Wolbachia

From [Wikipedia]: Wolbachia is a genus of bacteria which infects arthropod species, including a high proportion of insects, but also some nematodes. It is one of the world's most common parasitic microbes and is possibly the most common reproductive parasite in the biosphere. Its interactions with its hosts are often complex, and in some cases have evolved to be mutualistic rather than parasitic. Some host species cannot reproduce, or even survive, without Wolbachia infection. One study concluded that more than 16% of neotropical insect species carry bacteria of this genus, and as many as 25 to 70% of all insect species are estimated to be potential hosts.

Ants can be infected with Wolbachia and the bacteria's potential for altering sex allocation was at one time a hot topic in social insect biology. As explained by Keller et al. (2001): Sex allocation data in social Hymenoptera provide some of the best tests of kin selection, parent–offspring conflict and sex ratio theories. It has been suggested that maternally inherited parasites may influence sex allocation in social Hymenoptera. If the parasites can influence sex allocation, infected colonies are predicted to invest more resources in females than non-infected colonies, because the parasites are transmitted through females but not males. Prime candidates for such sex ratio manipulation are Wolbachia, because these cytoplasmically transmitted bacteria have been shown to affect the sex ratio of host arthropods by cytoplasmic incompatibility, parthenogenesis, male-killing and feminization.