Rev. sci. tech. Off. int. Epiz., 1994 ,13 (4), 1125-1158

Biology and control of tabanids, stable flies and horn flies

L.D. FOIL * and J.A. HOGSETTE **

Summary: Tabanids are among the most free-living adult flies which play a role as livestock pests. A single blood meal is used as a source of energy for egg production (100-1,000 eggs per meal), and females of certain species can oviposit before a blood meal is obtained (autogeny). Therefore, the maintenance of annual populations requires successful oviposition by only 2 % of females. Wild animal blood sources are usually available to maintain annual tabanid populations. Larval habitats are also independent of domestic livestock. Thus, the use of repellents or partial repellents is the only effective chemical strategy to reduce the incidence of tabanids on livestock. Permanent traps (and possibly treated silhouette traps) can be employed to intercept flies. Selective grazing or confinement can also reduce the impact of tabanids.

Stable fly adults are dependent on vertebrate blood for survival and reproduction, but the amount of time spent in contact with the host is relatively small. Stable fly larvae develop in manure, spilled feed and decaying vegetation. Management of larval habitats by sanitation is the key to stable fly control. Treatment of animals with residual insecticides can aid in control; thorough application to the lower body parts of livestock is important. Proper use of modified traps, using either treated targets or solar-powered electrocution grids, can be effective in reducing stable fly populations.

Adult horn flies spend the major part of their time on the host, and the larvae are confined to bovid manure. Therefore, almost any form of topical insecticide application for livestock is effective against horn flies, in the absence of insecticide resistance. Treatments should be applied when economic benefit is possible; economic gains are associated with increased weaning weights and weight gains of yearling and growing cattle. Oral chemical treatments (insect growth regulators or insecticides) administered at appropriate rates via bolus, water, food or mineral mixtures can inhibit horn fly larval development. However, adult horn fly movement among cattle herds limits the use of larval control for horn fly population management. The augmentation of native parasites, predators and competitors has been attempted and even promoted for horn fly and stable fly control, but evidence for the success of such programmes is equivocal.

K E Y W O R D S : Biology - Con t ro l - D e e r flies - H a e m a t o b i a - H o r n flies -Horse flies - Stable flies - Stomoxys - Tabanidae .

* Department of Entomology, Louisiana Agricultural Experiment Station, Louisiana State University (LSU) Agricultural Center, 402 Life Sciences Building, LSU, Baton Rouge, LA 70808-1710, United States of America.

** Medical and Veterinary Entomology Research Laboratory, United States Department of Agriculture, Agricultural Research Service, P.O. Box 14565, Gainseville, FL 32604, United States of America.

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INTRODUCTION

T h e u l t i m a t e s u c c e s s of m a n a g e m e n t of m o s t a r t h r o p o d - a s s o c i a t e d p r o b l e m s of l ives tock d e p e n d s o n se lec t ing a p p r o p r i a t e i n t e g r a t e d t e c h n i q u e s for t h e p e s t species involved. M e t h o d s for cont ro l l ing t he impac t of a r t h r o p o d s o n l ivestock m u s t b e linked wi th t h e life cycle a n d hos t d e p e n d e n c e of t he pes ts . I n fo rma t ion is p r e s e n t e d be low on t h e b i o l o g y of c e r t a i n s p e c i e s of f l ies , for u s e as a n a id in e s t a b l i s h i n g c o n t r o l p r o g r a m m e s .

T a b a n i d s , h o r n flies and s table flies a r e all pes ts of p a s t u r e d l ivestock; s tab le flies can a l so b e p e s t s of c o n f i n e d l i v e s t o c k . T h e s e flies r e p r e s e n t t h e e x t r e m e s of host d e p e n d e n c e a n d h o s t specificity, r ang ing f rom t h e c o m p l e t e l y h o s t - d e p e n d e n t h o r n fly t o t a b a n i d s , w i t h s t a b l e flies b e i n g i n t e r m e d i a t e . T a b a n i d p o p u l a t i o n s p r o b a b l y exist t o d a y w h i c h a r e i n d e p e n d e n t of t h e m o v e m e n t of h u m a n s a n d d o m e s t i c l i ves tock . T a b a n i d s a r e m e m b e r s of t h e family T a b a n i d a e , which conta ins over 4,000 species , many exhibi t ing different types of hos t -o r i en t ed behaviour . F e m a l e t aban ids feed o n b l o o d to s u p p o r t egg d e v e l o p m e n t , whi le b o t h males a n d females use c a r b o h y d r a t e s f rom nectars as a n e n e r g y s o u r c e . C o n t r o l p r o g r a m m e s for p e s t s ( l i k e t a b a n i d s ) w h i c h a r e not d e p e n d e n t o n d o m e s t i c a n i m a l s for p o p u l a t i o n m a i n t e n a n c e , a r e b a s e d o n m a n a g i n g l ives tock to avo id a r e a s of h igh pes t densi ty , i n t e r c e p t i n g pes t s b e f o r e t h e y e n c o u n t e r l ivestock, p rov id ing l ivestock wi th shel ter or applying pes t r epe l l en t s .

S tab le flies a n d h o r n flies a r e b o t h p l aced in t he family M u s c i d a e . L i k e t se t se , both sexes of h o r n flies a n d s t ab l e flies a r e b l o o d - f e e d e r s a n d a r e h o s t d e p e n d e n t . D u e to e v o l v e d o r s e l e c t e d d e p e n d e n c e o n l i v e s t o c k , d i s t r i b u t i o n s a n d l o c a l p o p u l a t i o n dens i t ies of h o r n flies a n d s t ab le flies h a v e b e e n inf luenced by t h e act ivi t ies of h u m a n s a n d d o m e s t i c l i v e s t o c k . S t a b l e fly l a r v a l d e v e l o p m e n t is a m p l i f i e d b y l i v e s t o c k e x c r e m e n t , b u t d e v e l o p m e n t can occur in subs t r a t e s ex t e rna l to l ives tock p r o d u c t i o n , s u c h as f e r m e n t i n g a q u a t i c v e g e t a t i o n . A l t h o u g h b l o o d m e a l s a r e r e q u i r e d by b o t h s e x e s for r e p r o d u c t i o n , s t a b l e flies l ive i n d e p e n d e n t l y of t h e v e r t e b r a t e h o s t for the ma jo r i ty of t h e adu l t life; a s ingle b l o o d m e a l s u p p o r t s t h e d e v e l o p m e n t of a b a t c h of eggs. L ives tock a r e t h e p r e f e r r e d hos t s of t he se flies, b u t a l t e rna t ive hos t s can b e used for p o p u l a t i o n m a i n t e n a n c e . F o r pe s t s wh ich a r e m o d e r a t e l y d e p e n d e n t o n l ivestock for survival , con t ro l of t h e vital subs t r a t e o b t a i n e d by the pes t is a p p r o p r i a t e . F o r stable flies, th is is c o n s t i t u t e d by t h e m a n u r e of l ives tock which , w h e n c o m b i n e d w i t h o the r s u b s t r a t e s , p r o v i d e s a n a m p l i f i c a t i o n of p o p u l a t i o n s w h i c h in t u r n f e e d o n the l i v e s t o c k . T h u s s a n i t a t i o n a n d l i m i t e d s t r a t e g i e s of i n s e c t i c i d e a p p l i c a t i o n a re a p p r o p r i a t e .

H o r n flies a r e d e p e n d e n t o n l i v e s t o c k t o p r o v i d e t h e i n t a c t b o v i n e m a n u r e pa t . A d u l t s can survive on t h e b lood of a l t e rna t ive hos t s (e.g. equ ids ) for e x t e n d e d per iods , b u t o v i p o s i t i o n m u s t occu r o n f resh b o v i n e m a n u r e for p o p u l a t i o n m a i n t e n a n c e ; the g e n e p o o l of s u b s e q u e n t g e n e r a t i o n s s t e m s f rom t h e flies w h i c h r e m a i n w i t h bov ids . Mul t ip l e b l o o d mea l s a re r e q u i r e d to s u p p o r t egg p r o d u c t i o n . F o r pes t s which a r e host d e p e n d e n t , t r ea t ing t he vital subs t ra tes ( m a n u r e or t he hos t ) wi th insect ic ides can break t h e d e v e l o p m e n t a l cycle. H o w e v e r , h o s t - d e p e n d e n t pe s t s o f ten d e v e l o p r e s i s t a n c e to e n v i r o n m e n t a l p ressu res such as insect icide appl ica t ion .

T h e b e s t o p t i o n s for t h e c o n t r o l of all t h r e e t y p e s of f l ies c o n s i d e r e d b e l o w are s u m m a r i s e d in Tab le I.

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T A B L E I

Synopsis of the best options for the control of tabanids, stable flies and horn flies

Type of control Tabanids

Fly species

Stable flies Horn flies

Chemical

Cultural

Mechanical

Biological

Use high-pressure pyrethroid sprays

Provide shelter or large grazing areas by vegetation control

Permanent traps

Apply residual insecticides to lower extremities of animals or treat targets

Sanitize larval habitats

Solar-powered electrocution traps or treated targets

Native predators (especially Nyssonine wasps)

Native parasitic hymenoptera, supplemented if possible

Wide variety of applications effective

Destroy manure pat integrity

Walk-through fly traps (effects on tabanids and stable flies have also been reported)

Native beetles (scarabs, hysterids and staphylinids) - importation of exotic species remains experimental

TABANIDS

Flies of t h e family T a b a n i d a e vary in colour , b o d y m a r k i n g s , wing m a r k i n g s a n d size (9-33 m m ) . T h e family is p l a c e d in t h e s u b o r d e r B r a c h y c e r a . T a b a n i d s h a v e a n t e n n a e composed of t h r e e s e g m e n t s ; t h e th i rd s e g m e n t is a n n u l a t e d a n d m a y h a v e a t oo th - l i ke process at t h e b a s e . C o m m o n n a m e s a r e u s e d for s o m e of t h e f r e q u e n t l y - e n c o u n t e r e d groups . D e e r flies (Chrysops s p p . ) a r e r e l a t i v e l y s m a l l (6 -11 m m in l e n g t h ) , y e l l o w -orange in co lour wi th d a r k b o d y m a r k i n g s and , usually, p i c t u r e d wings wi th dist inct da rk pa t t e rns . C l e g s (Haematopota s pp . ) a r e m e d i u m - s i z e d flies w i t h m o t t l e d w i n g s . T h e term ' h o r s e fly' c o v e r s a m u c h m o r e d i v e r s e g r o u p of f l ies, a n d is e s sen t i a l l y u s e d t o describe any t a b a n i d o t h e r t h a n d e e r flies a n d clegs.

B I O L O G Y

F e m a l e flies o b t a i n b l o o d m e a l s t o s u p p o r t egg d e v e l o p m e n t . M o s t spec ies d e p o s i t eggs in l a y e r e d m a s s e s o n v e g e t a t i o n a b o v e la rva l h a b i t a t s . T h e p e r i o d b e t w e e n b l o o d meals, du r ing which t h e f ema le c o m p l e t e s oogenes i s a n d ovipos i t ion a n d t h e n beg ins to search for a n o t h e r b l o o d m e a l , is t h r e e t o f o u r d a y s . L a r v a e f e e d o n o r g a n i c d e b r i s and/or smal l i n v e r t e b r a t e s in a v a r i e t y of a q u a t i c t o s e m i - a q u a t i c h a b i t a t s . T h e l a r v a e undergo r ap id g r o w t h du r ing w a r m w e a t h e r b u t a r e qu iescen t du r ing cold wea the r . T h e larvae m a t u r e a n d p u p a t e in d r i e r soil; t he adul t s e m e r g e o n e to t h r e e w e e k s later. Life cycles r e q u i r e f r o m t w o m o n t h s t o t w o y e a r s , d e p e n d i n g o n t h e s p e c i e s a n d t h e g e o g r a p h i c a l l o c a t i o n . I n m o s t r e g i o n s , a d u l t s of m o s t s p e c i e s a r e o n l y p r e s e n t fo r

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a p p r o x i m a t e l y o n e m o n t h , b u t a success ion of spec ies is o f t en s e e n . T h e r e su l t is that l ivestock m a y b e a t t a c k e d by o n e o r m o r e species of T a b a n i d a e t h r o u g h o u t all o r most of t he w a r m m o n t h s of t h e year. Males feed o n nectar , h o n e y d e w a n d o t h e r l iquids, and females feed o n t h e s e subs t ances a n d o n b lood . F e m a l e s of m o s t spec ies m u s t ob ta in a b l o o d m e a l p r i o r to t h e d e v e l o p m e n t of each b a t c h of eggs; however , s o m e spec ies lay o n e ba tch of eggs be fo re they seek an an imal hos t ( au togeny ) .

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

O n a wor ld -wide scale, t aban ids a r e a m o n g the ma jo r l ivestock pes t s , b u t t he relative i m p o r t a n c e of m o s t species var ies t empora l ly a n d geographica l ly . T a b a n i d s a r e painful b i te rs , caus ing e x t r e m e a n n o y a n c e and b lood loss (up to 0.5 ml p e r fly), with m o r e blood loss fo l lowing t h e b i t e d u e to ooz ing . Loca l r e a c t i o n s t o b i t e s i nc lude d e r m a l nodu les . T h e b i t e w o u n d s m a y se rve as s e c o n d a r y feed ing si tes for o t h e r flies o r as oviposi t ion s i t es for m y i a s i s - p r o d u c i n g f l ies . W e b b a n d Wel l s (140) e s t i m a t e d t h a t 25 t o 30 Hybomitra sonomensis a n d Tabanus punctifer f e ed ing o n a hos t for 6 h w o u l d t a k e at l e a s t 100 m l of b l o o d ; w e i g h t def ic i t s of a p p r o x i m a t e l y 45 k g b e l o w n o r m a l inc rease w e r e e s t i m a t e d for ca t t l e u n d e r h e a v y a t t ack . C o n t e m p o r a r y s tud ies h a v e es tab l i shed t h a t 66-90 h o r s e flies p e r day can r e d u c e daily weight gain by 0.1 kg p e r year l ing heifer, a n d p o p u l a t i o n s feeding on cat t le can far exceed this b u r d e n in m a n y reg ions . Losses in b e e f c a t t l e p r o d u c t i o n d u e t o t a b a n i d a t t a c k s w e r e e s t a b l i s h e d to b e U S $ 4 0 mi l l ion annua l ly in t h e U n i t e d Sta tes of A m e r i c a ( U S A ) in 1965; US$30 mil l ion w e r e a t t r ibuted t o r e d u c t i o n in we igh t ga ins (5) .

Taban ids h a v e b e e n descr ibed as t he mechanica l vectors of over 35 p a t h o g e n i c agents of l i ve s tock , i n c l u d i n g e q u i n e i n f ec t i ous a n a e m i a v i rus , Anaplasma marginale, Trypanosoma evansi and T. vivax, as well as the agents of cu t aneous an th rax , tu laraemia, bov ine viral leukosis, vesicular s tomati t is and hog cholera (26). Biological t ransmiss ion of Elaeophora schneiden (ar ter ial w o r m of deer ) by tabanids to elk, dee r a n d sheep has been d e s c r i b e d . Loa loa is t r a n s m i t t e d by d e e r f l ies, a n d Trypanosoma theileri is a ben ign o r g a n i s m b io log ica l ly t r a n s m i t t e d b y t a b a n i d s . T a b a n i d s a r e u sua l l y c o n s i d e r e d the p r i m a r y insec t v e c t o r of a g e n t s wh ich a r e r o u t i n e l y t r a n s m i t t e d b e t w e e n a n i m a l s by t r ans fe r of b lood . His tor ical ly , assoc ia t ions h a v e b e e n m a d e b e t w e e n p e a k s of t aban id feeding and the t ransmiss ion of agents resul t ing in acu te disease wi th in a relat ively short i n c u b a t i o n p e r i o d . A s s o c i a t i n g t a b a n i d s wi th t h e t r a n s m i s s i o n of a g e n t s w h i c h cause chronic disease or have long incubat ion per iods is m o r e of a chal lenge. T h e occur rence of b l o o d t r a n s f e r d u e t o h u m a n i n t e r v e n t i o n s ( m u l t i p l e - u s e n e e d l e s o r i n s t r u m e n t s ) or d u e t o insects o t h e r t h a n t aban ids shou ld always b e cons ide r ed du r ing invest igat ions of epizootics. F o r example , s table flies are often m o r e impor t an t vectors of T. evansi than taban ids in m a n a g e m e n t systems or ecosystems whe re t aban id bu rdens a re low.

S U R V E I L L A N C E

S u r v e i l l a n c e m e t h o d s for t a b a n i d s a n d t s e t s e h a v e m o s t l y e v o l v e d s e p a r a t e l y , but t h e r e is o f t e n c o n v e r g e n c e of t r a p s h a p e a n d c o l o u r . T h i s s t e m s f r o m a t t e m p t s to cons t ruc t t r aps which par t ly mimic an a t t rac t ive host . F o r t aban ids , a large b lack animal is c o n s i d e r e d t o b e m o s t a t t r a c t i v e , a n d the c u r r e n t l y - u s e d c a n o p y t r a p s o r b o x t raps e m p l o y this p r inc ip le a lone .

T h e M a n i t o b a fly t r a p was d e v e l o p e d by T h o r s t e i n s o n (131) a n d consists of a t r ipod a p p r o x i m a t e l y 2 m ta l l ; t h e t o p ha l f is c o v e r e d w i t h a c l e a r p l a s t i c c a n o p y a n d a col lec t ion c h a m b e r (normal ly a con ta ine r wi th an inver ted funnel) at t h e apex . A decoy,

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routinely a b lack s p h e r e , is s u s p e n d e d u n d e r t he canopy. Ca t t s (19) r edes igned this t r a p as a p y r a m i d wi th a c lea r t o p a n d a b l a c k b a s e ; t h e t r a p is e r e c t e d us ing a c e n t r a l p o l e and s t akes a t t h e e n d of r o p e s c o n n e c t e d t o t h e f o u r c o r n e r s of t h e p y r a m i d . R e c e n t updates of c a n o p y t r a p des igns a r e ava i l ab le (53) . T h e c a n o p y t r a p is easy t o t r a n s p o r t for use in r e m o t e loca t ions . H o w e v e r , t h e s e t r aps a r e n o t very effective w i t h o u t t h e use of carbon d iox ide ( C 0 2 ) .

