Sarcophagidae Flesh Flies

Flesh Fly Family Sarcophagidae
FIGURE 16.16 Red-tailed flesh fly, Sarcophaga hemorrhoidalis (Sar-cophagidae), adult. (From Greenberg, 1971.)

larviparous; the gravid female retains the eggs in an expanded, bilobed, uterine pouch until they are ready to hatch. Females produce 30-200 larvae, depending on the species involved. Flesh fly larvae (Fig. 16.17} are more robust than blow fly larvae and possess paired mandibles in all instars. Their posterior spiracles are recessed in a deep cavity, and the inner slit of each spiracle is parallel to, or slants away from, the ventral midbody line.

Sarcophaga species usually are associated with carrion or feces but can cause facultative wounds and accidental gastrointestinal myiasis. About 20 Sarcophaga species have been incriminated in cases of gastrointestinal

Sarcophagidae Larvae
FIGURE 16.17 Flesh fly, Sarcophagasp. (Sarcophagidae), third-instar larva, ps, posterior spiracular plate. (Original by E. P. Catts.)

myiasis. One widely distributed species is the red-tailed flesh fly (Sarcophaga haemorrhoidalis), which frequents feces and is attracted indoors by fecal odors. Only a few species in other sarcophagine genera have been recorded as causing myiasis of the gastrointestinal or wound type.

Few flesh flies cause obligatory myiasis. The most widespread and important species are in the miltogram-mine genus Wohlfahrtia. They include the Old World species W. magnified and the New World species W. opaca and W. vigil. These three species have evolved as primary invaders. Their females larviposit at moist body openings and at fresh wounds or scratches. Larvae can even penetrate thin, unbroken skin. The maggots burrow into the subcutaneous tissue to feed, inducing the formation of a boil-like cyst around groups of larvae with a small, common breathing pore opening to the outside.

Wohlfahrtia adults resemble large house flies with very distinct, longitudinal, thoracic stripes. Unlike other flesh flies, these have the abdomen clearly marked with black spots. A gravid Wohlfahrtia. female produces 120—170 larvae. In a host, the maggots grow rapidly and can cause considerable tissue destruction. After about 1 week, maggots drop to the ground to pupate and can overwinter in this stage.

The closely related W. nub a is not parasitic, but feeds only on necrotic flesh. It has been used successfully in treating ragged, infected wounds, similar to the use of Phaenicia sericata (Calliphoridae). Most other Wohlfahrtia species are scavengers, but all are probably capable of at least facultative myiasis.

A group of four unrelated genera of flesh flies cause facultative, and apparently obligatory, myiasis of certain amphibians and reptiles. In some cases they also attack amphibian and reptilian eggs, killing the developing embryos. These genera are Anolisimyia, Cistudinomyia, Eumacronychia, and Metoposarcophaga. Little is known of their biology.

Bot flies are the most highly evolved group of obligate myiasis-causing parasites of mammals. They are treated as four distinct subfamilies in the Oestridae. The most primitive are the Cuterebrinae, the New World skin bot flies. Their counterparts are the Hypodermatinae, the Old World skin botflies. The nose bot flies are in the Oestrinae, with their probable center of origin being in Africa. The remaining subfamily is Gasterophilinae, the stomach bot flies, which also appears to have evolved in Africa. All four of these subfamilies were recognized previously as families and are treated as such in earlier literature. The subfamilies of Oestridae can be separated as third-instar larvae by their general appearance and by the form of their caudal

Oestridae (Bot Flies)

spiracular openings. Bot-fly maggots are thick, robust, grubiike larvae with moderate to heavy spiny armature. As with most other flies discussed in this chapter, they pass through three larval instars, and they drop to the ground to pupate. Except for members of the Cuterebrinae, all bot flies overwinter as larvae in the host. The cuterebrines typically overwinter as diapausing pupae free from the host, although there are exceptions in subtropical and tropical regions.

