The effects of formulations of Dipel (Bacillus thuringiensis subsp. kurstaki), on immature and adult Hyposoter exiguae (Hymenoptera: Ichneumonidae) were assessed, using Heliothis virescens (Lepidoptera: Noctuidae) as a host. H. exiguae developing in treated hosts had a significantly (p = 0.05) lower percentage of pupation and adult emergence compared to parasitoids developing in nontreated hosts. The mean durations of the pupal and adult stages for parasitoids emerging from treated hosts were not generally affected. After 2 days of exposure, the survival of adult males of H. exiguae fed suspensions containing viable B. thuringiensis spores was significantly lower (p = 0.05) than the survival of wasps fed either control (sucrose solution), autoclaved Dipel, or inert formulation powder solutions. Survival of H. exiguae fed a low concentration of Dipel was not significantly reduced. Applications of B. thuringiensis in the field would very likely adversely affect immature H. exiguae more than adults, due to premature host death. none