Taxonomic Status of the Andricus mukaigawae Complex and Its Speciation with Geographic Parthenogenesis (Hymenoptera: Cynipidae)

Geographic parthenogenesis occurs in the Andricus mukaigawae complex, which consists of bivoltine heterogonic A. mukaigawae and univoltine thelytokous A. targionii. The former occurs in a more southerly region than the latter. The unisexual generation of A. mukaigawae is hardly distinguishable from A. targionii by external morphology. In the northern habitat of A. mukaigawae, A. targionii is considered to have evolved from A. mukaigawae almost instantaneously without spatial isolation. This phenomenon can be attributed to the failure of a genetically regulatory switch from thelytoky to bisexuality. Further, the change in voltinism—the deletion of bisexual generation—seems to result in adaptation to the cold northern climate. The bisexual adult of A. mukaigawae is described here. Unisexual adults, life cycles and galls of both A. mukaigawae and A. targionii are redescribed.