m a l p r o t e c t i o n for six t o e l e v e n days has b e e n ach ieved by apply ing p e r m e t h r i n (97) . P o u r i n g p h o s m e t o n graz ing ca t t le provided sat isfactory p r o t e c t i o n for five t o six w e e k s (48 ,49 ) .

PSYCHODIDAE


B l o o d - s u c k i n g s a n d f l i e s b e l o n g t o t h r e e of t h e five g e n e r a of t h e s u b f a m i l y P h l e b o t o m i n a e in t h e f ami ly P s y c h o d i d a e , n a m e l y : Phlebotomus, Lutzomyia a n d Sergentomyia. O n l y t h e f irs t t w o g e n e r a a r e k n o w n to h a v e m e d i c a l a n d v e t e r i n a r y importance . Phlebotomus a n d Sergentomyia s p p . a r e t h e sandf l i es of t h e O l d W o r l d , while Lutzomyia s p p . a r e p r e s e n t in t h e N e w W o r l d ( 9 6 ) . A l t o g e t h e r , m o r e t h a n 600 species of P h l e b o t o m i n a e exis t , i n h a b i t i n g m a i n l y d e s e r t , s e m i - a r i d a n d s a v a n n a areas - i.e. t he w a r m t ropica l , sub- t rop ica l a n d t e m p e r a t e zones of t he wor ld - a l t h o u g h some species e x t e n d to l a t i tude 50°N (46 ,96 ) .

B I O L O G Y

Sandflies (23 , 46 , 95 , 96, 102) (Fig . 3d ) a r e 1.5-4 m m long , w i th l ong a n t e n n a e a n d legs. Body co lou r r a n g e s f rom ye l low to grey, a n d wings a n d b o d y a r e hairy. T h e wings are character ised by t ape r i ng e n d s a n d a n e rec t r es t ing pos i t ion . T h e life cycle inc ludes the egg s tage, four larval ins ta rs , p u p a a n d adul t . P h l e b o t o m i n e s m a t e w i t h o u t fo rming swarms. Sandfl ies a r e p o o l f eede r s , ma in ly n o c t u r n a l a n d c repuscu la r . B o t h sexes feed on juices a n d s u g a r y p l a n t s e c r e t i o n s ( 2 3 ) . O n l y t h e f e m a l e s u c k s b l o o d , t a k i n g approximate ly 0.1 m g p e r m e a l a n d u s i n g b l o o d p r o t e i n s for egg p r o d u c t i o n . S o m e species of sandflies a r e a u t o g e n o u s a n d d o n o t suck b l o o d to p r o d u c e t h e first c lu tch of eggs. Phlebotomus s pp . h a v e b e e n r e p o r t e d t o b i t e a w i d e r a n g e of d o m e s t i c a n d wild mammals a n d b i r d s . F i v e t o s e v e n d a y s a f t e r s u c k i n g b l o o d f r o m a v e r t e b r a t e , t h e female lays 15-100 sh iny b r o w n ovo id eggs (Fig. 3a ) e a c h m e a s u r i n g 300-400 u m long , and deposits t h e m in small c racks a n d ho les in t he g r o u n d or in f loors, a m o n g leaf litter, between b u t t r e s s r o o t s , o r w h e r e v e r t h e t e m p e r a t u r e is mi ld a n d r e l a t i ve h u m i d i t y is approximately 1 0 0 % . U n d e r o p t i m u m c o n d i t i o n s , eggs h a t c h af ter 6-17 days . L a r v a e

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F I G . 3

Life cycle of Phlebotomus and transmission of Leishmania donovani (91,96)

e) Promastigotes f) Macrophage with

Leishman-Donovan bodies

d) Adult

c) Pupa

b) Larva

a) Egg

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(Fig. 3b) f eed o n o r g a n i c m a t t e r , fungi , d e c a y i n g fo res t l e a v e s , a n i m a l f aeces a n d t h e decomposing b o d i e s of a r t h r o p o d s . T h e g rey i sh o r y e l l o w i s h - c o l o u r e d m a t u r e f o u r t h instar l a r v a is 4-6 m m l o n g , w i t h a w e l l - d e f i n e d b l a c k h e a d c a r r y i n g a p a i r of s m a l l mandibles. This s tage is cha r ac t e r i s ed by thick br is t les , t e r m e d 'ma tchs t i ck ha i r s ' , o n t h e head and b o d y s e g m e n t s . M o s t spec ie s h a v e t w o pa i r s of l ong ha i r s , ca l led t h e c a u d a l brist les, o n t h e l a s t a b d o m i n a l s e g m e n t . L a r v a l d e v e l o p m e n t t a k e s 21 -60 d a y s , depending o n spec ie s , t e m p e r a t u r e a n d food . I n t h e M e d i t e r r a n e a n a n d in t e m p e r a t e areas, o v e r w i n t e r i n g is by d i a p a u s i n g of fu l ly-grown l a rvae . T h e f o u r t h l a rva l s t a d i u m pupates for 7-14 days . I n P. papatasi, t h e p u p a l l e n g t h is 2-2.5 m m (Fig . 3c) . A t t a c h e d remains of la rva l sk in a t t h e e n d a n d t w o pa i r s of c a u d a l br is t les cha rac t e r i s e t h e p u p a . The ent i re life cycle t akes 30-100 days , d e p e n d i n g on species a n d t e m p e r a t u r e . Fl ight is short-ranged, as sandfl ies a r e w e a k fliers, wi th a fo rward s p e e d of t h e o r d e r of 0.5 m/s in still air (80) , r e n d e r i n g t h e s e spec ie s v e r y sens i t ive t o w i n d s p e e d . T h e h o p p i n g f l ight distance is a p p r o x i m a t e l y 100-200 m , bu t sandfl ies m a y d i sperse u p to 1.5 k m (91) , wh ich indicates t h e r a n g e w i t h i n w h i c h c o n t r o l m e a s u r e s s h o u l d b e i m p l e m e n t e d t o p r o t e c t animals f rom sand f ly -bo rne d i seases . M a n y species in an o p e n a r e a t e n d to fly c lose t o the g r o u n d t o a v o i d d i s t u r b i n g w i n d s . S p e c i e s w i t h a t e n d e n c y t o v e r t i c a l f l ight a r e impor tan t , as flight a b o v e t h e b o u n d a r y l a y e r in a n o p e n a r e a e x p o s e s t h e m t o l o n g distance w i n d - b o r n e t r anspo r t . Sel lers (92) h y p o t h e s i s e d tha t ves icular s tomat i t i s in t h e USA was sp r ead by w i n d - b o r n e infected p h l e b o t o m i n e sandfl ies .


