Stomoxys calcitrans: Stable Fly Life Cycle & Habits PDF

Genus Stomoxys Geoffroy, 1762 Genus Stomoxys Geoffroy, 1762 Stomoxys calcitrans Geoffroy, 1764 is the commonest species of this genus and is known as the 'stable flv'. It occurs all over the world. The flies are about as large as Musca domestica. The proboscis is prominent, directed...

Genus Stomoxys Geoffroy, 1762 Genus Stomoxys Geoffroy, 1762 Stomoxys calcitrans Geoffroy, 1764 is the commonest species of this genus and is known as the 'stable flv'. It occurs all over the world. The flies are about as large as Musca domestica. The proboscis is prominent, directed horizontally forwards and has small labella. The Mi 4-2 vein curves gently forwards and the R5 cell is open, ending at or behind the apex of the wing. The thorax- is grey and has four longitudinal dark stripes, of which the lateral pair are narrow and do not reach the end of the scutum. The abdomen is shorter and broader than that of the house fly and has three dark spots on each of the second and third segments.  Life-cycle. Stomoxys sometimes lays its eggs in horse manure, but prefers decaying vegetable matter like straw and hay, especially when these are contaminated with urine. The material must be moist, otherwise it is unsuitable. A fly lays about 25-50 eggs at a time and may lay a total of 800. The eggs are dirty-white to yellow, about 1 mm long, and bear a longitudinal groove on one side. They hatch in one to four days or longer in cold weather. The larvae feed on the vegetable matter and in warm weather grow mature in 14- 24 days. The full-grown larva resembles that of Musca, but its stigmal plates are far apart and each has three S-shaped slits. Pupation takes place in the drier pans of the breeding material and this stage lasts about six to nine days, or much longer in cold weather. Oviposition begins about nine days after emergence of the fly and after a few meals of blood have been taken. The complete life-cycle may take about 30 days.  Habits and significance The flies are most abundant in summer and autumn and live about a month under natural conditions. They prefer a fairly strong light and are not seen in dark stables or houses. They enter buildings only in autumn or during rainy weather. They are swift fliers, but do not travel long distances. Both males and females are blood-suckers, attacking man, horses, cattle and other mammals, and even birds and reptiles. about three to four minutes are required for a meal and the fly often changes its position or flies to another animal to continue its feed. Trypanosoma evansi (surra of equines and dogs) and T. equinum (mal de caderas of equines, cattle, sheep and goats) are transmitted mechanically by Stomoxys. The species may also mechanically transmit T. gambiense and T. rhodesiense, the causes of human trypanosomiasis in Africa, and T-brucei and T. vivax, which cause nagana of cattle, sheep, goats and equines in Africa. It also serves as an intermediate host of the nematode Habronema majus  Habits and significance The role of S. calcitrans in the transmission of equine infectious anaemia is still under debate (Steelman 1976). However, the fly is responsible for the mechanical transmission of septicaemic infections such as anthrax. Its nuisance effecr has been estimated at S142 million in the USA (Steelman 1976) and Cheng (1958) has estimated that control measures were economical when levels of 25 stable flies per animal per day were reached in beef herds. The importance of biting flies in the transmission of disease and economic loss through 1 flv worry' has been reviewed by Stork (1979).  Control.. The fly is most troublesome in localities where suitable breeding-places are readily found. Control measures should therefore be directed toward destroying breeding- places by regular removal of moist bedding, hay and faeces from stables and yards, and food wastes from feeding troughs, and by preventing the accumulation of heaps of weeds, grass cuttings and vegetable refuse. Control by insecticides is similar to that for house flies. Stomoxys calcitrans : stable fly.  FAMILY: GLOSSINIDAE This genus previously has been included in the family Muscidae. It is now usual to regard the genus as the sole constituent of the family Glossinidae; this has been discussed by Pollock(1974The species of the genus Giossina or tsetse flies are important blood-sucking flies; they transmit several species of trypanosomes which cause fatal diseases, for example, nagana of domestic animals and sleeping -sickness of man. The genus is confined to subtropical and tropical pans of Africa was recorded in southern Arabia in rcjro but has not been found there again. The flies are narrow-bodied. yellowish to dark brown and 6-13.5 mm long- At rest the wings are held over the back, overlapping almost completely scissor-like. The rhorax frequently has a dull greenish ground colour and is marked with inconspicuous stripes or spots. The abdomen is light to dark brown, and six segments are visible from the dorsal aspect. The venation of the wing is very characteristic, especially the course of the Mi + 2 vein which produces the hatchet- or cleaver-shaped discal cell (first Ma cell). The proboscis is long, held horizontally and ensheached in long palps which are of an even thickness throughout. The antenna has a large, elongate third antennal segment which ends in a blunt, forwardly directed point, and an arista which bears 17-29 dorsal branching hairs. A description of the different species of Glossina goes beyond the scope of this book. They are described by Buxton (1955) and Potts (1973) who provides a key for the identification of species.  