Adonia variegata (Coleoptera : Coccinellidae) bears maternally inherited Flavobacteria that kill males only

Inherited bacteria that parasitically distort the pattern of sex allocation of their host, biasing allocation towards female progeny, are found in man y arthropods. One such manipulation is male-killing, where male progeny of infected females die during embryogenesis. We here provide evidence for a m ale-killing bacterium in the coccinellid beetle, Adonia variegata. We then address 3 questions. First, is this male-killing bacterium one that is foun d in other hosts, or does it represent a new transition to male-killing wit hin the eubacteria ? Using the sequence of the 16S rDNA of the bacterium, w e found that the male-killing bacterium is a member of the Flavobacteria-Ba cteroides group, most closely related to the male-killing bacterium in anot her lady bird beetle, Coleomegilla maculata. Secondly, is there any evidenc e that this bacterium affects female host physiology ? In a paired test und er nutritional stress, we found no evidence for a physiological benefit to infection, and weak evidence of a physiological cost, in terms of reduced f ecundity. Thirdly, is there any evidence of host involvement in the transmi ssion of the bacterium to the germ line ? We found no evidence of host invo lvement. Rather, bacteria migrated to the ovariole independently of host ce lls. We conclude that thr bacterium is a parasite, and discuss how 2 differ ent species of ladybird come to be infected with 1 lineage of bacterium, an d why case studies of male-killing bacteria have generally found little evi dence of any symbiont contribution to host physiological functioning.