T h e p o p u l a t i o n d e n s i t y of s a n d f l i e s in m o s t a r e a s is b e l o w t h e p e s t - c a t e g o r y threshold (46) ; t h e i m p o r t a n c e of t h e s e i n sec t s l ies in t h e i r r o l e as v e c t o r s . T h e m o s t impor tan t z o o n o s i s t r a n s m i t t e d b y s and f l i e s is l e i s h m a n i o s i s , a n o t i f i a b l e d i s e a s e in animals and h u m a n s , c a u s e d by severa l species of t he p r o t o z o a n genus Leishmania (42, 121). A p a r t f rom infect ions in e q u i n e s in S o u t h A m e r i c a , a n d in small r u m i n a n t s in E a s t and S o u t h A f r i c a , a n d t h e o c c a s i o n a l r e p o r t of l e i s h m a n i o s i s i n c a t s , t h e v e t e r i n a r y importance is l imi ted to t h e infect ion in dogs (Figs 3e a n d 3f). F o r ins t ance , L. infantum is among t h e m a i n spec ies caus ing d i sease in dogs , wh ich usua l ly occurs in a c o m b i n e d visceral a n d c u t a n e o u s fo rm. D o g s cons t i tu t e t h e m a i n r e se rvo i r of infect ion for an imals in the M e d i t e r r a n e a n a r ea . T h e i n c u b a t i o n p e r i o d is b e t w e e n t h r e e a n d seven m o n t h s , or even l o n g e r , a n d t h e d i s e a s e u s u a l l y b e c o m e s c h r o n i c ( 6 ) . T h e t a x o n o m y of Leishmania a n d t h e e p i d e m i o l o g y of t h e d i s e a s e a r e c o m p l i c a t e d , a n d wi l l n o t b e discussed f u r t h e r in t h e c o n t e x t of t h i s p a p e r . V e s i c u l a r s t o m a t i t i s is i n d u c e d b y a rhabdovirus wh ich p r i m a r i l y affects h o r s e s , b u t a l so ca t t l e a n d pigs , a n d is e n z o o t i c in the Nearct ic a n d n e o t r o p i c a l r eg ions (39, 47) . T h e vi rus i nduces ves icular les ions in t h e mouth and feet. I t has b e e n es tab l i shed t h a t ves icular s tomat i t i s virus I n d i a n a s t ra in can be regular ly i s o l a t e d f rom sandf l i es , a n d t h a t t h e s e flies s u p p o r t v i ra l r e p l i c a t i o n a n d transovarial t r ansmiss ion ( 3 9 , 1 0 7 , 1 0 8 ) . Seve ra l t ypes of ves icular s tomat i t i s virus h a v e been isolated f rom m o s q u i t o e s a n d Culicoides species (50) .

C O N T R O L

Preven t ion of d i s ea se s t r a n s m i t t e d b y sandf l ies c a n b e a c h i e v e d by c o n t r o l l i n g t h e flies, or by c o n t r o l l i n g o r d e s t r o y i n g t h e r e s e r v o i r r o d e n t s t o g e t h e r w i t h t h e i r n e s t s , habitats a n d food sources . Al te rna t ive ly , t h e an ima l s can b e p r o t e c t e d by r epe l l en t s such as d ie thyl to luamide (91 , 96) . D D T a n d l i n d a n e r e s idua l sprays in dosages of 1 o r 2 g / m 2

m houses h a v e b e e n f o u n d t o b e efficient (101) . H o w e v e r , for e n v i r o n m e n t a l r e a s o n s ,

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a l t e r n a t i v e i n s e c t i c i d e s h a v e b e e n s t u d i e d (81) a n d m e t h o x y c h l o r h a s b e e n r e c o m m e n d e d d u e t o i ts r e s i d u a l ac t iv i ty ( 1 1 9 ) . D i c h l o r o v o s h a s a l s o b e e n used. Sandfl ies a r e very suscept ib le t o m o s t insect icides a n d n o cases of res i s tance h a v e been r e p o r t e d . Re in fe s t a t ion of con t ro l led a reas is slow (46 ,96 ) .

CULICIDAE


T h e f ami ly C u l i c i d a e c o n t a i n s t h r e e s u b f a m i l i e s , of w h i c h t h e A n o p h e l i n a e and Cu l i c inae a r e of m e d i c a l i m p o r t a n c e . Ove ra l l , t h e Cu l i c idae c o m p r i s e 3,100 species in 34 g e n e r a (46) . Cu l i c inae a r e d i s t r i b u t e d f rom t h e t rop ics t o t h e A r c t i c Ci rc le , bu t are a b s e n t f rom A n t a r c t i c a . M o s q u i t o e s exist e v e n a t e leva t ions of 5,500 m a n d in mines at d e p t h s of 1,250 m b e l o w sea leve l . S o m e g e n e r a h a v e a ve ry w i d e d i s t r i b u t i o n , while o t h e r s a r e r e s t r i c t e d . In t h e n o r t h e r n t e m p e r a t e r e g i o n s a n d t h r o u g h o u t all t ropical a r e a s , t h e g e n e r a Culex, Aedes a n d Mansonia a r e f ound . Psorophora is a n A m e r i c a n g e n u s , f o u n d f r o m s o u t h e r n C a n a d a to A r g e n t i n a a n d in t h e C a r i b b e a n i s l ands . The g e n e r a Haemagogus a n d Sabethes a r e f o u n d on ly in C e n t r a l a n d S o u t h A m e r i c a (96).

