Biting Gnats

ARTHUR W. LINDQUIST AND WILLIAM C. MCDUFFIE.

THE MANY species of biting gnats that affect livestock may be classified in two major groups, Simulium and Culicoides.

The Simulium, or blackflies, are small, hump-backed, and dark-colored insects, commonly known as buffalo or turkey gnats.

The Culicoides are much smaller and usually are gray or black and have spots on the wings. They are known as punkies, no-see-ums, and sandflies.

The gnats in these groups are smaller than mosquitoes. Stockmen usually do not see the gnats, especially the night biters.

Blackflies suck blood from livestock and poultry, and so irritate them, interfere with their feeding, and sometimes kill them. In outbreaks such as occur in the Mississippi Valley, thousands of head of livestock have been killed by these vicious biters.

Some blackflies carry diseases and protozoan parasites of turkeys and ducks. In some countries they transmit filarial worms, which affect the eyes and cause blindness in people and animals. Blackflies transmit a similar filarial disease in cattle in Australia.

At least 8o different species of blackflies occur in the United States. They breed most abundantly in swift streams. They also are found in slowly moving streams and irrigation canals. The larvae and pupae are attached to stones, vegetation, and other objects in streams. Only one generation occurs a year in northern climates, but some species may produce several broods a Year in the Southern States.

The larvae can be controlled by applying DDT or TDE to the water where the larvae breed. An oil solution of DDT, applied at a rate of about 0.2 part per million of water flowing by a certain point for 3o minutes will destroy larvae for several thousand feet downstream. After the waterflow is calculated, the insecticide solution is dripped or sprayed on the water for about 30 minutes. All streams within 5 miles of the places to be protected should be treated.

Airplanes can be used to disperse insecticides over large areas in which are many streams. The spray is usually applied in strips of 100 to 300 feet across streams at intervals of one-fourth to one-half mile. About 0.1 pound of DDT per acre of water sprayed is satisfactory for strip spraying. The flow of the water will give adequate dispersion of the insecticide between strips and destroy the larvae throughout the stream.

Water emulsions of DDT are more toxic to fish and other aquatic life than oil solutions. Care should be taken therefore to apply them only in dosages that will not harm aquatic life.

Control of adult blackflies with insecticides has been successful in some localities but not in others. DDT oil sprays applied by aircraft or from the ground by fog machines or mist blowers have given good control in some places. Enough spray should be used to give 0.2 pound of DDT on an acre.

In places where it is impossible to destroy larvae in their breeding places, the farmer can protect his livestock by spraying them. Synergized pyrethrum formulations are best for this purpose but must be applied to the animals daily. This can be done with hand or power sprayers. Automatic or treadle-type sprayers also may be used.

Culicoides, or sandflies, are pests of man and animals over most of the country. About 60 species are known." They are vicious biters, cause severe irritation and discomfort, and transmit diseases.

At least one of the species transmits bluetongue, a virus disease of sheep that was discovered in Texas in 1948. It was apparently introduced in some unknown way from Africa several years earlier but had not been recognized as a new disease. Bluetongue has been prevalent in Texas, New Mexico, Arizona, California, and Utah.

Some species of sandflies breed in the mud or moist soil around the margins of streams, ponds, sloughs, and watering tanks. Some are found in holes in trees. Several species breed in vast numbers in the salt marshes along the Atlantic coast. The larvae are threadlike and move by a whipping motion through ooze or water.

Larval breeding, places can be destroyed by draining and filling. Since these measures are seldom practical, insecticides are usually applied to breeding areas to control the larvae. Control of these tiny pests over large areas requires organized effort and considerable money. Excellent control of the larvae in mangrove swamps along the Florida coast has been obtained with soil applications of 1 to 2 pounds an acre of lindane, chlordane, heptachlor, and dieldrin.

Sandflies can enter dwellings and livestock shelters through ordinary 16-mesh screens, which exclude mosquitoes and flies. Painting lindane or chlordane on window and door screens is helpful.

The livestock owner can protect his animals from sandflies by frequent application of pyrethrum insecticides.

Insect repellents are effective for protection of people against sandflies. They should be applied to the hands, face, and clothing.

ARTHUR W. LINDQUIST is, leader of the Insects Affecting Man and Animals Section, Entomology Research Branch, and is a graduate of Bethany College and Kansas State College.

WILLIAM C. McDUFFIE, assistant leader of the Insects Affecting Man and Animals Section of Entomology Research Branch, is a graduate of Mississippi Agricultural and Mechanical College.