Life-cycle. The female fly produces one larva at a time when the latter is full grown and ready to pupate. The larva grows in the uterus of the female, its mouth being attached to a ' teat' from which 'milk' is obtained for nourishment; its posterior extremity, which bears the stigma! plates, lies near the vulva. The gestation period lasts about ten days under suitable conditions, but is prolonged if food is scarce or in cold weather when the flies do not feed readily. It is estimated that a female can produce eight to ten, sometimes up to t2 larvae and one act of mating renders a female fly fertile for life. The larva is an oval, about 7 mm long. It wriggles into the soil to a depth of about 2 cm and turns into a pupa after 60-90 minutes. The larva has two large respiratory lobes at its posterior end, each perforated by about 500 spiracular openings. These lobes persist with the last larval skin, which forms the puparium covering the brown or black pupa, and they give the pupa the characteristic appearance. They vary in different species and are used for the identification of the pupae of different species. The pupa is about 6—7 mm l°ng- The length of the pupal period varies according to the temperature and the species concerned. It usually lasts about 35 days, with limits of about 17-90 davs. For example, the pupal period of G. pallidipes varies from 31 days in the summer to 149 days or more, usually about 92 days, in the winter.  Habits.The bionomics of tsetse flies, especially of certain species, have been studied intensively for many years and there is an extensive literature on the bionomics and biology of the fly (see Buxton 1955; Mulligan 1970; Potts 1973). Tsetse flies are found mainly in the central part of Africa, extending from the southern boundaries of the Sahara to southern Africa (e.g. Zimbabwe). In these regions the flies are confined to definite areas known as ' fly-belts '. the limits of which are controlled by various factors such as altitude, moisture, vegetation and the presence of hosts. The different species vary greatly in their adaptation to environment and consequently in their distribution. Potts (1973) gives the distribution of Glossina species along with the northern and southern limits in West Africa, Central Africa and East Africa for the various species. For example, G. palpalis occurs mainly in the areas drained by the Senegal, Niger and Congo rivers; G. morsitans occurs from Senegal to Ethiopia and extends south to Zimbabwe. G. pallidipes is essentially an East African species and is found from the Republic of South Africa to Uganda and Kenya. G. taehinoides can live at higher temperatures than most other species and is found in hot regions like northern Nigeria. More extensive information on the geographical distribution is given by Ford (1970a). The humidity of the atmosphere, the temperature and the presence of shade have an important bearing on the life of the fly. G. palpalis requires an almost saturated atmosphere and much shade and is therefore found near water, especially along the banks of rivers or lakes  Habits surrounded by overhanging trees or bushes. It is killed within a short time by direct sunlight and by temperatures over 30X, especially if the hu­midity is not high. Its natural range from water is about 30 m, but the fly will follow a host for 300 m or sometimes more away from water. G. morsi­tans and G. pallidipes are much less restricted to moisture and shade conditions and are most active in a moderately dry and warm climate. They occur in open ' parkland' type of vege­tation. G. pallidipes requires a moderate degree of humidity and is less independent of cover than G. morsitans. Both these species require trees or scrub for shelter and the former especially does not venture far into open country. The different species are each particularly associated with certain types of vegetation, an important factor which requires much further study. The vegetation as well as other controlling factors like the presence of water restrict the flies during bad seasons to certain areas known as 'primary fly centres' or permanent haunts, from which the}' migrate outwards along suitable courses to temporary haunts during favourable seasons. G. palpalis for instance, will ascend to the upper limits of rivers in rainy seasons and again descend when dry conditions set in. The