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| BLACK FLIES AND THEIR CONTROL |
Black flies of the family Simuliidae, commonly called buffalo or turkey gnats, are pests of man and animals in many areas of Pennsylvania. They are small dark flies. Most species are 2 to 3 mm. (l/8") long; a few species reach lengths of 4 to 5 mm. Of the more than 600 species of black flies, about 20 have been found in Pennsylvania. At least 33 species should be found in the Commonwealth since 13 other species have been recorded in nearby states.
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| INTRODUCTION |
Adult black flies are distinguished from other similar flies by having 9, l0, or 11 segments to their antennae (most species have 11) and no simple eyes (ocelli). The second body region (thorax) is strongly convex, giving a humped appearance. Only the female black fly bites. Male mouth parts, adapted for plant feeding, cannot penetrate the skin of humans or animals. All immature black fly stages (eggs, larvae, and pupae) require moving water for development since water movement provides their oxygen and food. They are usually found in those parts of a stream with riffles, not in quiet pools. Even though the species of black flies vary greatly in their biology and behavior, they may be considered as a group for convenience.
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| SEASONAL DEVELOPMENT |
The time required for development from egg to adult depends upon the species, water temperature, available food, and other factors. Females deposit from l50 to 500 eggs. Some species place them on submerged objects in the stream such as water plants, rocks, leaves, or twigs; others simply scatter the eggs over the water surface. Eggs will hatch in four or five days when the water temperature is 70 degrees F. Eggs deposited in the fall will not hatch until the water warms in the following spring. Larvae attach themselves to submerged objects and molt six times as they grow. They are easily distinguished from other aquatic immature insects in that they are elongate with the hind part of their bodies swollen. A head fan sweeps food material into the mouth. A single proleg on the thorax is used to hold onto a secreted silk thread. Spinning more thread allows the larva to migrate rapidly downstream. Rows of hooks at the hind part of the body enable attachment to submerged objects. The larva spins a pupal case and changes to a pupal stage within it. The long branching tentacles are used for breathing. Adults emerge from pupae in two to three days when the water is warm and are capable of immediate flight and mating. Although their flight range is usually less than ten miles, some may travel much farther from their place of origin. Some species of black flies do not feed as adults, others require a blood meal in order to produce eggs. Females live from a few days to more than three months. They prefer calm sunny days, and will not fly at night or on windy days. Black flies are attracted to their animal or human victims by the carbon dioxide and moisture present in exhaled breath, dark colors, convection currents, perspiration, perfumes and toiletries.
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| PUBLIC HEALTH AND ECONOMIC IMPORTANCE |
Black flies are annoying when numerous, even if they are not biting. They often fly into eyes, nose, ears, and mouth. Bites cause pain and dermatitis at the site of the bite because black fly saliva is toxic. Intense itching may last several days; serious allergic reactions may occur. Death can result from: suffocation, as a result of plugged nasal and bronchial tubes; exsanguination, when flies are numerous they can remove enough blood from their victim to cause death; and allergic reactions. Flies can discourage people from remaining in or visiting certain areas. Some recreational areas in Pennsylvania are not used to capacity because of black flies; tourists leave much earlier than they had originally planned. Losses to the livestock and poultry industries are difficult to evaluate, but there is usually a drop in milk, beef, and egg production where black flies are numerous. The flies are a source of irritation to livestock and cause accidental injury (in animals trying to avoid the flies), tougher beef, reduced reproductive capacity, and reduced resistance to disease. Black flies are known to be vectors of diseases. They transmit Leucocytozoon (protozoan) parasites to turkeys and wild birds. Although there have been no confirmed cases of this disease in Pennsylvania since l962, the black fly vector (Simulium jenningsi) is abundant in the Commonwealth. Black flies may prove to be transmitters of encephalitis. Some species of black flies feed on birds, and the encephalitis virus has been recovered from some species of birds.
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| CONTROL |
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The Pennsylvania State University 2004
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