Estimates of parasitoid-induced mortality obtained from the rearing or dissection of samples of hosts may underestimate the actual mortality attributable to parasitoids. In this study, the use of appropriate unparasitized control hosts allowed the authors to apply Abbott's formula to estimate total parasitoid-induced mortality. Gypsy moth,Lymantria dispar(L.), larvae at the age of 0, 3, 6, or 9 d were stung by the solitary endoparasitoid,Cotesia melanoscela(Ratzeburg). There were significant curvilinear relationships between host age at the time it was stung and parasitoid emergence and parasitoid-induced nonemergence mortality. Emergence rates were lowest and parasitoid-induced nonemergence mortality rates were highest among hosts stung on days 0 and 9. The negative effect of parasitism on growth rates was greatest among hosts stung on days 6 and 9, and parasitoid development time was longest within hosts stung on days 0 and 9.