Abstract The effects of gamma rays, from a Co 60 source on Ephestia cautella (Wlk.) adults, were investigated. The radiation affected longevity, caused reduced fecundity and a high degree of sterility. Male longevity was shortened only after a dose of 45 krad; female longevity was not affected by the same range of doses. Reduced fecundity was evident in irradiated females mated to normal males, after a dose of 20 krad and became more emphasised at higher doses; a dose of 40 krad reduced fecundity of irradiated females to one third. Normal females, mated to 45 krad irradiated males laid 55 per cent of the normal number of eggs. Doses of 40 and 45 krad induced 99·9 and 99·25 per cent sterility in females and males respectively. Only seven males out of sixty-two failed to transfer sperm after treatment with a dose of 45 krad.