When adult malePectinophora gossypiella(Saunders) less than 24 hours old were irradiated with 2.5, 5.0, 7.5, 10.0, or 12.5 krad of gamma irradiation and caged with virgin untreated females, the ability of the treated males to mate and transfer eupyrene sperm appeared to be unaffected, but fertility was reduced. Survival of the immature stages of the F1progeny was significantly decreased at all doses to P1males, and the sex ratio of the F1generation was significantly skewed in favor of males except at the lowest dose. When adult F1males and females were outcrossed to untreated mates or crossed with unrelated F1adults, the F1males mated but often failed to transfer normal quantities of eupyrene sperm; this effect was related to the dose received by the P1male. Thus, fertility of the F1males and females was significantly less than that of the controls, at all doses to the P1male above 2.5 krad. At doses of 7.5 krad and above, the F1males mated more often than the controls. In control programs that produced partial sterility in irradiated males, thus introducing conditional lethal mutations into native population, doses below 7.5 krad should be considered, because at higher doses lack of sperm transfer and lower fertility of the F1males would not favor the incorporation of the released genotype into the native population.