B I O L O G Y

A d u l t m o s q u i t o e s (Fig. 4d) ( 2 3 , 4 6 , 7 7 , 9 6 ) can b e d is t inguished f rom o t h e r dipterous insec t s by t h e c h a r a c t e r i s t i c v e n a t i o n a n d sca l ing o n t h e wings . Sca le s a r e o f t en also p r e s e n t o n t h e t h o r a x , a b d o m e n , h e a d a n d legs . T h e c o l o u r v a r i e s b e t w e e n species. M o s q u i t o e s h a v e a c o n s p i c u o u s f o r w a r d - p r o j e c t i n g p r o b o s c i s , w h i c h p e n e t r a t e s the capi l lar ies of t he hos t (i.e. they a re 'vessel f eeders ' ) . On ly the females suck b lood ; males h a v e r e d u c e d m o u t h p a r t s a n d c a n n o t p ie rce t he skin. T h e m o s q u i t o b o d y is s l ender and m e a s u r e s 4-6 m m in l e n g t h , a n d is d is t inc t ly d i v i d e d i n t o h e a d , t h o r a x a n d a b d o m e n . T h e h e a d bea r s a pa i r of c o m p o u n d eyes a n d a pa i r of f i l amentous s e g m e n t e d an tennae , wh ich a r e f ea the ry in m a l e s , a n d h a v e shor t ha i r s in females . T h e p a l p a l l eng th differs with sex and b e t w e e n a n o p h e l i n e a n d culicine adul ts . In A n o p h e l i n a e females , t h e palps a r e as long a n d s t ra ight as t he probosc is . T h e tho rax is slightly h u m p e d a n d the scales on the dorsa l surface give m a n y species dis t inct ive p a t t e r n s . Wings a t res t a r e p l aced over t h e a b d o m e n like a c losed pa i r of scissors. Legs a r e long a n d s lender . O n l y e ight of the t en a b d o m e n s e g m e n t s a re visible a n d well d i f ferent ia ted . T h e last a b d o m i n a l segment t e r m i n a t e s in a pa i r of cerci in t he female a n d a pa i r of c laspers in t h e m a l e . Living adult A n o p h e l i n a e c a n b e d i s t i n g u i s h e d f r o m C u l i c i n a e by t h e typ ica l r e s t i n g s t a n c e . The p r o b o s c i s , h e a d , t h o r a x a n d a b d o m e n of A n o p h e l i n a e fo rm a s t r a igh t l ine at an acute angle t o the surface. M o s t species of m o s q u i t o e s m a t e shor t ly after e m e r g e n c e from the p u p a , a n d each female m a t e s a n d is i n s e m i n a t e d only once . I n m a n y spec ies , ma t ing is p r e c e d e d by m a l e s w a r m i n g o v e r a m a r k e r , w h i c h m a y b e a n y p r o m i n e n t object , e.g. t r e e t o p o r g r o u n d o b j e c t c o n t r a s t i n g w i t h t h e b a c k g r o u n d (26 ) . V i r g i n females o r i e n t a t e t o w a r d s t h e s e m a r k e r s a n d e n c o u n t e r t h e m a l e s w a r m , f r o m w h i c h males d e p a r t to c o p u l a t e on d e t e c t i n g t h e f e m a l e . M o s q u i t o e s of b o t h sexes feed on sugary s u b s t a n c e s t o p r o v i d e e n e r g y for flight a n d d i spe rsa l , b u t t h e f ema le s of m o s t species r e q u i r e a b lood mea l f rom a hos t to ob ta in t he nu t r i en t s necessary for egg development . H o s t de t ec t ion and loca t ion a r e accompl i shed by b o t h visual a n d chemica l (hos t odours) m e a n s and occur at up to 20 m. Mos t m o s q u i t o species a r e n o c t u r n a l or crepuscular , and on ly s p e c i e s of Aedes a r e d i u r n a l b i t e r s . A v e r y w i d e h o s t r a n g e is e x p l o i t e d by the v a r i o u s m o s q u i t o spec ie s , i n c l u d i n g o n e spec ie s which feeds on m u d s k i p p e r fish and

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F I G . 4

Life cycle of Anophe l inae and Culicinae (96)

other species wh ich feed o n rep t i l es , a m p h i b i a n s , b i rds a n d m a m m a l s . T h e v o l u m e of a blood m e a l is a p p r o x i m a t e l y 4 .0-4.5 µl (12) a n d is c o n s u m e d in o n l y a few m i n u t e s . Autogenous spec ies exist , wh ich c a n d e v e l o p t h e first a n d s u b s e q u e n t b a t c h e s of eggs without t a k i n g a b l o o d m e a l . D i g e s t i o n of a b l o o d m e a l is d e p e n d e n t o n t e m p e r a t u r e

d) Aduli

c) Pupa

b) Larva

a) Eggs

A n o p h e l i n a e C u l i c i n a e

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a n d t akes two to t h r e e days in t ropica l species . T h e ovar ies d e v e l o p eggs in para l le l with t he d iges t ion p rocess . Th i s p roces s of b l o o d feeding , egg m a t u r a t i o n a n d ovipos i t ion is ca l led t h e g o n o t r o p h i c cycle. F e m a l e Anopheles gambiae in Af r i ca c a n u n d e r g o up to 13-14 g o n o t r o p h i c cycles over a 5-6 week pe r iod . I n t h e t e m p e r a t e z o n e , adu l t s diapause ( h i b e r n a t e ) a n d c a n l ive fo r u p to n i n e m o n t h s . O n l y t h e o l d e r f e m a l e s e c t o r of the p o p u l a t i o n is i m p o r t a n t in p a t h o g e n t r a n s m i s s i o n , as t h e p a t h o g e n u n d e r g o e s an i n c u b a t i o n p e r i o d of o n e t o t h r e e w e e k s in t h e m o s q u i t o b e f o r e t h e f e m a l e b e c o m e s in fec t ive . T h e ac t ive fl ight of m o s q u i t o e s is s h o r t a n d r a n g e s f r o m 1-5 k m , b u t wind ca r r i age m a y d i sperse t h e insects over 280 k m or m o r e (35, 92).

