APPLIED 
RADIATION 
CASE HISTORY 
NO. 3 
Irradiated Males 
In 16 months a fly factory in a converted airplane hangar 
turned out three billion sterile flies to eliminate a costly 
menace to cattle herds of Southeastern ranches 
By MERRILL E. JEFFERSON, Department of Agriculture, Washington, D. C. 
THANKS TO RADIATION, cattle herds of Southeastern United 
States are no longer menaced by the screwworm fly. A 
fly factory capable of producing 100 million sterile flies a 
week overwhelmed the natural fly population with sterile 
males, raised and sterilized in captivity and then released 
from airplanes. 
So successful was the method that the factory discon- 
tinued production last November 14—mission completed— 
several months ahead of the anticipated schedule. Ap- 
propriations of ~$10-million from the Federal Govern- 
ment and Southeastern States supported the effort to 
eliminate a pest costing Southeastern livestock producers 
an average of $20-million a year. 
Life of the Fly 
The red-eyed, blue-bodied screwworm fly (Callitroga 
hominivoraz) can kill a full-grown steer in 10 days. The 
female lays its eggs in any open wound of a warm-blooded 
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animal. The eggs hatch and tiny larvae (screwworms) 
burrow into the wound and gouge out a pocket in the flesh. 
After they have lived for four or five days and done their 
damage to the host animal, the larvae drop to the ground 
and develop into flies. The total life cycle is only 21-28 
days, and because the insects are subtropical, a cold winter 
kills off the pests. They remain a menace, however, when 
they are introduced into mild climates like those of the 
southern states, the West Indies, Mexico and South 
America. The flies migrate northward each season or 
spread by movement of infested animals. They can 
survive the winter in South America, Mexico, Florida and 
extreme southern parts of the Southwest. 
Eradication 
Usual methods of insect elimination are not good enough 
for the screwworm problem. You can treat all domestic 
animals with ointments and sprays. These, however, are 
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