Wolbachia infection associated with all-female broods in Hypolimnas bolina (Lepidoptera: Nymphalidae): evidence for horizontal transmission of a butterfly male killer

Inherited bacteria that kill male hosts during embryogenesis infect a wide range of insect species. In order to ascertain if there are patterns to host infection, with particular male killing bacteria specialising on particular taxa, we investigated the male killing trait in the butterfly Hypolimnas bolina. All-female broods were first reported in this species in the 1920s. Investigation of this system in the Fiji Islands revealed the causal agent of sex ratio distortion in H. bolina to be a male killing Wolbachia bacterium. This bacterium is identical in wsp and ftsZ sequence to a male killer in the butterfly Acraea encedon in Tanzania, suggesting it has moved between host species, yet retained its phenotype. The prevalence of the Wolbachia was calculated for three different island groups of Fiji, and found to vary significantly across the country. Antibiotics failed to cure either the male killing trait or the Wolbachia infection. The implications of these results are discussed.