Son-killer: a third extrachromosomal factor affecting the sex ratio in the parasitoid wasp, Nasonia (=Mormoniella) vitripennis.

An extrachromosomal factor, termed son-killer (sk), affects the sex ratio in a parasitoid wasp, Nasonia (=Mormoniella) vitripennis. The factor is maternally transmitted and alters the secondary sex ratio of an infected female through mortality of approximately 80% of the male embryos. No effect on the primary (zygotic) sex ratio is observed. Ninety-five percent of the daughters of an infected female inherit son-killer. The factor can also be transmitted contagiously when the progeny of infected and uninfected females develop simultaneously on a single host. In newly infected strains, the sex ratio effects are equivalent to those in the original.