Some stockmen prefer a liquid screw-worm remedy. Preparations containing a thickening agent usually provide a longer period of protection against attack than do liquids containing the same percentage of lindane. However, a liquid remedy can be prepared by omitting the thickening agent, silica aerogel, that is used in EQ 335 and increasing the percentage of mineral oil proportionately.

Smears 62 and 82 were also developed by Department entomologists and have been found to be good remedies for screw-worms. They should be used when the new smear EQ 335 is not available or when supplies of the older smears are on hand.

Smear 62 contains (in parts by weight) diphenylamine (the technical grade), 3.5; benzol (the commercial grade), 3.5; turkey red oil (sulfonated castor oil, pH 10 or neutral), 1; lampblack, 2.

Smear 82 was formulated as a substitute for smear 62 when one of the ingredients, turkey red oil, became scarce. It contains (parts by weight) diphenylamine, 35 ; benzene (benzol), 32; triton X-300 (sodium salt of an alkylated aryl polyether sulfate), 2; n-butyl alcohol, 10; lampblack, 21.

Most screw-worm infestations are due to man-made injuries or to injuries that man can prevent. Stockmen who know all about the screw-worm and practice good livestock management can prevent most infestations and greatly reduce losses. The stockman should be especially alert for screw-worms when the animals have experienced snags and scratches, surgical operations, tick bites, shear cuts, hog bites, dog bites, injuries to mouths of sheep and goats, wire cuts, warts, pink eye, and cancer eye.

Snags and scratches form a major group of predisposing conditions for infestation. The injuries may be due to the sharp horns of cattle and goats that hook one another; briers, thorns, or palmettos; the milk teeth of suckling pigs; and the rough handling of livestock striking them with whips, sticks, or boards, or confining them in poorly constructed pens and chutes. Rushing cattle through gates and gaps and hurrying them through the woods cause many injuries. Most of the injuries can be prevented by handling livestock gently; removing rough edges from gates and gaps and protruding nails and slivered boards from fences, pens, and chutes; avoiding the use of catch dogs; and by dehorning or tipping the sharp horns of cattle.

Dehorning, marking, registration tagging, branding, castration, lamb docking, and similar operations should be done when screw-worms are not present or during winter when they are least active. If those recommendations do not fit into the management program, the wounds should be treated with an approved remedy and the animals kept in a hospital pasture where they can be examined and treated until the wounds are healed.

All animals born during the screw-worm season are susceptible to navel infestations. Controlled breeding so that all calves are dropped in winter and careful inspection of all newborn animals and their dams will eliminate an important cause of attack. This type of infestation is the most common among all breeds of domestic animals. All animals born during the screw-worm season should be given extra care. A light application of EQ 335, or smears 62 or 82, will protect against infestation. In treating the navel of a newborn calf, it is advisable to tie off the umbilical cord, cut off the surplus, paint the cord with iodine, and apply the remedy to the area around the navel opening. It is wise also to make a light application of the remedy around the vulva of the mother before and after she gives birth. It is advisable to examine the mouths of cattle, sheep, and goats. They lick their wounds and often get some of the maggots into the mouth, where they become attached to the gums between the teeth. An examination of the mouths of the mothers of calves with navel infestations frequently discloses screw-worms in their gums. Screw-worm remedies should not be used in the mouths of livestock. The worms should be removed with blunt forceps and destroyed.

Dehorning should be done when calves are small because the horn cavities will heal more quickly, they are less apt to be infested, and the operation will not interfere with normal growth. The sharp horns of mature animals can be tipped at any time without danger of infestation.

Infestations following castration can be reduced or eliminated by the use of the bloodless emasculator on cattle, sheep, and goats. It has not proved successful on hogs. Castrated hogs should be kept in small, dry pens so the remedy will not be washed off if the hog wallows in mud and water. A convenient way to make frequent applications of screw-worm remedies to castration wounds in hogs is by the use of a long-handled mop while the hogs are feeding.

Infestations from branding and marking can be prevented by keeping the wound covered with the remedy until it is healed.

Especially troublesome are the bites of the Gulf Coast tick or the ear tick, which attack cattle, sheep, and goats. Dipping or spraying with one of the new insecticides, such as 0.5 percent of toxaphene or a mixture of 0.5 percent of DDT and 0.03 percent of lindane, will control those ticks.

