The importance of cytoplasmic male killing elements in natural populations of the two spot ladybird, Adalia bipunctata (Linnaeus) (Coleoptera: Coccinellidae)

Adalia bipunctata, the two spot ladybird, is polymorphic for a cytoplasmically inherited element which produces female-biased sex ratios by effecting the death of male offspring during embryogenesis. The levels of this element were assessed in Cambridge populations. Six out of 82 females tested showed both a female-biased sex ratio and low egg hatch rates consistent with the presence of this element. Population sex ratios were assessed by collecting pupae from the Cambridge area. The population sex ratio was found to be 1.15:1, female biased, significantly different from 1:1, and consistent with predictions based on a model incorporating the observed level of the sex ratio element in the population.