G r a v i d f e m a l e s h a v e spec ie s - spec i f i c c h e m i c a l a n d v i sua l a t t r a c t a n t s t o b r eed ing sites. T h e y lay 30-300 eggs p e r ovipos i t ion , d e p e n d i n g on species a n d source of b lood . In m a n y C u l i c i n a e , eggs a r e e l o n g a t e d o r a l m o s t o v o i d , w h i l e in A n o p h e l i n a e t h e y are b o a t - s h a p e d a n d e q u i p p e d with air-filled floats (Fig. 4a) . In Anopheles, Culex a n d some Mansonia spp . , eggs a r e laid o n t h e w a t e r sur face . T h o s e of Anopheles a r e laid singly, w h e r e a s t h o s e of Culex a n d s o m e Mansonia a r e l a id in ' egg r a f t s ' . E g g s of t h e above g e n e r a c a n n o t w i ths t and dess icat ion. Aedes, Psorophora a n d Haemagogus lay the i r eggs jus t b e y o n d t h e w a t e r l ine o n m u d , leaf l i t t e r o r o t h e r d a m p s u b s t a n c e s . E g g s of these m o s q u i t o e s c a n w i t h s t a n d v a r y i n g d e g r e e s of d e s s i c a t i o n fo r p e r i o d s r a n g i n g from severa l w e e k s t o severa l yea r s , d e p e n d i n g o n t h e species . Th i s f ea tu re is i m p o r t a n t for p a t h o g e n s such as Rift Valley fever virus , wh ich a r e t r a n s m i t t e d t r ansovar i a l ly and for which t h e eggs se rve as a reservoi r (60) . Eggs h a t c h after 2-3 days in t he t ropics and after 7-14 d a y s in t e m p e r a t e a r e a s . L a r v a e (46, 9 6 , 1 1 7 ) c a n l ive in e v e r y t y p e of s tanding wa te r , e x c e p t l a k e su r faces e x p o s e d to w a t e r a c t i on . T h e l a r v a e (F ig . 4 b ) a r e legless, wi th a b u l b o u s t h o r a x which is w ide r t h a n e i the r t h e h e a d or t h e a b d o m e n . T h e h e a d has a pa i r of a n t e n n a e , a pa i r of c o m p o u n d eyes a n d a pai r of m o u t h b rushes , which a re used to s w e e p w a t e r - b o r n e food pa r t i c l e s i n t o t h e m o u t h . F o o d cons is t s of yea s t , bacter ia , p r o t o z o a a n d m a n y o t h e r p l a n t a n d a n i m a l m i c r o o r g a n i s m s . T h e t h o r a x b e a r s various types of ha i r s . T h e a b d o m e n has n i n e dis t inct s e g m e n t s , usua l ly b e a r i n g ha i r s ; t he last s e g m e n t b e a r s a r a t h e r c o m p l i c a t e d a r r a n g e m e n t of ha i r s , a sc l e ro t i sed p l a t e a n d two p a i r s of gills, w h i c h func t ion in o s m o r e g u l a t i o n . T h e ' e i g h t h s e g m e n t ca r r i e s a pa i r of do r sa l sp i rac les wh ich e n a b l e t h e la rva to b r e a t h e a t m o s p h e r i c air. M i n u t e l a r v a e may b r e a t h e t h r o u g h the skin. This f ea tu re of surface b r e a t h i n g m a k e s t h e l a rvae vulnerable t o c o n t r o l by oil sp ray ing . In Cul ic inae (Fig. 4 b ) , t he se spiracles a r e s i t ua t ed a t t he end of a s ingle d a r k - c o l o u r e d t u b e , t e r m e d t h e s iphon . A n o p h e l i n a e (Fig. 4b) d o n o t have s i p h o n s a n d b r i n g t h e i r sp i r ac l e s i n t o c o n t a c t w i t h t h e air by p o s i t i o n i n g t hemse lves para l le l to a n d be low t h e w a t e r surface. Anopheles spp . a r e surface feeders ; m a n y other s p e c i e s a r e b o t t o m f e e d e r s . T h e r e a r e f o u r l a r v a l i n s t a r s , w h i c h take 7-14 days to deve lop . In t e m p e r a t e a reas , severa l species ove rwin te r as l a rvae , t he larval s tage the re fo re last ing for several m o n t h s .

P u p a e (96) a r e a q u a t i c a n d c o m m a - s h a p e d (F ig . 4c ) . T h e h e a d a n d t h o r a x are c o m b i n e d in t he c e p h a l o t h o r a x which b e a r s a pa i r of dorsa l r e sp i r a to ry t r u m p e t s . Only e i g h t of t h e t e n a b d o m e n s e g m e n t s a r e v i s ib l e ; t h e l a s t s e g m e n t t e r m i n a t e s in flat padd le s . P u p a e a r e c apab l e of act ive m o v e m e n t b u t d o no t feed, a n d s p e n d m o s t of their t i m e b r e a t h i n g at t he w a t e r surface. T h e p u p a l p e r i o d lasts for 2-3 days in t h e t ropics and 9-12 days in t e m p e r a t e reg ions .


