Torymus sinensis is an introduced parasitoid used to control chestnut gall wasp, Dryocosmus kuriphilus. After the release of T. sinensis, morphologically-intermediate individuals between T. sinensis and the native parasitoid, T. beneficus appeared in the field, which were suspected to be the result of interspecific hybridization. In order to confirm whether the intermediate individuals were hybrids of T. sinensis and T. beneficus (early-season strain), their genotype for malic enzyme was analyzed by polyacrylamide gel electrophoresis. Nine individuals of 821 analyzed Torymus females showed a banding pattern (FS genotype) of hybrids between T. sinensis and the early-season strain of T. beneficus. Of 388 individuals categorized as morphologically-intermediate, only 2 individuals showed the FS genotype.