Flies That Affect Livestock

E. F. KNIPLING AND WILLIAM C. McDUFFIE.

FLIES affect livestock in two ways by biting them and sucking their blood and by transmitting diseases.

The hornfly, stablefly, and a hundred or more kinds of horseflies and deerflies that flourish in the United States are a constant worry to cattle and to other livestock during the fly season. The horseflies and deerflies are doubly important because they also transmit certain diseases directly or by inoculation from one animal to another.

The common housefly, which occurs wherever livestock are raised, is a nonbiter, but it is capable of mechanically spreading filth and disease organisms, and it serves as an intermediate host of certain internal parasites.

We did not fully realize the losses caused by flies until control measures were developed. Then we could compare the productivity of the animals treated for hornfly control with that of untreated animals. Tests conducted by the Department of Agriculture in 1945 in cooperation with several Midwestern States showed that beef cattle subjected to heavy attacks of hornflies gained an average of 50 pounds less during the fly season than did cattle treated with insecticides. Research at the University of Illinois in 1947 showed that dairy cows protected from hornflies produced 10 to 20 percent more milk than unprotected cows.

The stablefly and the horseflies and deerflies generally are less abundant than the hornfly; severe attacks by them are more restricted in area, or they are present during shorter periods. They are more severe biters, however, and when they are present in large numbers can cause more worry than the hornfly. Horseflies in moderate numbers may lower the butterfat production of dairy cows as much as 20 percent.

THE HORNFLY is primarily a pest of cattle. It breeds only in cattle droppings. It entered this country from Europe in the 19th century.

The adult is about one-half as large as the housefly. As far as we know, they are not vectors of any cattle diseases, but hundreds or thousands of the insects may be on the animals and their constant attack prevents the animals from feeding properly, so that they lose weight and fall off in milk production. Before any suitable control measures were developed, hornflies caused annual losses to stockmen estimated at 150 million dollars. The losses have been greatly reduced since DDT, methoxychlor, toxaphene, and TDE were discovered.

Freshly laid eggs of the hornfly hatch in less than 24 hours. The larvae mature and pupate in 5 to 10 days, depending on the temperature. Flies may emerge from the pupae in 3 to 7 days and begin laying eggs a few days later.

Adult hornflies can be controlled With most of the insecticides now generally available. As the adults stay on the cattle almost continuously leaving only briefly to deposit eggs on fresh droppings applications of some of the newer, long-lasting insecticides Provide effective control for 2 to 4 weeks. Repeated treatment of cattle at those intervals during the hornfly season will keep populations at a low level.

Spraying is the best method of applying the insecticides for the control of hornflies on cattle. The amount of spray to apply depends on the size of the animal and the thoroughness of the treatment. One or two quarts is enough to treat the backs of cattle, where the adult flies prefer to rest and feed.

Treatment of the entire animal takes 2 to 4 quarts or more, depending on the type of animals treated. A thorough treatment designed to control lice or ticks as well as hornflies is often necessary or desirable.

The small hand-pressure or knapsack types of sprayers of 2- or 3-gallon capacity are satisfactory for treating small herds of dairy or beef cattle. Power sprayers are more practical for large herds. Power sprayers should be equipped with agitators to keep large volumes of spray well mixed during spraying operations.

Methoxychlor is the preferred insecticide for the control of hornflies on dairy cattle. Unlike other chlorinated hydrocarbon insecticides, it is not excreted to any extent in milk. Methoxychlor is usually used at a concentration of 0.5 percent, especially if sprays are applied to the entire animal. Higher concentrations of 1.5 percent or more are used in some sections of the country, but proportionately less spray is applied. Either emulsifiable or wettable powder concentrates of methoxychlor may be used to prepare sprays. Treatments with this insecticide are effective about 3 weeks. Methoxychlor may also be used as a dust. About one heaping tablespoon of the 50-percent wettable powder concentrate should be applied evenly on the back of the animal with a shaker can or by hand.

Synergized pyrethrum sprays are also suitable and effective. The finished spray should contain from 0.025 to 0.1 percent of pyrethrins and from 0.25 to 1.0 percent of a pyrethrum synergist. These concentrations may be obtained by diluting a synergized pyrethrum concentrate containing 1 percent of pyrethrins and 10 percent of activator. The finished spray should be applied at the rate of about 2 quarts per animal with hand or power equipment.