S e v e r e m o s q u i t o a t t ack can kill l ives tock by exsangu ina t i on ; sma l l e r b u r d e n s cause a n n o y a n c e a n d b l o o d loss , r e s u l t i n g i n r e d u c e d w e i g h t g a i n s a n d m i l k p r o d u c t i o n

1189

(52 ,104,117) . Mass ive m o s q u i t o a t t ack can cause a loss in egg p r o d u c t i o n by d o m e s t i c fowl (28). H o w e v e r , t h e p r inc ipa l e c o n o m i c i m p o r t a n c e of m o s q u i t o e s is in t h e ro l e of transmitting an ima l p a t h o g e n s , especial ly a rbov i ruses . Af r i can h o r s e s ickness occurs (in addition t o Afr ica) in Spa in , P o r t u g a l a n d ea s t e rn M e d i t e r r a n e a n coun t r i e s . M o s q u i t o e s are though t t o p lay a s e c o n d a r y ro l e in t h e t r ansmi s s ion of t h e virus , whi le t h e p r i m a r y role in the field is p l ayed by Culicoides spp . ( 5 9 , 8 4 ) .

A m o r e i m p o r t a n t ro le is p l a y e d by m o s q u i t o e s in t he t r ansmiss ion of A k a b a n e virus, the aet iological agen t of congen i t a l a r t h r o g r y p o s i s - h y d r a e n c e p h a l y s y n d r o m e in ca t t le , sheep and goa ts (52) . T h e d i sease has b e e n r e p o r t e d f rom J a p a n , A u s t r a l i a a n d I s rae l , but a n t i b o d i e s h a v e b e e n r e p o r t e d f r o m m u c h w i d e r a r e a s a n d t h e v i r u s h a s b e e n isola ted f r o m Anopheles funestus in K e n y a , a n d Aedes vexans a n d Culex tritaeniorhynchus in J a p a n .

Bovine e p h e m e r a l fever (47, 88) is a n acu t e viral d i sease of ca t t le a n d buffalo, which occurs in s u b - t r o p i c a l a n d t e m p e r a t e r e g i o n s of Afr ica , A s i a a n d A u s t r a l i a . T h e v i rus has b e e n i s o l a t e d f r o m v a r i o u s s p e c i e s of Culicoides a n d t h e A u s t r a l i a n m o s q u i t o , Anopheles bancrofti. To d a t e , n o species has b e e n p r o v e d to be a vec to r by t h e cr i ter ia of the F o o d a n d A g r i c u l t u r e O r g a n i s a t i o n of t h e U n i t e d N a t i o n s , b u t Culicoides s pp . a r e generally cons ide r ed to b e t h e m o s t l ikely vec to r s .

Rift Valley fever (47, 5 2 , 1 0 0 ) is o n e of t h e m o s t i m p o r t a n t viral d iseases t r a n s m i t t e d by m o s q u i t o e s . T h e d i s ea se o c c u r s on ly in Af r i ca as an a c u t e febr i le d i s ea se of ca t t l e , sheep a n d h u m a n s , w h i c h is c h a r a c t e r i s e d b y h i g h m o r t a l i t y in l a m b s a n d ca lves , a n d abor t ion in a d u l t s h e e p a n d c a t t l e . T h e v i r u s h a s b e e n i s o l a t e d f r o m n i n e m o s q u i t o species a n d e x p e r i m e n t a l l y t r a n s m i t t e d by f o u r t e e n spec ies . T h e i m p o r t a n t v e c t o r s in South Afr ica a r e Culex theileri a n d Aedes caballus; in E g y p t , Cx. pipiens is t h e vec tor . Epizootics h a v e b e e n assoc ia ted wi th h e a v y ra ins , i r r iga t ion in dry coun t r i e s a n d winds . Long-distance wind ca r r i age of infec ted insects f rom n o r t h e r n S u d a n t o E g y p t h a s b e e n suggested as t h e sou rce of t he Rift Valley fever o u t b r e a k in E g y p t in 1977 (94).

J a p a n e s e e n c e p h a l i t i s (52) o c c u r s in t h e w e s t e r n Paci f ic i s l ands f r o m J a p a n to t h e Phi l ipp ines , a n d in m a n y e a s t e r n a r e a s of A s i a f r o m K o r e a t o S i n g a p o r e a n d I n d i a . Sero logica l e v i d e n c e i n d i c a t e s w i d e s p r e a d i n f e c t i o n s of s w i n e , p o s s i b l y i n c l u d i n g reproduct ive d i s o r d e r s , pa r t i cu l a r l y still b i r th . T h e ma jo r i ty of in fec t ions a r e p r o b a b l y inapparent . T h e vi rus causes occas iona l ep izoo t ics of encepha l i t i s in ho r se s . T h e m a j o r vector is Cx. tritaeniorhynchus.

V e n e z u e l a n e q u i n e e n c e p h a l o m y e l i t i s (52) is a p o t e n t i a l l y f a t a l v i r u s d i s e a s e of horses . T h e m o s t f r e q u e n t s y m p t o m s a r e d e p r e s s i o n , s t u p o r , h i g h t e m p e r a t u r e , impaired vis ion a n d i m p a i r e d c o o r d i n a t i o n . T h e virus a lso infects h u m a n s , in w h o m it p r o d u c e s i n f l u e n z a - l i k e s y m p t o m s . T h e d i s e a s e is k n o w n o n l y f r o m t h e w e s t e r n hemisphere , i.e. in Texas a n d fu r the r s o u t h in C e n t r a l A m e r i c a n c o u n t r i e s . E p i z o o t i c s occur a t i n t e r v a l s of six t o t e n y e a r s . T h e v i r u s h a s m u l t i p l e m o s q u i t o v e c t o r s a n d various spec ies h a v e b e e n r e p o r t e d f rom s e v e r a l c o u n t r i e s , e.g. four Psorophora s pp . were i d e n t i f i e d as v e c t o r s in a n e p i z o o t i c in T e x a s , t h e p r i n c i p a l s p e c i e s b e i n g Ps. columbiae ( 7 5 , 7 6 ) . I so la t ions w e r e a lso m a d e f rom five Aedes spp . , four Culex spp . and species f rom four o t h e r m o s q u i t o g e n e r a .

