An Introduction to Medical Entomology
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Also See: <Oestridae Details>
Oestridae (Gastrophilidae). -- The warble flies and botflies lay their eggs on the hair of the rear legs of animals. The larvae burrow into the shanks, pass into the intestines, burrow through the intestinal wall and eventually come to lie in the back of the animal just under the skin. This results in the hide being reduced in value because of ensuing fly exit holes in the back. Pupation occurs in the ground. Systemic insecticides have been used for control.
Several serious botflies, Gasterophilus spp., are discussed as follows:
Horse Botflies., -- These flies produce eggs that are swallowed by horses, after which the hatched spiny larvae attach themselves to the wall of the horse's intestines. Horses lose energy and weight following infection. The flies overwinter in their alimentary canal and the larvae mature in late winter or spring. The maggots attach themselves to the stomach lining. They detach in late spring and burrow into the soil to pupate. Adults emerge in early summer but do not bite.
Common Botflies. -- Female flies can lay over 800 eggs on hairs in the upper portion of the front legs of animals. The animal licks the area and the eggs hatch. The larvae live a short while in the animal's mouth and then are swallowed.
Throat Botflies. -- Eggs are laid on the throat, but stimulation by licking is not required here. The larvae hatch out and crawl into the animal's mouth where they feed along the gum line. Later the larvae enter the stomach where feeding continues.
Nose Botflies. -- This is the most serious of all the botflies, although it is less common. Eggs are laid on the upper lip of the animal. Moisture there induces hatching. The larvae then tunnel through the lips and into the mouth, causing severe soreness. They are then swallowed and enter the digestive tract. Control has involved keeping animals stabled during daytime, using repellent materials, sponging off areas with warm water and phenol, and providing internal dosages of carbon disulfide.
Cattle Grubs and Ox Warbles (Hypoderma spp.). -- Included are the Heel Fly and Bomb Fly. They are primarily pests of cattle, often infesting over 75 percent of a herd. The animals will lose weight, the hides are ruined and milk production falls.
During their life history in winter the larvae exist as cysts in the backs of animals under their hide. They feed on secretions from the irritations they cause. A breathing hole is cut through the hide. Maturity is in late winter. In springtime the larvae wiggle through the breathing hole and drop to the soil where they pupate. Adult flies are found in pastures through the summer and into autumn.
Adult flies lay eggs on the belly or legs of the animals, which become very annoyed by their buzzing. Bomb flies prefer to lay the eggs in sunshine on the belly and legs, while heel flies lay eggs in the shade on the heels. Ensuing larvae of bomb flies go directly to the back of animals, while larvae of heel flies migrate to the gullet area to feed, after which they move up to the back.
Sheep Nose or Bot Flies, e.g., Oestrus ovis L.) -- These attack sheep, goats, deer and rarely humans. They are responsible for nasal infections, insanity, blindness and even death. The larvae are deposited in the nostrils of animals after which they migrate to the brain area through the sinuses. They remain several months in the area underneath the horns. They then wiggle out through the nostrils and pupate in the ground. Containment involves painting the animal's nostrils with a repellant, such as pine tar, and to run sheep into dark sheds in daytime at the worst time of the year.
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[Additional references may be found at: MELVYL Library]