I'm reading Microcosm: E. coli and the New Science of Life which has been a great book for a person with more than passing interest in biology but not a scientist by any stretch of the word. I ran into two paragraphs about Wolbachia that read like this:
Genes come into similar conflict in all species. Many insects are infected with a microbe called Wolbachia, for example, that can only live inside their cells. It relies for survival almost entirely on being passed down from one generation to the next. This strategy has on major shortcoming: Wolbachia cannot infect sperm, and so males are a dead end for its posterity. In other words, the success of Wolbachia's genes and those of its male hosts are in conflict.
Wolbachia has evolved many ways to win this struggle. In some species of wasps, for example, Wolbachia manipulates infected females so that they give birth only to females, and it alters their offspring so that they have no need to mate with males to reproduce. In other species, Wolbachia kills an infected mother's male eggs. The bacteria in the male eggs die as well, but the strategy ensures the overall success of Wolbachia genes: the Wolbachia-infected female eggs survive, and when they hatch the female larvae don't face competition for food from their brothers. In fact, their brothers become their food. Wolbachia, in other words, has hit on some of the same strategies that viruses use to thrive in E. Coli.
Wikipedia goes further:
Wolbachia are known to cause four different phenotypes:
Male killing: death of infected males. This allows related infected females to be more likely to survive and reproduce.
Feminization: infected males develop as females or infertile pseudo-females.
Parthenogenesis: reproduction of infected females without males.
Cytoplasmic incompatibility: the inability of Wolbachia-infected males to successfully reproduce with uninfected females or females infected with another Wolbachia strain. This has the advantage of making the Wolbachia strain more likely to become prevalent as opposed to other strains of Wolbachia. This can have the additional result of making Wolbachia more common as a whole.
WOLBACHIA HAS NO USE FOR THE MEN FOLK. INSTEAD OF OPTING FOR A NICE LIVE-AND-LET-LIVE PHILOSOPHY, THE MEN FOLK ARE COMPETITION FOR THE WOMEN FOLK SO THEY MUST ALL DIE... or become women.