BACTERIAL-INFECTIONS OF HEMOCYTES ASSOCIATED WITH THE MATERNALLY INHERITED MALE-KILLING TRAIT IN BRITISH POPULATIONS OF THE 2 SPOT LADYBIRD, ADALIA-BIPUNCTATA

Adalia bipunctata, the two spot ladybird, carries a vertically transmi tted bacterial agent which kills male progeny during embryogenesis. So me matrilines of A. bipunctata give rise to strongly female-biased sex ratios, 16S rDNA sequence analysis revealed a bacterium of the genus Rickettsia associated with this trait, a conclusion which is corrobora ted here, Using light microscopy, an association between a bacterium l ocated in A. bipunctata hemocyte cytoplasm and matrilines which show t he sex ratio trait was found. This element was not found in hemocytes taken from females from normal sex ratio lines, nor in hemocytes taken from males. The association is confirmed by study of the inheritance of the sex ratio trait. Only daughters of sex ratio crosses that bear this cytoplasmic bacterium also show the sex ratio trait, with other d aughters being normal with respect to sex ratio. Transmission electron microscopy of hemocytes revealed a walled bacterium, bearing features of members of the genus Rickettsia, free in the cytoplasm of hemocyte s taken from infected lines, but not in those taken from uninfected li nes. (C) 1996 Academic Press, Inc.