Coinfection of <scp> <i>Mesenetia</i> </scp> and rescuing <scp> <i>Wolbachia</i> </scp> in the coconut hispine beetle

Abstract Maternally transmitted bacterial symbionts can induce cytoplasmic incompatibility (CI) in host arthropods. In CI, symbionts cause toxic effects in sperm and kill embryos unless they are rescued by an antidote of maternal origin provided by the symbionts. Thus, uninfected females seldom produce offspring by mating with infected males. Different species or strains of CI‐inducing bacterial symbionts may coinfect in a single host. It has been known that some CI‐inducing symbionts induce CI in singly infected hosts, but not when coinfection occurs. However, the mechanisms of this phenomenon are still unknown. In this study, we found that coconut hispine beetles ( Brontispa longissima ) in Japan were infected with Mesenetia , Wolbachia or both. Crossing tests revealed that Mesenetia induced CI in both singly and coinfected males. Coinfected Wolbachia did not induce CI; however, a part of singly infected Wolbachia did. Genetic analysis showed that singly and coinfected Wolbachia belonged to different strains; the former strain causes both toxic and rescuing effects (referred to as mod+/resc+) and the latter one causes no toxic effect but can rescue it (referred to as mod−/resc+). This is the first report of coinfection of mod−/resc+ Wolbachia and other CI inducers, which explains why Wolbachia in coinfected hosts does not induce CI.