Trypsin modulating oostatic factor (TMOF) acts in adult female mosquitoes to reduce expression of trypsin and inhibit protein digestion. When fed to mosquito larvae, TMOF also inhibits digestion, causing death by starvation. In vitro tests designed to mimic the effect of digestive enzymes on TMOF show that the enzyme leucine aminopeptidase rapidly degraded TMOF from its active form to inactive products. In vivo tests of oral toxicity in mouse and duck models and dermal toxicity in a rabbit model indicate that TMOF had no detectable deleterious effects upon ingestion or dermal application. Finally, chronic toxicity testing with Daphnia magna indicated that at high levels of exposure, TMOF was not toxic to daphnids, and caused no reduction in number of molts, time to first brood, number of brood, or size of the adult daphnid. Based on these end point indices of toxicology, TMOF appeared to be an environmentally safe insecticide. Chemical and peptidic analogs are under development as TMOF mimics designed to have activity against Lepidopteran pests of agricultural crops, including cotton.