Invasion of one insect species, Adalia bipunctata, by two different male-killing bacteria

Male-killing bacteria, which are inherited through the female line and kill male progeny only, are known from five different orders of insect. Our kno wledge of the incidence of these elements has stemmed from discovery of the ir phenotype in different species, Our estimate of the frequency with which insects have been invaded by these elements therefore depends on each obse rvation of the male-killing phenotype within a species being associated wit h a single microorganism. We here record an example of a single insect spec ies being infected with two taxonomically distinct male-killing bacteria. W estern European populations of the two-spot ladybird, Adalia bipunctata, ha ve previously been shown to bear a male-killing Rickettsia, However, we her e show that the majority of the male-killing lines tested from Central and Eastern Europe do not bear this bacterium. Rather, 16S rDNA sequence analys is suggests male-killing is associated with st member of the genus Spiropla sma. We discuss this conclusion in relation to the evolutionary genetics of male-killing bacteria, and the evolution of male-killing behaviour in the eubacteria.