? Annu. Rev. Microbiol. 1999. 53:71–102 Copyright c  1999 by Annual Reviews. All rights reserved W OLBACHIA PIPIENTIS: Microbial Manipulator of Arthropod Reproduction R. Stouthamer 1 , J. A. J. Breeuwer 2 , and G. D. D. Hurst 3 1 Laboratory of Entomology, Wageningen Agricultural University, 6700 EH Wageningen, Netherlands; 2 Department of Fundamental and Applied Ecology, University of Amsterdam, Kruislaan 320, 1098 SM Amsterdam, Netherlands; 3 Department of Biology, University College London, Wolfson House, London NW1 2HE, United Kingdom Key Words cytoplasmic incompatibility, parthenogenesis, male killing, feminization, α-proteobacteria ■ Abstract The α-proteobacterium Wolbachia pipientis is a very common cyto- plasmic symbiont of insects, crustaceans, mites, and filarial nematodes. To enhance its transmission, W. pipientis has evolved a large scale of host manipulations: partheno- genesis induction, feminization, and male killing. W. pipientis’s most common effect is a crossing incompatibility between infected males and uninfected females. Little is known about the genetics and biochemistry of these symbionts because of their fas- tidious requirements. The affinity of W. pipientis for the microtubules associated with the early divisions in eggs may explain some of their effects. Such inherited microor- ganisms are 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 improvement of parasitoid wasps in biological pest control, and as a new method for interfering with diseases caused by filarial nematodes. INTRODUCTION Bacteria belonging to the genus Wolbachia have recently been recognized to in- fect a high proportion of insects, mites, isopods, and filarial nematodes. These intracellular α-proteobacteria were reported for the first time in 1924, by Hertig & Wolbach (45), as the unnamed rickettsia in the ovaries of the mosquito Culex pipiens, and they were formally named in 1936 by Hertig (44) as Wolbachia pipi- entis in honor of his collaborator Wolbach. Until 1970, hardly any work on these bacteria was reported. In 1971, Yen & Barr (162) discovered that W. pipientis in mosquitoes caused a crossing incompatibility between infected males and un- infected females. Uninfected eggs fertilized by sperm from infected males died. Interest in this group increased when it was found that the infection and its effect were not limited to mosquitoes but were also present in several other insect species 0066-4227/99/1001-0071$08.00 71 Annu. Rev. Microbiol. 1999.53:71-102. Downloaded from arjournals.annualreviews.org by CAPES on 10/11/07. For personal use only.