Exposure of adult rusty grain beetles, Cryptolestes ferrugineus (Stephens), saw-toothed grain beetles, Oryzaephilus surinamensis (L.), and red flour beetles, Tribolium castaneum (Herbst), to filter papers treated with the organophosphorus insecticides malathion or chlorpyrifos-methyl often affected offspring production in survivors. Groups of five male and five female survivors were placed on ground wheat at 30°C and C. ferrugineus and O. surinamensis adults produced fewer offspring with prolonged exposure to chlorpyrifos-methyl; malathion had no effect. Tribolium castaneum adults produced significantly more offspring with increasing exposure to both malathion and chlorpyrifos-methyl indicating stimulation of oviposition or a selection for increased fitness in survivors.