Screwworm Factory

Worst plague of Florida cattle is a large bluish fly called the screwworm. The adult female lays eggs on wounds or scratches! and the eggs hatch into maggots that literally eat the victim alive. Screwworm maggots can kill a full-grown steer in less than ten days. But last week, with the enthusiastic approval of cattlemen, planes were scattering millions of live screwworm flies over Florida rangelands.

Reason behind this unlikely procedure is the pest's fatal weakness: the female mates only once. If a female happens to mate with a sterile male, she will lay nothing but infertile eggs for the rest of her short (three weeks) life. The U.S. Department of Agriculture scientists concluded that if males could be sterilized and released in large number, they would find the fertile females, mate with them, and thus eliminate them permanently as progenitors.

Tried out in 1954 on the West Indian island of Curac,ao, the scheme exterminated the island's flies in less than a year (TIME. Feb. 7, 1955). Last spring the USDA and the Florida Livestock Board set up a million-dollar screwworm factory at Sebring, Fla. The fierce, legless maggots are fed on 80,000 Ibs. a week of mixed whale and horse meat flavored with 4,500 gals, of beef blood. When they get their growth and turn into pupae, they are harvested, packed into aluminum canisters, and exposed for 6-2 minutes to gamma rays from radioactive cobalt.

At the end of this experience, both males and females are sterile but otherwise undamaged. When they emerge from the pupa cases two days later as vigorous adults, they are packed into small cartons, loaded into airplanes for release over Florida and parts of adjacent states.

The campaign has already proved its worth. Last year practically every calf born in Florida was infested with screwworms, and total infestations of cattle averaged 35,000 per month. Since March, only 600 cases were reported--the equivalent of a saving of many millions of dollars for Florida cattlemen.

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