physical, vegetational and animal influences, as well as population dynamics, are discussed by Glasgow (1970). All the species of Glossina feed on the blood of vertebrates. The hosts of Glossina species are discussed by Weitz (1970). Some species of hosts are more suitable than others and the prevalence of flies is dependent on the number and suitability of hosts. G. palpalis thrives best on the blood of warm-blooded animals and is stated to prefer human blood, but it can also feed on cold-blooded animals like crocodiles. It is generally agreed that this species is not dependent on big game for its existence. G. morsitans feeds on any large mammal or bird, but is not able to exist permanently where big game or cattle are absent. This fly disappeared from the Transvaal with the big game which was killed out by rinderpest. Occasionally G. morsi­tans has been found where big game was scarce, but since the pupal period is long, such flies may have emerged some time after the main stock of  Control Recent developments in techniques for tsetse control are reviewed by Jordan (1978). Almost all present-day control methods depend on the use of insecticides and older methods such as bush-ciearing, slaughter of game, etc. are not dealt with here in detail. Catching and trapping. Catching with hand nets is not practicable except in small areas. It is a method of determining the fly density in a given locality. Numerous types of traps have been designed, mainly on the principle that the fly is attracted by a horizontal shadow and flies in underneath it. Bush-clearing. In the case of flies like G. palpalis, which require much shade, this measure is important and the clearing of bush around settlements, wells, landing-places and fords on rivers and on either side of roads has given excellent results in providing protection from the fly. Wholesale clearing of large areas, however, presents many difficulties, especially the expense incurred and the rapid regrowth of the bush.  Control Insecticides. The majority of present-day control programmes depend on the use of insecticides. This is discussed by Jordan (1978). Persistent insecticides, such as DDT and dieldrin, applied from the ground, have provided useful control. In the Sudan and the savanna vegetation zone of Nigeria 2.5% DDT wettable powder ap­plied in the dry season achieved eradication of G. submorsilans, G. tachinoides and G. palpalis. Be­- cause of the susceptibility of Glossina species to these insecticides, discriminative application and selective spraying are effective methods of use. Thus with G. tachinoides spot spraying of riverine vegetation up to 70 cm from the ground is suf­- ficient to give control, while spraying up to 1 m gives control of G. pa/pa/is. Where the seasonal factors van-, application techniques for insecticides also must be modified and are less discriminative than above. However, using the ground spray technique, Nigerian authorities have reclaimed some 180000 km of tsetse-infested country (Jordan 1978). The application of insecricide from the air, usually using helicoptors rather than fixed- wing aircraft, has been practiced in East and West Africa with good results. Spraying is limited to the dry season and is carried out when temperature inversion conditions exist. This limits application to a period of one to two hours in early morning or at dusk. The technique of spraying (e.g. speed, height of the helicoptor above the canopy) and the formulation of insecticide, usually dieldrin, is discussed by Jordan (1978). Non-persistent insecticides applied from the air, often by fixed-wing aircraft, at repeated in­tervals (five to six), coinciding with the length of the pupal period, have produced useful control. Endosulfan as an ultra-low-volume formulation is used most extensively, while isobenzan has also been used as a non-persistent insecticide. FAMILY: OESTRIDAE , / SAMOUELLE, 1819 This family includes the genera Hypoderma, Oestrus and others, but the genus Gasterophilus is now assigned to the family Gasterophilidae (Free­man 1973). The adults are hairy flies which have rudimentary mouth parts and do not feed. They usually lay their eggs on animals. The larvae are parasitic maggots and consist of 12 segments, of which the first two are fused together. Oral hooks are usually present, but there is no head. The posterior stigmata open through semicircular plates which may be retractile. The larvae moult twice during their parasitic life and leave the host when they are full grown to pupate in the ground. They feed on the body fluids of the host or on  FAMILY: OESTRIDAE Oestrus ovis Linnaeus, 1761, the 'sheep nasal fly', has a dark grey colour with small black spots which are especially prominent on the thorax and it is covered with light brown hair. The flies hide in warm corners or crevices and in the early morning they can be seen sitting against walls or other objects in the sun. They occur from spring to autumn, particularly in summer, but in warm climates they are active