Infestations after shear cuts can be avoided in sheep by shearing before the worms appear and by the application of an approved remedy to all cuts. Sheep that are badly cut should be kept in a hospital pen or holding pasture and treated until the wounds are healed. The use of the long-comb shearing equipment on goats greatly reduces the danger from shear cuts.

Many screw-worm infestations follow injuries suffered by swine in fighting. The teats of sows may be injured by the sharp milk teeth of suckling pigs. Often it has been necessary to extract the long tushes from hogs and the milk teeth of suckling pigs.

The use of dogs for catching hogs or driving other livestock results in many dog bites and subsequent infestations. Such injuries can be avoided by working livestock without dogs and destroying stray dogs that attack sheep and goats in the pasture. Infestations in the mouths of sheep and goats develop primarily in injuries suffered from eating pricklypears. This injury is being eliminated gradually by eradication of the pricklypear from grazing areas.

Many of the injuries and diseases I have mentioned cannot be avoided, but the protection of the wounds and the prompt treatment of infestations will prevent serious losses.

FIELD TESTS were conducted in 1951 of the use of radiant energy against the screw-worm. The new method involves the carefully timed liberation of laboratory-reared insects after exposing them to radiation that sterilizes them. A treated female fly lays infertile eggs that do not hatch. When a radiated male has mated with a normal female in the laboratory, the eggs from the female are deposited as usual, but do not hatch. The female fly mates only once, and if this mating is with a treated male, none of the eggs she lays will hatch.

Cage tests indicate that when there are 5 to 10 times as many radiated as normal males in a mating area, eggs from most females are infertile and there is only slight reproduction.

Entomologists developed a laboratory method for mass rearing of the flies. Because of the relatively small number of flies that survive the winter in Florida, the results of the cage tests indicated that it may be proved practical to rear and liberate the infertile-treated flies in numbers 5 to 10 times as great as the wild flies in the area. If field results compare with the laboratory results, the following generation in the field would then be much reduced below the number surviving the winter. The hope is that by continuing mass liberations of treated flies over two winters and the intervening summer, the complete elimination of the fly can be attained in the Southeast.

In the preliminary experiments that revealed this possibility, the radiation was with X-rays. The Bureau of Entomology and Plant Quarantine arranged with the Atomic Energy Commission for tests of atomic radiations as sources of sterilizing rays that might prove equally effective and less expensive for treatments. The research staff of the General Electric Company also became interested in the development and plans to provide irradiation with cathode rays for test groups of the pests. The laboratory work has indicated that close and accurate timing of treatment is necessary to make it effective. The pupal or resting stage of the pest lasts about 8 days. If the pupae are irradiated at 2 days of age the rays do not sterilize the males. Their sixth day has proved the most effective time.

The laboratory experiments suggested that an eradication campaign might proceed approximately as follows: Mass rearing laboratories would be set up ready for production of millions of the insects each week, starting early in the year. The insects would be irradiated on their sixth pupal day, and the flies when hatched would be distributed over the infested area from airplanes. Rearing and distribution would be continued through the normal season of the insects and into the following winter unless the scientists found convincing evidence that the pest had been eradicated and that the campaign could be discontinued.

The original research was done at the Department's laboratory at Kerrville, Tex. X-ray equipment was used at a hospital near San Antonio. Small-scale field tests were conducted on an island off the west coast of Florida a pilot plant" test against wild flies designed to try the method under practical conditions and to give the scientists practical experience in the mass rearing, mass irradiation, and liberation of the treated flies.

Knowledge that X-rays can sterilize insects traces back to earlier genetic studies with fruit flies. Over-exposure, it was noted, left the flies sterile. The Kerrville experiments showed that with a heavy excess of X-rayed males, eggs from most female screw-worm flies failed to hatch.

W. G. BRUCE, an entomologist, joined the Bureau of Entomology and Plant Quarantine in 1928. He has conducted research on insects affecting animals in many sections of the United States. He received his undergraduate and graduate training at Kansas State College. In 1951 he was named director of the southeastern region of the Bureau of Entomology and Plant Quarantine, with headquarters in Gulfport, Miss. He directs regulatory, control, and administrative functions in Alabama, Arkansas, Florida, Georgia, Louisiana, Mississippi, North Carolina, South Carolina, and Tennessee.

Horse bot fly with sketch of side view.