Male-killing Wolbachia in two species of insect

The inherited bacterium Wolbachia spreads through the manipulation of host reproduction, and has been suggested to be an important factor in arthropod evolution: from host speciation to the evolution of sex-determination syst ems. Past work has shown that members of this group may produce cytoplasmic incompatibility, feminize genetically male hosts, and induce host partheno genesis. Here, we report an expansion of the range of reproductive manipula tions produced by members of this clade, recording Wolbachia strains that k ill male hosts during embryogenesis in two host species, the ladybird Adali a bipunctata, and the butterfly Acraea encedon. Both male-killing bacteria belong to the B group of Wolbachia. However, phylogenetic analyses were una ble to resolve whether the bacteria in the two species are monophyletic, or represent independent origins of male-killing among the B-group Wolbachia. We also found significant divergence within the wsp gene of Wolbachia stra ins found in different A. bipunctata individuals, suggesting this host spec ies contains two Wolbachia strains, diverged in wsp sequence but monophylet ic. Our observations reinforce the notion that Wobbachia may be an importan t agent driving arthropod evolution, and corroborates previous suggestions that male-killing behaviour is easily evolved by invertebrate symbionts.