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an order of insects with complete metamorphosis. In Diptera, only one pair of wings is developed (the front pair), the hind wings are reduced and take the form of knoblike halteres. The head is rounded, with large, faceted eyes on the sides. The antennae are either multisegmented (Nematocera) or short and trisegmented (Brachycera). Diptera have sucking mouthparts. The head is movably joined to the thorax by a thin stalk. The wings are membranous, with few veins that often merge in the anterior part of the wing. The larvae are always more or less wormlike and legless. (The larvae have prolegs—unsegmented processes—on the abdominal segments.) The larvae of Nematocera and of lower Brachycera usually have a head and chewing mouth-parts. The larvae of higher Brachycera have a reduced head, the mouthparts consist of two hooks that move parallel to one another, and digestion is external. The pupa of Nematocera and of lower Brachycera is obtect, and in higher Brachycera (true flies) it is keg-shaped; the last larval skin serves as the casting for the pupa.
There are over 80,000 species of Diptera; in the USSR there are more than 10,000. They are distributed over the entire globe from the northern tundra to the tropics and deserts. There are species whose whole cycle of development takes place in the sea; but usually the larvae develop in the soil, decaying plant tissues, bodies of fresh water, living plants, and animal carcasses or as animal parasites. Adult Diptera may feed on the nectar of flowers or on decaying matter, or they may suck the blood of animals; some do not feed.
The larvae of many Diptera (crane flies, the hessian fly, frit fly, and the olive fruit fly) are dangerous pests of plants. Many Diptera are carriers of human disease (the house fly, gnats, malarial mosquito, and horseflies) and of diseases of domestic animals (horseflies and stable flies). The larvae of some Diptera (such as Wohlfahrtia magnifica) develop in body tissues of humans, causing special illnesses—myiases; the larvae of many Diptera (warble flies and horse botflies) parasitize farm animals, causing harm to livestock raising. Bloodsucking Diptera, known under the collective name of bloodsucking flies, are found in some places in large numbers and decreases the efficiency of people and the productivity of farm animals. Some Diptera, whose larvae develop in the bodies of harmful insects (for example, Tachinidae), are beneficial, since they decrease the number of pests and are used in the biological control of pests. Some Diptera are beneficial as pollinators of plants (for example, many hover flies) and as active soil builders (fungus flies and many others).
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Krivosheina, N. P. Ontogenez i evoliutsiia dvukrylykh nasekomykh. Moscow, 1969.
Lindner, E. Die Fliegen der Palaearktischen Region, fasc. 1. Stuttgart, 1924.
M. S. GOILIAROV