Abstract
Screw-worms ( Cochliomyia hominivorax (Coquerel)) have shown variable response to the standard dose level of gamma rays from cobalt60 sources used in routine production of sterile flies for eradication of this insect. The primary influence was found to be availability of oxygen during irradiation. When pupae were irradiated in a carbon dioxide atmosphere, a dosage of of 11,100 roentgens (r) was required to sterilize the females, compared with only 5,500 r to 6,200 r required in oxygen and air (forced ventilation). Anoxia induced by consumption of oxygen by the pupae produced radiation-protection effects that were intensified by delay prior to irradiation and/ or increased rate of oxygen uptake as pupae advanced in age. In practical tests, a canister made of 1/8-inch mesh aluminum screen provided sufficient diffusion of air to standardize the dosage safely at 6,900 r, with up to 30 minutes’ delay prior to treatment for pupae 5 days of age or older. This dosage reduces by 50% that required under maximum conditions of anoxia encountered in production when a closed canister is used.
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