The M a n n i n g t r a p or box t r a p was an evo lu t ion of t h e M a n i t o b a t r a p t o w a r d a m o r e permanent site surve i l lance too l . T h e s e t r aps cu r ren t ly consis t of a w o o d e n box ( p a i n t e d black or b r o w n ) wi th a s c reen t o p n a r r o w i n g to a ca t ch con ta ine r . T h e s e t r aps a r e u s e d in the U S A for t a b a n i d c o n t r o l in c e r t a i n a r e a s w h e r e t a b a n i d s a r e f r e q u e n t p e s t s of h u m a n s . F u r t h e r d e t a i l s o n t r a p s fo r c o n t r o l a r e p r o v i d e d u n d e r t h e h e a d i n g 'Mechanical c o n t r o l ' be low.

T h e M a l a i s e t r a p i n c o r p o r a t e s s o m e f o r m of f l i g h t - i n t e r c e p t i n g m e s h p a n e l s (normally g r e e n o r g rey p las t i c s c r e e n o r n y l o n ) . T h e p a n e l s a r e c o n s i d e r e d n o t t o b e perceived by flies a n d t o p r o v i d e a m e a s u r e of r a n d o m flight densi ty. T h e s e p a n e l s c a n be a r r anged in a cross u n d e r a c e n t r a l p y r a m i d r o o f n a r r o w i n g to a ca tch con ta ine r , o r the p a n e l s m a y b e u s e d t o f o r m a l o n g i n t e r c e p t o r u n d e r a r o o f - l i k e t o p w i t h c a t c h conta iners a t b o t h e n d s . V a r i o u s m o d i f i c a t i o n s of t h e s e t r a p s u s i n g c o m b i n a t i o n s of visual and olfactory cues h a v e b e e n desc r ibed (103).

T h e accu racy of e x t r a p o l a t i o n f rom t r a p ca t ches t o t h e t a b a n i d b u r d e n of l ives tock can be l imi ted . T h e q u a n t i t y a n d c o m p o s i t i o n of ca t ches in s i l houe t t e t r a p s m a y n o t b e equivalent t o t h o s e of c a t ches o b t a i n e d us ing a n i m a l ba i t s . F o r e x a m p l e , of 4,077 flies (four s p e c i e s ) c o l l e c t e d in C 0 2 - b a i t e d c a n o p y t r a p s a n d f r o m b u l l o c k s , a h i g h e r pe rcen tage of Tabanus fuscicostatus (55 .1%) w a s c a u g h t u s i n g t r a p s t h a n was c a u g h t using an imal s (31 .1%) . A l o w e r p e r c e n t a g e of T. wilsoni was c a u g h t u s ing t r a p s (3.7%) than us ing a n i m a l s (24 .9%) . T h e g o n o t r o p h i c s t a t u s of flies c a u g h t o n a n i m a l s a n d in traps was c o m p a r e d , a n d it was f o u n d t h a t p a r i t y r a t e s d id n o t v a r y s ignif icant ly (66) . Thus, t he flies o b s e r v e d o n an ima l s a n d c a u g h t in t r a p s a r e p r o b a b l y r e p r e s e n t a t i v e of the s a m e p o p u l a t i o n . R e c e n t w o r k h a s i n d i c a t e d t h a t t r a p ef f ic iency differs b e t w e e n tabanid species, a n d tha t C 0 2 a n d o t h e r hos t o d o u r s b o t h a t t rac t t aban id s a n d affect t r a p efficiency. T h e r e f o r e , t r a p d a t a can genera l ly b e assoc ia ted wi th overa l l t a b a n i d an ima l bu rden , b u t a c o r r e l a t i o n m a y n o t o c c u r w h e n i n d i v i d u a l s p e c i e s a r e c o n s i d e r e d . Recently, a n u m b e r of s tudies h a v e eva lua t ed semiochemica l s as bai ts for ho r se fly t r aps . Trap ca tch can b e i n c r e a s e d by t h e a d d i t i o n of C 0 2 (145) , o c t e n o l (29) , a m m o n i a (53) , and a mix tu re of oc teno l a n d p h e n o l s (93).

W h e n t a b a n i d surve i l lance s tudies a r e c o n d u c t e d , t h e t ype of t r a p shou ld b e m a t c h e d to the q u e s t i o n a s k e d , a n d t h e h u m a n r e s o u r c e s , t i m e a n d m o d e s of t r a n s p o r t a t i o n available. F o r e p i d e m i o l o g i c a l s tud ies c o m p a r i n g i nc idence of t a b a n i d s wi th i nc idence of t ransmission of d i sease agen t s , c a n o p y t r aps can b e r e c o m m e n d e d . Mu l t i p l e sites can be s ampled w i t h m i n i m a l effort . A d d i t i o n of C 0 2 , h o s t o d o u r s , o r t r a p m o d i f i c a t i o n s such as baffles (i .e. c o m b i n i n g Ma la i se a n d s i l houe t t e t r aps ) will inc rease t h e catch; t he resources of t h e surve i l l ance effort will d e t e r m i n e t h e bes t c o m b i n a t i o n . F o r l o n g - t e r m studies o n t h e t r e n d s of p o p u l a t i o n s of t a b a n i d s in a p a r t i c u l a r g e o g r a p h i c a l a r e a , t h e Manning o r b o x t r a p m a y b e p r e f e r a b l e . F o r s t u d i e s o n spec ies d ivers i ty , t h e M a l a i s e trap is super ior . R e g a r d l e s s of t h e cho ice of surve i l lance m e t h o d , severa l fac tors shou ld be considered. T a b a n i d flight activity a n d hos t - seek ing b e h a v i o u r is in f luenced by daily rhy thms , w e a t h e r a n d l o c a t i o n of v e g e t a t i o n ; t h e i n f l u e n c e of t h e s e f a c t o r s d i f fe rs between species .

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C O N T R O L

Chemical control

Taban ids a r e cons ide r ed t o b e t he m o s t chal lenging l ivestock pes t s to con t ro l , d u e to a n u m b e r of f ac to r s , m o s t l y a s s o c i a t e d wi th t h e life cycle of t a b a n i d s . F e m a l e s spend o n l y fou r m i n u t e s f e e d i n g o n a h o s t t o g e n e r a t e eggs , w h i c h d e v e l o p i n t o a d u l t s the fol lowing year. D i r e c t obse rva t ion of flight b e h a v i o u r is no t poss ib le ; adu l t life his tory is o f ten c a l c u l a t e d o n t h e bas is of ca t ches f rom t r a p s which a r e ineff icient . P r o b a b l y the m o s t i m p o r t a n t fac tor is t h e t e n d e n c y to genera l ize a b o u t a family of over 4,000 species a n d a t l eas t 137 g e n e r a . D u e to t h e c o m p l e x life cycle w h i c h is p a r t l y i n d e p e n d e n t of l ivestock, i n t eg ra t ed con t ro l s t ra tegies a r e r e q u i r e d t o r e d u c e t he i m p a c t of t he se pests.

T h e p o t e n t i a l for a r e a - w i d e c o n t r o l of t a b a n i d p o p u l a t i o n s u s i n g i n s e c t i c i d e s has b e e n s tud ied . A s wi th m o s t o t h e r flies, c o n t r o l of t he larval h a b i t a t is m o s t effective, if such c o n t r o l is poss ib le . S tud ie s in b o t h Afr ica a n d t h e U S A d e m o n s t r a t e d t h a t larval t a b a n i d p o p u l a t i o n s a n d s u b s e q u e n t adu l t p o p u l a t i o n s cou ld b e d r ama t i ca l l y r educed by the w i d e s p r e a d appl ica t ion of pe rs i s t en t insect ic ides o n larval hab i t a t s . H o w e v e r , this a r e a of r e s e a r c h h a s r e c e i v e d l i t t l e a t t e n t i o n o v e r t h e l a s t t w e n t y y e a r s d u e t o the d e m o n s t r a t e d ha rmfu l e n v i r o n m e n t a l impac t s a s soc ia ted wi th such t r e a t m e n t s . These s tudies will b e ins t ruc t ive if se lect ive con t ro l agen t s a r e d e v e l o p e d in t h e fu ture . Area-wide con t ro l of adu l t t aban id s has m e t wi th less success, and this has of ten b e e n blamed o n t h e mob i l i t y of a d u l t t a b a n i d s . M o s t s t ud i e s wi th in t h e last f if teen y ea r s h a v e used u l t r a l ow v o l u m e a p p l i c a t i o n of p y r e t h r o i d s a n d a c h i e v e d s o m e in i t i a l p o p u l a t i o n r educ t ion . Popu l a t i ons often r e t u r n to p r e - t r e a t m e n t levels wi th in 1-3 days , indicat ing a r a p i d inf lux of a d u l t flies (42) . I t w o u l d b e i n a p p r o p r i a t e , o n t h e bas i s of t h e l imited a m o u n t of r e sea rch in this a rea , t o d i scount t he po ten t i a l of adu l t t a b a n i d con t ro l for all s i tua t ions . F e m a l e s of cer ta in t aban id species can b e at least loosely l imi ted in dispersal f r o m l a rva l h a b i t a t s for a b l o o d m e a l d u e t o t h e n e e d to r e t u r n t o o v i p o s i t i o n sites. F u r t h e r m o r e , c a r b o h y d r a t e s o u r c e s for f l ight e n e r g y m a y b e spec i f ic t o t h e n o r m a l h a b i t a t s of d i f fe ren t spec i e s . I n r e g i o n s w i t h s h o r t t a b a n i d s e a s o n s a n d s y n c h r o n o u s adul t e m e r g e n c e , adu l t con t ro l could b e effective in small , i so la ted hab i t a t s . In tropical a n d sub t rop ica l reg ions , a succession of t a b a n i d species e m e r g e t h r o u g h o u t m u c h of the yea r . W i t h th i s a s y n c h r o n o u s e m e r g e n c e of a d u l t t a b a n i d s , t h e t i m i n g of s h o r t - t e r m p e s t i c i d e u s e t o kil l a d u l t s w o u l d n o t b e p r a c t i c a l . I n t h e s e a r e a s , a d u l t c o n t r o l with insec t i c ides w o u l d p r o b a b l y b e m o s t effect ive , us ing i n s e c t i c i d e - i m p r e g n a t e d targets s imilar to those used for t se t se (136). Howeve r , t h e t a rge t s wou ld h a v e t o b e specifically des igned for t aban ids .

T h e effect on t he t a b a n i d b u r d e n of t h e use of insect ic ides a n d r epe l l en t s app l ied to l ivestock has b e e n s tud ied to s o m e deg ree . E a r l y w o r k es tabl ishing t h e e c o n o m i c impact of t a b a n i d s on ca t t le was c o n d u c t e d us ing synerg ized Pyre th r ins t o p r o v i d e pro tec t ion from t aban id a t tack (11). T h e major i ty of t he p roduc t s used for e q u i n e p r o t e c t i o n have h i s t o r i c a l l y c o n t a i n e d s y n e r g i z e d P y r e t h r i n s w i t h s o m e c o m b i n a t i o n of k n o w n r e p e l l e n t s . D u e to l i m i t e d r e s i d u a l ac t iv i ty a n d e x p e n s e , t h e u s e of P y r e t h r i n s is n o r m a l l y conf ined to va luab l e s tock u n d e r in tens ive m a n a g e m e n t . M a n y of t h e newer fo rmula t ions for e q u i n e cont ro l con ta in o n e of several py re th ro ids , such as pe rmethr in , r e s m e t h r i n or Cypermethr in . W o r k c o n d u c t e d by the au tho r s has ind ica ted t h e potential ro le of py re th ro id s in reduc ing the impac t of t aban ids on o t h e r types of l ivestock.

T h e p y r e t h r o i d f e n v a l e r a t e w a s a p p l i e d u s i n g a h i g h - p r e s s u r e ( 1 0 0 - 2 0 0 psi = 7-14 x 1 0 5 P a ) s p r a y as a m o d e l for d e t e r m i n i n g t h e effects of p y r e t h r o i d s o n tabanid f eed ing success . F e e d i n g t i m e was f o u n d t o b e significantly lower ( 3 5 % r e d u c t i o n ) on

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treated cows for t h e h o r s e fly species obse rved , a n d t h e a m o u n t of b l o o d c o n s u m e d was also significantly r e d u c e d (by 30%) . R e d u c i n g t h e feed ing t i m e of a p o p u l a t i o n of h o r s e flies by 3 5 % w o u l d r e s u l t in a 3 5 % r e d u c t i o n of f l ies o n t h e a n i m a l a t a n y t i m e . Reducing t h e a m o u n t of b l o o d losses by a p p r o x i m a t e l y 3 0 % w o u l d a l so b e p o s s i b l e . M a r k / r e c a p t u r e a n d d i s s e c t i o n ( p a r i t y ) s t u d i e s i n d i c a t e d t h a t a t l e a s t 2 0 % of t h e tabanids feed ing o n ca t t l e c o n t i g u o u s t o l a rva l h a b i t a t s h a d fed in t h a t a r e a wi th in t h e previous four days . A 4 4 % r e d u c t i o n in daily b l o o d loss d u e t o t a b a n i d feeding for ca t t le t r ea ted w i t h f e n v a l e r a t e w o u l d b e p r e d i c t e d f r o m t h e c o m b i n a t i o n of r e d u c e d subsequent feeding a n d r e d u c e d size of b l o o d m e a l s ( 2 7 , 6 4 ) .

As 2 0 % of t h e p o p u l a t i o n can essent ia l ly b e con t ro l l ed , t he efficacy of p y r e t h r o i d e a r tags and s p r a y s w a s e v a l u a t e d a g a i n s t t a b a n i d s u n d e r f ie ld c o n d i t i o n s in L o u i s i a n a . Overall fly m o r t a l i t y r a t e s w e r e 3 % in c o n t r o l s , 9 % us ing p e r m e t h r i n tags , 1 5 % us ing fenvalerate tags , 6 7 % us ing f enva l e r a t e s p r a y a t 0 . 0 1 % , 7 9 % us ing f enva l e ra t e sp ray a t 0.02%, and 1 0 0 % using 1-cyhalothrin tags (65) . A t ce r t a in c o n c e n t r a t i o n s of p y r e t h r o i d s , a large p e r c e n t a g e ( u p t o 60%) of flies w h i c h feed o n ca t t l e will su rv ive ' k n o c k - d o w n ' under l a b o r a t o r y c o n d i t i o n s . A m a r k / r e c a p t u r e e x p e r i m e n t w a s c o n d u c t e d t o d e t e r m i n e w h e t h e r s i m i l a r s u r v i v a l r a t e s c o u l d b e o b s e r v e d u n d e r f ie ld c o n d i t i o n s (i.e. in t h e p r e s e n c e of p r e d a t o r s , e t c . ) . I t w a s d e t e r m i n e d t h a t 7 4 % of t h e flies w h i c h would survive a k n o c k - d o w n d o s e u n d e r l a b o r a t o r y c o n d i t i o n s w o u l d ac tua l ly surv ive under field cond i t ions . T h e r e f o r e , k n o c k - d o w n c a n n o t b e cons ide r ed as a n ind ica to r of potential mor t a l i t y in t he field.

Studies o n t h e t r e a t m e n t of l ives tock wi th r e s idua l insec t ic ides p r i o r to p y r e t h r o i d s found little effect o t h e r t h a n adu l t mor ta l i ty after t h e flies h a d c o m p l e t e d a b l o o d mea l . Parity s tudies c o n d u c t e d by t h e a u t h o r s h a v e s h o w n t h a t this can h a v e a l imi ted i m p a c t on the t a b a n i d b u r d e n of l ivestock ove r t ime . T h e r e a p p e a r s to b e s o m e ind ica t ion t h a t the use of p y r e t h r o i d sprays p r o v i d e s pa r t i a l p r o t e c t i o n for l ivestock.

Cultural control

A n i m a l m a n a g e m e n t c a n i n f l u e n c e t h e i n c i d e n c e of t a b a n i d s o n l i v e s t o c k . F e w tabanid species will e n t e r b a r n s o r o t h e r s t r u c t u r e s ; t h e spec ies of h o r s e flies wh ich d o enter s t r u c t u r e s a r e u s u a l l y ac t i ve d u r i n g c r e p u s c u l a r o r n o c t u r n a l p e r i o d s . T a b a n i d attack can b e r e d u c e d e v e n w h e n ca t t l e a r e s t a n c h i o n e d b e n e a t h r o o f s s u p p o r t e d b y posts and wi th o p e n s ides . G i v e n access t o s u i t a b l e s t r u c t u r e s , f r e e - r o a m i n g l ives tock will seek she l te r f rom t a b a n i d a t tack .

F e w e r p r o b l e m s will b e e n c o u n t e r e d o n p a s t u r e s l o c a t e d we l l a w a y f rom w o o d e d areas. R. C o m b s (pe rsona l c o m m u n i c a t i o n ) found tha t of t aban ids col lec ted f rom s teers , 3 1 % were col lected 120 m in to t h e woods , 3 4 % at 20 m in to t h e w o o d s a n d 1 2 % , 7 % , 6 % , 5% and 5 % at 20 m , 120 m, 220 m, 420 m a n d 720 m f rom e d g e of t h e w o o d , respectively. In o the r s t u d i e s , r e d u c e d c a t c h e s of t a b a n i d s w e r e r e p o r t e d w h e n c a n o p y t r a p s w e r e placed away f rom t h e edge of t h e w o o d , a n d the n u m b e r of dee r flies a t t r ac ted to h u m a n s was reduced app rox ima te ly 90-fold w h e n r e sea rche r s m o v e d f rom w o o d e d edges t o 50 m into cult ivated fields (43). T h e r e f o r e , l a rger pa s tu r e s shou ld b e used dur ing p e a k t a b a n i d activity. M a n a g e m e n t of grazing a reas re la t ive t o t aban id seasona l occur rence m a y b e an element to cons ider in in t eg ra t ed m a n a g e m e n t of t aban ids .

