The alpha-proteobacterium Wolbachia pipientis is a very common cytoplasmic
symbiont of insects, crustaceans, mites, and filarial nematodes. To enhance
its transmission, W. pipientis has evolved a large scale of host manipulat
ions: parthenogenesis induction, feminization, and male killing. W. pipient
is's most common effect is a crossing incompatibility between infected male
s and uninfected females. Little is known about the genetics and biochemist
ry of these symbionts because of their fastidious requirements. The affinit
y of W. pipientis for the microtubules associated with the early divisions
in eggs may explain some of their effects. Such inherited microorganisms ar
e thought to have been major factors in the evolution of sex determination,
eusociality, and speciation. W. pipientis isolates are also of interest as
vectors for the modification of wild insect populations, in the improvemen
t of parasitoid wasps in biological pest control, and as a new method for i
nterfering with diseases caused by filarial nematodes.