Occurrence and hybridization of two parasitoid wasps, Torymus sinensis Kamijo and T-beneficus Yasumatsu et Kamijo (Hymenoptera : Torymidae) in the Oki islands

Torymus sinensis, an introduced parasitoid of Dryocosmus kuriphilus, was fo und to be present in the Oki islands though it had never been released ther e. To investigate the seasonal occurrence of two parasitoid wasps, T. sinen sis and Torymus beneficus, and their hybrids, we collected 611 withered gal ls formed by D. kuriphilus in March 1996. Ninety-three females and 182 male s of Torymus emerged from the galls. We separated species by the morphology and genotype of the malic enzyme (ME). Both parasitoids were found and T. sinensis was dominant. Seven females showed 5 bands of ME migrating between the S and F bands and were hybrids of T. sinensis with early-emerging T. b eneficus. Only 8% of females were hybrids. Hybridization seemed to occur at low frequency in the field. Oki's T. sinensis is considered to have been a ccidentally introduced long before our investigation and was classified int o a Chinese ecotype judging from their eclosion period.