Species Of Medical Veterinary Importance

Adults and larvae of some important muscid flies can be identified tentatively from external characteristics and from features of their behavior, habitat, and geographic location.

House fly (Musca domestica)

This nonbiting filth fly occurs on all continents except Antarctica. It is native to the Afrotropical and Oriental regions and was probably introduced into the Americas by Europeans during colonial times. Adults are gray and black flies, 6—9 mm long, with four black vittae on an otherwise gray thorax (Figs. 14.1 and 14.13A). The wing has a sharp forward bend in vein Ml (Fig. 14.1 OA). The abdomens of typical females are checkered gray and black at the dorsal midline and creamy yellow on the sides, which in North America is sufficient to distinguish this species from the face fly. Larvae have large caudal spiracles that resemble back-to-back D's, and the slits are sinuous (Fig. 14.4B).

Immatures can be found in a wide variety of decaying organic substrates. Major breeding sites include human garbage dumps, open privies, livestock manure, soiled bedding, poultry litter, and wastes around fruit and vegetable processing plants. Breeding continues year-round in tropical and subtropical regions but is interrupted by winter in temperate regions. From a public health standpoint, the house fly is probably most significant as a nuisance and potential vector of enteric pathogens. Although the house fly can become quite abundant where livestock, poultry, and companion animals are housed, its direct effects on animal health are comparatively unimportant.

Bazaar fly (Musca sorbens) This nonbiting filth fly is the most abundant synanthro-pic muscid fly in many parts of the Afrotropical, Oriental, and Pacific regions. It was introduced through commerce into Hawaii and probably would flourish elsewhere in tropical latitudes of the Americas. Greenberg's (1971) key provides characteristics to

Maxillary Palp Fannia Scalaris

FIGURE 14.13 Muscid flies, adult females. (A) house flv {Musca domestica)-, (B) false stable Ov (Muscina stabulans)-, (C) stable fly (Sfe-moxys calcitrant); (D) little house fly (Fannin cankularis); (E) born fly (Haematobia irritara)-, (F) biack garbage fly (Hydrotaea ignava). Not to scale, (original drawings by F. Gregor, and published in Greenburg, 1971, reprinted by permission ofPrinceton University Press)

FIGURE 14.13 Muscid flies, adult females. (A) house flv {Musca domestica)-, (B) false stable Ov (Muscina stabulans)-, (C) stable fly (Sfe-moxys calcitrant); (D) little house fly (Fannin cankularis); (E) born fly (Haematobia irritara)-, (F) biack garbage fly (Hydrotaea ignava). Not to scale, (original drawings by F. Gregor, and published in Greenburg, 1971, reprinted by permission ofPrinceton University Press)

distinguish the bazaar fly from other Musca species in the Afrotropical and Oriental regions.

The species recognized as M. sorbens before 1970 apparently consists of a complex of at least three species that are partially distinguishable by the ratio of the width of the male's frons (area between compound eyes) to the width of the head {including eyes). The 4'broad-frons" form is known correctly as the bazaar fly (M. sorbens), and this species occurs from Africa east through the Orient and on many Pacific islands. A "narrow-frons" form occurs in Australia and Papua

New Guinea and is considered a distinct species, the bush fly (M. vetustissima). A second "narrow-frons" form (M. biseta) coexists with the bazaar fly in Africa and eastward, but further study is needed to resolve distinctions between M. biseta and the bush fly in southern Asia and the Orient (Pont, 1991).

Adult bazaar flies are strongly exophilic, being far less inclined than the house fly to enter buildings. Larvae have been recorded in unburied human stools and dog feces and, less commonly, in feces of other animals, in carrion, and in garbage. The bazaar fly is important to public health, but it is probably unimportant to the health of domestic animals.

Bush fly (Musca vetustissima)

This nonbiting dung fly occurs in Australia, where it is a major nuisance to humans and livestock. It is related closely to the bazaar fly and keys out as M. sorbens in Greenberg (1971). Adults are attracted to large mammals as sources of fluids for nourishment and feces for oviposition. Several authors have speculated that the bush fly was originally associated with aboriginal encampments, but that its abundance increased when domestic cattle were imported. Larvae have been recorded from the feces of a wide variety of large mammals, but in nature cattle dung pats are overwhelmingly the most productive. Breeding is continuous in subtropical Australia, and southward migrations serve to repopulate temperate Australia and Tasmania each spring (Hughes, 1977).

