Abstract: Wolbachia is a group of maternal-transmitted endosymbionts which are widely spread in arthropods and nematodes. The fungi of this genus cause several reproductive manipulations in hosts such as cytoplasmic incompatibility (CI), parthenogenesis, feminization and male-killing, among which CI means the crosses between infected males and either uninfected females (unidirectional CI) or females infected by different strains of Wolbachia (bidirectional CI) do not produce offspring or few offspring. The effect of CI makes the infected females have advantage of reproduction. In return, the advantage makes the fast spreading of Wolbachia happen in host populations. Different mechanisms have been proposed to explain the CI and most mechanisms concentrate at the cytological level. Among these mechanisms, the widely-accepted modification-rescue model states that Wolbachia in testis can modify sperm in hosts and make the fusion between paternal and maternal pronuclei abnormal, and that the fusion ecomes normal when the females have the same strain of Wolbachia which rescue the modified sperm. The exploration of molecular mechanisms of CI begins in the study of transcriptomes, genomes and miRNA of some insects. Factors influencing CI expression include host background, Wolbachia strain, Wolbachia genotype, density of endosymbionts, male age, environmental parameters and distribution of endosymbionts in reproductive organs of hosts. In recent years, attempts to use CI to control pests (mosquitoes in particular) and human diseases have been made and some promising progresses achieved.

Key words: Endosymbionts, Wolbachia, cytoplasmic incompatibility, host, reproduction manipulation