As s t a t e d a b o v e , in r e g i o n s w h e r e w o o d e d h a b i t a t s p r e d o m i n a t e , t h e i n c i d e n c e of tabanids o n l ives tock m a y b e i n f l u e n c e d by t h e p r o x i m i t y of w o o d e d a r e a s t o g r az ing areas. D e e r flies a r e p r imar i ly a m b u s h feeders , a t t ack ing m o v i n g v e r t e b r a t e s u p o n en t ry into or within w o o d e d a reas . R e m o v a l of t r ee s a n d o t h e r vege t a t i on has b e e n assoc ia ted with r e d u c t i o n in d e e r fly n u m b e r s . I n c r e a s i n g p a s t u r e s ize a n d l i m i t i n g a c c e s s t o

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w o o d e d a r e a s c a n s e r v e m u l t i p l e f u n c t i o n s i n c l u d i n g i n c r e a s e d f o r a g e p r o d u c t i o n , a l l o w i n g a n i m a l s a d e q u a t e d i s t a n c e t o m o v e t o a r e a s of l o w t a b a n i d a t t a c k r a t e , r e d u c i n g t a b a n i d a t t a c k w i t h i n w o o d e d a r e a s a n d r e d u c i n g t ick b u r d e n s . V e g e t a t i o n con t ro l can also r e d u c e oviposi t ion if the oviposi t ion subs t r a t e occurs a long the margins of aqua t i c hab i t a t s .

T h e use of vege ta t ive ba r r i e r s has b e e n p r o p o s e d to p r e v e n t m o v e m e n t of sal tmarsh t a b a n i d s in to s t ra teg ic a r eas . M o r g a n a n d L e e (81) r e p o r t e d h ighe r ca tches of Tabanus nigrovittatus a t g a p s in a d e n s e wal l of b u s h e s a n d g r a s s e s s e p a r a t i n g fly b r e e d i n g g r o u n d s f rom r e c r e a t i o n a l a r e a s . R o b e r t s (103) o b s e r v e d t h a t t a b a n i d s w o u l d n o t fly over an 8 ft (2.4 m ) high fence c o m p o s e d of 1/4-inch (0.6 cm) m e s h h a r d w a r e c lo th wire t o feed on s t ee r s . T h e s e s tud ies s u p p o r t m u l t i p l e o b s e r v a t i o n s t h a t t a b a n i d s fly round ba r r i e r s r a t h e r t h a n over t h e m .

W a t e r m a n a g e m e n t is a l so a t o o l w h i c h c a n b e u s e d for m a n a g i n g t a b a n i d larval h a b i t a t s . U n f o r t u n a t e l y , t h e r e is s u c h a p a u c i t y of i n f o r m a t i o n o n l a r v a l h a b i t a t s in g e n e r a l t h a t r a t i o n a l d e c i s i o n s c a n n o t b e m a d e r e g a r d i n g t h e p o t e n t i a l e f fec t s of d r a i n i n g . F o r e x a m p l e , d r a i n i n g o n e h a b i t a t t o c o n t r o l o n e c o m p l e x of s p e c i e s may c rea t e add i t iona l larval hab i t a t s for o t h e r species . S t ra tegica l ly- t imed flooding of certain larval h a b i t a t s can b e pa r t i cu la r ly effective in inh ib i t ing adu l t e m e r g e n c e or l ead ing to t he d e a t h of l a rvae o r p u p a e . A n d e r s o n a n d K n e e n (2) d e m o n s t r a t e d th is p r inc ipa l by t e m p o r a r y i m p o u n d m e n t of s a l t m a r s h e s t o c o n t r o l d e e r f l ies . T h i s p r i n c i p a l is also d e m o n s t r a t e d in n a t u r e in f l o o d e d h a r d w o o d fo res t h a b i t a t s . P r i o r t o p u p a t i o n , the l a rvae t rave l u p t o dr ier a reas w h e r e p u p a t i o n occurs . If these a reas a r e f l ooded d u e to e x c e s s i v e r a i n s , a d u l t p o p u l a t i o n s a r e g r e a t l y r e d u c e d . S p r a y i n g k e r o s e n e o r o ther sur fac tants on t he surface of small na tu r a l or artificial wa t e r poo ls w h e r e t aban ids drink has also b e e n m e n t i o n e d as a m e t h o d of survei l lance a n d con t ro l (1).

Mechanical control

T h e s a l t m a r s h g r e e n h e a d , T. nigrovittatus, is c o n s i d e r e d t o b e a n i m p o r t a n t h u m a n p e s t a l o n g t h e A t l a n t i c c o a s t of t h e U S A , a n d t h e u s e of p e r m a n e n t t r a p s for adult T. nigrovittatus con t ro l has b e e n advoca ted . Modif ica t ions of t he M a n i t o b a t r a p a n d the M a n n i n g t r a p h a v e evo lved in to t he n o w wide ly-used box t r a p (137) . T h e s e t r aps have b e e n s h o w n t o co l l ec t g r e a t n u m b e r s of s a l t m a r s h g r e e n h e a d s , t h u s r e d u c i n g bit ing ac t iv i ty o n h u m a n s . H o w e v e r , l o n g - t e r m p o p u l a t i o n s u p p r e s s i o n is n o t c o n s i d e r e d poss ible . T. nigrovittatus females a re a u t o g e n o u s , and t r app ing does n o t p r e v e n t t h e first oviposi t ion.

Biological control

W h e n c o n s i d e r i n g b io log ica l c o n t r o l , it s h o u l d b e r e c o g n i s e d t h a t t a b a n i d s a r e no e x c e p t i o n a m o n g i n s e c t s ; t h e r e a r e m a n y n a t u r a l i n f e c t i o u s d i s e a s e s , p a r a s i t e s and p r e d a t o r s at all life s tages of t a b a n i d s . H o w e v e r , t he m a n i p u l a t i o n of n a t u r a l mortal i ty factors has rare ly b e e n exp lo red for the suppress ion of t a b a n i d p o p u l a t i o n s . Therefore , this sec t ion will b e a b b r e v i a t e d wi th s o m e prac t ica l n o t e s . C o m p r e h e n s i v e r ev iews are ava i lab le o n t h e desc r ip t ion of d iseases , pa ras i t e s a n d p r e d a t o r s ( 1 , 1 0 0 ) . T h e diversity a n d d y n a m i c s of t a b a n i d p o p u l a t i o n s buffer th is g r o u p aga ins t d e p l e t i o n by paras i tes a n d p r e d a t o r s . F o r e x a m p l e , adu l t t a b a n i d p r o d u c t i o n f rom flooded h a r d w o o d forest f loors in L o u i s i a n a a v e r a g e s 1 fly p e r sq. ft (1 sq. ft = 0.09 m 2 ) of soil su r face , which is equ iva l en t t o 43,500 adu l t t a b a n i d s (21,750 females) p e r acre . T h e a u t h o r s h a v e found t h a t a p p r o x i m a t e l y 5 0 % of t h e s e f e m a l e s success fu l ly c o m p l e t e a b l o o d m e a l and depos i t a r o u n d 200 eggs (or 2,150,000 eggs in to ta l ) . T h u s , only 2 % survival f rom egg to adul t is r e q u i r e d to ma in t a in annua l popu la t ions .

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T h e m a j o r n a t u r a l e n e m i e s of t a b a n i d eggs a r e h y m e n o p t e r o u s p a r a s i t e s . P a r m a n (85) a t t e m p t e d t o s u p p l e m e n t p a r a s i t i s m of eggs d e p o s i t e d in a speci f ic h a b i t a t ; t h e e x p e r i m e n t a l d e s i g n of t h i s s t u d y p r e c l u d e d i n t e r p r e t a t i o n of t h e d a t a . M e r m e t h i d n e m a t o d e s a p p e a r t o a c c o u n t for a p p r o x i m a t e l y 4 0 % of i n f e c t i o n ( a n d a s s u m e d mortal i ty) in ce r t a in l a rva l t a b a n i d p o p u l a t i o n s . M a n y t y p e s of in fec t ious a g e n t s h a v e been iso la ted f rom t a b a n i d l a rvae , b u t t h e r e h a v e b e e n few ep idemio log ica l s tud ies on these l a r v a e . V e r t e b r a t e a n d i n v e r t e b r a t e p r e d a t o r s , as we l l as c a n n i b a l i s m a m o n g tabanid la rvae , a p p e a r to h a v e litt le effect o n t a b a n i d p o p u l a t i o n s .

F u n g i a n d p r o t o z o a ( e s p e c i a l l y m i c r o s p o r i d i a ) h a v e b e e n i s o l a t e d f r o m v a r i o u s t aban id life s t a g e s b u t , as w i t h p a t h o g e n i c b a c t e r i a , i n t r o d u c t i o n of a g e n t s i n t o popu la t ions is a l im i t i ng fac tor . M o r e r ecen t l y , s p i r o p l a s m a s ( m o l l i c u t e s ) h a v e b e e n isola ted , a n d h o r i z o n t a l t r a n s m i s s i o n of t h e s e a g e n t s m a y o c c u r . S i n c e t a b a n i d popu la t ions a r e r e s i s t a n t t o n a t u r a l l y - o c c u r r i n g b i o l o g i c a l c o n t r o l a g e n t s , m o l e c u l a r m a n i p u l a t i o n of a g e n t s t r a n s m i t t e d h o r i z o n t a l l y b e t w e e n t a b a n i d s wil l m o s t l i k e l y provide the first tool for r educ ing t a b a n i d p o p u l a t i o n s us ing biological con t ro l .

In p r a c t i c e , t h e o n l y f o r m of b i o l o g i c a l c o n t r o l w h i c h p r o v i d e s p r o t e c t i o n fo r livestock occurs w h e n p r e d a t o r s i n t e r c e p t h o s t - s e e k i n g t a b a n i d s n e a r a n i m a l s . U n d e r some c i r c u m s t a n c e s , s a r c o p h a g i d s a n d d r a g o n f l i e s c a n i n t e r r u p t t a b a n i d f e e d i n g . Howeve r , t h e m o s t d r a m a t i c r e d u c t i o n in t a b a n i d f e e d i n g r e l a t i v e t o p r e s e n c e of p r e d a t o r s o c c u r s w h e n B e m b e c i n e w a s p s ( N y s s o n i n e ) a r e a c t i v e a r o u n d l i v e s t o c k . Tabanids a re c a p t u r e d by t he se wasps a n d used as food for the i r l a rvae , a n d t h e n u m b e r of t aban ids f e e d i n g o n l ives tock is r e d u c e d b e l o w t h e level of p r e d a t i o n as a r e su l t of tabanids avo id ing c o n t a c t wi th t he se wasps . U n f o r t u n a t e l y , t he larval h a b i t a t s of t he se wasps a re usual ly specific, a n d s ea sona l p o p u l a t i o n p e a k s of t h e wasps a r e m u c h s h o r t e r than those of t a b a n i d s .

Control summary

Repe l len t s a n d select ive graz ing or c o n f i n e m e n t m a y b e used to r e d u c e t h e i m p a c t of tabanids . M a n i p u l a t i o n of l a rva l h a b i t a t s c o u l d b e u s e d for p o p u l a t i o n c o n t r o l if t h e need was e s t a b l i s h e d . P e r m a n e n t t r a p s ( a n d poss ib ly t r e a t e d s i l h o u e t t e t r a p s ) c a n b e employed to i n t e r cep t flies. Insec t ic ide u s e for o t h e r pe s t s ( ea r tags , sprays or dips) m a y have a par t ia l i m p a c t o n t h e t a b a n i d b u r d e n u n d e r ce r t a in cond i t ions .

STABLE FLIES

T h e s t a b l e fly Stomoxys calcitrans (L . ) a n d s e v e n t e e n o t h e r spec i e s c o m p r i s e t h e genus Stomoxys; m o s t of t h e s e m u s c o i d flies a r e f o u n d in Afr ica (147) . A d u l t s of b o t h sexes a re b l o o d feeders , which b inds these flies to a close r e l a t i onsh ip wi th hos t an imals , including d o m e s t i c species of l ivestock. Of all t he species of Stomoxys, S. calcitrans is t he most widely d i s t r i bu t ed a n d is c o n s i d e r e d t o b e a c o s m o p o l i t a n pes t . S. niger M a r q u a r t (formerly S. nigra) has also a t t a i n e d pes t s ta tus in ce r t a in pa r t s of Afr ica (86) .

A d u l t s a r e bas ica l ly g r e y in co lou r , w i t h f o u r b l a c k s t r i p e s o n t h e t h o r a x , a n d t h e abdomen is t e s s e l l a t e d ( c h e c k e r e d ) in b l ack . T h e e x t r e m e w i d t h of t h e f rons a n d t h e characteristic m a r k i n g s o n t h e a b d o m e n a re usual ly sufficient for ident i f ica t ion of t h e s e species. Size r a n g e is 4-7 m m for S. calcitrans, a n d 5-7 m m for S. niger (147). S. calcitrans greatly r e s e m b l e s t h e h o u s e fly Musca domestica L . t o t h e u n t r a i n e d e y e , u n t i l o n e notices t h e s w o r d - l i k e p r o b o s c i s p r o j e c t i n g f r o m b e n e a t h t h e h e a d . S t a b l e flies a r e

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c o m m o n l y m i s t a k e n for sma l l s p e c i e s of h o r s e flies ( T a b a n i d a e ) d u e t o t h e i r bi t ing activity, or for o t h e r flies s imilar in size a n d co lour t o t h e s table fly.

B I O L O G Y

W h e n s tudying the biology and habi t s of h ighly-mobi le pes t species, such as t h e stable fly, it is i m p o r t a n t to b e familiar wi th all s tages of t he life cycle, especial ly w h e n planning c o n t r o l s t r a t e g i e s . M a n y l i ves tock p r o d u c e r s d o n o t r ea l i ze t h a t fly l a r v a e (maggots ) even tua l l y b e c o m e t h e w i n g e d adu l t wh ich is a n n o y i n g the i r an ima l s . S o m e p roduce r s r e p o r t tha t , a few days after not ic ing small flies o n cat t le , these flies have b e c o m e larger; th is is of c o u r s e i nco r rec t . A f t e r t h e adu l t fly e m e r g e s f rom its p u p a l case , it g rows no l a rge r wi th t i m e . T h e size of adu l t flies is d e p e n d e n t o n t h e d e v e l o p m e n t a l condi t ions (e .g . n u t r i t i o n , t e m p e r a t u r e a n d m o i s t u r e ) t o w h i c h t h e i m m a t u r e flies ( l a r v a e ) have b e e n subjec ted . T h e life cycle of t he s table fly is c o m p o s e d of four stages; egg, larva , pupa a n d adul t . S tab le fly eggs h a t c h after 12-24 h in to small , f irst- instar l a rvae . T h e s e larvae g r o w a n d m o l t i n t o t h e l a r g e r s e c o n d - a n d t h i r d - i n s t a r l a r v a e . T h i r d - i n s t a r larvae eventua l ly fo rm the pupa l s tage. A t 27°C, this process t akes approx ima te ly 12-13 days for S. calcitrans (63) a n d 28-32 days for S. niger (77) . Af t e r a p p r o x i m a t e l y 7-14 days in the p u p a l s tage for S. calcitrans a n d S. niger, respectively, adul ts e m e r g e t o seek a hos t and a b l o o d mea l . A d u l t s beg in m a t i n g w h e n 3-5 days old and females begin laying eggs when 5-8 days old. A d u l t s mus t h a v e b l o o d mea l s to successfully m a t e , a n d females n e e d blood m e a l s for egg p r o d u c t i o n . F e m a l e s of b o t h species lay b e t w e e n 60 a n d 130 eggs during o n e cycle and m o v e frequently, depos i t ing eggs in small n u m b e r s t h r o u g h o u t t h e chosen m e d i u m . A n o t h e r b l o o d m e a l m u s t b e t a k e n b e f o r e a s e c o n d b a t c h of eggs c a n be p r o d u c e d . R e p o r t s of l i f e t i m e egg p r o d u c t i o n a r e v a r i a b l e for b o t h s p e c i e s , but p r o d u c t i o n r anges b e t w e e n 60 a n d 800 eggs. S. calcitrans adul t s will live u p t o 35 days in t h e l a b o r a t o r y , b u t p r o b a b l y su rv ive less t h a n t w o w e e k s in t h e field (56) . L a b o r a t o r y survival of S. niger adul t s is t en days (77).

S tab le fly l a rvae d e v e l o p in m a n u r e , spilled feed and decaying vege t a t i on (74) . Pupae m a y also b e f o u n d in t he se mate r i a l s or in t he subs t ra te immed ia t e ly b e l o w or adjacent t o t h e s e m a t e r i a l s . B e c a u s e p u p a e a r e usual ly found close t o la rva l d e v e l o p m e n t sites, t h e fo l lowing d iscuss ion is gene ra l ly l imi ted t o m a t e r i a l s u s e d for la rva l deve lopmen t .

D e c a y i n g v e g e t a t i o n is u s e d a l m o s t exc lus ive ly by b o t h S. calcitrans a n d S. niger, l a r v a e a r e n o t u sua l l y f o u n d in a s s o c i a t i o n w i t h c o w m a n u r e , un l e s s t h e m a n u r e has b e e n d r o p p e d o n v e g e t a t i o n . In th is case , t h e v e g e t a t i o n b e c o m e s w e t w i t h mo i s tu r e f rom t h e m a n u r e . W i t h t h e o n s e t of f e r m e n t a t i o n , t h e v e g e t a t i o n b e c o m e s a sui table m e d i u m fo r l a r v a l d e v e l o p m e n t . L a r v a e d e v e l o p in t h e v e g e t a t i o n n e a r the v e g e t a t i o n / m a n u r e in te r face , b u t n o t in t h e m a n u r e itself. S t ab l e fly l a rvae a n d pupae h a v e b e e n o b s e r v e d in m a n u r e w h e n mois t m a n u r e wi th a dry c rus ted surface has been c o v e r e d w i t h l aye r s of h a y w h i c h a r e d r y a n d n o t in a s t a t e of d e c o m p o s i t i o n . In this case , t he m a n u r e is m o r e sui table for fly d e v e l o p m e n t t h a n the hay (50).

