Nose Bot Flies Oestrinae

Equine Bot Fly
FIGURE 16.38 Common horse bot fly, Gasteropbilus intestinalis {Oestridae, Gasterophilinae), adult female. (A) Dorsal view; (B) lateral view. (From lames, 1947.)

distantly related mammalian groups. Eggs which are ingested with forage or wetted by self-grooming of the front legs hatch after a brief incubation. Eggs located on the host's head hatch spontaneously. Upon burrowing into the oral tissues for a brief period, first-instar larvae eventually are swallowed and attach to the stomach or intestinal wall. The site of attachment is specific for each fly species. Maggots overwinter in the gastrointestinal tract. After larval development is completed, the mature larvae are expelled with the host feces during the warmer seasons. Pupation occurs in the soil soon after larvae drop from the host, with the pupal stage lasting about 3 weeks. Adult flies emerge, mate, and quickly resume activity near potential equine hosts. If hosts are not available, the bot flies move to high points to aggregate and mate, following which the females initiate a longer-distance search for hosts.

The common horse stomach bot fly (G. intestinalis) (Figs. 16.38 and 16.39) is worldwide in distribution and is the predominant species in North America. It prefers to oviposit on the lower forelegs of horses, The two other species in North America are the throat horse bot (G. nasalis) and the rarer nose horse bot (G. haemorrhoidalis). The former oviposits on the hairs of the chin and lower jaw and the latter on the hairs of the nose and lips. The dark-winged horse bot (G. pecorum) is the most commonly encountered species in Eurasia and Africa. It is the most pathogenic fly in this genus and can cause host fatalities

FIGURE 16.39 Common horse stomach bot, Gasterophilus intestinalis (Oestridae, Gasterophilinae), third-instar larva, ps, posterior spiracular plate. (Original by E. R Catts.)

resulting from constricted swelling of the esophagus due to attached maggots.

Other genera of stomach bots include Gyrostigma (three species) in rhinoceroses and Cobboldict (three species) parasitizing African and Indian elephants. Their life histories are similar to that of Gasterophilus. Two other obligate-myiasis fly species are associated with the African elephant. Both are cutaneous parasites. Ruttenia loxodontis develops in warble-like skin boils on the buttocks and flanks of elephants, whereas Neo-cuterebra squamosa develops in shallow ulcers in the skin crevices of the elephant's feet. Both produce a pseudowar-ble during their development. The phylogenetic relationship of these unplaced genera to other bot flies is uncertain, Zumpt (1965) suggests that both represent early gasterophilines.

Other Oestroid Flies

There are three other families of flies included in the Oestroidea in which the species do not parasitize vertebrate animals: Tachinidae, Rliinophoridae, and Mystaci-nobiidae. All members of the Tachinidae are obligate par-asitoids of other insects. None is involved in myiasis. The Rhinophoridae are a small sister group of the tachinids which parasitize isopods. Mystacinobiidae, a sister group of the calliphorids, includes but a single species in New Zealand that is coprophagous on bat guano and phoretic on the bats themselves. None of these families includes myiasis-causing species.

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