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New Screwworm Diet Helps Save Money for Eradication Program

By Linda McGraw
December 4, 2000

Parasitic screwworm flies, once the scourge of the U.S. livestock industry, are now being fed a meatless, biodegradable artificial diet that promises to save the U.S. Department of Agriculture’s screwworm eradication program as much as $100,000 annually.

That estimate comes from Agricultural Research Service entomologist Muhammad F. Chaudhury. In 1999, he made several changes to the artificial diet used to rear millions of screwworm flies at a factory operated by the U.S.-Mexican Commission for Eradication of Screwworms in Tuxtla Gutierrez, Chiapas, Mexico. The factory-raised screwworm flies are subsequently sterilized by irradiation. These sterile flies are released to mate with wild screwworm flies--matings that produce no viable eggs and therefore reduce and ultimately eliminate the wild screwworm population.

Previously, screwworm flies for the eradication program were raised on a diet of horse meat and honey. The new diet consists of spray-dried eggs and either honey or molasses. Female screwworm flies laid more eggs on the meatless diet than on the horsemeat diet.

Yet another improvement: Recycled newspaper can be used in the screwworm diet to replace an absorbent gel now used for bulk in the larval diet. Besides further reducing the cost of rearing the insect larvae, recycled newspaper is biodegradable, while the absorbent gel is not. Larger factory-scale trials will be conducted in January. Chaudhury presented information about the economic savings of the new diets at a meeting of the Entomological Society of America (ESA) from Dec. 3-7 in Montreal, Canada.

The insect rearing facility in Tuxtla currently produces 150 million sexually sterile flies per week and air shipments are made to support the U.S.-Panama Screwworm Eradication Program in Panama City.

On Oct. 4, 2000, Costa Rica was declared free of screwworms. Panama is currently the only Central American country still working to eradicate the destructive pest. Total eradication in Panama is expected by 2001. Screwworms, obligate parasites because their larvae eat living flesh, nearly devastated the U.S. livestock industry in the 1900s. ARS achieved its worldwide reputation for screwworm control based on the pioneering work of Edward F. Knipling and Raymond C. Bushland, who developed the sterile insect technique.

ARS is the chief scientific research agency for the U.S. Department of Agriculture.

Scientific contact: Muhammad F. Chaudhury, ARS Screwworm Research Laboratory, Tuxtla Gutierrez, Chiapas, Mexico, telephone 011-529-614-1441, fax 011- 529-614-1415,