Wes te rn e q u i n e e n c e p h a l o m y e l i t i s (52) is a febr i le n e u r o l o g i c a l v i rus d i sease which can kill h o r s e s , b u t is n o t u s u a l l y fa ta l in h u m a n s . T h e m o s t o b v i o u s s y m p t o m s a r e motor d i s tu rbances , h igh fever a n d ano rex i a . T h e d i sease is p r e s e n t in t h e w e s t e r n a n d central n o r t h e r n U S A a n d in C a n a d a . T h e virus h a s mul t ip l e m o s q u i t o vec to r species of which the m o s t i m p o r t a n t is Culex tarsalis. I so l a t i ons h a v e also b e e n m a d e f rom o t h e r

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spec ie s , e.g. five Aedes spp . , four Culex spp . , t w o Psorophora spp . , Culiseta inornata, Mansonia perturbans a n d Anopheles earlei.

E a s t e r n e q u i n e encephalomyel i t i s (52 ,112) is a potent ia l ly fatal v i rus d isease of birds a n d h o r s e s , w h i c h m a y a l so in fec t h u m a n s . I n f e c t e d h o r s e s s h o w a b i p h a s i c febri le r e s p o n s e in s e v e r e ca se s : c l in ica l s igns in t h e first f e b r i l e p h a s e a r e a n o r e x i a and dep res s ion ; t h o s e in t h e s e c o n d p h a s e inc lude p r o f o u n d dep re s s ion , in wh ich t h e horse h a s a w ide s t ance wi th t h e h e a d h a n g i n g low unt i l t h e n o s e a lmos t t o u c h e s t h e ground, d r o o p i n g ears a n d flaccid lips. T h e m a i n d isease a reas a re a long the ea s t e rn s e a b o a r d of N o r t h a n d S o u t h A m e r i c a (40). Bi rds a re t he reservoi r of t h e virus , which is t ransmit ted a m o n g b i rds p r imar i ly by Culiseta melanura. T h e vec to rs which a r e t h o u g h t t o transmit t he virus from birds to m a m m a l s a re Aedes solicitans, A. vexans and A. canadensis.

West Ni le m e n i n g o e n c e p h a l i t i s virus (47) is k n o w n in Afr ica, Ind ia , B o r n e o a n d the M e d i t e r r a n e a n a r e a . I n F r a n c e , t h e v i r u s af fec ts h u m a n s a n d h o r s e s , caus ing e n c e p h a l i t i s ( 118 ) . B i r d s a r e c o n s i d e r e d t o b e t h e r e s e r v o i r f r o m w h i c h t h e vi rus is t r a n s m i t t e d t o m a m m a l s b y Culex univittatus a n d Cx. theileri in S o u t h A f r i c a , and Cx. antennatus in E g y p t . I s o l a t i o n s h a v e b e e n m a d e f r o m o t h e r Culex s p p . , some Anopheles spp. , o n e Mansonia sp. a n d also from ticks (40).

T u r k e y m e n i n g o e n c e p h a l i t i s is a n e u r o p a r a l y t i c d i s e a s e of a d u l t t u r k e y s which, u n d e r field cond i t ions , affects b i rds o lde r t h a n t en w e e k s (43) . T h e d isease was repor ted in I s rae l in 1960, a n d o n o n e occas ion in S o u t h Afr ica (7) . T h e vi rus was i so la ted once f r o m a n u n s o r t e d p o o l of m o s q u i t o e s , o n c e f rom a p o o l of e n g o r g e d Cx. pipiens and twice f rom u n s o r t e d p o o l s of Culicoides (17) . L a b o r a t o r y in fec t ion a n d t ransmiss ion e x p e r i m e n t s w i t h Cx. pipiens w e r e success fu l ( 71 ) . T h i s b i r d - b i t i n g s p e c i e s and Aedes caspius w e r e found to b e d o m i n a n t in t u rkey runs in I s rae l (17).

H o g c h o l e r a is a h i g h l y c o n t a g i o u s d i s e a s e w h i c h c a u s e s f eve r , d e p r e s s i o n and d e g e n e r a t i o n of sma l l b l o o d vesse l s , a n d m a y r e s u l t in d e a t h (110 ) . P igs e x p o s e d to m o s q u i t o e s c o l l e c t e d d u r i n g a n e p i z o o t i c c o n t r a c t e d t h e d i s e a s e . E x p e r i m e n t s with Aedes aegypti p r o v e d t h a t m e c h a n i c a l t r ansmis s ion is feasible a n d t h a t t h e vi rus could b e r e t a i n e d in t he m o s q u i t o e s for t h r e e days (52 ,105) .

A d d i t i o n a l a rbov i ruses h a v e b e e n iso la ted from m o s q u i t o e s , bu t t he poss ib le role of t he se viruses in caus ing an ima l d iseases is n o t k n o w n .

E q u i n e i n f e c t i o u s a n a e m i a w a s t h o u g h t t o b e m e c h a n i c a l l y t r a n s m i t t e d by m o s q u i t o e s a n d o t h e r b i t ing flies (115), b u t r ecen t ev idence po in t s p r imar i ly t o species in t he family T a b a n i d a e (33).

Fowl pox virus can b e t r ansmi t t ed mechanica l ly by ch icken-bi t ing m o s q u i t o e s . In the Sydney a r ea in Aus t ra l i a , t he pr inc ipa l vec to r was found to b e Cx. fatigans; t h e virus was r e c o v e r e d from ten pools of this species (53).