Face fly (Musca autumnalis)

This nonbiting dung fly is native to Europe and central Asia and was introduced into North America before 1952 (Krafsur and Moon, 1997), It occurs in all southern Canadian provinces and in the United States north of Arizona—Georgia (35°N). The adult resembles the house fly (Figs. 14.1 and 14.13A), is 6—10 mm long, has four black vittae on an otherwise gray thorax, and has a sharp forward bend in wing vein ml (Fig. 14.10A). The male's abdomen has a distinct, black longitudinal band along the midline and bright yellow sides. The female has a characteristic yellow patch on the ventrolateral aspect of the first visible abdominal segment; the remaining segments are gray—black to the ventral midline. The egg has a distinct brown— black respiratory stalk (Fig. 14.2B). Mature larvae are bright yellow with black, D- shaped spiracular plates (Fig. 14.5A), and puparia are white due to calcification.

During the fly breeding season, adult face flies occur around grazing catde and horses. Their larvae develop exclusively in fresh cattle dung pats. In autumn, newly emerged adults enter diapause, aggregate on buildings, and eventually accumulate behind siding, in wall voids, in attics, and occasionally in interior rooms. Thousands buffalo fly (H. exigua). However, Zumpt (1973) concluded that they are subspecies of H. irritans, based mainly on subtle morphological differences and al-lopatric distributions. The horn fly is native to northern Africa, Europe, and central Asia and was introduced into North America from Europe in the middle 1880s. It has since spread to all cattle-producing regions in the Americas, including Hawaii. The buffalo fly is native to southern Asia, the Orient, Indonesia, and several Pacific islands. It spread through commerce into New Guinea and Australia before 1840. It is possible that the two subspecies intergrade in parts of Asia.

The adult horn fly (Fig. 14.13E) is 3—5 mm long and has a piercing/sucking proboscis (Fig. 14.8B). The maxillary palps are held appressed to the haustellum and are almost as long as the haustellum. Wing vein ml is gently curved (Fig. 14.10C). Adults of both subspecies are specific to cattle, bison, and water buffalo; aberrant hosts include horses and other large mammals. The flies occur mainly on the withers, back, and sides but will move to the belly when weather is hot. Females of both flies lay their eggs exclusively under edges of dung pats, usually within minutes of host defecation. For unknown reasons, dung from horses, sheep, and other large mammals is unsuitable. Horn flies occur in far greater numbers on grazing cattle than on animals confined in drylots or indoors. Reproduction is continuous and populations are multivoltine. The horn fly overwinters as a diapausing pupa in temperate latitudes. Neither subspecies poses any threat to human health, but both species are serious economic pests of grazing beef and dairy cattle.

of flies can occur in such aggregations. The face fly was first recognized as a nuisance in European households due to its overwintering habits. It became recognized as a pest of cattle and horses after it was introduced into North America.

Cluster fly (Pollenia rudis)

The cluster fly is discussed here because it often occurs along with the face fly in household infestations. This calliphorid fly is native to Europe and North Africa and was introduced into North America, where it now occurs in all southern provinces of Canada and throughout the United States. The adult is 7—9 mm long, the abdomen is completely black with silvered checking, and crinkly golden hairs occur on the head and thorax. Cluster fly larvae are internal parasites of earthworms (.Allolobophom spp., Lumbricidae) and produce two to four generations per year. Adults can be a nuisance in households, but they do not affect domestic animals.

Stable fly (Stomoxys calcitrans) This biting filth fly (Figs. 14.12 and 14.13C) is native to Africa, Europe, Asia, and the Orient and was probably introduced into the Americas and Australia during colonial times. At least three common names are used regionally for the stable fly. It is known as the beach fly because of outbreaks on recreational beaches, the dog fly because it pesters dogs, and the lawn-mower fly because larvae have been found in damp, matted grass on the undersides of lawn mowers. The stable fly is also misleadingly called the biting house fly because of its superficial resemblance to the house fly.

The adult is 5—7 mm long, has seven circular black spots on an otherwise gray abdomen (Fig. 14.13C), and has a piercing/sucking proboscis with short maxillary palps (Fig. 14.8A). Larvae and pupae have uniquely shaped, subtriangular posterior spiracles (Fig. 14.5B) that are far apart; the horizontal space between them is greater than twice a plate's width. Larvae occur in decaying fibrous substrates such as straw bedding, wet hay, algal mats, and wet grass clippings. Other larval habitats include accumulations of manure from dairy and beef cattle, mixtures of soil and partially composted bedding and animal manure, and byproducts of crop processing, such as peanut hulls, beet pulp, and sugarcane bagasse. Breeding is continuous in tropical and subtropical climates, and the species is thought to overwinter as immatures in colder climates. Stable flies are important to public health because they will attack and annoy people, but they are much more important from a veterinary perspective.

