Chrysomya bezziana

Chrysomya bezziana, also known as the Old World screwworm fly or screwworm, is an obligate parasite of mammals. Obligate parasitic flies require a host to complete their development. Named to honor the Italian entomologist Mario Bezzi, this fly is widely distributed in Asia, tropical Africa, India, and Papua New Guinea. The adult can be identified as metallic green or blue with a yellow face and the larvae are smooth, lacking any obvious body processes except on the last segment. The fly feeds on decaying organic matter, while the fly larvae feed on the living tissue of warm-blooded mammals as opposed to necrotic tissue that many other fly larvae feed on. Since the larvae can cause permanent tissue damage, C. bezziana has led to much public concern. Management procedures include both prevention of colonization of the fly and treatment of a current infestation. Chrysomya bezziana is widely distributed throughout tropical areas in the Old World. It is most prevalent in Southeast Asia, tropical and subtropical Africa, some countries in the Middle East, India, the Malay Peninsula, the Indonesian and Philippine Islands, and Papua New Guinea. C. bezziana is not found at altitudes higher than 2500 meters above sea level. In countries where Chrysomya bezziana does not exist, scientists and those in agriculture are worried that commercial flights, boats, or vehicles will distribute the fly. The climates C. bezziana thrives in are present in Australia and the Americas; the fly requires climates similar to its New World relative Cochliomyia hominivorax. Spread of the pest from Papua New Guinea to Australia has become a concern for Australia, as the presence of C. bezziana could cost livestock industries up to $500 million a year. Chrysomya bezziana belongs to the fly family Calliphoridae. This family comprises blow flies, carrion flies and cluster flies. Other parasitic screwworms are found in this family, such as Cochliomyia hominivorax and Cochliomyia macellaria. The body of the C. bezziana adult is typically metallic green or blue. The face of these flies is typically yellow with soft fine yellow hairs. The length of an adult fly ranges between 8 and 12 millimeters. The abdominal tergites (the segments of the dorsal portion of the fly) have narrow darker bands and the legs are black or dark-brown. Only the bases of the wings are infuscated; the wings have a glassy appearance. The anterior spiracles (small openings on the surface for the respiratory system) range from dark-brown to orange. Another close relative, Chrysomya megacephala, occurs in many of the same regions as C. bezziana; therefore, it is important to be able to distinguish between the flies. The male fly can be distinguished from Chrysomya megacephala by their eye facets. C. bezziana does not have a boundary dividing the upper and lower eye facets, while C. megacephala does have a boundary distinguishing the upper and lower portions. The female does not have as distinct differences and cannot be as easily distinguished from C. megacephala, but they can be identified by analyzing the frons (the uppermost part of the head of an insect). The frons of C. bezziana is more parallel, while C. megacephala has a frons that is distinctly narrow in the center. The third-instar larvae are smooth, lacking obvious body processes except on the last segment. The posterior spiracles are not hidden in the body cavity, and the peritreme of these spiracles is open. The larvae can be distinguished from its New-World relative C. hominivorax by observing the dorsal tracheal trunks. Those of C. hominivorax are darkly pigmented from the 12th segment to the 10th or sometimes 9th segment, while those of C. bezziana are only pigmented for the last half of the 12th segment. The anterior spiracle has 4-6 lobes, with 7 on occasion.