Mating receptivity mediated by endosymbiont interactions in a haplodiploid thrips species

Many arthropods carry maternally inherited endosymbionts that cause cytoplasmic incompatibility (CI), manifested as embryonic mortality in matings of infected males with uninfected females. Infected females, however, do not suffer this cost. Therefore, in populations with mixed endosymbiont infections, selection is expected to favour mechanisms that enable hosts to avoid or mitigate CI. This may include changes in mating behaviour, such as reduced female receptivity to mating and/or remating when approached by incompatible males. Here, we investigated mating behavioural traits in haplodiploid thrips naturally associated with two CI-inducing endosymbionts, <i>Cardinium</i> and <i>Wolbachia</i>. Compared with females with both endosymbionts, those with only <i>Cardinium</i> showed reduced receptivity to males carrying both. However, surprisingly, females without endosymbionts were not less receptive to incompatible males. Furthermore, in contrast to females without endosymbionts, females with <i>Cardinium</i> were far less likely to remate with incompatible than compatible males irrespective of the compatibility type of the first mating. Our results suggest that endosymbiont-specific sexual selection processes occur, whereby females carrying only <i>Cardinium</i> recognize <i>Wolbachia</i> in coinfected males to avoid CI. This may hinder a CI-driven <i>Wolbachia</i> spread. Endosymbiont-mediated mating behaviours may be crucial for the dynamics of CI-inducing endosymbionts and their application in pest management strategies.