The House Fly As A Vector Of Human And Animal Disease

House flies, particularly in large numbers, are a nuisance to humans when they enter houses, land and feed on human food, and spot windows with their feces. Of greater importance to humans, however, is their ability to spread human and veterinary disease agents. House flies have been associated with over 100 pathogens that can cause disease in humans and animals. Unlike the pathogens responsible for many other insect-borne diseases, the pathogens spread by the house fly do not usually multiply within the fly, nor do they require association with the fly for part of their life cycle. Instead, the usual association between house flies and pathogenic organisms is one of physical transmission of pathogens the flies pick up on their bodies at one feeding site (e.g., a garbage can or manure pile) and transfer to human and/or animal food when they land and feed. House flies have been associated with the transfer of a variety of viral and bacterial diseases, such as typhoid fever, cholera, dysentery, and infantile diarrhea, as well as a variety of parasitic worms.

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Chemoreception • Medical Entomology • Urban Habitats Further Reading

Colwell, A. E., and Shorey, H. H. (1977). Female-produced stimuli influencing courtship of male house flies (Musca domestica). Ann. Entomol. Soc. Am. 70, 303—308. Crosskey, R. W., and Lane, R. P. (1995). House flies, blowflies and other allies (calyptrate Diptera). In "Medical Insects and Arachnids" (R. P. Lane and R. W. Crosskey, eds.). Chapman & Hall, London. Greenberg, B. (1971). "Flies and Disease," Vol. I of "Ecology, Classification and Biotic Associations." Princeton University Press. Princeton, NJ. Greenberg, B. (1973). "Flies and Disease." Vol. II of "Biology and Disease

Transmission." Princeton University Press. Princeton, NJ. Huckett, H. C., and Vockeroth, J. R. (1987). Muscidae. In "Manual of Nearctic Diptera" (J. F. McAlpine, B.V. Peterson, G. E. Shewell, H. J. Teskey, J. F. Vockeroth, and D. M. Wood, eds.), Vol. 2, pp. 1115—1131. Biosystematic Research Institute Research Monograph 28, Ottawa, Ontario, Canada.

Tobin, E. N., and Stoffolano, J. G., Jr. (1973). The courtship of Musca species found in North America. 1. The house fly, Musca domestica. Ann. Entomol. Soc. Am. 66, 1249—1257. West, L. S. (1951). "The Housefly. Its Natural History, Medical Importance, and Control." Comstock, Ithaca, NY.

Donald L. J. Quicke

Imperial College, University of London

The Hymenoptera are a major order of holometabolous insects. That is, they undergo complete metamorphosis with distinct egg, larval, pupal, and adult stages. They are one of the five megadiverse insect orders along with Coleoptera, Diptera, Lepidoptera, and Heteroptera, and perhaps even the most species rich of any insect order—certainly this is true at temperate latitudes. They are generally cosmopolitan and, except for some specialized groups, they are most speciose in the tropics.

Although after working with Hymenoptera for a while it becomes easy to recognize members of this order, there are almost no conspicuous defining characters, because the majority of hymenopteran attributes are plesiomorphic; that is, they are shared with the common ancestors of various other orders. It is not surprising therefore that although almost everyone on earth, save perhaps those living at extreme northern latitudes, is familiar with ants, bees, and social wasps and has vernacular names for these particular taxa, there is not a single vernacular name in any language that refers to them in toto. Hymenoptera are also diverse in terms of their life histories: they include phytophagous, parasitoid, and predatory taxa, both solitary and highly social species, and they range in size from the rather large and intimidating spider-hunting pompilid wasps that can reach 12 cm wingspan down to the tiniest parasitic wasps that are approximately 0.1 mm in length (males of the wingless mymarid chalcidoid, Dicopomorpha echmepterygis). It is hard to overstate their ecological importance because they are collectively involved in so many types of interaction, and it is likely that many are effectively keystone species in their own habitats.

The Hymenoptera get their name from the Greek words humen and pteron, meaning membrane and wing, respectively, and this gives the first clue to identifying them. Excluding the numerous exceptions of apterous and brachypterous species that are widely distributed through the order, hymenopterans possess two pairs of membranous wings that are devoid of scales. The forewings are larger than the hind wings, and the two are interlocked during flight by a row of special hooks called hamules (or hamuli) that are on the anterior margin of the hind wing; these hamuli engage (or interlock) with a fold on the posterior edge of the forewings. This system makes the Hymenoptera functionally dipterous (two-winged) during flight, since the wing surfaces on either side of the body acts as a single aerofoil. Hamules are unique to this order of insects.

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