"Smooth maggot" Chrysomya species
Chrysomya is a common and abundant genus of the Old World tropics and subtropics, where it largely replaces the Calliphora and Lucilia of the Temperate zone, and is the Old World equivalent of the New World Cochliomyia. It includes the Old World screwworm fly, Chrysomya bezziana, as well as several other species, with a tendency to facultative parasitism, which can be involved in wound myiasis as secondary invaders. The so-called "hairy maggot" flies, Chrysomya albiceps, C. rufifacies and C. varipes, are members of this genus but are dealt with separately.
Description
Adults are medium to large (5-12mm), thick-set flies of dark green or blue, sometimes metallic, coloration. They are not easy to identify and expert assistance should be sought if identification to species is necessary.
Some Chrysomya species have only been described as adults and their immature stages remain unknown. This makes identification of mature larvae impossible in some cases and attempts should always be made to rear some of the larvae collected to adults if identification to species is necessary. The obligate parasite, Chrysomya bezziana, the Old World screwworm fly (OWSF), can be distinguished from the other species as a third instar larvae by the bands of larger well developed spines on each body segment, and the anterior spiracles which have only 4 to 6 branches.
Biology & Distribution
Most members of this genus are of the typical "smooth maggot" form, with narrow bands of spines around the segments and smooth cuticle between. They are usually carrion breeders but may act as secondary myiasis species, sometimes associated with C. bezziana myiases, where they feed at the edges of the wound. Some species also develop in human and animal faeces, and can be major domestic pests because of their habit of breeding in pit latrines e.g. C. megacephala and C. putoria.
Chrysomya megacephala is commonly called the oriental latrine fly because of its habit of breeding in faeces as well as on carrion and other decomposing organic matter. It may occur in large numbers around latrines and may also become a nuisance in slaughterhouses and open-air meat and fish markets. The larvae may become involved in wound myiasis of humans and animals.Chrysomya megacephala was restricted to the Old World only, throughout the Oriental region and Australasia. In recent years the species has been introduced into several locations through the actions of man. In Africa it was known only from some islands in the Madagascar region (Zumpt, 1965) but has now been reported in North Africa and South Africa (see distribution map in Spradbery 1991). In the Americas it was first introduced into Brazil, spreading to Argentina and Paraguay, plus a more recent separate introduction into Southern Mexico (Baumgarter 1988). It has also now been reported from Spain. There have been occasional reports of myiasis on tortoise and other reptiles caused by Chrysomya megacephala (Frank, 1981).
In Africa both C. chloropyga and C. putoria have been reported from cases of myiasis, as primary and secondary causes of sheep myiasis in South Africa. The taxonomic identity of these two species has been confused for many years, with several authors treating them as the same species, or as subspecies. They have now been demonstrated to be good species (Rognes & Paterson 2005) with distinct biologies. Chrysomya chlorpyga is a typical carrion breeder, also involved in myiasis in sheep and cattle. Chrysomya putoria occupies a niche similar to C. megacephala, preferring to breed in faeces, and only occasionally occurring in carrion. Chrysomya marginalis is a very common carrion breeder in Africa south of the Sahara, but is only rarely encountered in wound myiasis. Chrysomya inclinata is a less common carrion breeder in Africa, also rarely found in cases of myiasis (Zumpt, 1965). Chrysomya mallochi and Chrysomya saffranea are minor agents of myiasis in Australia and New Guinea (Zumpt, 1965; Smith, 1986).
References
- Baumgartner, D.L. (1988). Spread of introduced Chrysomya blowflies (diptera: Calliphoridae) in the Neotropics with records new to Venezuela. Biotropica 20(2): 167-168.
- Frank, W. 1981. Ectoparasites. Chapter 10, pp. 357-383 in, Diseases of the Reptilia, Volume 1, Cooper, J.E. & Jackson, O.F. (Eds.), xi + 383 + xxxii pp.
- Rognes, K. & Paterson, H.E.H. (2005). Chrysomya chloropyga (Wiedemann, 1818) and C. putoria (Wiedemann, 1830) (Diptera: Calliphoridae) are two different species. African Entomology 13(1): 49-70.
- Smith, K.G.V. 1986. A manual of forensic entomology. London, British Museum (Natural History). 205 pp.
- Spradbery, J.P. (1991). A Manual for the Diagnosis of Screw-worm Fly. Commonwealth Scientific and Industrial Research Organization (CSIRO) Division of Entomology, Canberra, Australia, 64 pp.
- Zumpt F. (1965). Myiasis in Man and Animals in the Old World. Butterworths, London,UK, 267 pp.