even in winter. The larvae occur in the nasal cavity and the adjoinins sinuses in sheep and rarely in goats and have aiso been found in the blesbock (Damaliscus albifrons) and, in Egypt, in the camel. Oestrus ovis some­times also deposits its larvae in the eyes, nostrils and on the lips of man, where they may develop, causing serious trouble. Shepherds are said to be especially susceptible to myiasis by this fly and ~ also persons associated with cheese-making from sheep milk. The flies deposit their young larvae around the nostrils of the host, whence they crawl upwards. Sometimes they enter cavities which have small openings, like those of the turbinate bones or a branch of the frontal sinus, with the result that they are not able to get out when they have grown fully and so they die there. The rate of , development of the first larval instar varies / considerably, this instar remaining in the nasal I passages for two weeks to nine months during the cold months. The second instar passes into the frontal sinuses and may develop rapidly, leaving I the sheep 25 days after infection or considerably lonser. Finally the full-grown larvae crawl out and pupate in the ground for three to six weeks or longer during the cold season, before the fly emerges. The young larvae are white or slightly yellow; when they become mature, dark transverse bands develop on the dorsal aspects of the segments. The full-grown larva is about 3 cm long, tapering anteriorly and ending with a flat surface posteriorly. There are large, black, oral hooks, connected to an internal cephalopharyngeal skeleton. The ventral surface bears rows of small ipines and the black stigmal plates are conspicuous on the posterior surface.  Pathogenesis. The flies cause great annoyance when they attack the sheep to deposit larvae; the animals stop feeding and become restless. They shake their heads or press their noses against the ground or in between other sheep. When the flies are plentiful, they may cause considerable inter­- ference with the feeding of the animals.' The larvae irritate the mucosa with their oral hooks and spines, causing the secretion of a viscid mucous exudate, on which they feed. Erosion of (ne bones of the skull may occur and even injury to the brain and then such signs as high-stepping Sa'C and incoordination may suggest infection w'th Coenurus cerebralis (see p. 117). For this reason the infection has been called ; false gid '. Infected sheep have a nasal discharge and  Diagnosis can only be made tentatively from the clinical signs, excluding other possible causes like "ngworms and chronic bronchial or pulmonarv leases. Treatment. This is difficult since the larvae are difficult to reach: frequently the openings into the sinuses are narrowed or occluded. At one time direct injections into the frontal sinus were made, using an emulsion of tetrachlorethylene, but this has now been largely discontinued. Instillation of HCH in oil (.1-4%) into the nostrils while the sheep is lying on its back has been practised in the Republic of South Africa, with good results. The use of systemic insecticides, such as the organophosphorus compounds, is a more rational approach. Sheep given 55-88 mg/kg of a mixture of 2 g ofNeguvon (Bayer L 13/59) a°d 0.2 g of Asuntol (Bayer L 21/199) were cleared of the infection (Stampa 1959). Crufomate (Ruelene, Dowco B2) as a dip (35%) or as a 'pour-on' (r3-5%) has been useful while rafoxanide as a drench (7.5 mg/kg) greatly reduces infection. Horak and Snijders (1974) compared two large groups of Merino lambs infected with Oestrus ovis and one group being treated with rafoxanide (7.5 mg/kg). Over a two-year period the treated group showed a reduction in nasal discharge, an in­crease in weight gain and virtual freedom from the parasite in the nasal passage and sinuses. Prophylaxis. This is difficult since the present fly repellents are short lasting. One method is to feed sheep in narrow troughs, the edges of which are smeared with tar. The animals automatically tar themselves and this acts as a repellent. Oestrus ovis: pupa and adult fly. Oestrus ovis: second stage larvae. Oestrus ovis: third stage larvae in nasal cavity Oestrus ovis: purulent nasal discharge in sheep Genus: Hypoderma Latreille, 1818/ The larval stages of H. bovis (de Geer, 1776) and H. lineatum (de Villiers, 1789) (syn. H. lin-eata), the ' ox warbles', are common parasites of cattle, rarely also of man and horses, in man)' countries in the northern hemisphere. They occur between latitudes 25° and 6o°. Apart from infections in imported animals the genus is not established in the southern hemisphere. H. bovis is about 15 mm long; H. lineatum measures 13 mm. The flies are hairy and have no functioning mouth parts. The hairs on the head and the an­terior part of the thorax are yellowish-white in H. lineatum and greenish-yellow in H. bovis. The abdomen is covered with light yellow hairs an­teriorly, followed by a band of dark hairs; the posterior portion bears orange- yellow hairs. Hypo-derma bovis is referred to as the northern cattle grub in North America and H- lineatum as the common cattle grub or the heel fly. This species has also been reported from the American bison {Bison bison) where it shares range with cattle (Capelle 1971).  