Mesenetia-induced cytoplasmic incompatibility in the coconut hispine beetle in Japan

Some maternally inherited endosymbionts are known to cause Cytoplasmic incompatibility (CI), in which uninfected females cannot or seldom produce offspring by mating with infected males. Mortality by CI may vary depending on the bacterial strain, the host’s genotype, or the host’s age. Mesenetia is an alphaproteobacterial endosymbiont infecting the coconut hispine beetle Brontispa longissima (Gestro) (Coleoptera: Chrysomelidae), a serious pest of the coconut palm. This bacterium was discovered in the Pacific clade B. longissima, which causes 100% CI mortality. The Mesenetia infection in the other Asian clade, which is considered more invasive than the Pacific clade, was then discovered; however, the CI was unknown. We investigated the CI ability of Mesenetia infecting the Asian clade using different ages of hosts originally collected in Japan. The effects of the host’s age on bacterial density were also investigated with qPCR. The results of crossing tests showed that infected males caused CI with approximately 70% mortality with uninfected females in all age groups: 21–30, 30–40, 60–70, or 90–100-day-old males. CI mortality did not differ among the males’ ages. Infected females rescued CI caused by infected males in all age groups: 15–20, 30–40, 60–70, or 90–100-day-old females. Results of qPCR showed that, in males, bacterial density did not diverge according to age in the testis, hindleg, foregut, midgut, and hindgut. In females, aged insects tended to have higher bacterial density than younger ones in the ovary and, to a lesser extent, in the hindgut.