We investigated the effects of exposure to diazinon, an organophosphate insecticide, on the expression of antioxidant and detoxification factors in the silkmoth. Exposure to diazinon resulted in induction of mRNA encoding manganese containing superoxide dismutase (SOD) and omega-class glutathione S-transferases (GST), whereas no changes were observed in catalase, other class of GST and acetylcholinesterase. Liquid chromatography showed that the amount of reactive oxygen species was increased, whereas the amount of glutathione was decreased in the silkmoth fat body after exposure to diazinon. These results suggest that SOD and omega-class GSTs can contribute to organophosphate resistance in Lepidopterans. [ABSTRACT FROM AUTHOR]