Life-cycle The flies occur in summer, especially from late May to July. They are most active on warm days, when they attack cattle to lay their eggs. However flies have been observed to oviposit at temperatures as low as 4C'C (Andrews 1978). The flies are limited in flight and rarely exceed 5 km though Beesley (1974*) has noted flights up to 14 km. Hypoderma lineatum tends to appear about one month before H. bovis. The eggs are about 1 mm long and are fixed to the hairs by means of small terminal clasps. especially on the legs, but more rarely on the bod} as well. H. bovis lays its eggs singly, while n- lineatum deposits a row of six or more on a hair-The flies are very persistent in approaching the animals and one female mav lay 100 or more egg-s on one individual. The larvae hatch in about four days and crawl down the hair to the skin, through which they penetrate. They wander in the subcutaneous connective tissue up the leg and then towards the diaphragm and gradually increase in size, though such first-stage larvae may be found in many different sites of the body, including intermuscular connective tissue, the surface of internal organs etc. Beesley (1974ZO designates the ' winter resting sites ' of first-stage larvae as the submucosal connective tissue of the oesophageal wall in the case of H. lineatum and the region of the spinal canal and epidural fat for H. bovis. Larvae reach these sites weeks or months after hatching and remain in them for the autumn and winter, growing to about 12-16 mm in length. Eventually during January and February the now second-stage larvae travel towards the dorsal aspect of the body and reach the subcutaneous tissue of the back where they mature to the third stage. This is the ' spring resting site' of the larvae (Beeslev 19746). When the parasites arrive under the skin of the back, swellings begin to form, measuring about 3 cm in diameter. The skin over each swelling becomes perforated and the larva then lies with its posterior stigmal plate directed towards the pore for the purpose of respiration. This is the ' warble' stage of the infection. This stage lasts about 30 days. The younger larvae are almost white, changing to yellow and then to light brown as they grow older. The full-grown third stage larva of H. bovis is 27-28 mm long; that of//. lineatum 25 mm. Each segment of the third-st2se larva bears a number of flat tubercles and small spines are present on all segments but the last in H. lineatum and on all but the last two in H. bovis. In spring the mature larva wriggles out of its cyst and falls on the ground into which it penetrates to pupate. The pupal case is black and the fly emerges from it, after 35-36 days, by pushing open an operculum at the anterior end. Among other hosts on which these two species of Hypoderma may lay eggs, especially when cattle are not available, are horses and man, though the larvae do not usually mature in these.  Incidence Studies in the UK indicate that the overall infection level has increased gradually in the last few years. Regional variations occur and Scotland and northern England show higher infection rates than elsewhere. Based on the percentage of hides with warble larva damage, 2 lower level occurred in cow and bull hides than from heifer and ox (Andrews 1978). Calves and young cattle are more frequently and more se­verely infected than older animals. It is possible that cattle develop a degree of immunity to the larvae. However, Rich (1970) did not observe such differences between range cows and their yearling suckler calves in Canada. In other countries the infection rate is lower and some have instituted control programmes which have reduced the incidence to very low levels or have eradicated the parasite.  Pathogenesis and economic importance. When adult flies approach an animal to lay eggs, animals become apprehensive and disturbed and attempt to escape the fly by running away, often aimlessly (o-adding). Animals may damage themselves on fences or wire or may be killed by gadding into water or falling over heights. Additionally this results in reduced weight gain and milk yield. In the UK in 1978, animal losses due to gadding were estimated at £3 million by the Hides and Allied Trades Improvement Society. Estimates of the loss in milk production vary from country to country, from 10-15% ' n Europe to up to 50% in Canada (Andrews 1978). Control by insecticides resulted in a 7-11% increase in milk production. Losses in meat production similarly vary, but all studies indicate a reduction of weight gain associated with the presence of larvae; further a direct relationship between the number of larvae (or warbles) and reduction of weighc gain was evident. Several studies have indicated a significant increase in