Effect of climate change on environmentally transmitted insect-microbe mutualism or evaluating the effect of eesiccation on eaballeronia in soil and subsequent acquisition by true bugs

The association between eukaryotes and their microbial symbionts is often assumed to be mutualistic. While the effect of microbial partners on host fitness is frequently studied, similar studies quantifying the effect of the host on symbiont fitness are lacking. Thousands of species of true bugs benefit from their association with soil bacteria in the genus Caballeronia, which they acquire from the environment every generation. In the presence of the symbiont, the host exhibits faster development to adulthood, better fecundity, and larger body mass, but the impact of this relationship on symbiont fitness was not known. Here, we determine the effect of association with the coreid insect, Leptoglossus phyllopus, on the free-living population of Caballeronia grimmiae. First, we quantified the abundance of Caballeronia in soil in the presence and absence of the host over a period of seven months using qPCR. Second, we quantified the abundance of Caballeronia in soil at different bug densities. Our results showed that the soil had a higher abundance of Caballeronia in the presence of the host. Caballeronia population in the soil was also positively correlated with bug density. Additionally, soil moisture affected the abundance of Caballeronia, with wetter soil supporting a larger population. This study indicates that the leaffooted bugs enrich the soil with their microbial symbiont, confirming that this association is truly mutualistic. This represents one of only a few studies that have quantified the benefit a eukaryotic host provides to its bacterial symbiont.