Three nonpeptidic chemical analogs (IBI-152, IBI-156 and IBI-172) of trypsin modulating oostatic factor (TMOF), an insect hormone inhibiting trypsin biosynthesis in mosquitoes, were synthesized based on the structure of the native peptide. The median lethal concentration (LC50) for TMOF and these analogs was estimated for larvae of the northern house mosquito, Culex pipiens, using a static 5-day bioassay. IBI-152 demonstrated the same larvicidal activity as TMOF while IBI-156 and IBI-172 were 1.2- and 1.5-fold more active than TMOF, respectively. All three TMOF analogs were more toxic by injection than TMOF in fourth instars of the tobacco hornworm (Manduca sexta), tobacco budworm (Heliothis virescens), and the cotton bollworm (Helicoverpa zea). Injection of TMOF into second stadium tobacco hornworms had no effect on trypsin activity or growth. Apparently the mosquito hormone is inactive in this species and at the developmental stage examined. Finally, results of a two- choice feeding bioassay with the tobacco budworm indicated that IBI-152 has anti-feedant properties.