S t a b l e flies h a v e b e e n f o u n d in m i x e d m a n u r e a n d sp i l l ed f e e d s a m p l e s from cage- layer houses at an inc idence of 1 % or less of t he to ta l p o p u l a t i o n of h o u s e flies and s t ab le flies (46) . L a r v a e d e v e l o p in t h e b e d d i n g of o u t d o o r calf h u t c h e s , pa r t i cu la r ly if t he b e d d i n g is coarse s t raw a n d the d ra inage b e n e a t h hu tches is p o o r (109). L i t t e r from s tab les is a lso a f r equen t sou rce of s tab le fly d e v e l o p m e n t . Stall l i t ter d u m p e d in wind­r o w s o r in i n d i v i d u a l s m a l l p i l e s , c o m b i n e d w i t h r a i n o r p o o r d r a i n a g e , p r o d u c e s mate r i a l s which r e m a i n we t e n o u g h to p r o d u c e flics for long pe r iods of t i m e (47) .

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O n ca t t le f eed lo t s in t h e m i d - w e s t e r n U S A , ca t t l e m a n u r e is a n i m p o r t a n t m e d i u m for s table fly la rva l d e v e l o p m e n t (120) . C o n c e n t r a t e d n u m b e r s of ca t t l e p r o d u c e l a rge a m o u n t s of m a n u r e in r e l a t i v e l y s m a l l a r e a s . D u r i n g t h e s u m m e r fly s e a s o n , h i g h ambient t e m p e r a t u r e s c a u s e e x p o s e d m a n u r e t o b e c o m e d ry a n d crusty. M o i s t u r e a n d nu t r i en t s a r e s e a l e d b e n e a t h t h e s u r f a c e , t h u s i n c r e a s i n g t h e p o t e n t i a l fo r m a n u r e u t i l iza t ion o v e r l o n g p e r i o d s ; t h e s t a t u s of fly d e v e l o p m e n t in t h e s e a r e a s m u s t b e determined by inspec t ion , i.e. by digging b e n e a t h t h e surface .

H a y d r o p p e d by c a t t l e w h i l e f e e d i n g f r o m l a r g e b a l e s of h a y m a y c o n s t i t u t e t h e g rea tes t s i ng l e s t a b l e fly b r e e d i n g m e d i u m in c e r t a i n a r e a s . A n a v e r a g e of 28,000 l a r v a e / m 2 was f o u n d in h a y r e s i d u e s o n a da i ry n e a r T a l l a h a s s e e , F l o r i d a (89) . Residues can r e m a i n act ive as b r e e d i n g sites for severa l m o n t h s a n d b e c o m e qu i t e th ick, especially w h e n n e w hay is rou t ine ly p l aced o n t o p of decay ing r e m n a n t s f rom p rev ious bales. Wi th u r i n e , m a n u r e a n d r a in b e i n g m i x e d in as n e w r e s i d u e s a r e d e p o s i t e d , t h e habitat offers flies a var ie ty of t o l e r ab le t e m p e r a t u r e a n d m o i s t u r e r anges . T h e r e s idues insulate l a r v a e f rom a m b i e n t t e m p e r a t u r e s a n d p r e v e n t t h e m f r o m b e i n g c r u s h e d by cattle. If t he ra ins a r e i n t e r m i t t e n t a n d res idues b e c o m e a l t e rna te ly dry a n d mois t , larval activity m a y a l so b e i n t e r m i t t e n t u n t i l t h e r e s i d u e s a r e n o l o n g e r a t t r a c t i v e as oviposition s i tes . I n s p e c t i o n is m a d e b y d igging b e n e a t h t h e sur face layer ; t h e sur face layer of hay m a y look t h e s a m e o n act ive a n d inact ive r e s idues (50).

S t ab l e f l ies h a v e b e e n f o u n d t o o v i p o s i t in r o l l e d h a y b a l e s s t o r e d in f ie lds ( 3 9 ) , d e m o n s t r a t i n g t h a t s t a b l e f l ies c a n d e v e l o p in m a t e r i a l s a n d in a r e a s w h i c h a r e n o t usually suspect .

R e s i d u e s f r o m s p i l l a g e o r o v e r f e e d i n g of g r e e n c h o p ( t h e t o p p o r t i o n s of y o u n g forages which h a v e b e e n cut a n d fed i m m e d i a t e l y ) a r e also la rva l hab i t a t s . T h e hab i t a t s provided by g r e e n c h o p a n d ro l led hay r e s idues similarly p r o v i d e wide t e m p e r a t u r e a n d moi s tu re r a n g e s a n d p r o t e c t i o n f r o m c a t t l e a n d a m b i e n t t e m p e r a t u r e . S u c c u l e n t g reenchop r e s i d u e s d e c o m p o s e m u c h f a s t e r t h a n d r y r o l l e d h a y r e s i d u e s , a n d d o n o t require as m u c h m o i s t u r e f rom o u t s i d e sou rces t o r e m a i n a t t r ac t ive to s t ab le flies (50) . Silage is an exce l l en t m e d i u m for t h e d e v e l o p m e n t of s t ab l e fly l a rvae . L a r v a e m a y b e found in p e r i p h e r a l a reas of t r e n c h a n d b u n k e r silos a n d in spil lage a r o u n d up r igh t silos and feed b u n k s . S e m i - p e r m a n e n t h a b i t a t s h a v e a l so b e e n o b s e r v e d o n f a r m s w h e r e silage is fed r o u t i n e l y d u r i n g t h e fall a n d w i n t e r m o n t h s . S i l a g e is u t i l i z e d b y overwintering s t ab le fly p o p u l a t i o n s in m a n y pa r t s of t he U S A (74).

In Africa, S. niger deve lops in decay ing vege t a t i on in forests or f rom agr icu l tu re , b u t it is associated par t icu la r ly wi th debr i s which a c c u m u l a t e s du r ing t h e ha rves t i ng of sugar cane. A s m a n y as 50-60 l a r v a e a n d p u p a e of S. niger h a v e b e e n f o u n d p e r m 3 of s u g a r cane debris . Suga r c a n e can b e u s e d by S. niger four h o u r s after cu t t ing a n d for t h r e e t o four m o n t h s the rea f t e r (60) .

In coas ta l a r e a s , m a r i n e a n d f r e s h w a t e r g rasses a n d a lgae w a s h e d or h a u l e d a s h o r e are t h e on ly k n o w n n a t u r a l l y - o c c u r r i n g m e d i a p o t e n t i a l l y a v a i l a b l e for l a r g e - s c a l e d e v e l o p m e n t of s t a b l e fly l a r v a e . H a b i t a t s p r o v i d e d b y a q u a t i c g r a s s e s a r e v e r y short-lived; only o n e g e n e r a t i o n of flies m a y b e ab le t o fully uti l ize t h e m e d i u m be fo re it becomes u n s u i t a b l e for l a rva l d e v e l o p m e n t (118) . A l t h o u g h it was or ig ina l ly b e l i e v e d that s table flies d e v e l o p e d in b a y grasses a long coas ta l a r ea s a n d t h e n m o v e d in l and in large n u m b e r s t o a n n o y l i ve s tock (57) , f u r t h e r r e s e a r c h h a s s h o w n t h a t a g r i c u l t u r a l areas are t h e p r i m a r y sources of fly d e v e l o p m e n t a n d t h a t fly o u t b r e a k s occur in coas ta l areas e v e n w h e n d e p o s i t s of g r a s s e s o n t h e b a y s h o r e s a r e n o n - e x i s t e n t ( 144 ) . A f t e r arriving in coas ta l a r e a s , t h e p r i m a r y ( i .e . m o s t c o m m o n l y e n c o u n t e r e d ) h o s t s of t h e

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s t a b l e fly a r e h u m a n s . F a v o u r e d feed ing si tes a r e t h e b a c k of t h e k n e e a n d t h e elbow, a n d l a n d i n g r a t e s of 80-100 flies p e r m i n u t e o n h u m a n s a r e n o t u n c o m m o n du r ing o u t b r e a k s (50).

I n ag r i cu l tu r a l a r e a s , t h e s t ab l e fly is ma in ly a pes t of l ives tock. H u m a n s a r e rarely b i t t e n u n l e s s fly p o p u l a t i o n s a r e l a r g e a n d n o c a t t l e o r o t h e r l i v e s t o c k a r e p r e s e n t n e a r b y . F l i e s u s u a l l y f eed b e l o w t h e k n e e s a n d h o c k s of a n i m a l h o s t s , b u t t h e y may m o v e o n t o t h e s ides a n d b a c k if p o p u l a t i o n s a r e la rge (>25 p e r leg) . S tab le flies t e n d to wa i t in o n e l o c a t i o n , r a t h e r t h a n fo l lowing t h e ca t t l e , p a r t i c u l a r l y in da i r i e s (51) , but t h e y m a y d i s p e r s e 5 k m o r m o r e in s e a r c h of b l o o d m e a l s (50 ) . T h e p o s s i b i l i t y of l ong - range fly d i spersa l was su spec t ed after it b e c a m e ev iden t t h a t s t ab le flies invading coas ta l zones w e r e no t deve lop ing in l i t toral depos i t s of m a r i n e grasses (144). By t h e use of m a r k e d , l a b o r a t o r y - r e a r e d s t ab l e flies, a flight r a n g e of 112 k m was e s t ab l i shed and t h e c a p a c i t y for l o n g - r a n g e flight c o n f i r m e d (4) . T h e abi l i ty of s t a b l e flies t o migra te o v e r e v e n l o n g e r d i s t a n c e s w a s d e m o n s t r a t e d in 1981 w h e n wi ld s t a b l e f l ies w e r e c a p t u r e d on b e a c h e s 225 k m from in land m a r k i n g sites. A l t h o u g h l ong - r ange dispersal has n o t b e e n o b s e r v e d for S. niger, d a t a f rom var ious au tho r s suggest t h a t t he se flies can m o v e 3 k m (77, 60, 86).

O b s e r v a t i o n s of s t a b l e flies p r o b i n g f lowers , p r e s u m a b l y in s e a r c h of n e c t a r (132), s u p p o r t t h e t heo ry t h a t coas ta l p o p u l a t i o n s a r e in a mig ra to ry p h a s e . R e c o r d s of similar b e h a v i o u r can b e found in t h e l i t e ra tu re (127 ,41) , bu t little significance was given to this p h e n o m e n o n , as it was a s s u m e d t h a t s t ab le flies cou ld no t survive for m o r e t h a n a few days wi thou t a b l o o d mea l . H o w e v e r , s tab le flies h a v e b e e n s h o w n to survive for as long as 15 a n d 19 d a y s o n v a r i o u s m e d i a ( h o n e y p lu s p o l l e n e x t r a c t s , a n d p o l l e n ex t rac t s , r e spec t ive ly ) (54) . A l t h o u g h b l o o d is n e e d e d for r e p r o d u c t i o n , t h e n u t r i e n t s in nectar a n d p o l l e n e x t r a c t s w o u l d k e e p flies a l ive , a n d t h u s i n c r e a s e t h e i r c h a n c e s of finding b l o o d m e a l s a n d u l t i m a t e l y r e p r o d u c i n g . S t a b l e flies can p r o b a b l y s t o r e n e c t a r in the c r o p a n d digest it as n e e d e d for ene rgy (54), an ability which has b e e n o b s e r v e d in other b lood - f eed ing D i p t e r a ( 2 2 , 1 2 6 ) . Th i s s t o r age a n d ut i l iza t ion m e c h a n i s m w o u l d enable s t a b l e flies t o s u r v i v e d u r i n g p e r i o d s of p r o l o n g e d f l ight a n d p r o v i d e t h e m w i t h an a l t e rna t ive food source w h e n b l o o d mea l s a r e no t avai lable .

E C O N O M I C I M P A C T

A n a n n u a l cos t of US$9 .80 p e r h e a d ( m o r e t h a n US$100 mil l ion to t a l ) was es t imated in 1993 for S. calcitrans c o n t r o l in t he cat t le indus t ry in t he U S A , a n d for we igh t losses resul t ing f rom s table fly activity (15). W h e n the causes of weight loss w e r e eva lua ted , it was f o u n d t h a t a p p r o x i m a t e l y 7 2 % was d u e t o b u n c h i n g of a n i m a l s a n d t h e resu l t ing h e a t s t ress , a n d t h e r e m a i n i n g 28 % was d u e to ac tua l s t ab le fly feeding a n d t h e energy u s e d to fight t h e flies (142) . T h r e s h o l d e s t i m a t e s for e c o n o m i c d a m a g e to b e e f catt le h a v e b e e n e x p r e s s e d in va r ious t e r m s , a n d suscep t ib i l i ty va r i e s b e t w e e n b r e e d s (18). A v e r a g e daily c o u n t t h r e sho ld es t imates r a n g e from 25 (124) to 50 flies p e r an ima l (16). Less t h a n t w o flies pe r leg was e s t ima ted to b e sufficient t o cause e c o n o m i c d a m a g e to f eeder heifers (17). S tab le flies h a v e b e e n s h o w n to cause r educ t ions in milk p roduc t ion in d a i r y c a t t l e (12 , 7 9 ) , b u t f r ee a c c e s s t o h i g h - e n e r g y f eeds a p p a r e n t l y n e g a t e s the effects of fly feeding (75).

A l t h o u g h m o r e l i m i t e d in d i s t r i b u t i o n t h a n S. calcitrans, S. niger is a s e r i o u s and of ten u n d e r - r a t e d pes t of l ives tock , pa r t i cu l a r ly ca t t l e , in Afr ica . F l ies a t t a c k ca t t l e in large n u m b e r s , often causing debi l i ta t ion as a resul t of t h e loss of b l o o d (77, 60, 86).

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Stable flies c a n h a v e a s ignif icant i m p a c t o n t h e t o u r i s t indus t ry . T h i s h a s p r o b a b l y been bes t d o c u m e n t e d in n o r t h - w e s t F l o r i d a (83 ) , w h e r e s w a r m s of s t a b l e flies h a v e reportedly caused t h e c o m p l e t e e v a c u a t i o n of b e a c h e s a n d tour i s t r e so r t s (57). D o g s can be s u b j e c t e d t o u n r e l e n t i n g a t t a c k s w h i c h wi l l e v e n t u a l l y m u t i l a t e t h e i r e a r s ( 5 0 ) . Although S. niger s e e m s to p re fe r beef a n d da i ry ca t t le , this species a lso a t t acks h u m a n s , dogs and a n u m b e r of o t h e r v e r t e b r a t e hos t s (60) .

Diseases

Stable flies h a v e b e e n s h o w n to t r a n s m i t a n u m b e r of d i sease o rgan i sms . T h e s t ab le fly can b e an i m p o r t a n t m e c h a n i c a l vector , in t h e a b s e n c e of t a b a n i d s . Seve ra l r ev i ews are available which de ta i l t h e ro l e of t h e s t ab le fly in d i sease t r ansmis s ion ( 3 2 , 1 4 7 ) . Of part icular s igni f icance is t h e abi l i ty of S. calcitrans t o m e c h a n i c a l l y t r a n s m i t T. evansi and equine infect ious a n a e m i a ( ' s w a m p fever ' ) , a viral d i sease .

S. calcitrans is a n i n t e r m e d i a t e h o s t fo r s o m e s p e c i e s of Habronema, n e m a t o d e parasites found in t h e s t o m a c h of h o r s e s . A c u t a n e o u s fo rm of h a b r o n e m o s i s , s u m m e r sores, is a skin d isease of ho r ses which deve lops if infec ted flies passively r e l ea se l a rvae while feeding on skin w o u n d s or sores . In fec ted flies r e s o r t t o feed ing o n o p e n w o u n d s because t he h a b r o n e m a l a rvae in te r fe re wi th t h e abil i ty of t h e flies t o p i e r ce t h e skin of the host (147).

S U R V E I L L A N C E

T h e m o s t e f f ec t ive d e v i c e s fo r s u r v e i l l a n c e o r m o n i t o r i n g of a d u l t s t a b l e fly populat ions a r e c o m p o s e d of a ref lect ive m a t e r i a l such as f ibreglass . T h e first of t h e s e , the Wi l l i ams t r a p ( 1 4 3 ) , c o n s i s t e d of t w o r e c t a n g u l a r p a n e l s of f i b r e g l a s s n o t c h e d halfway t h r o u g h t h e l o n g s ides a n d f i t t ed t o g e t h e r in a c ross c o n f i g u r a t i o n . W i l l i a m s traps were i n se r t ed in to s takes a p p r o x i m a t e l y 100 c m h igh a n d c o a t e d wi th a n adhes ive material to ca tch t h e a t t r a c t e d flies.

T h e b a s i c W i l l i a m s t r a p h a s b e e n m o d i f i e d i n a n u m b e r of w a y s . T o f a c i l i t a t e c leaning, s o m e r e s e a r c h e r s p r e f e r r e d t o a p p l y t h e a d h e s i v e t o c l e a r p l a s t i c s l e e v e s slipped ove r t h e f ibreglass i n s t e a d of d i rec t ly o n t o t h e f ibreglass su r face (111) . W h e n fluorescent dus t was a p p l i e d t o t h e f ibreglass i n s t e a d of an adhes ive , t he Wi l l i ams t r a p became an a t t rac t ive se l f -mark ing dev ice for m a r k i n g wild s t ab le flies (48) . C o r r u g a t e d fibreglass was f o r m e d in to a cyl inder t r a p (8) a n d this was s u b s e q u e n t l y commerc i a l i zed . The c o m m e r c i a l c y l i n d e r t r a p is n o t c o a t e d w i t h a n a d h e s i v e , b u t is c o v e r e d w i t h a disposable, c lear-plast ic adhes ive s leeve.

A cy l inde r t r a p c o n s i s t i n g of f ib reg lass w i t h a s c r e e n c o l l e c t i o n d e v i c e a n d b a i t e d with C 0 2 was d e v e l o p e d for cap tu r ing live s tab le flies for d i spersa l s tudies (31) . Seve ra l traps h a v e b e e n m a d e f r o m r e f l e c t i v e p l a s t i c in c o n j u n c t i o n w i t h a d h e s i v e s o r electrocution gr ids (99) a n d s o m e of t h e s e a r e be ing sold commercia l ly .

Trap p l a c e m e n t is p a r a m o u n t to success , as n u m b e r s of c a p t u r e d flies will vary f rom place to p lace in any l ives tock facility. F o r cons i s ten t ly h igh t r a p c o u n t s , t r a p s m u s t b e placed w h e r e f l ies n o r m a l l y c o n g r e g a t e ( e .g . c a t t l e l o a f i n g s i t e s , h o l d i n g p e n s n e a r milking pa r lou r s in dai r ies , p e n s o n t h e p e r i m e t e r s of feedlo ts ) (50) .

