Rickettsia associated with male-killing in a buprestid beetle.

Many populations of the buprestid leaf-mining beetle, Brachys tessellatus, from central South Carolina, USA, show highly skewed sex ratios, ranging from 1.3 to 6.0 females per male. We have identified a Rickettsia bacterium that is associated with sex ratio distortion (SRD) and selective killing of male embryos in B. tessellatus. Molecular assays of infection by this bacterium are highly associated with SRD within families, and treatment with an antibiotic (tetracycline) increases the number of male eggs that hatch and develop. The 16S rDNA sequence indicates that this is a novel Rickettsia, most closely related to Rickettsia bellii (a tick-associated bacterium) and a pea-aphid Rickettsia. It is also related to a Rickettsial bacterium that causes male-killing in an unrelated ladybird beetle species. Low levels of parthenogenesis are also observed in this system (about 10% of females) and may be the result of selection due to male rarity, or a direct result of infection by the Rickettsia.