Hydroprene, when topically applied, terminated sexual diapause of adultHypera postica(Gyllenhal). Significant changes in gonadal development, oviposition, and feeding were related to the concentration applied. A 1-μg amount of hydroprene terminated diapause in 15% of weevils, did not influence testis size, produced small increases in ovary size, instigated atypical oviposition in 10% of females, and increased feeding for 27 days. A five-μg amount terminated diapause in 37% of weevils, produced moderate increases in testis and ovary size, instigated atypical oviposition in 20% of females, and increased feeding for 27 days. A 10-μg amount terminated diapause in 66% of weevils, produced large increases in testis and ovary size, instigated atypical oviposition in 60% of females, and increased feeding for 37 days. A 50-μg amount terminated diapause in 100% weevils, produced large increases in testis and ovary size, instigated typical oviposition in 90% of females but with reduced egg fertility, and increased feeding for 49 days.