In beef a n d da i ry f eed lo t s , c o u n t i n g t h e n u m b e r of s t ab l e flies o n t h e f ront legs of a p r ede t e rmined n u m b e r of a n i m a l s is a c o n v e n i e n t su rve i l l ance t e c h n i q u e , a n d seve ra l sampling m e t h o d s h a v e b e e n d e v e l o p e d (69) . U n d e r c o n f i n e m e n t c o n d i t i o n s , c a t t l e

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readi ly face t he observer , thus facilitating t he count ing process . This t e chn ique is difficult to use with p a s t u r e d cat t le , as cat t le m a y face the obse rve r or tu rn a n d walk away.

A ' s t a n c h i o n e d c a l f t e c h n i q u e w a s d e v e l o p e d for m o n i t o r i n g a d u l t s t a b l e fly p o p u l a t i o n s (130) . D a t a co l l ec t ed us ing th is t e c h n i q u e c o r r e l a t e f avorab ly wi th those co l l ec t ed us ing Wi l l i ams t r aps a n d front leg c o u n t s , thus a l lowing d a t a co l l ec t ed using any of the t h r e e m e t h o d s to b e easily conve r t ed for the p u r p o s e of compar i son .

C O N T R O L

A l l p h a s e s of s t a b l e fly c o n t r o l h a v e b e e n d e s c r i b e d in t w o r e c e n t r e v i e w art icles, w h i c h s h o u l d b e c o n s u l t e d for a c o m p l e t e h i s t o r i c a l o v e r v i e w of t h i s t o p i c (76 , 34). A brief listing of the m o r e i m p o r t a n t con t ro l t echn iques is g iven below.

Chemical control

A n u m b e r of pes t ic ides a n d repe l len t s a r e avai lable for t h e m a n a g e m e n t of s table fly p o p u l a t i o n s on l ivestock. H o w e v e r , t he efficacy of m a n y of these is re la t ively short-l ived ( severa l h o u r s ) . T r e a t m e n t of la rge n u m b e r s of an ima l s is imprac t i ca l un less s t ab le fly p o p u l a t i o n s a r e e x t r e m e l y pes t i f e rous . If t r e a t m e n t s a r e app l i ed to an ima l s , c a r e must b e t a k e n to t h o r o u g h l y c o a t t h e l o w e r e x t r e m i t i e s , w h e r e s t a b l e flies n o r m a l l y feed.

P e r m e t h r i n E C (emuls i f iable c o n c e n t r a t e ) and W P (we t t ab le p o w d e r ) formula t ions h a v e b e e n t e s t e d as c o n t a c t r e s i d u a l s o n u n p a i n t e d w o o d in s h a d e d l o c a t i o n s (50). H o w e v e r , t he pe r s i s t ence of r e s idues is n o t p r e d i c t a b l e over t ime . Sub- l e tha l exposure levels m a y b e found less t h a n o n e m o n t h after appl ica t ion.

B y a p p l y i n g p e s t i c i d e s t o t h e f ib reg la s s , t h e W i l l i a m s t r a p b e c o m e s a s h o r t - t e r m toxicant device for kill ing flies (72). H o w e v e r , o r lon ya rn i m p r e g n a t e d wi th pe rme th r in E C (58) and w r a p p e d in a con t inuous coil a r o u n d the fibreglass pane l s of Wil l iams traps (omi t t ing t he adhes ive ) is m u c h m o r e effective (50). Yarn is s o a k e d in a 1 % so lu t ion of p e r m e t h r i n at 66°C for 20-30 min and a l lowed to air dry (58). T h e u p p e r and lower edges of the f ibreglass pane l s a r e n o t c h e d at 1.3 c m in tervals , enab l ing t h e ya rn to b e fixed in p lace (133). T h e s e toxic devices r e m a i n active in t he field for a m i n i m u m of t h r e e months wi th n o a p p a r e n t d e c r e a s e in efficacy fo l lowing e x p o s u r e t o sun , r a in or t e m p e r a t u r e e x t r e m e s . T r e a t e d y a r n can b e u s e d i m m e d i a t e l y after i m p r e g n a t i o n , or m a y b e stored i ndoo r s in plast ic bags for u p t o o n e year. I m p r e g n a t e d ya rn is r e c o m m e n d e d ins tead of direct appl ica t ion of pest icides t o w o o d for t he following reasons :

- ya rn m a y b e left in t he field for t h r e e m o n t h s with n o dec rease in efficacy;

- y a r n - w r a p p e d tox ic devices m a y b e u s e d in t e rmi t t en t ly du r ing the yea r t o reduce fly p o p u l a t i o n s to des i red levels.

Y a r n - w r a p p e d toxic devices m a y b e p l aced o n s t akes or h u n g singly o n fences (50).

I n s e c t i c i d e - i m p r e g n a t e d e a r t a g s a n d e a r t a p e s h a v e b e e n s h o w n t o a id in the r educ t i on of s tab le fly popu l a t i ons in s o m e cases (35 ,49 ) . Unfor tuna te ly , t h e b o d y areas r e c e i v i n g t h e b e s t c o v e r a g e f rom e a r t ags - i .e. t h e n e c k a n d s h o u l d e r s (7) - a r e not w h e r e s tab le flies no rma l ly feed (i.e. lower po r t ions of t he legs) .

It h a s b e e n s h o w n t h a t s t a b l e fly p o p u l a t i o n s in w e s t e r n K a n s a s h a v e d e v e l o p e d levels of r e s i s t a n c e t o pes t i c ides u s e d for fly c o n t r o l on feed lo t s . R e s i s t a n t flies were found on feedlots which h a d neve r used chemica l pest ic ides . This fur ther demons t r a t e s t h e o c c u r r e n c e of fly d i spersa l b e t w e e n fa rms , a n d e m p h a s i z e s t h e n e e d for a rea-wide con t ro l p r o g r a m m e s (21).

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Cultural control

Cul tura l c o n t r o l ( s a n i t a t i o n ) is t h e m o s t i m p o r t a n t m e t h o d for on-s i t e r e d u c t i o n of s table fly p o p u l a t i o n s ( 3 4 ) . C o n t r o l of a d u l t s is fu t i l e if n e w , r e p l a c e m e n t a d u l t populat ions a r e be ing p r o d u c e d on-s i te as quickly as t h e p r e v i o u s p o p u l a t i o n s a r e be ing e l iminated . D e v e l o p m e n t a l s i tes a n d s u b s t r a t e s a r e d e s c r i b e d a b o v e in t h e ' B i o l o g y ' section. P r o p e r m a n a g e m e n t of t h e s e a r e a s a n d subs t r a t e s will r e n d e r t h e m u n s u i t a b l e for use by s tab le flies.

Stacking a n d b u r n i n g act ive ro l led h a y r e s idues can resu l t in a r ap id d e c r e a s e in adu l t s table fly p o p u l a t i o n s ( 5 0 ) . A s a n a l t e r n a t i v e t o b u r n i n g , w e t h a y r e s i d u e s m a y b e s tacked , c o v e r e d w i t h b l a c k p o l y e t h y l e n e a n d left t o c o m p o s t . M o r e c o m p a c t i b l e mater ia l s , s u c h as s ta l l l i t ter , m a y b e c o m p o s t e d b y s t a c k i n g m a t e r i a l s in l a r g e p i l e s . Even w i t h o u t a p l a s t i c c o v e r i n g , s t a c k i n g r e d u c e s t h e su r face a r e a wh ich flies u s e for d e v e l o p m e n t . I n t e r n a l m a t e r i a l s wil l c o m p o s t , e s p e c i a l l y if w e t , a n d t h e r e s u l t i n g elevated t e m p e r a t u r e s will fu r the r l imit fly d e v e l o p m e n t (47).

If l a r g e h a y b a l e s b e i n g f ed t o s t o c k a r e p l a c e d o n w a g o n s ( o r o t h e r m o b i l e p la t fo rms) , r e s i d u e a c c u m u l a t i o n s c a n b e m i n i m i z e d b y m o v i n g t h e w a g o n s a s h o r t d i s tance o n c e o r t w i c e a w e e k . T h e s m a l l a m o u n t s of h a y d e p o s i t e d t e n d to d r y completely, w i t h o u t b e c o m i n g a t t r a c t i v e o v i p o s i t i o n s i tes . R o u t i n e r e m o v a l of r o l l e d hay res idues grea t ly r e d u c e s o r e l imina tes s tab le fly p o p u l a t i o n s .

Fly d e v e l o p m e n t in b e d d i n g in calf h u t c h e s c a n b e m i n i m i z e d b y u s i n g m a t e r i a l s which t e n d t o s t ay d ry , a n d by i m p r o v i n g t h e d r a i n a g e u n d e r h u t c h e s . O f al l t h e mate r i a l s t e s t e d , s a w d u s t b e d d i n g p r o v e d t o b e t h e m o s t e f f ec t i ve in r e d u c i n g fly populat ions (110).

Mechanical control

With t h e a d v e n t of p e s t i c i d e r e s i s t a n c e a n d i n c r e a s i n g c o n c e r n o v e r t h e u s e of s y n t h e t i c p e s t i c i d e s , r e n e w e d e m p h a s i s h a s b e e n p l a c e d o n t h e u s e of t r a p s , pa r t i cu la r ly for a d u l t p o p u l a t i o n s . T r a p s w e r e p r e v i o u s l y c o n s i d e r e d use fu l for t h e m a n a g e m e n t of fly p o p u l a t i o n s , b u t t h e y h a v e a l s o b e e n v i e w e d as t o o l s for t h e elimination of p o p u l a t i o n s (141).

Since t h e d e v e l o p m e n t of t h e W i l l i a m s t r a p , t h i s h a s b e e n u s e d as a s u r v e y t o o l . However , in o n e d o c u m e n t e d i n s t a n c e , it w a s u s e d for m a n a g e m e n t of fly p o p u l a t i o n s ( 1 0 6 ) . A m a j o r c h a n g e in t h e d e s i g n of W i l l i a m s - t y p e s t i c k y t r a p s commenced wi th t h e d e v e l o p m e n t of t he p y r a m i d t r a p (95, 97) a n d t h e o c t a h e d r a l t r a p , which a t t rac t s face flies (Musca autumnalis D e G e e r ) t o t h e u p p e r sur faces a n d s t ab l e flies to t he lower surfaces (96).

Traps emp loy ing e l ec t rocu t ion gr ids a r e very p o p u l a r for fly con t ro l , a n d t h e s e can b e effective w h e n c o m b i n e d wi th a t t r a c t a n t s s u c h as u l t r a v i o l e t l ight a n d C 0 2 ( 8 0 , 1 1 2 ) . U n f o r t u n a t e l y , u l t r a v i o l e t l i gh t fo r d i u r n a l t r a p p i n g is e f f ec t i ve o n l y i n d o o r s , a n d c u r r e n t l y - a v a i l a b l e C 0 2 s o u r c e s a r e c u m b e r s o m e for u s e in t h e f ie ld . H o w e v e r , by combining e l e c t r o c u t i o n gr ids wi th t h e re f lec t ive m a t e r i a l s u s e d in t h e p y r a m i d t r a p s , ba t t e ry -powered a n d t h e n s o l a r - p o w e r e d e l e c t r o c u t i o n gr id t r a p s w e r e d e v e l o p e d for use in t he field ( 9 4 , 9 8 ) . Severa l m o d e l s of so l a r -powered t r aps which a t t rac t b o t h h o u s e flies and s tab le flies a r e be ing p r o d u c e d commercia l ly .

A w a l k - t h r o u g h t r a p for u s e by ca t t l e a n d a b a i t e d t r a p for u s e a r o u n d ca t t l e p e n s have b e e n u s e d for r e d u c t i o n of S. niger p o p u l a t i o n s in E a s t Af r ica (77) . E a s t A f r i c a n

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f a rmers also physical ly p r e v e n t S. niger f rom coming in to con tac t wi th cat t le by placing t h e an imals in d a r k e n e d s t raw hu t s . Howeve r , flies will a t t e m p t t o e n t e r t he se da rkened s t ruc tu res if d r iven by h u n g e r (77).

Biological control

Biologica l c o n t r o l of s t ab le flies h a s b e e n s tud ied by a n u m b e r of r e s e a r c h workers , p a r t i c u l a r l y in t h e m i d - w e s t e r n U S A a n d Af r i ca . A l t h o u g h m u c h p r o g r e s s h a s been m a d e , effect ive sys t ems h a v e ye t t o b e d e v e l o p e d for a n u m b e r of b o n a f ide r easons . S e v e r a l b o o k s c o n t a i n r e s e a r c h s u m m a r i e s o r r e v i e w ar t ic les s h o w i n g t h e p r o g r e s s of r e s e a r c h in th is a r e a (88 , 87, 9 2 , 1 0 7 ) . A br ief o v e r v i e w of t h e m o r e r e c e n t f indings is given below.

A l t h o u g h m u c h effort has b e e n e x p e n d e d on s tudies of b iological con t ro l agen t s for s tab le flies, l i t t le a t t en t i on has b e e n pa id t o t he ro le of p r e d a t o r s of t h e i m m a t u r e stages. Lists of k n o w n p r e d a t o r s h a v e b e e n a s s e m b l e d a n d t h e effects of p r e d a t i o n h a v e been quant i f ied (40 ,114 ) . T h e use of p r e d a t o r s in a u g m e n t a t i v e re leases has b e e n l imi ted by t h e lack of mass - r ea r ing t echn iques (90).

Paras i t i c h y m e n o p t e r a h a v e b e e n used m o r e widely, wi th vary ing deg rees of success, a n d m o s t s tudies involving the s tab le fly as t he ma jo r hos t species h a v e b e e n per formed in t h e m i d - w e s t e r n U S A . I t h a s b e e n d e t e r m i n e d t h a t p a r a s i t e s p u r c h a s e d from c o m m e r c i a l i n s e c t a r i e s for r e l e a s e in a p a r t i c u l a r g e o g r a p h i c a r e a m u s t b e na tu ra l ly effect ive in t h a t a r e a if t h e p a r a s i t e s a r e t o succeed (123, 9 1 , 33) . T h e p a r a s i t e species m o s t c o m m o n l y a t t ack ing s tab le fly p u p a e in Kansas , N e b r a s k a a n d F lo r ida is Spalangia cameroni Pe rk in s (73 ,36 ) . C o n t r o l p r o g r a m m e s can fail if commerc i a l insec tar ies d o not supply a d e q u a t e quan t i t i e s of p u r e cul tures of t he species r e q u e s t e d (3).

Control summary

M a n a g e m e n t of l a r v a l h a b i t a t s by s a n i t a t i o n is t h e k e y t o s t a b l e fly c o n t r o l . T r e a t m e n t s of an ima l s with res idua l insect ic ides can aid in cont ro l ; t h o r o u g h application t o t h e l o w e r b o d y p a r t s of a n i m a l s is i m p o r t a n t . P r o p e r u s e of m o d i f i e d t r a p s , using e i the r t r e a t e d ta rge t s o r so l a r -powered e lec t rocu t ion grids, can b e effective.

HORN FLIES AND BUFFALO FLIES

Haematobia is a g e n u s of m u s c o i d fly which con t a in s s eve ra l spec ies , b u t t h e exact n u m b e r h a s sti l l n o t b e e n r e s o l v e d t a x o n o m i c a l l y . O v e r t h e p a s t t w o d e c a d e s , t a x o n o m i s t s h a v e l i s ted 4 (121) , 6 (147) o r 8 spec ies (119) . A l l spec ies w e r e originally found in t h e O l d Wor ld , b u t H. irritans (L.) was i n t r o d u c e d in to t h e N e w W o r l d in the la te 19th cen tu ry (147). H. irritans irritans, t h e h o r n fly, has t h e wides t d i s t r ibu t ion and h a s b e e n f o u n d a l m o s t t h r o u g h o u t t h e w o r l d ( 3 2 , 1 4 7 , 1 1 9 ) . C u r r e n t l y , t h e h o r n fly is f o u n d t h r o u g h o u t E u r o p e , N o r t h A f r i c a , A s i a M i n o r a n d t h e A m e r i c a s . T h e mos t r e c e n t e x p a n s i o n of t he r a n g e of t h e h o r n fly has occu r r ed t h r o u g h o u t S o u t h Amer ica , inc lud ing a l m o s t t h e w h o l e of Brazi l , Pa raguay , U r u g u a y a n d Bol iv ia , a n d o v e r half of A r g e n t i n a . T h e c l o s e l y - r e l a t e d b u f f a l o fly (H. irritans exigua) is f o u n d in India , I ndones i a , Malays ia , P a p u a N e w G u i n e a , Ch ina a n d n o r t h e r n Aus t r a l i a (6) . M o s t of the b io logy a n d c o n t r o l of t h e s e t w o flies is c o m m o n . B e c a u s e of t h e l imi ted d i s t r ibu t ion a n d e c o n o m i c significance of t he r e m a i n d e r of t he Haematobia species , this rev iew will b e l imi ted to h o r n flies and buffalo flies.

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A d u l t Haematobia a r e bas ica l ly g rey in co lour , w i t h s o m e d a r k e r m a r k i n g s o n t h e thorax in s o m e r e g i o n s . T o t h e u n t r a i n e d e y e , t h e s e f l ies a r e s i m i l a r in s ize a n d appea rance t o s o m e spec ies of t h e a n t h o m y i d family a n d t h e g e n u s Fannia. H o w e v e r , two cha rac te r i s t i c s u sua l ly s e p a r a t e Haematobia f rom t h e s e o t h e r g r o u p s : t h e s w o r d ­like p r o b o s c i s p r o j e c t i n g f r o m b e n e a t h t h e h e a d , a n d t h e c l o s e a s s o c i a t i o n of Haematobia wi th a hos t an ima l . T h e p robosc i s is less p r o m i n e n t t h a n t h a t of Stomoxys and is pa r t i a l l y o b s c u r e d by t h e p a l p s . Size r a n g e of a d u l t h o r n flies is 3-5 m m (147) .

B I O L O G Y

T h e biology of H. irritans is p r o b a b l y similar t h r o u g h o u t t h e geograph ica l r a n g e , d u e to the c lose r e l a t i o n s h i p w i t h h o s t s a n d b e c a u s e f resh m a n u r e is u s e d for o v i p o s i t i o n . This s p e c i e s c a n t o l e r a t e a h i g h d e g r e e of c l i m a t i c a n d t o p o g r a p h i c v a r i a t i o n , a n d spreads rapidly i n to n e w geograph ica l a reas .

