The Japanese ladybirds, Coccinula crotchi and Coccinula sinensis, are infected with very closely related strains of male-killing Flavobacterium

Male-killing is 1 of 4 known strategies that inherited parasitic endosymbionts have evolved to manipulate their host＇s reproduction. In early male-killing, infected male offspring are killed early in embryogenesis. Within the Insecta, male-killing bacteria have been found in a wide range of hosts. The Coccinellidae families of beetles, better known as ladybirds, are particularly prone to male-killer invasion. In samples of the coccinellid, Coc- cinula crotchi, from Japan, a new male-killing bacterium was revealed by phenotypic assay. Molecular genetic analysis revealed the identity to be a tetracycline-sensitive Flavobac- terium that causes female-biased offspring sex ratio. Furthermore, that Flavobacterium strain was found to be closely related to the Flavobacterium causing male-killing in the congeneric Japanese coccinellid, Coccinula sinensis, which was collected from the same region. However, we found slightly different Flavobacterium strains infecting C. sinen- sis from regions with different environmental conditions. This may be an indication of horizontal transmission of male-killing Flavobacterium between these 2 ladybird spices. Finally, environmental conditions may affect the spread of male-killing bacteria among their hosts.

Characterization of the first Wolbachia from the genus Scaptodrosophila,a male-killer from the rainforest species S.claytoni

The Scaptodrosophila genus represents a large group of drosophilids with a worldwide distribution and a predominance of species in Australia,but there is little information on the presence and impacts of Wolbachia endosymbionts in this group.Here we describe the first Wolbachia infection from this group,wClay isolated from Scaptodrosophila claytoni(van Klinken),a species from the east coast of Australia.The infection is polymorphic in natural populations,occurring at a frequency of around 6%–10%.wClay causes male killing,producing female-biased lines;most lines showed 100%male killing,though in 1 line it was<80%.The lines need to be maintained through the introduction of males unless the infection is removed by tetracycline treatment.wClay is transmitted at a high fidelity(98.6%)through the maternal lineage and has been stable in 2 laboratory lines across 24 generations,suggesting it is likely to persist in populations.The infection has not been previously described but is closely related to the male-killing Wolbachia recently described from Drosophila pandora based on multilocus sequence typing and the wsp gene.Male-killing Wolbachia are likely to be common in drosophilids but remain difficult to detect because the infections can often be at a low frequency.