Cochliomyia

Cochliomyia is a genus in the family Calliphoridae, known as blowflies, in the order Diptera. Cochliomyia is commonly referred to as the New World screwworm flies, as distinct from Old World screwworm flies. Four species are in this genus: C. macellaria, C. hominivorax, C. aldrichi, and C. minima. C. hominivorax is known as the primary screwworm because its larvae produce myiasis and feed on living tissue. This feeding causes deep, pocket-like lesions in the skin, which can be very damaging to the animal host. C. macellaria is known as the secondary screwworm because its larvae produce myiasis, but feed only on necrotic tissue. Both C. hominivorax and C. macellaria thrive in warm, tropical areas. In general, all Diptera have three body regions (head, thorax, and abdomen), three pairs of legs, one pair of forewings used for flight, one pair of halteres which are modified hindwings, and one pair of antennae. New World screwworm flies share many characteristics of the common house fly. When keying out a dipteran specimen, it is important to first note whether bristles on the meron are present or absent. All species in the family Calliphoridae have bristles on their merones, plumose arista, and well-developed calypters. Both C. macellaria and C. hominivorax are metallic green to bluish green in major coloration, with setae on the dorsal surface of the stem vein, orange gena, pale white anterior spiracles, filiform palps, and three black longitudinal stripes (vittae) on the notum of the thorax. The species C. macellaria has pale setulae on the fronto-orbital plate outside the row of frontal bristles, while C. hominivorax has dark setulae on the fronto-orbital plate outside the row of frontal bristles. The female C. macellaria has a yellowish basicosta while the female C. hominivorax has a brown basicosta. C. macellaria is 6–9 mm in length. C. hominivorax is 8–10 mm in length. The larvae of both C. macellaria and C. hominivorax have cylindrical bodies tapering anteriorly with 10 or more robust spines around the spiracular area, incomplete peritremes, an indistinct or absent button, and bands of small spines on each segment. The C. hominivorax larvae have distinctly pigmented tracheal trunks. C. macellaria larvae do not have pigmented tracheal trunks; they have spines in a V shape on the anal protuberance and no oral sclerite. The mature third instars of both species' larvae can reach a length of 17 mm. The general life cycle of Cochliomyia is similar to any other Diptera in that they are holometabolous. The four stages are egg, larva, pupa, and adult. This entire life cycle lasts an average of 21 days at prime conditions (preferably a warm, moist environment), and can last as long as three months in colder climates. Females only lay eggs once in a lifetime and can lay 100 to 400 in a clutch. Females usually lay their eggs on the edge of an open wound. The warm and moist conditions are the perfect combination of home and food source. The nasal, oral, or anal areas of a host are especially prone to Cochliomyia oviposition. Larvae hatch about 12–21 hours after the eggs have been laid. The larvae are a cream color. C. hominivorax larvae dive head-first into whatever food source is nearest, and burrow deeper, eating into live flesh if available. This results in a pocket-like lesion that causes severe pain to the host. C. macellaria larvae only feed on the necrotic tissue of a wound. After five to seven days, the larvae drop and move away from the food source to pupate. The larvae burrow into the first layer of topsoil, beneath leaves or garbage, and begin their pupation. The pupa is a dark brown color. This stage can last from seven days at a warm temperature to as long as two months if the weather is much colder. The adults emerge and spend a day or two finishing maturity. Adults of C. hominivorax breed only once in their lifetimes. Sexually mature adults breed 3–4 days after emerging from the pupa. Males mature rapidly, and spend their time waiting and eating nearby vegetation and the nectar of flowers. The females, however, are predatory, and feed on the fluids from live wounds. The females can fly long distances to find a mate. The adult flies of this species live around two to three weeks. The primary screwworm, C. hominivorax, is a parasitic species, whose larvae are renowned for eating and infesting the flesh of living organisms, primarily warm-blooded animals such as cattle and other livestock. Their larvae cause myiasis ('flystrike'), an infestation of maggots in lesions or other wounds and injuries that the host animal may have. Flystrike may occur due to such farming processes as branding, castrating, dehorning, and tailing of the host animals. These processes, along with barbed-wire cuts and flea bites, lead to myiasis in the host animal. Navels of newborns also can be the sites of infestation. C. hominivorax tends to reproduce only on the flesh of a living host. Unlike most other maggots, these maggots attack and consume healthy living tissue along with decaying tissue (hominivorax literally translates to “man-eating”). The larvae are responsible for their common name, the screwworm, because they possess small spines on each body segment that resemble a screw's threads. After the larvae hatch, they dive into the wound and burrow deeper, perpendicular to the skin surface, eating into live flesh, again resembling a screw being driven into an object. The larvae then continue to feed on the wound fluids and the animal's tissue. The sterile insect technique was proposed by scientists Edward F. Knipling and Raymond C. Bushland, and was rapidly adopted by the United States Department of Agriculture in 1958. The technique centers on a unique reproductive handicap that prevents female C. hominivorax flies from mating more than once. The scientists reasoned that if it were possible to clinically sterilize and release huge numbers of males as breeding time approached, fertile males might be outcompeted and the majority of female flies would lay sterile eggs. Irradiating the males was used for sterilization.