Highly transmissible cytoplasmic incompatibility by the extracellular insect symbiont .

Cytoplasmic incompatibility (CI) is a form of reproductive manipulation caused by maternally inherited endosymbionts infecting arthropods, like , whereby matings between infected males and uninfected females produce few or no offspring. We report the discovery of a new CI symbiont, a strain of  causing CI in the parasitoid wasp . Its extracellular occurrence enabled us to establish CI in uninfected adult insects by transferring -infected hemolymph. We sequenced the CI- genome and did not find any homologues of any of the genes discovered to cause CI in , suggesting independent evolution of CI. Instead, the genome contains other potential CI-causing candidate genes, such as homologues of high-mobility group (HMG) box proteins that are crucial in eukaryotic development but rare in bacterial genomes. 's extracellular nature and broad host range encompassing medically and agriculturally important arthropods make it a promising tool to study CI and its applications.