Eggs a re d e p o s i t e d o n fresh b o v i n e m a n u r e a n d h a t c h after 20-24 h i n t o smal l , first-instar l a r v a e . T h e s e l a r v a e g r o w a n d m o l t i n t o t h e l a r g e r , s e c o n d - a n d t h i r d - i n s t a r larvae. T h i r d - i n s t a r l a r v a e e v e n t u a l l y fo rm t h e p u p a l s t age . D e v e l o p m e n t f rom egg to pupa t akes a p p r o x i m a t e l y 4-8 days for H. irritans, d e p e n d i n g o n t h e t e m p e r a t u r e (68) . After a p p r o x i m a t e l y 6-8 d a y s in t h e p u p a l s t a g e a t s u m m e r t e m p e r a t u r e s , H. irritans adults e m e r g e t o s eek a hos t a n d a b l o o d m e a l . A d u l t s of b o t h sexes a r e b l o o d feede r s , and spend a l a rge p o r t i o n of t he i r l ives o n h o s t a n i m a l s , i nc lud ing d o m e s t i c spec ies of livestock. A d u l t s beg in m a t i n g w h e n 3-5 days old a n d females beg in laying eggs w h e n 3 -8 days old. H o w e v e r , t h e r e a r e r e p o r t s of females laying eggs w h e n on ly 2 days old (67) . Adults m u s t h a v e b l o o d m e a l s t o successfully m a t e , a n d females n e e d b l o o d m e a l s for egg p roduc t ion . F e m a l e s lay b e t w e e n 11 a n d 13 eggs (singly o r in smal l n u m b e r s ) du r ing one cycle, o n f r e s h l y - d e p o s i t e d m a n u r e (84 , 67) . A n o t h e r b l o o d m e a l m u s t b e t a k e n before a s econd b a t c h of eggs can b e p r o d u c e d . To ta l l i fet ime p r o d u c t i o n is 100-200 eggs (84). H. irritans adu l t s live u p t o 21 days in t h e l abora to ry , b u t p r o b a b l y survive less t h a n 1-2 weeks in t h e field.

H o r n flies e n t e r a facul ta t ive d i a p a u s e , a n d ove rwin t e r as p h a r a t e adu l t s wi th in the i r pupar ia (128) . F l i e s e n t e r d i a p a u s e in t h e fall b e c a u s e of d e c r e a s i n g d a y l e n g t h s a n d dec rea s ing t e m p e r a t u r e s ( 2 3 , 2 4 , 1 4 6 ) . D i a p a u s e is t e r m i n a t e d i n t h e s p r i n g b y increasing t e m p e r a t u r e s of t h e subs t r a t e ( 6 3 , 1 2 9 , 1 3 0 , 6 7 ) .

H o r n fly l a r v a e d e v e l o p p r imar i l y , if n o t exc lus ive ly , in t h e m a n u r e of c a t t l e (68 ) , while p u p a e m a y b e found in t he m a n u r e p a t o r in t he subs t r a t e n e a r o r b e n e a t h t h e p a t (128). Surv iva l d e p e n d s o n t h e ab i l i ty of l a r v a e a n d p u p a e t o w i t h s t a n d a n u m b e r of factors wi th in o r n e a r t h e m a n u r e pa t , such as v a r i a t i o n in m a n u r e n u t r i t i o n a l c o n t e n t (108), var ia t ion in t e m p e r a t u r e a n d m o i s t u r e level (70 ,20 ) , in t raspec ies c o m p e t i t i o n a n d c o m p e t i t i o n w i t h o t h e r d u n g - b r e e d i n g s p e c i e s , a n d t h e e f fec t s of p r e d a t o r s a n d parasites (25).

Adu l t flies t e n d to s tay o n t h e hos t a n i m a l t h r o u g h o u t t h e day a n d n ight (59) , leaving only to lay eggs in fresh m a n u r e . Fl ies h a v e b e e n o b s e r v e d m o v i n g f rom t h e shou lde r s of cattle to t h e a r e a n e a r t h e tai l , as an ima l s d e p o s i t m a n u r e . Fl ies t h e n fly t o t h e m a n u r e , lay t he i r eggs a n d r e t u r n a f t e r a n a b s e n c e of l ess t h a n o n e m i n u t e ( 1 0 2 ) . F l i e s f e e d mainly o n t h e b a c k a n d s i d e s of a n i m a l s . T h e n a m e ' h o r n f ly ' o r i g i n a t e s f r o m t h e tendency of t h e s e flies t o c lus ter a t t h e b a s e of h o r n s of t h e hos t , b u t c lus ter ing of flies o n horns is n o l o n g e r as c o m m o n as in p r e v i o u s t i m e s . B o t h m a l e s a n d f e m a l e s a r e b l o o d feeders, t a k i n g 20-30 b l o o d m e a l s p e r day. H o r n flies wil l f e e d o n a n u m b e r of h o s t s other than cat t le , such as w a t e r buffalo, ho r se s , a n d ( ra re ly ) h u m a n s a n d dogs (38) .

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Di spe r sa l of adu l t h o r n flies was t h o u g h t to be l imited after t he c o m p l e t i o n of several i n i t i a l s t u d i e s ( 4 1 , 6 8 ) . H o w e v e r , w h e n p e s t i c i d e r e s i s t a n c e b e c a m e a n i s s u e , the de t ec t ion of res i s tan t flies in loca t ions w h e r e pest ic ides h a d no t b e e n u s e d ra i sed further q u e s t i o n s r e g a r d i n g t h e ab i l i ty of t h e h o r n fly t o d i s p e r s e in t h e e n v i r o n m e n t (117) . S u b s e q u e n t l y , s e v e r a l d i s p e r s a l s t u d i e s p e r f o r m e d w i t h w i ld h o r n fl ies h a v e d e m o n s t r a t e d t h a t t h e h o r n fly will d i sperse 5 k m a n d p r o b a b l y m u c h fu r the r (13 ,116) . A s m i g h t b e e x p e c t e d , d i spers ing p o p u l a t i o n s a r e p r e d o m i n a n t l y f emales ( 3 7 , 7 1 ) . It is sugges ted tha t d ispersa l of flies p r imar i ly involves n e w l y - e m e r g e d flies; once t h e hos t is loca ted , t he flies stay wi th in t h e he rd .

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

A l t h o u g h t h e h o r n fly is only o n e of m a n y d i p t e r a n ( two-winged) pes t s of l ivestock, it can b e t h e m o s t obv ious b lood-suck ing pes t of cat t le . It has b e e n specu la t ed t h a t annual e c o n o m i c losses d u e to h o r n flies in t he U S A a re over US$800 mil l ion, a n d t h a t at least U S $ 6 0 mil l ion w o r t h of insect ic ides a r e app l ied each yea r (5).

T h e i m p a c t of t h e h o r n fly v a r i e s in r e l a t i o n t o c l i m a t e , r e g i o n , p a s t u r e c h a r a c t e r i s t i c s , m a n a g e m e n t t e c h n i q u e s , p r o d u c t i o n s y s t e m s , b r e e d t y p e a n d calving p e r i o d s . In t e m p e r a t e a r ea s , H. irritans has b e e n cons ide red a se r ious pes t of pas tu red beef ca t t le dur ing t h e w a r m e r m o n t h s of t h e year. In subt ropica l a reas , t h e s e flies can be f o u n d on ca t t l e a l m o s t t h r o u g h o u t t h e year , b u t p o p u l a t i o n p e a k s occu r a c c o r d i n g to local c l imat ic cond i t ions . I n N o r t h A m e r i c a , w h e n p o p u l a t i o n s r e a c h levels of 200 flies p e r an ima l , it has b e e n cons ide r ed t o b e economica l ly exped i en t t o con t ro l this pes t . The e c o n o m i c t h r e s h o l d for t he buffalo fly has n o t b e e n es tab l i shed , b u t it is a s s u m e d to be b e t w e e n 200 a n d 500 flies p e r an ima l (6) . D i p t e r a o t h e r t h a n h o r n flies (e.g. ho r se flies, m o s q u i t o e s a n d s tab le flies) m a y cause e c o n o m i c d a m a g e d u e to b l o o d loss, annoyance o r d i sease t r ansmis s ion , b u t c o n t r o l of t he se pes t s r e q u i r e s m o r e t h a n a s ingle s t ra tegy b a s e d o n t h e u s e of i n s e c t i c i d e s . T h u s , t h e c o n t r o l of h o r n flies is o f t en t h e focus of l imi ted pes t con t ro l p r o g r a m m e s .

A s h o r n flies c a n b e f o u n d o n c a t t l e t h r o u g h o u t m o s t of t h e y e a r ( e x c e p t du r ing e x t r e m e win t e r t e m p e r a t u r e s in m a n y a reas ) , it is i m p o r t a n t t o cons ide r descr ip t ions of t h e e c o n o m i c ga in s a s s o c i a t e d w i t h h o r n fly c o n t r o l . H o r n flies h a v e b e e n s h o w n to r e d u c e t he milk p r o d u c t i o n of cows, which is associa ted wi th d ec r ea s ed w e a n i n g weights of calves. F u r t h e r m o r e , we igh t gains in year l ing or g rowing cat t le can b e inf luenced by h o r n fly con t ro l .

Weaning weight

U n t i l recent ly , e s t ima tes of t he e c o n o m i c benef i t s of h o r n fly con t ro l for ca t t le have b e e n b a s e d on s tud ies us ing e x t r e m e l y effective con t ro l m e a s u r e s for t r e a t e d animals , of ten ach iev ing 1 0 0 % con t ro l . S tud ies ind ica ted po t en t i a l beneficial effects of h o r n fly c o n t r o l o n we igh t gain of ca lves n u r s i n g spr ing-ca lv ing bee f cows . C a m p b e l l (14) was o n e of t he first r e sea rche r s t o d e m o n s t r a t e an associa t ion b e t w e e n h o r n fly con t ro l and e n h a n c e d p r o d u c t i o n of cow-cal f pa i r s . A t w e a n i n g , s t e e r ca lves of t r e a t e d H e r e f o r d cows w h i c h a v e r a g e d 30 flies p e r c o w o v e r t h e 153-day t r i a l w e r e o n a v e r a g e 5.9 kg h e a v i e r (0 .04 kg a v e r a g e da i ly ga in [ A D G ] ) t h a n ca lves f rom u n t r e a t e d co w s which a v e r a g e d 938 flies. In a two-yea r study, Q u i s e n b e r r y a n d S t r o h b e h n (101) r e p o r t e d an i n c r e a s e d w e a n i n g w e i g h t of a n a v e r a g e of 5.6 kg for c r o s s - b r e d ca lves f rom t r e a t e d cows which h a d an ave rage of o n e fly pe r cow over a 102-day pe r iod , c o m p a r e d to calves f rom u n t r e a t e d ca t t le wh ich a v e r a g e d 58 flies p e r cow. H a u f e (45) sugges t ed t h e need

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for e s t a b l i s h m e n t of fly-free g raz ing ( F F G ) c o n d i t i o n s t o o b t a i n t h e t y p e of i n c r e a s e d p e r f o r m a n c e d e s c r i b e d a b o v e . T h e F F G s y s t e m w a s c o n s i d e r e d i m p o r t a n t b e c a u s e behav iou ra l c h a n g e s of c a t t l e c o u l d b e i n d u c e d by l o w leve l s of h o r n fly i n f e s t a t i o n . Howeve r , c o n t e m p o r a r y s t u d i e s o n w e a n i n g w e i g h t g a i n s a s s o c i a t e d w i t h h o r n fly control for spr ing-ca lv ing sys tems ( e i t he r w i th o r w i t h o u t F F G ) h a v e fai led t o s u p p o r t earlier s tudies (113, 52) . In a s even -yea r study, G e r h a r d t a n d S h r o d e (30) d e m o n s t r a t e d that d i f f e r e n c e s in w e i g h t g a i n s b e t w e e n t r e a t m e n t s m a y v a r y f r o m y e a r t o y e a r . Therefore, o n e - y e a r o r e v e n two-yea r s tudies on cow-calf p e r f o r m a n c e m a y b e t o o shor t to p roduce re l iab le e c o n o m i c da ta . T h e level of h o r n fly con t ro l r e q u i r e d for F F G is n o longer a t t a i n a b l e in m o s t p a r t s of t h e U S A , d u e t o t h e d e v e l o p m e n t of i n s e c t i c i d e resistance. H o g s e t t e et al. (52) w e r e t he first t o t h e add res s this p r o b l e m , a n d c o n c l u d e d that e c o n o m i c bene f i t s of h o r n fly c o n t r o l for cow-cal f pa i r s a n d r e p l a c e m e n t he i f e r s could no t b e a t t a i n e d us ing s p r a y s o r d u s t b a g s , a n d t h a t c a t t l e in n o r t h - w e s t F l o r i d a could to le ra te a v e r a g e fly p o p u l a t i o n s of ove r 200 p e r an imal .

Recen t ly , D. M o r r i s o n a n d L . Fo i l ( u n p u b l i s h e d f ind ings ) m e a s u r e d t h e effects of horn fly c o n t r o l o n fa l l -ca lving bee f cow p r o d u c t i o n . C a l v e s w e r e b o r n in S e p t e m b e r and O c t o b e r of e a c h yea r , a n d cow-ca l f p a i r s w e r e m a n a g e d as a s ing l e g r o u p f r o m calving un t i l t h e i n i t i a t i o n of t h e s t u d y in l a t e M a r c h ; c a t t l e w e r e t h e n spl i t i n t o t w o equal g roups o n the basis of calf we igh t a n d age . T h e t h r e e - y e a r seasona l a v e r a g e for t h e number of flies p e r an ima l du r ing t h e s tudy was 45 a n d 246 for t r e a t e d a n d c o n t r o l cows, respectively. Ca lves f rom c o n t r o l cows g a i n e d 9 kg m o r e t h a n calves f rom t r e a t e d cows in one year. In t h e o t h e r t w o yea r s , calves f rom t r e a t e d cows g a i n e d 10 kg a n d 2 kg m o r e than c o n t r o l c a l v e s ; t h e s e d i f f e r e n c e s w e r e n o t s ign i f i can t . T h e r e s u l t s of t h i s s t u d y indicated tha t spr ing h o r n fly p o p u l a t i o n s h a v e l i t t le or n o i m p a c t on t he w e a n i n g we igh t of fal l-born ca lves , e v e n w h e n fly n u m b e r s o n u n t r e a t e d cows e x c e e d 200 p e r a n i m a l . The po ten t ia l for e c o n o m i c benef i t of con t ro l l ing h o r n flies o n cows wi th nu r s ing calves is not a se t t led issue. H o w e v e r , m o s t p r o d u c e r s p re fe r to con t ro l h o r n flies, in v iew of t h e obvious i r r i ta t ion i n d u c e d by t he se flies.

Yearling and growing cattle

Various s tud ies c o n d u c t e d o v e r t he last fifteen yea r s h a v e r e p o r t e d benef i t s of h o r n fly control in increas ing we igh t gains of year l ing cat t le of A n g u s a n d H e r e f o r d b r e e d s in the U S A . H a r v e y a n d B r e t h o u r (44) r e p o r t e d in a s i x - y e a r s t u d y ( a v e r a g e g r a z i n g period 163 days) an 8 kg a d v a n t a g e in to ta l gain (0.05 kg A D G ) for t r e a t e d ( ave rage of 48 horn flies) over u n t r e a t e d year l ings ( ave rage of 322 flies). K u n z et al. (61), in a t h r e e -year study, found tha t t r e a t e d year l ing s teers (wi th essent ia l ly n o flies) h a d f rom 0.08 kg to 0.10 k g h i g h e r da i l y g a i n s t h a n c o n t r o l s ( w i t h a n a v e r a g e of o v e r 700 f l ies ) for 90-120 day graz ing p e r i o d s .

R e c e n t l y , S. D e R o u e n a n d L . F o i l ( u n p u b l i s h e d f i n d i n g s ) s t u d i e d t h e p o t e n t i a l e c o n o m i c b e n e f i t s f r o m m o d e r a t e l e v e l s of h o r n fly c o n t r o l fo r 2 5 - 5 0 % B r a h m a n -in f luenced (Bos indicus) y e a r l i n g c a t t l e u n d e r a g r a z i n g p r o d u c t i o n s y s t e m in t h e sou thern r e g i o n of t h e U S A . H o r n fly p o p u l a t i o n s w e r e c o n t r o l l e d o n y e a r l i n g ca t t l e during the grazing seasons a t m o d e r a t e levels ( an a v e r a g e of 87 flies o n u n t r e a t e d ca t t le compared to 275 o n t r e a t e d ca t t l e ) . Weigh t gains of year l ings w e r e affected by h o r n fly control; t r e a t e d ca t t l e g a i n e d 0.12 k g / d a y m o r e t h a n u n t r e a t e d a n i m a l s . T h e s e r e su l t s indicate t h a t B r a h m a n - i n f l u e n c e d year l ings r e s p o n d e d benef ic ia l ly t o h o r n fly con t ro l , as was found in p r e v i o u s s tudies of B. taurus year l ings . T h e r e f o r e , m o s t r e p o r t s s u p p o r t findings by H a u f e (45 ) , w h o s u g g e s t e d t h a t y e a r l i n g o r g r o w i n g c a t t l e s h o w a l o w e r tolerance to h o r n fly p o p u l a t i o n s than m a t u r e cat t le .

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L o c a t i o n , age of ca t t l e a n d rea l is t ic levels of h o r n fly c o n t r o l m u s t b e c o n s i d e r e d to d e t e r m i n e t h e e c o n o m i c benef i t s of h o r n fly c o n t r o l s t r a t eg i e s . M o s t of t h e e c o n o m i c d a t a a s soc ia t ed wi th h o r n fly con t ro l h a v e b e e n g a t h e r e d in r e l a t i o n t o t h e p ro d u c t i o n a n d sa le of j u v e n i l e ( p r e d o m i n a n t l y B. taurus) c a t t l e w h i c h a r e so ld for f in i sh ing on g r a in . T h e leve l of B r a h m a n b r e e d i n g has a s ignif icant i m p a c t o n t h e n u m b e r of horn flies on ind iv idua l an ima l s , a n d this is u n r e l a t e d t o co lou r (135) . C o n s i d e r a b l e s tudy is still r e q u i r e d o n t h e h o r n fly as an e c o n o m i c p e s t of p r o d u c t i o n s y s t e m s p r o d u c i n g a m a t u r e or n e a r m a t u r e grass-fed an imal .