R e t i c u l o e n d o t h e l i o s i s v i ru s in c h i c k e n s is a n o t h e r v i ru s w h i c h is n o t a r t h r o p o d -b o r n e , b u t e v i d e n c e f r o m A u s t r a l i a s u g g e s t s t h a t t h e v i r u s c a n b e m e c h a n i c a l l y t r a n s m i t t e d b y m o s q u i t o e s . T h e v i r u s w a s i s o l a t e d o n s e v e n o c c a s i o n s w h e n the d o m i n a n t species was Cx. quinquefasciatus. E x p e r i m e n t a l t r ansmiss ion f rom donor s to rec ip ient chickens was ach ieved using Cx. annulirostris (67).

T h e r e is ev idence tha t Eperythrozoon ovis, a r icket ts ia l b l o o d pa r a s i t e of s h e e p , has b e e n mechan ica l ly t r a n s m i t t e d by Cx. annulirostris which could r e m a i n infective for at l e a s t f o u r t e e n h o u r s (24 , 52 ) . S imi la r ly , Eperythrozoon suis in p igs h a s been

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exper imental ly t r a n s m i t t e d by A. aegypti. M o s q u i t o spec ies a r e t h e r e f o r e l ikely t o b e mechanical vec tors u n d e r n a t u r a l cond i t ions (82) .

M o s q u i t o e s w e r e s u s p e c t e d as p o s s i b l e m e c h a n i c a l s e c o n d a r y v e c t o r s of t h e bac te r ium Borrelia anserina in c h i c k e n s a n d g e e s e , w h e n t h e p r i m a r y v e c t o r s , Argas persicus a n d Dermanyssus gallinae w e r e a b s e n t (86, 8 7 ,1 2 2 ) .

Allergic d e r m a t i t i s in h o r s e s , c a u s e d by a l l e rgens in t h e sal iva of b i t ing insec t s , h a s been r e p o r t e d p r i n c i p a l l y as a s s o c i a t e d w i t h Culicoides s p p . H o w e v e r , s o m e r e p o r t s have associated m o s q u i t o e s wi th this al lergy ( 3 2 , 8 3 ) .

C O N T R O L

Mosqui toes a r e m o s t i m p o r t a n t as vec tors of h u m a n p a t h o g e n s , such as t h o s e caus ing malaria, ye l low fever a n d d e n g u e fever, a n d t h e r e f o r e t h e h e a l t h a n d / o r e n v i r o n m e n t a l au thor i t i e s a r e in c h a r g e of t h e c o n t r o l of t h e s e i n s e c t s in i n h a b i t a t e d a r e a s . T h e p ro t ec t i on of a n i m a l s a n d t h e c o n t r o l of m o s q u i t o b r e e d i n g s i t e s w i t h i n f a r m s a r e generally t he respons ib i l i ty of f a rm o w n e r s . T h e a r sena l of pes t i c ides a n d o t h e r m e a n s of control is t o o l a rge a n d d ive r se t o b e d e t a i l e d h e r e . C u r r e n t c o n t r o l po l icy u s e s t h e pr inciples of i n t e g r a t e d p e s t m a n a g e m e n t . T h e s e p r i n c i p l e s i n c l u d e e n v i r o n m e n t a l control , e.g. d r a i n i n g of s w a m p s a n d p r e v e n t i n g s e e p a g e s of w a t e r a n d s e w a g e f r o m animal houses , a n d bio logica l c o n t r o l us ing l a rv ivorous fish, n e m a t o d e s , fungi, e tc . T h e most efficient m e a n s of r educ ing m o s q u i t o p o p u l a t i o n s is by con t ro l l ing insect b r e e d i n g sites. Selected pes t ic ides r e c o m m e n d e d for larval con t ro l inc lude m a l a t h i o n , t e m e p h o s , chloropyrifos, o t h e r o r g a n o p h o s p h o r o u s c o m p o u n d s , Bacillus thuringiensis israelensis (H-14), b a c t e r i a l p r e p a r a t i o n a n d m e t h o p r e n e , a n in sec t g r o w t h r e g u l a t o r . S e l e c t e d r e c o m m e n d e d p r o d u c t s for k i l l ing a d u l t m o s q u i t o e s i n c l u d e t h e o r g a n o p h o s p h o r o u s c o m p o u n d s m a l a t h i o n , n a l e d , c h l o r o p y r i f o s a n d d i a z i n o n , t h e o r g a n o c h l o r i n e me thoxych lo r , t h e c a r b a m a t e s c a r b a r y l a n d p r o p o x u r , t h e b o t a n i c a l p y r e t h r i n , a n d synthet ic p y r e t h r o i d s s u c h as r e s m e t h r i n , a l l e t h r i n , d e l t a m e t h r i n a n d p e r m e t h r i n . Spraying of h o u s e d a n i m a l s w i t h c o m m e r c i a l i n s e c t i c i d e / i n s e c t - r e p e l l e n t m i x t u r e s provides s h o r t - t e r m p r o t e c t i o n (2 , 52 ) ; h o w e v e r , p y r e t h r o i d s h a v e d e m o n s t r a t e d a n ability to p r o t e c t an ima l s f rom bi t ing flies for seven to twe lve days (115).

A C K N O W L E D G E M E N T S

T h e a u t h o r w i shes t o e x p r e s s t h a n k s t o D r F. G a l k e r for t h e g r a p h i c a l w o r k o n t h e Figures, and to M r s F. G o l a n d e r for p rov id ing ass is tance in t he l i t e ra tu re search .

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NÉMATOCÈRES ( C É R A T O P O G O N I D É S , P S Y C H O D I D É S , S I M U L I D É S E T CULICIDÉS) ET M E T H O D E S D E LUTTE. - Y. Braverman.

Résumé : L'auteur décrit et discute l'importance biologique et vétérinaire de certains nématocères, ainsi que la lutte contre ces insectes.

