The impact of the plant growth regulator gibberellic acid (GA₃) on parasitoid development and reproduction was examined using the endoparasitoid Apanteles galleriae Wilkinson (Hymenoptera: Braconidae). The effects of GA₃ were assessed by rearing A. galleriae on hosts fed the growth regulator and then measuring a several life history traits: developmental time from egg to adult, adult longevity, body sizes, fecundity, and sex ratios. GA₃ treatment yielded dose-dependent changes in adult longevity and duration of development. For example, at GA₃ doses >10 ppm, the life span of both male and female adult wasps decreased by 19–23 d in comparison with parasitoids that developed on GA₃-free hosts. Likewise, the length of development from egg to adult emergence significantly increased when A. galleriae developed on hosts fed the growth regulator at doses >200 ppm. In contrast, GA₃ did not seem to alter adult body sizes, sex ratios, or fecundity, with the exception that F₂ progeny production decreased by >40% at high concentrations (≥200 ppm). The potential significance of plant growth regulators on natural enemies used in integrated pest management programs is discussed.