The effects of 5-Aza-2′-deoxycytidine (5-Aza-dC), an inhibitor of DNA methyltransferase, were assessed on egg-to-adult developmental time, longevity, size, number of offspring produced, and sex ratio of the larval endoparasitoid Apanteles galleriae Wilkinson (Hymenoptera: Braconidae) and on egg-to-adult developmental time of the host Achroia grisella F. (Lepidoptera: Pyralidae). 5-Aza-dC-treated parasitoids required 1-18 d longer than controls to complete development. In contrast, egg-to-adult developmental time of treated A. grisella was not longer than untreated hosts. Adult longevity and size of the parasitoid species decreased because of 5-Aza-dC application. Likewise, the total number of offspring produced by wasps was reduced >50% in all treatment groups. The sex ratio of adults was in favor of males in 5-Aza-dC-treated groups. © 2007 Entomological Society of America.