"Hairy maggot" Chrysomya species

"Hairy 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. Some species have now been transferred to the Americas through human activity.

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.

The larvae of Chrysomya albiceps and the related Chrysomya rufifacies have what are commonly known as "hairy maggots" because of the fleshy projections (tubercles) on their bodies. The larvae of Chrysomya varipes also have fleshy projections, but they have fewer than the other hairy maggots and are smaller when they mature in similar conditions (11 mm compared to 18 mm).

Chrysomya albiceps and C. rufifacies are very similar in appearance both as adults and larvae, and have been considered as separate species and a single species by different authors at different times (Zumpt, 1965). Currently they are considered good species, with reliable characters for separating the 3rd instar larvae (Wells et al, 1999; Tantawi, and Greenberg, 1993). In Chrysomya albiceps the dorsal tubercles have relatively small apical spins, usually pointing toward the centre, and the scales at the base of the tubercles are without pigmented points. In Chrysomya rufifacies the dorsal tubercles have relatively large apical spines, usually pointed away from the centre, and the scales on the tubercle base are with pigmented points. For the adults however doubt has been cast on the value of using the prostigmatic bristle (usually absent in C. albiceps and present in C. rufifacies) to distinguish the two (Tantawi & Greenberg 1993); this character was found to be unreliable. A molecular phylogeny using mitochondrial DNA confirmed them as separate species (Wells & Sperling 1999).

Biology

The "hairy maggot" flies are facultative parasites that normally lay their eggs on carcasses, preferably among clusters of other blowfly eggs. The first instar larvae feed on exudations of the decomposing flesh, but second and third instars are also predacious, feeding on other blowfly larvae. They may even be cannibalistic. Although the eggs are normally laid on carcasses, they may also be laid on neglected wounds, where the larvae can cause tissue destruction. They are frequently involved in secondary myiasis in sheep and goats, following initial damage by Lucilia species and Wohlfahrtia magnifica.

The facultative predatory nature of the 3rd instar larvae is thought to have had a significant impact on their ability to establish new populations following accidental introductions. By predating the larvae of the native saprophagous blowfly fauna in mixed infestations they out-compete the indigenous species, rapidly replacing them. In addition there is evidence that they are maybe assisting in the expansion of Chrysomya megacephala, which has also been introduced into South America. Chrysomya rufifacies and C. megacephala are historically sympatric together and it is hypothesised the later may have evolved some resistance to attack. In laboratory cultures where C. rufifacies, C. megacephala, and the native Cochliomyia macellaria larvae were mixed, theCochliomyia macellaria suffered consistently higher death and injury from C. rufifacies attacks than did the C. megacephala (Wells & Kurahashi 1997). The results suggest that in a natural infestation the presence of C. rufifacies would give the C. megacephala larvae a selective advantage over the Cochliomyia macellaria larvae.

Distribution

Originally C. albiceps and C. rufifacies had disjunct, non-overlapping, distributions. Chrysomya albiceps in the Palaearctic and Afrotropical regions, and C. rufifacies replacing it in the Australasian and Oriental regions. Both species have now been introduced into the New World, and may have overlapping distributions in Argentina (Mariluis & Schnack 1989). Chrysomya albiceps was first introduced into Brazil (Guimarães et al, 1978) and is now established in South America and has been reported from Peru, Bolivia, Paraguay, Argentina, Venezuela & Ecuador (Baumgartner, 1988; Tantawi & Greenberg, 1993). Chrysomya rufifacies first appeared in Costa Rica in 1978 (Jirón, 1979) and now occurs throughout most of Central America and into the southern states of the continental USA (Baumgartner, 1988; Tantawi & Greenberg, 1993; Wells, 2000).

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.
• Grassberger, M., Friedrich, E. and Reiter, C. (2003). The blowfly Chrysomya albiceps (Diptera: Calliphoridae) as a new forensic indicator in Central Europe. International Journal of Legal Medicine, 117: 75-81.
• Guimarães, J.H., Pardo, A.P. and Linhares, A.X. (1978). Three newly introduced blowfly species in southern Brazil (Diptera: Calliphoridae). Rev. Bras. Entomol. 22: 53-60.
• Jirón, L.F. (1979). Sobre moscas califoridas de Costa Rica (Diptera: Cyclorrhapha). Brenesia 16, 221-222.
• Mariluis, J.C. and Schnack, J.A. (1989). Ecology of blowflies of an eusynanthropic habitat near Buenos Aires (Diptera: Calliphoridae). Eos (Madrid) 65: 93-101.
• Smith, K.G.V. 1986. A manual of forensic entomology. London, British Museum (Natural History). 205 pp.
• Tantawi, T.I. and Greenberg, B. (1993). Chrysomya albiceps and C. rufifacies (Diptera: Calliphoridae): contributions to an ongoing taxonomic problem. J. Med. Entomol. 30(3): 646-648.
• Wells, J.D. and Kurahashi, H. (1997). Chrysomya megacephala is more resistant to attack by C. rufifacies in a laboratory arena than is Cochliomyia macellaria (Diptera: Calliphoridae).Pan-Pacific Entomologist 73(1): 16-20.
• Wells, J.D., Byrd, J.H., and Tantawi, T.I. (1999). Key to third insatr Chrysomyinae (Diptera: Calliphoridae) from carrion in the continental United States. J.Med. Entomol. 36(5): 638-641.
• Wells, J.D. and Sperling F.A.H. (1999). Molecular phylogeny of Chrysomya albiceps and C. rufifacies (Diptera: Calliphoridae). J. Med. Entomol. 36(3): 222-226.
• Wells J.D. (2000). Introduced Chrysomya (diptera: Calliphoridae) flies in northcentral Alabama. J. Entomol. Sci. 35(1): 91-92.
• Zumpt F. (1965). Myiasis in Man and Animals in the Old World. Butterworths, London,UK, 267 pp.