Identification of Torymus sinensis and T. beneficus (Hymenoptera: Torymidae), introduced and indigenous parasitoids of the chestnut gall wasp Dryocosmus kuriphilus (Hymenoptera: Cynipidae), using the ribosomal ITS2 region

The parasitoid wasps Torymus sinensis and T. beneficus (Hymenoptera: Torymidae) are introduced and indigenous natural enemies, respectively, of the chestnut gall wasp Dryocosmus kuriphilus (Hymenoptera: Cynipidae), an invasive pest of chestnuts in Japan. T. beneficus has two emergence types in spring, here tentatively designated as the early-spring strain and late-spring strain. It is very difficult to distinguish these two Torymus species accurately according to their morphological and ecological characteristics. Although the sequences of internal transcribed spacer 2 of the nuclear ribosomal DNA (ITS2) of these parasitoids are very similar, we have developed a pair of primers for amplifying a part of ITS2 that distinguishes species and emergence type. By performing high-resolution electrophoresis of PCR products amplified by this specific primer pair, we have succeeded in accurately identifying T. beneficus (early-spring strain) and some T. sinensis parasitoids. However, this technique was discovered to be inapplicable to identify other T. sinensis and T. beneficus (late-spring strain) parasitoids with the same ITS2 genotype. In spite of this problem, the ITS2 marker appears to be more powerful than any other molecular markers so far reported, since it is applicable to detection of T. beneficus, T. sinensis, and their hybrids.