Wolbachia-mediated parthenogenesis induction in the aphid hyperparasitoid Alloxysta brevis (Hymenoptera: Figitidae:...

Thelytokous parthenogenesis (thelytoky), in which females can produce female offspring without mating, can be caused by parthenogenesis-inducing endosymbiotic bacteria in the genus Wolbachia. This interaction is well known in hymenopteran parasitoids, where unfertilized eggs typically develop as males via haplo-diploidy in the absence of parthenogenesis-inducing bacteria. We report on a case of thelytoky in Alloxysta brevis (Thomson) (Hymenoptera: Figitidae), a globally widespread aphid hyperparasitoid. A previous study had shown that sex ratios of this species collected in Minnesota (USA) were extremely female biased, and we found here that unmated females reared from field-collected hosts produced female offspring without exposure to males. This result demonstrated thelytoky, and we tested for the role of bacterial endosymbionts by comparing offspring production of unmated females fed the antibiotic rifampicin to offspring production of control females not fed antibiotics. Antibiotic-fed females produced almost exclusively male offspring, and control females produced mainly females. This result showed that antibiotic treatment facilitated male production by unmated Alloxysta brevis females, thus implicating bacterial symbiosis in the expression of thelytoky. We then used molecular analyses to determine the identity of the symbiont. These analyses identified a Wolbachia strain from supergroup B, and excluded other bacteria known to mediate parthenogenesis induction, such as Cardinium and Rickettsia. While Wolbachia had been previously detected by molecular analysis in this species, these are the first experiments demonstrating Wolbachia-mediated parthenogenesis in the figitid subfamily Charipinae.