Horn fly (Haematobia irritans irritans) and buffalo fly

(Haematobia irritans exigua) These biting dung flies were once recognized as two separate species: the horn fly (H. irritans) and the

False stable fly (Muscina stabulans) and its relatives These nonbiting filth flies include the false stable fly, which has been spread worldwide through commerce, and another 10 species that occur mainly in the Ho-larctic region. The name M. assimilis, used widely in older literature for a relative of the false stable fly, has been relegated to a synonym of M. levida (Skidmore, 1985). The false stable fly (Fig. 14.13B) and its relatives are stout flies, 8—12 mm long, with brown-black bodies and a rounded bend in wing vein ml (Fig. 14.10D). The tip of the scutellum of the false stable fly is red—orange. The posterior spiracular plates are roughly circular; they are separated by one plate's width, and the slits are bowed and arranged radially (Fig. 14.5D). Third-instar larvae are facultatively predatory, and adults overwinter in a prereproductive diapause. These species can affect public health, but they are not thought to affect the health of domestic animals.

Little house fly (Fannia canicularis) and its relatives There are about 100 species of these nonbiting filth flies in North America (Chillcott, 1961) and

FIGURE 14.14 Little house fly (Fannia caniculetris), third-instar larva. (From McAlpine et al., 1981 reproduced with permission of Minister of Public Works and Government Services, Canada)

additional ones in Latin America, Africa, Europe, and Asia. The little house fly (F. canicularis) and the Latrine fly (P. scalaris) have spread by commerce throughout the world. Fannia species are 5—8 mm long, with dark thoraces and abdomens variously marked with yellow (Fig. 14.13D). The arista lacks setae and the second anal vein (a2) curves toward the first anal vein (al) (Fig. 14.10E). Larvae and puparia have characteristic lateral and dorsal processes (Fig. 14.14) whose function is unknown. Males form mating swarms in shady locations, and it is this swarming behavior that most often brings them into contact with people. The little house fly is probably the most endophilic and commonly encountered species of this genus in North America. The latrine fly is more exophilic. Although these flies are most noticeable where domestic and zoo animals are confined, they are not important to public and veterinary health.

Garbage flies (Hydrotaea spp.)

There are seven known species of garbage flies, and at least one species occurs in every biogeographic region. This group of nonbiting filth flies, once placed in the genus Ophyra, has been merged into Hydrotaea (Huckett and Vockeroth, 1987). Accordingly, the scientific names of the common species have changed. The black garbage fly, known in older literature as Ophyra leucostoma, is now Hydrotaea ignava. It is native to the Old World and has been introduced into North America (Skidmore, 1985). The black dump fly, formerly O. aenescens, is now H. aenescens. It is native to the New World, occurs in the eastern Pacific Islands, including Hawaii, and has been introduced into Europe.

The garbage flies are 4-7 mm long, with shiny black thoraces and abdomens (Fig. 14.13F). Wing vein ml is virtually straight (Fig. 14.10F). Posterior spiracles of mature larvae and puparia are roughly circular; they are separated by less than one plate's width and have slightly curved slits that barely diverge from a faint scar (Fig. 14.5E). Adults are strongly exophilic. Larvae have been recorded in a great variety of filthy substrates, including carrion. Third instars are facultative predators and will consume larvae of other flies that cohabit their breeding medium. These filth flies pose a modest threat to public health, but they arc not known to harm domestic animals.

Sweat flies (Hydrotaea spp.,) About 50 species of sweat flies occur in the Palearctic region, and fewer species occur in the remaining biogeographic regions. Sweat flies are gray to black and 3—8 mm long, with an arista that lacks setae. Although the female has no simple distinguishing characters, the male has a ventral notch or depression at the distal end of the fore femur. Third-instar larvae are facultative predators. Their spiracular plates are stalked, with radially arranged slits (Fig. 14.5F).

Females of 6 of the 24 North American species, including H. meteorica and H. scambus, are persistent in their attempts to imbibe perspiration and secretions from the eyes, nostrils, lips, and other parts of mammalian hosts. The remaining North American species are apparently not attracted to animals (Huckett, 1954). In Europe, the sheep head fly (H. irritans) is a primary pest of sheep, cattle, and deer.

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