Les Cu l i co ides spp. (famille des Cératopogonidés) transmettent les arbovirus de la fièvre catarrhale du mouton, de la peste équine, de la fièvre éphémère bovine et d'Akabane. D'autres arbovirus ont été isolés chez ces

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espèces ; la variole aviaire est également transmise par des Culicoides, comme cela a été démontré expérimentalement. Ces insectes sont aussi les vecteurs des protozoaires parasites, Leucocy tozoon caulleryi et H a e m o p r o t e u s net t ionis , ainsi que des nématodes parasites, O n c h o c e r c a gu t t u ro sa , O . g ibson i et O. cervical is . Ils provoquent, par ailleurs, une hypersensibilité estivale récurrente chez les chevaux, les poneys, les ânes, les bovins et les ovins.

Le bétail peut succomber à une attaque massive de Simulium spp., vecteurs des L e u c o c y t o z o o n s imondi et L. smithi ainsi que des filaires O . gut turosa , O. linealis et O. ochengi. Les virus de l'encéphalomyélite équine vénézuélienne (EEV) et de la fièvre de la Vallée du Rift (FVR) ont été isolés chez des Simulidés et on a observé la réplication du virus de la stomatite vésiculeuse (souche New Jersey) chez Simulium vittatum. Les Simulidés sont reconnus comme étant les vecteurs de O. volvulus, responsable de l'onchocercose (ou cécité des rivières).

La famille des Psychodidés comprend les genres Ph lebotomus et Lutzomyia (sous-famille des Phlébotominés), vecteurs de Leishmania spp. chez l'homme ainsi que chez les chiens et autres mammifères. La souche Indiana du virus de la stomatite vésiculeuse a régulièrement été isolée chez les phlébotomes ou sandflies.

Une attaque massive de moustiques peut également s'avérer fatale pour les animaux d'élevage. Les moustiques sont, en outre, des vecteurs des virus d'Akabane, de la fièvre éphémère bovine, de la FVR, de l'encéphalite japonaise, de l'EEV, de l'encéphalomyélite équ ine de l'Ouest, de l'encéphalomyélite équ ine de l'Est et de la fièvre du Nil occidental, ainsi que des vecteurs secondaires de la peste équ ine et des vecteurs présumés de la méningo-encéphalite de la dinde en Israël. Les moustiques sont des vecteurs passifs des virus de la peste porcine classique, de la variole aviaire, de la réticulo-endothéliose, des rickettsies E p e r y t h r o z o o n ovis et E . suis, et de la bactérie Borrel ia anserina. Ces insectes provoquent également une dermatite allergique chez les équidés. Ils transmettent plusieurs filaires de l'homme ou des animaux et jouent un rôle très important en médecine humaine en tant que vecteurs de maladies telles que le paludisme, la fièvre jaune, la dengue et beaucoup d'autres affections dues à des arbovirus.

M O T S - C L É S : Culicidés - Culicoides - Maladies animales - Ph lebo tomus -Prophylaxie - Simulium - Vecteurs.

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N E M A T Ó C E R O S ( C E R A T O P O G O N I D A E , P S Y C H O D I D A E , S I M U L I I D A E Y CULICIDAE) Y MÉTODOS D E L U C H A . - Y. Braverman.

Resumen: El autor se refiere a la importancia biológica y veterinaria de ciertos netnatóceros y a la lucha contra estos insectos.

Cul ico ides spp. (de la familia de los Ceratopogonidae) transmiten los arbovirus de la lengua azul, la peste equina, la fiebre efímera bovina y Akabane. Otros arbovirus fueron aislados en estas especies; la viruela aviar también es transmitida por Culicoides, según se demostró experimentalmente. Estos insectos son asimismo vectores de protozoarios parásitos como Leucocytozoon caulleryi y H a e m o p r o t e u s nettionis, así como de nematodos parásitos como Onchocerca gutturosa, O. gibsoni y O. cervicalis. Provocan,

1 1 9 3

por otra parte, una hipersensibilidad estival recurrente en caballos, ponis, asnos, bovinos y ovinos.

El ganado puede sucumbir debido a un ataque masivo de S imul ium spp., vectores de Leucocy tozoon s imondi y L. smithi y de las filarias O. gut turosa, O. linealis y O. ochengi. Los virus de la encefalo mielitis equina venezolana y de la fiebre del Valle del Rift fueron aislados en Simuliidae y se observó la replicación del virus de la estomatitis vesicular (cepa de New Jersey) en Simulium v i t t a tum. Los Simuliidae han sido reconocidos como vectores de O. volvulus, responsable de la oncocercosis humana (o ceguera de los arroyos).

La familia Psychodidae incluye los géneros P h l e b o t o m u s y L u t z o m y i a (subfamilia Phlebotominae), vectores de Le i shmania spp. en el hombre tanto como en los perros y otros mamíferos. La cepa Indiana del virus de la estomatitis vesicular se ha aislado regularmente en los flebótomos (también llamados moscas de arena o beatillas).

Un ataque masivo de mosquitos puede también llegar a ser fatal para el ganado. Los mosquitos son, además, vectores de los virus de Akabane, la fiebre efímera bovina, la fiebre del Valle del Rift, la encefalitis japonesa, la encefalomielitis equina venezolana, la encefalomielitis equina del Oeste, la encefalomielitis equina del Este y la fiebre del Nilo occidental, así como también vectores secundarios de la peste equina, vectores presuntos de la meningoencefalitis del pavo de Israel y vectores pasivos de los virus de la peste porcina clásica, la viruela aviar, la reticuloendoteliosis, las rickettsias Epery th rozoon ovis y E . suis, y la bacteria Bor re l ia anser ina . Estos insectos provocan también una dermatitis alérgica en los equinos. Transmiten varias filarias del hombre o de los animales y son muy importantes para la medicina humana en la medida en que son vectores de enfermedades tales como el paludismo, la fiebre amarilla y el dengue, entre muchas otras provocadas por arbovirus.

P A L A B R A S C L A V E : Cul ic idae - Cul ico ides - E n f e r m e d a d e s an imales -Phlebotomus - Profilaxis - Simulium - Vectores.

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Nematocera (Ceratopogonidae, Psychodidae, Simuliidae and