The pyrethrum sprays are effective against the hornfly only about 3 to 7 days. The treatment is therefore less effective than methoxychlor, but has the advantage of providing better protection against stableflies, horseflies, and deerflies.

DDT, toxaphene, and TDE may be used for controlling hornflies on beef, but they are not recommended on dairy cattle because they may cause excessive insecticide residues in milk. Methoxychlor, which is recommended for use on dairy cows, may also be applied to beef cattle. The four insecticides are all used at a concentration of 0.5 percent; the sprays are prepared from either emulsifiable or wettable powder concentrates. Treatments will usually be required at intervals of 3 or 4 weeks.

Community cooperation in treating all cattle will reduce the number of hornflies in an area to a point where less frequent treatments are required.

Self-treatment devices are used sometimes for cattle. One of these, developed at the South Dakota Agricultural Experiment Station, is a rubbing device consisting of a post wrapped with insecticide-treated burlap sacks or a cable similarly wrapped and stretched between two posts. The cable a chain or several strands of wire is stretched from the top of a 4 foot post to an anchor at ground level 15 to 20 feet away. It is effective when cattle rub their backs and sides against the burlap. It should be placed near watering and feeding places or where animals rest, so cattle will rub against it to relieve irritation from biting flies and lice. For dairy cattle, the sacks should be treated with a 5-percent methoxychlor oil solution. For beef or dairy cattle, 5-percent oil solutions of DDT, methoxychlor, toxaphene, or TDE may be used. About 1 gallon of oil solution is required to treat 15 or 20 feet of burlap sacks.

The sacks should be re-treated every 3 to 5 weeks.

Another self-treatment device is the automatic or treadle-type sprayer developed at the Illinois Agricultural Experiment Station. It consists of a narrow chute equipped with a spray unit, which is set in operation as the animal walks through it. The treadle sprayers are usually installed in the gateway between pastures and watering or feeding places so that the cattle must pass through them. Since the cattle go back and forth once or twice daily, the units are designed to dispense only 2 to 4 milligrams of insecticide per animal. This amount is ample only for immediate control, and almost daily applications are necessary to keep hornflies under control.

Synergized pyrethrins or methoxychlor oil solutions are satisfactory for use in treadle sprayers for hornflies on dairy cattle. They and DDT, toxaphene, or TDE may be used on beef or dry dairy cattle.

THE STABLEFLY has piercing mouth parts like those of the hornfly, but it is about twice as large. It is like the non-biting housefly in looks and size and often breeds in the same situations. Unlike the hornfly, the stablefly stays on an animal only long enough to engorge with blood. Stableflies during warm weather may feed several times a day. After feeding, the adult rests on nearby walls, trees, or other objects while digesting the blood meal. The stablefly is known as the do-fly in some parts of the country.

Stableflies feed readily on manor any type of livestock. They are most troublesome and damaging to cattle and horses. The legs and lower parts of animals are the preferred sites for feeding. A relatively small number of stableflies can cause severe annoyance to cattle.

The preferred breeding sites of the stablefly on livestock farms are wet straw, manure, and decaying vegetable matter. Eggs hatch in 1 to 3 days. The larvae develop to maturity and pupate in 11 to 30 days. Maturation of the pupae and emergence of adults may take 6 to 20 days, depending on the temperature. The life cycle may be completed in about 3 weeks in summer. High populations of the stablefly and consequent serious damage to livestock often occur in Midwestern States and along coastal areas, where the insect often breeds in great numbers in seaweeds. Severe local outbreaks of the stablefly also occur in peanut-growing areas, where they breed in peanut litter.

The stablefly can be controlled by proper sanitation so as to prevent the accumulation of breeding material, by spraying barns and the other resting places, and by treating animals with insecticides.

The greatest returns for the effort often can be had by preventing the accumulation of plant waste and manure, the insect's favorite breeding places. Manure should not be allowed to accumulate but should be spread at least two times a week. Plant material, such as hay, peanut litter, citrus pulp, celery waste, and other vegetable products, should not be permitted to accumulate, especially during rainy periods. Where extensive waste products accumulate, it may be necessary to organize community control programs to cope with the problem and arrange to dispose of breeding material or to apply appropriate insecticides to the waste materials to keep the flies from breeding.

Good barnyard sanitation and the application of insecticides to livestock barns, corral fences, trunks of trees, or similar places where the flies like to rest will usually reduce the problem of stableflies on individual farms.