Field Observations on the Effects of Releasing Sterile Screw-worms in Florida1

Approximately 500 sterile male screw-worm flies (Callitroga hominivorax (Cqrl.)) were released weekly per square mile over a 2,000-square-mile area in Florida. The insects had been irradiated as pupae, within 2 days of adult emergence, with 6,200 to 8,300 r gamma rays from cobalt-60. They were packaged at the rate of 880 (later 550) pupae per release carton. Flies were distributed daily in 6-mile swaths by small aircraft. Shifting of flight lanes resulted in the area being covered in 1-mile swaths weekly. Egg-mass collections in the treated area declined from a weekly average of 41 per station during the first 2 months to 11 in the 12th week. Check stations indicated a continuing high population north of the treated area but a decline on the west and south. However, at the end of 3 months 70% of the egg masses were sterile.