Gypsy moth,Lymantria dispar(L.), populations in North America support 11 introduced parasitoids and recent imports are released annually. Multiparasitism effects on parasitization rates and parasitoid emergence success were assayed using the establishedCotesia melanoscelusRatzburg and recent importGlyptapanteles flavicoxisMarsh. For each species, oviposition into a parasitized host reduced emergence. The emergence rate forC. melanoscelusfell from 55.9 to 26.7%, andG. flavicoxisemergence was reduced from 22.8 to 14.2%.C. melanoscelusemerged significantly more often thanG. flavicoxisin 50% of the competitive interactions. This suggests thatC. melanoscelusout-competesC. flavicoxisfollowing multiparasitism. A second experiment showed that percent parasitism increased significantly as the proportion of searching adultC. melanoscelusincreased. We concludeC. flavicoxisshould be released for gypsy moth biological control only after the first generationC. melanoscelusoviposition period. ReleasingG. flavicoxisbeforeC. melanoscelusoviposition will not improve total gypsy moth parasitism and may reduce the effectiveness of the establishedC. melanoscelus.