The effects of sub-lethal doses of cypermethrin onto the larval host Achoria grisella Fabr. (Lepidoptera : Pyralidae) were evaluated on egg-adult development time, number of offspring produced, sex ratio, longevity, and size of the larval endoparasitoid Apanteles galleriae Wilkinson (Hymenoptera : Braconidae). Overall time to adult eclosion increased by more than 50% when Ap. galleriae was reared on cypermethrin-treated host larvae and the development time of the wasp increased in a dose-dependent manner. Adult longevity and the number of surviving offspring produced decreased with increasing insecticide dose. The number of surviving offspring decreased more than 50% at the lowest dose of the insecticide. Neither sex ratio nor adult body sizes were altered by cypermethrin exposure when compared to untreated wasps. This work suggests that sublethal doses of the insecticide could limit the development, survival, and growth of parasitoid wasps due to possible metabolic, hormonal, and nutritional deficiencies. The potential adverse effects that cypermethrin has on the natural enemy of the pest can impact on the success of IPM programs.