The red bollwormDiparopsis castaneaHmps. is an important pest of cotton in Central and Southern Africa. The adult moth can be effectively sterilised by the aziridine chemosterilant tepa applied topically. This substance is rapidly degraded once applied to the insect and this would therefore minimise possible environmental hazards associated with the release of chemosterilised mass-reared insects. Oral application of tepa is also effective and the recent isolation and synthesis of the sex-pheromones of the female moth has given stimulus to the possible development of chemosterilising bait-stations. For direct application methods, potentially less hazardous chemosterilants are required. Representatives of other groups of potential chemosterilants have therefore been evaluated, including other alkylating agents, phosphoramides, s-triazines, organo-metals, antibiotics, juvenile hormone analogues and insecticides. Application of certain s-triazines and sub-lethal doses of the insecticide carbaryl to female moths enhanced the rate of egg-laying without reducing fertility. Treatment of male moths with these substances often caused an increase in mating disfunction possibly associated with hyperactivity of the accessory glands. Spectrophotofluorometric analysis showed that such activity was associated with an increased level of catecholamines, a major component being noradrenaline. In contrast application of reserpine induced sterility and suppressed egg-laying in female moths, in association with detectable amounts of serotonin. The induction of such biogenic amines as the result of chemosterilant application may therefore have a direct effect on the insect endocrine system, thereby causing a stimulation or suppression of an insect hormone at the wrong time in its life-cycle. Application of such substances may result in the absorption of mature eggs, a suppression of later larval or even adult stages after apparently normal initial embryological development in the egg, and aberrant mating behaviour.