Doses Wolbachia induce unisexuality in oak gall wasps? (Hymenoptera: Cynipidae)

Heterogony (cyclical parthenogenesis) is a remarkable characteristic of oak gall wasps, Cynipini, which is the largest tribe in Cynipidae. A few species of Cynipini are exceptionally univoltine and thelytokous, probably due to deletion of the bisexual generation from their heterogonic ancestor-species. Since the close association between Wolbachia presence and unisexuality has been known in two other tribes of Cynipidae, we searched for Wolbachia using polymerase chain reaction (PCR) primers for the ftsZ and wsp genes in a taxon of the Cynipini, the Andricus mukaigawae complex. This taxon consists of closely related bivoltine heterogonic and univoltine thelytokous species, so that it is a most suitable taxon to clarify a possible role of Wolbachia in unisexuality of heterogonic and thelytokous species of Cynipini. Our PCR assay on the unisexual adults showed that only two of the six populations of the bivoltine heterogonic species tested were highly infected with Wolbachia. The nucleotide sequence of bacterial wsp fragment indicates that these endosymbiotic bacteria are a member of supergroup A. Conversely, Wolbachia were not detected from any populations of the univoltine thelytokous species examined. In conclusion, Wolbachia is not responsible for unisexuality in heterogonic or thelytokous species of Cynipini.