weight gain following the, control of infection with organophosphate compounds (Andrews 1978). Carcass and hide depreciation are important aspects of Hypoderma spp. infection. Rich (1970) in Canada associated one to five larvae with the trimming of 0.7 kg of carcass and 11 or more larvae with the necessity to trim 1.2 kg from a carcass. Damage caused includes discoloration of meat along the tracks of larvae, meat may also be gelatinous; the name of licked ' beef is applied to such lesions. Local abscess formation may occur at the site of a warble, especially if an abortive extraction of an immature larva has been made. Hide damage is a well recognized consequence °f infection and significant differences in monetary value of hides result from holes and other flaws caused by Hypoderma larvae. Overall loss were estimated at £13 million in Great Britain ' n 1978. In the USA, in 1956, losses were estimated ar S192 million.  Pathogenesis and economic importance The aberrant migration of larvae in other animals may cause serious results. An acute neurological disease of a horse associated with the intracranial, migration of first-stage larvae was reported in western Montana (Hadlow et al. 1977). Olander (1967) has described the lesions caused by the migration of larvae of Hypoderma lineatum in the brain of a horse. Warbles may occur in the back of horses, making the wearing of a saddle or harness difficult. Infection of man rarely occurs. Abdominal pain, subdermal migratory tracts and local warble formation have been reported. Hypersensitivity responses associated with accidental or deliberate rupture of larvae in the warble may be associated with allergic responses (Hadwen &: Bruce 1917) and McDougall (1930) demonstrated the reaction to be anaphylactic in nature. Such response may attend the treatment of infected animals with organophosphate com­pounds (see below).  Clinical signs. Except for poor growth in bad cases and decreased milk yield the animals show no appreciable signs until the larvae appear along the back, when the swellings can be felt and seen. The larva lies in a cyst which also contains yellow- purulent fluid. Diagnosis. Diagnosis based on the presence of the larvae under the skin of the back. The eggs may also be found on the hairs of the animals in summer. However, as control programmes reach their terminal stages there may be a need for immunodiagnostic tests which will detect animals infected with migrating larvae and indicate those requiring treatment.  Treatment. Treatment may be undertaken in a variety of forms. Mechanical removal of larvae. Mature larvae may be squeezed out of the warble swelling. This is less successful when the larvae are not mature. Rupture of the larvae during extraction may lead to a localized inflammation and abscess formation or even a generalized anaphylaxis in a few animals. This method of treaiment is the least satisfactory. Insecticides. Until the advent of the organophosphorus insecticides, derris, or its active principle rotengne, was widely used as a larvicide. Derris was usually used as a wash and applied to the back of infected cattle after the scabs covering the warble swellings had been removed by scrub­bing with a soapy mixture. This treatment was highly effective but for adequate control re­peated treatment of stock was necessary during the warble season. A disadvantage was that the warble fly larvae were killed only when they had migrated through the body and produced damage to flesh and hides. The introduction of the or-ganophosphorus systemic insecticides allowed control of the larvae while they were in the early stages of migration and before they reached the backs of animals. Nevertheless eradication of the parasite was achieved with rotenone in Denmark and Cyprus. The systemic insecticides are applied once in autumn or winter before larvae appear on the back. Compounds may be administered orally, parenterally or dermally; the last method, using a ' pour-on' formulation, is the most acceptable in most countries though spraying may be used with range cattle. The organophosphate compounds available include: crufofnateTRueiene), famphur, fenthion (Tiguvon), phospmet (Profacte). (As well as being acfrvFagainst Hypoderma larvae they also have activity against lice.) These compounds can be used at any time of the year except between December and March inclusive, when larvae may be in the oesophagus or spinal canal. The compounds available will lead to 90% or more control of infection. Hypoderma bovis: adult fly.  Hypoderma bovis: numerous warbles with a purulent discharge.  Hypoderma bovis: mature warble showing the stigmates. Hypoderma bovis: manual extraction of a third instar larva Hypoderma bovis: lesions the underside of the skin. Hypoderma bovis: second (first on the left) and third instar larvae. A pupa is visible on the right. Hypoderma sp.: adult fly emergence. Hypoderma bovis: developing larvae under the skin. Hypoderma bovis: gadding of catlle due to the characteristic buzzing noise.