Bot flies differ from other obligatory myiasis producers in several ways. First, the adults do not feed or take in nutrients. Most of them have only rudimentary, nonfunctional mouthparts and are unable to feed. Those with functional mouthparts and an associated alimentary tract probably only imbibe water to maintain an internal fluid balance. Second, bot flies either show a high degree of host specificity or they parasitize only a small group of related hosts. Although some bot fly maggots occasionally occur on atypical hosts, the susceptibility of a host does not necessarily imply the suitability of that host for normal, or successful, bot fly development. Third, bot fly maggots show a marked level of site specificity in a normal host. In abnormal hosts, site specificity can be erratic and can lead to dire results for both host and parasite. Fourth, the site of invasion by the first-instar bot maggot generally is not the site of maggot development. With the exception of Dermatobia} first-instar maggots of oestrid flies move from the point of invasion to a different site for further development. Interaction between the host and its developing bot fly maggots is generally benign, with the associated pathology and parasite burden being tolerated well by native, coevoived hosts. Bot fly maggots generally cause little injury to their hosts at low to moderate population levels.

Humans are not among the normal hosts for any bot fly species, including the so-called human bot fly (Dermatobia hominis). However, people may become incidentally infested by bot flies under certain circumstances. In such cases, the associated pathology tends to be more severe than that of their normal hosts.

Burrowing first-instar bot fly larvae occasionally cause paralysis or death of the host. Developing larvae located in warbles at critical sites such as around the eyes and on the feet can increase the risk of predation by interfering with the host's ability to see or escape. Small mammalian hosts encumbered by an ever-enlarging cluster of warbles also may have difficulty in foraging.

Another characteristic of bot flies is that the beelike adults usually aggregate at specific topographic sites for pairing and copulating. Favored sites are hilltops, cliff faces, steep slopes, prominent rocks or trees, and streambeds. Male flies remain at these sites throughout their brief life, but females leave the sites soon after mating to search for suitable hosts or oviposition sites.

The major importance of bot flies is the economic losses that they cause in livestock operations (e.g., cattle, sheep, goats, reindeer, and horses). Secondary microbial infection of the bot warble is rare because bot fly maggots produce a bacteriostatic secretion as they develop. However, after the larva exits the warble, other myiasis-causing flies may exploit the empty wound. Bot fly maggots cannot complete their development in a dead host. If the host dies, so do its bots.

The evolutionary history of bot flies is not known but warrants comment. Zumpt (1965) proposed two possible routes for bot fly evolution. One route is through blood-sucking larvae such as nest maggots or floor maggots. The other is through carrion-breeding species and screwworms. Both alternatives seem plausible with regard to skin bots, but they do not explain how the more internally adapted groups such as nose bots and stomach bots originated. The nose bots may have evolved from myiasis-causing flies that were attracted to mucopurulent nasal secretions in hosts suffering from respiratory infections. Stomach bots, on the other hand, may have originated from fly species infesting decaying, fermenting forage, a diet favored by many large herbivores. In any case this obligate form of parasitism appears to have arisen independently among different groups of flies associated with certain hosts.

There are 6 genera and 83 species in this subfamily of bot flies, all restricted to the Western Hemisphere. The largest genus is Cuterebra (ca. 70 species), which includes the largest bot flies. Some of these robust, thick-bodied bot flies (Fig. 16.18) are up to 30 mm in length. Their

FIGURE 16.18 Rodent bot, Cuterebra, fontinettn, adult female (Oestridae, Cuterebrinae); reared from white-footed mouse, Peromyscus leucopus. (Photo by Sturgis McKeever.)
Emergency Preparedness

Emergency Preparedness

Remember to prepare for everyone in the home. When you are putting together a plan to prepare in the case of an emergency, it is very important to remember to plan for not only yourself and your children, but also for your family pets and any guests who could potentially be with you at the time of the emergency.

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Responses

  • fnan
    How do flesh flies attached to skin?
    1 year ago

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