Male-killing bacterium in a fifth ladybird beetle, Coleomegilla maculata (Coleoptera:Coccinellidae).

Inherited symbionts which selectively cause the death of male hosts are found widely across the Insecta. Previous studies have shown a single, but different micro-organism to be responsible for male-killing in each taxonomic group studied. We here produce evidence that within a group of insects, the Coccinellidae, there is more than one causal agent of male lethality. We report a novel observation of a male-killing trait in the species Coleomegilla maculata. Six of 26 crosses were found to produce a female-biased sex ratio associated with a low egg hatch-rate. The trait was matrilinearly inherited and was observed to be tetracycline-sensitive. However, tests which indicate the presence of a Rickettsia, previously found to cause male-killing in another member of the Coccinellidae, Adalia bipunctata, proved negative. We therefore conclude that the phenomenon of male-killing is multicausal, within, as well as between, taxonomic groups of the Insecta.