D i s e a s e transmission

T h e h o r n fly is t h e k n o w n i n t e r m e d i a t e hos t of t h e filarid n e m a t o d e Stephanofilaria stilesi, which causes sk in les ions of bovids . T h e lesions a re c i rcumscr ibed , can b e crusty, a n d a r e loca ted o n t h e a b d o m e n n e a r t he mid l ine . T h e buffalo fly h a s b e e n l inked with s imi l a r l e s i o n s of c a t t l e in A u s t r a l i a (55) . N e w s h o l m e et al. (82) r e p o r t e d u l c e r a t e d l e s i o n s o n t h e l a t e r a l a s p e c t s of b o v i d s a s s o c i a t e d w i t h Haematobia meridiana and poss ib ly a filarid t r a n s m i t t e d by the flies.

Fo i l et al. (28) d e s c r i b e d a s e a s o n a l v e n t r a l m i d l i n e d e r m a t i t i s a s s o c i a t e d wi th the feeding of h o r n flies. T h e flies fed o n a reas of hair-loss induced by Onchocerca cervicalis a n d c r e a t e d les ions which w e r e de sc r ibed as c o m p o s e d of crust a n d ulcer. Fl ies d id not h a v e d e v e l o p i n g s t ages of Stephanofilaria. T h e r e f o r e , u l c e r a t e d c rus ty l e s ions can be f o r m e d strictly by t h e f eed ing of h o r n flies aggrega t ing at a r ea s of hair- loss d u e t o injury o r o t h e r m e c h a n i s m s . T h e h o r n fly is g e n e r a l l y c o n s i d e r e d t o b e a r e l a t i ve ly u n i m p o r t a n t m e c h a n i c a l v e c t o r of p a t h o g e n i c a g e n t s . H o w e v e r , t h e s e f l ies will a c c u m u l a t e a r o u n d o p e n b i o p s y w o u n d s , a n d c a r e s h o u l d b e t a k e n t o p r e v e n t flies m o v i n g a m o n g an imal s if mu l t ip l e b iops ies a r e t a k e n .

S U R V E I L L A N C E

A s t h e m a j o r p a r t of t h e life of t h e a d u l t is s p e n t o n t h e hos t , t h e r e h a v e b e e n few a t t e m p t s to d e v e l o p t r aps for h o r n fly survei l lance . Tugwell et al. (134) r e p o r t e d catches of h o r n flies o n a s t i cky b l a c k b a r r e l c o n t a i n i n g d ry ice ( C 0 2 ) . C u r r e n t l y , e f for ts are b e i n g m a d e t o d e v e l o p g e n e t i c p r o b e s o r o t h e r t e c h n i q u e s t o i d e n t i f y i n d i v i d u a l res i s tan t flies. S u b s e q u e n t t o this d e v e l o p m e n t , s tudies o n t h e m o v e m e n t of res is tance a n d o t h e r g e n o t y p e s w i t h i n a n d a m o n g h o r n fly p o p u l a t i o n s wi l l b e p o s s i b l e , and effective h o r n fly t r aps will b e n e e d e d .

C u r r e n t l y , t h e c o u n t i n g of flies on a n i m a l s is t h e s t a n d a r d su rve i l l ance m e t h o d for h o r n f l ies . T h e t e c h n i q u e is c o n s i d e r e d a c c u r a t e u p t o a p p r o x i m a t e l y 500 f l ies per an imal wi th the aid of b inocu la r s , if an imals can b e a p p r o a c h e d by vehicle or h o r s e . A n a p p r o p r i a t e n u m b e r of an ima l s t o a l low stat ist ical c o m p a r i s o n s is cu r ren t ly cons idered t o b e 10 a n i m a l s p e r g r o u p , o r 1 0 % of t h e h e r d if t h e h e r d s ize is a b o v e 100. Wi th in he rds , t h e r e is an i r regular d i s t r ibu t ion of h o r n flies. Bulls will h a r b o u r a h ighe r n u m b e r of flies t h a n cows, a n d d a r k e r an imals will usual ly h a v e m o r e flies. E v e n wi thin b r e e d s of u n i f o r m colour , c e r t a i n ind iv idua l s will cons i s t en t ly h a v e h igh n u m b e r s of flies while o t h e r ind iv idua l s will h a v e low n u m b e r s (125) . T h e p r e f e r r e d n u m b e r t o r e c o r d is the to ta l n u m b e r of flies p e r an imal . H o r n flies f requent ly feed on a n d fly b e t w e e n different b o d y reg ions of an imals in large g roups . A hos t defensive m o v e m e n t such as a swing of t h e h e a d to o n e s ide can resu l t in h u n d r e d s of flies o n o n e s ide of t h e a n i m a l a n d very few on the o t h e r s ide. Fl ies m o v e to t he ven t ra l side of an imals in br igh t sunl ight during w a r m m o n t h s of t he year. T h e r e f o r e , coun t ing flies in t he ear ly m o r n i n g h o u r s provides

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the best resul ts du r ing t he se p e r i o d s . M a l e flies r e p o r t e d l y s p e n d m o r e t i m e o n t h e legs than f e m a l e s . P y r e t h r o i d - r e s i s t a n t flies a l so a g g r e g a t e o n t h e v e n t r a l a r e a s of c a t t l e treated with p y r e t h r o i d ea r tags . T h e d i s t r ibu t ion of insect ic ides o n an imals t r e a t e d wi th ear tags is a resu l t of con tac t b e t w e e n an imals ; t h a t is, t h e insec t ic ide s p r e a d s t o t h e ha i r of animals f rom t h e tags by con tac t . T h e lowes t c o n c e n t r a t i o n s of insect ic ides a r e found on the a b d o m e n . O n e of t h e m e c h a n i s m s of r e s i s t a n c e t o p y r e t h r o i d s by h o r n fl ies inc ludes d e v e l o p m e n t of a h i g h e r s e n s i t i v i t y t o a n d t h u s m o v e m e n t a w a y f r o m t h e pyre thro id in sec t i c ides (122) . D u e to t h e a b o v e v a r i a b l e s w h i c h affect t h e l o c a t i o n of horn flies o n a n i m a l s , a t h o r o u g h i n v e s t i g a t i o n of b o t h s i d e s of e a c h a n i m a l is preferable, w h e n poss ib le .

The i m p o r t a n t fac to r t o b e a r in m i n d for h o r n fly su rve i l l ance is cons is tency. W h e n poss ib le , t h e s a m e p e r s o n s h o u l d m a k e c o u n t s t h r o u g h o u t t h e s t u d y . A l s o , it is r e c o m m e n d e d t h a t a nov ice c o u n t e r shou ld s ta r t w h e n n u m b e r s a r e low on t h e an imals (early in t h e s e a s o n o r shor t ly after t r e a t m e n t ) . Th i s will resu l t in t h e abil i ty t o c o u n t in pat terns of 25-50 flies w h e n n u m b e r s a r e e leva ted .

C O N T R O L

A l t h o u g h i n s e c t i c i d e s a n d a p p l i c a t i o n t e c h n i q u e s a r e s u m m a r i z e d e l s e w h e r e , a review of t h i s m a t e r i a l r e l a t i v e t o t h e p r a c t i c a l a s p e c t s of h o r n fly c o n t r o l for r a n g e catt le is m o s t a p p r o p r i a t e . S i n c e t h e h o r n fly s p e n d s a l m o s t i ts e n t i r e a d u l t l ife o n livestock, t he major i ty of insect ic ides a n d app l i ca t ion t e c h n i q u e s h a v e b e e n successful in con t ro l l ing h o r n flies a t s o m e p o i n t in t i m e . A t l e a s t in t h e U S A , e a c h o n e of t h e s e success s tor ies is fo l lowed by o n e of significant loss of c o n t r o l o r res i s tance d e v e l o p m e n t over t i m e of u s e . S p a r k s et al. ( 122) p r e s e n t e d a n e x c e l l e n t r e v i e w o n i n s e c t i c i d e r e s i s t ance in t h e h o r n fly. C o n f i r m e d r e p o r t s of r e s i s t a n c e t o o r g a n o c h l o r i n e s a n d o r g a n o p h o s p h o r u s c o m p o u n d s o c c u r r e d in t h e 1970s, a n d desc r ip t ions of r e s i s t ance t o p y r e t h r o i d e a r t a g s w e r e n u m e r o u s i n t h e 1980s . R e c e n t l y , r e s i s t a n c e t o t h e n e w e r o r g a n o p h o s p h o r u s - i m p r e g n a t e d e a r t ags h a s b e g u n t o a p p e a r . T h e r e f o r e , it s h o u l d b e obvious t h a t t h e h o r n fly d e v e l o p s r e s i s t a n c e t o p e r s i s t e n t e x p o s u r e t o i n s e c t i c i d e s whe the r t h e p e r s i s t e n c e is d u e t o t h e m o l e c u l a r s t r u c t u r e of t h e i n s e c t i c i d e o r t o t h e release s y s t e m (e .g . e a r t a g s ) . S t u d i e s o n t h e m e c h a n i s m s of h o r n fly r e s i s t a n c e h a v e been l imi ted , b u t it a p p e a r s t h a t a l m o s t a n y m e c h a n i s m w h i c h h a s b e e n d e s c r i b e d for insect res i s tance t o different chemica l classes can occur in res i s tan t h o r n fly p o p u l a t i o n s .

Mechanical control

A n y effor t t o d e s t r o y t h e i n t e g r i t y of m a n u r e p a t s wil l r e d u c e l a r v a l su rv iva l a n d adult e m e r g e n c e . Th i s is t he o b v i o u s e x p l a n a t i o n for t h e fact t h a t t h e h o r n fly is n o t a pest of conf ined a n i m a l s . D r a g g i n g p a s t u r e s or e m p l o y i n g o t h e r m e c h a n i c a l m e a n s of disturbing t h e m a n u r e can b e effect ive. In s o m e p a s t u r e s , f lood ing c a n a l so inh ib i t fly product ion.

B r u c e (9) d e s c r i b e d a w a l k - t h r o u g h t r a p w h i c h c o n s i s t s of a d a r k s t r u c t u r e w i t h sunlight p r o v i d i n g s ide l i gh t ing . C a t t l e a r e t r a i n e d t o wa lk t h r o u g h t h e s t r u c t u r e s by gradually assembl ing t h e t r a p at a gap which cat t le m u s t pass t o ob t a in water , food, e tc . When ca t t le walk t h r o u g h t h e t r a p , s o m e of t h e flies l e a v e t h e a n i m a l s (s t r ips of fabr ic hang from t h e t o p of t h e t r a p t o b r u s h flies off) a n d a r e t r a p p e d in t h e sides which h a v e screen baffles. C lean ing flies ou t of t h e s ides m a y b e neces sa ry in s o m e reg ions , b u t an ts often k e e p t h e t r aps free of a c c u m u l a t e d fly bod ie s . T h e t r aps a r e re la t ive ly inexpens ive to bu i ld a n d p r o v i d e a c o n t r o l l e v e l of a p p r o x i m a t e l y 5 0 % . I n t h e o r y , c o m b i n i n g

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physica l c o n t r o l w i th c h e m i c a l c o n t r o l can de lay r e s i s t ance d e v e l o p m e n t . In prac t ice , chemica l con t ro l m e a s u r e s last l onger w h e n the ca t t le use t h e t raps . A l t h o u g h this is an old idea , it still w o r k s for ca t t le wi th a mild t e m p e r a m e n t .

Chemical control

T h e fly t r a p was d iscussed first b e c a u s e it is a modi f i ca t ion of se l f - t r ea tmen t devices u s e d wi th insec t i c ides . B r u c e a n d D e c k e r (11) u s e d a s p r a y dev i ce a c t i v a t e d by catt le wa lk ing t h r o u g h an al ley t o app ly P y r e t h r i n s . T h e r e h a v e b e e n m a n y mod i f i ca t ions of ac t iva ted sp ray sys tems ; s o m e a re c o m m e r c i a l l y ava i l ab le . L ikewi se , ac t i va t ed dust ing s y s t e m s h a v e a l so b e e n d e v e l o p e d . A c t i v a t e d s p r a y a n d d u s t s y s t e m s a r e f r equen t ly des igned a r o u n d the use of m ine ra l f eeders for r a n g e ca t t le .

T h e dus t bag a n d cab le b a c k - r u b b e r a r e self-appl icat ion sys tems which h a v e t h e least d e g r e e of compl ica t ion . T h e s e sys tems a r e p l aced a r o u n d mine ra l s , salt b locks or water, n e a r w a t e r or loafing a r ea s or in f r equen t ly -used gaps o r alleys. T h e dus t b a g m a y range in s o p h i s t i c a t i o n f r o m o n e b u r l a p sack c o n t a i n i n g d u s t p l a c e d in s ide a n o t h e r b u r l a p sack, to commerc i a l l y - ava i l ab l e uni t s . C a t t l e pass ing u n d e r t h e bags a re t r e a t e d o n the h e a d a n d back . D u s t bags a r e a p p r o p r i a t e for ca t t l e which r o u t i n e l y f r e q u e n t a n area, b u t d u s t b a g s m a y r e q u i r e s h e l t e r a n d m a y b e u n s a t i s f a c t o r y in h u m i d c l i m a t e s . The c a b l e b a c k - r u b b e r is a n o t h e r s e l f - a p p l i c a t i o n d e v i c e w h i c h c a n b e u s e d in a r e a s f r e q u e n t e d by r a n g e ca t t l e . T h e b a c k - r u b b e r is easy t o c o n s t r u c t a n d d u r a b l e . A 20 ft (6 m ) cha in (or mul t ip l e s t r ands of b a r b e d wire w o u n d t o g e t h e r ) is s u s p e n d e d be tween p o s t s or t r e e s ; t h e e n d s of t h e cha in a r e a t t a c h e d t o t h e t r e e o r p o s t at a h e i g h t of 4 ft (1.2 m) a n d the cen t r e is a l lowed to sag t o 18 inches (0.5 m) a b o v e the g r o u n d . T h e back-r u b b e r is t r e a t e d w i t h o n e g a l l o n of i n s e c t i c i d e a n d d i l u e n t ( r o u t i n e l y a p e t r o l e u m p r o d u c t ) m i x t u r e p r e p a r e d by fo l lowing t h e i n s t r u c t i o n s of t h e m a n u f a c t u r e r . Ca t t le p a s s i n g u n d e r t h e b a c k - r u b b e r s a r e t r e a t e d . T h e b a c k - r u b b e r s a r e r e c h a r g e d at 2-3 w e e k in tervals , d e p e n d i n g on local condi t ions .

S e l f - a p p l i c a t i o n a n d o t h e r m e t h o d s a r e u s e d to a d m i n i s t e r i n sec t i c ides a n d insect g r o w t h r e g u l a t o r s for t h e p u r p o s e s of p r e v e n t i n g d e v e l o p m e n t of h o r n fly l a r v a e in m a n u r e . T h e se l f -appl ica t ion m e t h o d s consis t of m i x t u r e s in mine ra l s , feed a n d water, whi le t h e r u m i n a n t b o l u s is r o u t i n e l y u s e d to a d m i n i s t e r c o m p o u n d s wh ich a r e slowly r e l eased in to t h e m a n u r e . M a n y different forms of sus ta ined- re lease sys tems h a v e been d e v e l o p e d for b o l u s e s . M o o n et al. (78) f o u n d t h a t c o m m e r c i a l l y - a v a i l a b l e m i n e r a l b l o c k s c o n t a i n i n g f e e d - t h r o u g h insec t i c ides w e r e inef fec t ive in c o n t r o l l i n g the d e v e l o p m e n t of h o r n flies in t h e m a n u r e of p a s t u r e d ca t t le . A d u l t h o r n flies h a v e been f o u n d to d i s p e r s e m o r e r o u t i n e l y a n d wide ly t h a n was p r e v i o u s l y c o n s i d e r e d . This m o v e m e n t expla ins obse rva t ions tha t larvicides d o little to d immish the n u m b e r of adult flies o n c a t t l e in h e r d s w h i c h a r e n e a r (6-8 k m ) u n t r e a t e d h e r d s . L a r v i c i d e s can be successful w h e n used in a r ea -wide cont ro l p r o g r a m m e s w h e r e all an imals a r e effectively t rea ted . Of course , the effects of the selected insecticides on dung fauna and decomposi t ion of dung mus t b e cons idered before massive area-wide p r o g r a m m e s a re a t t empted .

W h e n s p r a y s a n d d ip s a r e u s e d for t h e c o n t r o l of o t h e r a r t h r o p o d p e s t s , h o r n fly c o n t r o l is a l so a t t a i n e d . T h e s e a p p l i c a t i o n s a r e u s u a l l y m a d e w i t h s o l u t i o n s which c o n t a i n s u i t a b l e c o n c e n t r a t i o n s of i n s e c t i c i d e t o s u p p r e s s e v e n t h e m o s t r e s i s t a n t p o p u l a t i o n s of h o r n flies for s e v e r a l w e e k s . O n e ea r ly m o d i f i c a t i o n of d i p p i n g vats m e n t i o n e d as i nc r ea s ing h o r n fly c o n t r o l was t he a d d i t i o n of sp lash b o a r d s w h e n less effective chemica l s w e r e ava i l ab le (10) . T h e b o a r d s w e r e p l aced a long the s ides of the vat at a he ight of 4 ft (1.2 m) a b o v e the surface of t he so lu t ion , at an angle of 60° to the u p w a r d vert ical , caus ing the solut ion splashing up o n t o the b o a r d s to be def lec ted down

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onto t he b a c k s of t h e an ima l s . A p o p u l a r t e c h n i q u e for app ly ing h o r n fly t r e a t m e n t s is the ' pour -on ' . A c o n c e n t r a t e d f o r m u l a t i o n of t he insec t ic ide is p o u r e d a long the b a c k s of cattle. G r o u p s of ca t t le can b e t r e a t e d quickly wi th very litt le s t ress if p r o p e r facilities are ava i lab le . T h e efficacy of t h e p o u r - o n for h o r n fly c o n t r o l is n o r m a l l y e q u a l t o o r greater t h a n t h a t of s p r a y app l i ca t i on . ' S p o t - o n ' t r e a t m e n t s invo lve t h e a p p l i c a t i o n of even m o r e c o n c e n t r a t e d fo rmula t ions t o a s ingle spo t o n t he b a c k s of ca t t le . A v e r m e c t i n pour -ons a r e n o w a v a i l a b l e w h i c h a c h i e v e i n t e r n a l p a r a s i t e c o n t r o l in a d d i t i o n t o external pa ras i t e con t ro l ( d u r a t i o n of 4-6 w e e k s agains t h o r n fly).

