Incidence of male-killing Rickettsia spp. (alpha-proteobacteria) in the ten-spot ladybird beetle Adalia decempunctata L. (Coleoptera : Coccinellidae)

The diversity of endosymbiotic bacteria that kill male host offspring durin g embryogenesis and their frequencies in certain groups of host taxa sugges t that the evolution of male killing and the subsequent spread of male-kill ing symbionts are primarily determined by host life history characteristics . We studied the Ill-spot ladybird beetle, Adalia decempunctata L. (Coleopt era: Coccinellidae), in which male killing has not been recorded previously , to test this hypothesis, and we also assessed the evolution of the male k iller identified by DNA sequence analysis. Our results show that A. decempu nctata harbors male-killing Rickettsia (a-proteobacteria). Male-killing bac teria belonging to the genus Rickettsia have previously been reported only for the congeneric two-spot ladybird beetle, Adalia bipunctata L. Phylogene tic analysis of Rickettsia DNA sequences isolated from different population s of the two host species revealed a single origin of male killing in the g enus Rickettsia. The data also indicated possible horizontal transfer of sy mbionts between host species. In addition, A. bipunctata is known to bear a t least four different male-killing symbionts in its geographic range two o f which coexist in the two locations from which A. decempunctata specimens were obtained for the present study. Since only a single male-killing taxon was found in A. decempunctata, we assume that the two closely related lady bird beetle species must differ in the number and/or geographic distributio n of male killers. We discuss the importance of these findings to our under standing of the evolution and dynamics of symbiotic associations between ma le-killing bacteria and their insect hosts.