The i n s e c t i c i d e - i m p r e g n a t e d ea r t ag was i n t r o d u c e d as a m e t h o d for con t ro l l ing ea r ticks in the 1970s a n d quickly b e c a m e p o p u l a r for h o r n fly con t ro l . A p p l i c a t i o n of tags is easy and cat t le can b e t r e a t e d u n d e r any w e a t h e r cond i t ions . If a suscept ib le p o p u l a t i o n of horn flies is e x p o s e d to a n effective e a r t ag app l i ca t i on , u p t o 4-6 m o n t h s of c o n t r o l can be o b t a i n e d . T h e first p y r e t h r o i d e a r tags ( f e n v a l e r a t e a n d p e r m e t h r i n ) w e r e ve ry effective for c o n t r o l l i n g f l ies ; b u t w i t h i n t h r e e y e a r s of e x t e n s i v e u s e , p y r e t h r o i d resistance d e v e l o p e d in fly p o p u l a t i o n s . M o r e r e c e n t e a r t ags c o n t a i n m o r e effect ive pyre thro ids o r o r g a n o p h o s p a t e s wi th o r w i t h o u t syne rg i s t s . H o w e v e r , r e s i s t a n c e c a n develop w i t h c o n t i n u e d u s e , a n d c r o s s - r e s i s t a n c e t o p y r e t h r o i d s is c o m m o n . I n t h e laboratory, r e s i s t ance t o insect ic ides can b e se lec ted rou t ine ly wi th in forty g e n e r a t i o n s . As d e v e l o p m e n t c a n o c c u r in a p p r o x i m a t e l y t e n d a y s in s u b t r o p i c a l c l i m a t e s , a n d seasons a re long (wi th a lmos t t w e n t y g e n e r a t i o n s of h o r n flies p e r y e a r ) , r e s i s t ance can appear after t h r e e yea r s of c o n t i n u e d use . B y con t ras t , in m o r e n o r t h e r n c l imates t h e r e are fewer g e n e r a t i o n s p e r year, a n d res i s t ance d e v e l o p s at a s lower p a c e . R e g a r d l e s s of the mechan i sms , se lec t ion for res i s tance is g rea t e s t w h e n fly p o p u l a t i o n s a re e x p o s e d to s lowly-decreas ing i n s e c t i c i d e l eve l s o v e r a l o n g p e r i o d . T h e r e f o r e , r e s i s t a n c e t o t h e insecticides in commerc ia l ly -ava i l ab le ea r tags is very p r o b a b l e .

S e v e r a l r e c o m m e n d a t i o n s ex i s t for t h e u s e of e a r t ags in c o n t r o l p r o g r a m m e s . Alternat ing chemica l classes of tags year ly is a s t r a t egy for s lowing the d e v e l o p m e n t of insecticide r e s i s t a n c e in loca l h o r n fly p o p u l a t i o n s . A d d i t i o n a l r e c o m m e n d a t i o n s for reducing t h e p r o b a b i l i t y of d e v e l o p m e n t of in sec t i c ide r e s i s t a n c e in h o r n flies i n c l u d e the following:

- delay tagging unt i l fly p o p u l a t i o n s r e a c h 200 flies p e r cow - use t he r e c o m m e n d e d n u m b e r of tags p e r cow - tag all adu l t an ima l s in t h e h e r d - r e m o v e old tags w h e n they a r e n o longer effective.

At t imes of t h e y e a r w h e n tags a re n o t b e i n g used , o r if tags b e g i n t o fail b e f o r e t h e end of t he fly s e a s o n , i m p l e m e n t o t h e r fly c o n t r o l s t r a t eg i e s such as t h e u s e of sp rays , pour-ons, dus t bags o r b a c k - r u b b e r s .

Several b ioassay t e c h n i q u e s exist wh ich can b e u s e d to d e t e r m i n e t h e suscept ib i l i ty of fly p o p u l a t i o n s t o v a r i o u s c o m p o u n d s . A n e x a m p l e is t h e a s s a y d e v e l o p e d by Sheppard (115) which uses two-fold d i lu t ions of insect ic ides app l i ed to filter p a p e r a n d placed in p e t r i d i shes . F l i e s a r e r e m o v e d f r o m ca t t l e a n d p l a c e d in t h e p e t r i d i shes in groups of a p p r o x i m a t e l y 25 flies ( t h r e e g r o u p s p e r c o n c e n t r a t i o n ) for 4 h. T h e n u m b e r s of alive a n d d e a d flies for e a c h c o n c e n t r a t i o n of insec t i c ide t e s t e d a r e r e c o r d e d a t t h e end of t h e assay . T h e r e s u l t s of t h e f i l t e r p a p e r a s s a y s a r e r e p o r t e d as L C 5 0 ( t h e c o n c e n t r a t i o n of i n s e c t i c i d e o n f i l te r p a p e r r e q u i r e d t o kil l 5 0 % of t h e flies in 4 h ) . Susceptibility levels for t h e va r ious chemica l s a re d e t e r m i n e d by expos ing a suscept ib le l a b o r a t o r y s t r a i n of flies t o t h e t e s t e a c h t i m e n e w t e s t k i t s a r e p r e p a r e d . W h e n

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p y r e t h r o i d r e s i s t a n c e d e v e l o p s , t h e L C 5 0 fo r c e r t a i n p y r e t h r o i d s c a n i n c r e a s e dramatical ly . H o w e v e r , t he assay is n o t as sensi t ive for o r g a n o p h o s p h a t e - r e s i s t a n t flies.

Biological control

T h e b io logica l c o n t r o l of h o r n flies a n d buffa lo flies is a c h i e v e d by c o m p e t i t i o n for d u n g ( t h e h o r n fly la rva l h a b i t a t ) a n d by p r e d a t i o n . S ince h o r n flies ov ipos i t o n fresh m a n u r e , t h e t i m e f r a m e fo r c o m p e t i t i o n fo r d u n g m u s t o c c u r w i t h i n t h e la rva l d e v e l o p m e n t p e r i o d t o h a v e a n i m p a c t o n fly p o p u l a t i o n s . T h e b io log i ca l c o n t r o l of d u n g is an i m p o r t a n t a r ea of l ivestock p r o d u c t i o n i n d e p e n d e n t of fly con t ro l ; this can be a p r o b l e m in g e o g r a p h i c a l a r e a s d e v o i d of a n e v o l u t i o n of d u n g b e e t l e s w i t h l a rge r u m i n a n t s . F o r e x a m p l e , t h e n a t i v e s p e c i e s of d u n g b e e t l e s in A u s t r a l i a w e r e not su f f i c ien t t o r e m o v e t h e d u n g of c a t t l e w h i c h w e r e i m p o r t e d b y E n g l i s h co lon i s t s . W a t e r h o u s e (139) ca lcu la ted t h a t an adu l t b o v i n e averag ing a p r o d u c t i o n of 12 pa t s per d a y c o u l d r e d u c e t h e f o r a g e a v a i l a b i l i t y b y 2 0 % p e r a c r e p e r y e a r in t h e a b s e n c e of crit ical insect fauna .

F r o m 1967 u p to t h e 1980s, m u l t i p l e spec ies of Af r i can d u n g - b u r y i n g s ca r ab beet les w e r e successfully i m p o r t e d in to p a r t s of A u s t r a l i a , a n d d u n g d isposa l was significantly a u g m e n t e d . A l t h o u g h t h e r e w e r e s o m e ea r ly i n d i c a t i o n s of r e d u c e d fly p o p u l a t i o n s , t h e r e a p p e a r s t o b e n o m e a s u r a b l e effect o n buffalo fly p o p u l a t i o n s ; s imilar resul t s have b e e n o b s e r v e d in t h e U S A . T h i s m a y b e d u e t o i n t e r a c t i o n w i t h o t h e r bene f i c i a l a r t h r o p o d species which also affect d u n g d ispersa l o r survival of flies, such as p reda to r s a n d p a r a s i t o i d s (105 ) . C l i m a t i c c o n d i t i o n s (a c o m b i n a t i o n of m i l d w i n t e r s a n d high s u m m e r rainfall favours h igh d u n g b e e t l e popu l a t i ons ) a n d d ispersa l of r e l ea sed scarabs a l so a f fec t t h e i m p a c t of i m p o r t e d d u n g b e e t l e s o n h o r n fly p o p u l a t i o n s , thus compl ica t ing t h e eva lua t ion of t h e l o n g - t e r m success of r e l ease p r o g r a m m e s .

T h e i m p a c t of p r e d a t o r s a n d p a r a s i t o i d s o n h o r n fly p o p u l a t i o n s h a s b e e n s tudied u s i n g s e v e r a l t e c h n i q u e s . R o t h et al. (104) u s e d d i f f e ren t i a l e x c l u s i o n t e c h n i q u e s to e v a l u a t e t h e c o n t r i b u t i o n s of s ca rabs a n d p r e d a t i o n as m o r t a l i t y fac tors of t h e buffalo fly. A l t h o u g h s ca r abs w e r e t h e m o s t i m p o r t a n t g r o u p , p r e d a t o r y b e e t l e s a lso p l a y e d a s ign i f i can t r o l e in b u f f a l o fly s u r v i v a l . B e e t l e s in t h e f ami l i e s S t a p h y l i n i d a e and H i s t e r i d a e a r e t h e m a i n p r e d a t o r s of i m m a t u r e h o r n fly a n d buffalo fly, a n d the impact of foreign i m p o r t s of t he se p r e d a t o r s in to Aus t r a l i a a n d the U S A has b e e n eva lua t ed to s o m e d e g r e e . P r e d a t o r y mi tes , which a r e p h o r e t i c o n ( t r a n s p o r t e d by) d u n g bee t l e s and a t t a c k t h e eggs a n d l a r v a e of d u n g - i n h a b i t i n g D i p t e r a , h a v e a lso b e e n i n t r o d u c e d for buffa lo fly c o n t r o l in A u s t r a l i a (138) . I n m o s t r eg ions of t h e w o r l d , n a t i v e a r t h r o p o d s c o n t r i b u t e significantly t o t h e r e d u c t i o n of individuals in t he genus Haematobia, a n d the r o l e of t h e s e n a t i v e s p e c i e s s h o u l d b e e v a l u a t e d b e f o r e i m p o r t a t i o n of e x o g e n o u s a r t h r o p o d s is cons ide red .

Control summary

A v a r i e t y of t e c h n i q u e s a r e a v a i l a b l e for h o r n fly c o n t r o l . T r e a t m e n t s s h o u l d be a p p l i e d w h e n e c o n o m i c b e n e f i t is p o s s i b l e ; e c o n o m i c g a i n s a r e a s s o c i a t e d with i n c r e a s e d w e a n i n g w e i g h t s a n d w e i g h t g a i n s of y e a r l i n g a n d g r o w i n g c a t t l e . T h e e c o n o m i c t h r e s h o l d is v a r i a b l e , b u t 200 flies p e r a n i m a l is a s t a n d a r d in p a r t s of the U S A . S e l f - a p p l i c a t i o n t e c h n i q u e s a r e a p p r o p r i a t e for c a t t l e w h i c h a r e w o r k e d infrequent ly. R e s i s t a n c e t o highly-effective t r e a t m e n t s , such as insec t ic ide- impregna ted e a r tags , rou t ine ly deve lops wi th in forty gene ra t i ons of c o n t i n u o u s p r e s su re .

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TABANIDÉS, L A M O U C H E D E S É T A B L E S E T L A M O U C H E D E S C O R N E S : BIOLOGIE ET M É T H O D E S D E LUTTE. - L.D. Foil et J.A. Hogsette.

Résumé : Les tabanidés comptent parmi les mouches parasites du bétail les plus indépendantes à l'état adulte. Un seul repas sanguin suffit pour produire de 100 à 1 000 œufs et les femelles de certaines espèces peuvent même pondre avant tout repas (autogénie). Le renouvellement annuel des populations est ainsi assuré par 2 % seulement de femelles pondeuses. Les prélèvements sanguins effectués sur les animaux sauvages permettent habituellement aux populations de tabanidés de se renouveler d'année en année. Le cycle évolutif des larves est également indépendant des animaux domestiques. Les répulsifs ou répulsifs partiels constituent donc la seule méthode chimique pour réduire les effets des tabanidés sur le bétail. Une autre méthode consiste à installer des pièges permanents (éventuellement des pièges-silhouettes traités) pour intercepter les mouches. On peut également recourir au pâturage sélectif ou à l'élevage en espace clos pour limiter l'impact des tabanidés.

Le stomoxe adulte ou mouche des étables dépend du sang des vertébrés pour survivre et se reproduire bien que la durée du contact avec l'hôte soit relativement courte. Les larves de stomoxe se développent dans le fumier, les déchets alimentaires et les matières végétales en décomposition. Une bonne hygiène est indispensable pour limiter le développement des larves et venir à bout des stomoxes. On peut également traiter les animaux en insistant sur le bas du corps, à l'aide d'insecticides à effet rémanent. Une bonne utilisation de pièges modifiés, qu'il s'agisse de cibles traitées ou de grilles électriques à énergie solaire, peut aussi s'avérer efficace contre la mouche des étables.

La plus grande partie du cycle évolutif de H a e m a t o b i a adulte, ou mouche des cornes, se déroule chez l'hôte ; quant aux larves, elles se développent dans le fumier des bovidés. Dès lors, en l'absence de résistance, n'importe quel insecticide approprié ou presque peut donner de bons résultats contre cette mouche, en application topique. Ce type de traitement s'impose lorsqu'on peut en retirer un avantage économique : un poids supérieur au sevrage et des gains de poids pour les animaux d'un an et les bovins en croissance. Les traitements chimiques par voie orale (régulateurs du développement des insectes ou insecticides), administrés à des doses appropriées par bol, dans l'eau, les aliments ou en mélange avec des substances minérales, peuvent empêcher le développement des larves. Toutefois, la lutte contre les larves reste limitée du fait de la mobilité de la mouche des cornes parmi les troupeaux de bovins. On a essayé de recourir à des parasites, prédateurs et concurrents locaux, voire d'encourager leur développement, pour venir à bout des hématobies et des stomoxes, sans obtenir de résultats probants pour l'instant.

M O T S - C L É S : Biologie - H a e m a t o b i a - Lut te - Mouche des cerfs - Mouche des cornes - Mouche des étables - Stomoxys - Tabanidés - Taons.

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TABÁNIDOS, M O S C A B R A V A Y M O S C A D E LOS C U E R N O S : B I O L O G Í A Y MÉTODOS D E L U C H A . - L.D. Foil y J.A. Hogsette.

Resumen: Los tabánidos se cuentan entre las moscas parásitas del ganado más independientes en su estadio adulto. Una sola ingestión de sangre representa una fuente de energía capaz de producir de 100 a 1.000 huevos. Las hembras de

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ciertas especies son incluso capaces de aovar antes de toda ingestión de sangre (autogenia); puede así darse una renovación anual de las poblaciones con solamente un 2% de hembras ponedoras. La sangre que los tabánidos toman de animales salvajes es en general suficiente para permitir la renovación anual de las poblaciones. El habitat de las larvas también es independiente de los animales domésticos, de modo que el único método químico eficaz para reducir sus efectos en el ganado consiste en el uso de productos repelentes o repelentes parciales. Dentro de los métodos no químicos se cuenta la instalación de trampas permanentes (y eventualmente de trampas siluetas tratadas) y también el recurso al pastoreo selectivo o la cría del ganado en espacios cerrados.

La mosca Stomoxys calcitrans adulta o mosca brava necesita de la sangre de los vertebrados para sobrevivir y reproducirse, pero su contacto con el huésped puede ser de relativamente corta duración. Las larvas de la mosca brava se desarrollan en el estiércol, los restos de alimentos y las materias vegetales en descomposición. Las medidas de higiene en los hábitats de las larvas son un elemento clave en la lucha contra las poblaciones de moscas. También se puede tratar el ganado aplicando insecticidas de acción remanente en las partes bajas del cuerpo de los animales. Asimismo, la utilización adecuada de trampas modificadas tales como blancos tratados o parrillas eléctricas alimentadas con energía solar, suele ser eficaz.

La mayor parte del ciclo evolutivo de la mosca Haematob ia adulta o mosca de los cuernos se lleva a cabo en el huésped; las larvas se desarrollan en el estiércol de los bovinos. Por lo tanto, casi cualquier insecticida de aplicación tópica puede dar buenos resultados contra la mosca de los cuernos, pues ésta no presenta resistencia a los insecticidas. Los tratamientos deben aplicarse siempre y cuando se espere obtener beneficios tangibles desde el punto de vista económico: concretamente, un mayor peso de los jóvenes en el momento del destete, y un aumento de peso en los animales de un año y los bovinos en período de crecimiento. Los tratamientos con productos químicos por vía oral (reguladores del desarrollo de los insectos o insecticidas), suministrados en dosis apropiadas en el bolo, el agua, los alimentos o las mezclas minerales, pueden contribuir a impedir el desarrollo de las larvas de las moscas de los cuernos. Pero el éxito de la lucha contra estas larvas se ve restringido por la movilidad de la mosca adulta en los rebaños de bovinos. Se intentó y planificó el aumento de las poblaciones de parásitos, depredadores y competidores locales para luchar contra ambas especies de moscas, pero no se han obtenido hasta ahora resultados claramente concluyentes al respecto.

P A L A B R A S C L A V E : Bio log ía - C o n t r o l - H a e m a t o b i a - M o s c a d e los c iervos - Mosca de los c u e r n o s - Mosca b rava - S t o m o x y s - T a b á n i d o s -Tábanos .

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