Effect of Leptoglossus phyllopus on Caballeronia abundance

We quantified the effect of host association on symbiotic bacteria in the bug-<i>Caballeronia</i> symbiosis. Thousands of species of true bugs in the coreoid and lygaeoid superfamilies depend on a symbiotic relationship with free-living <i>Caballeronia</i> bacteria. The insects require the bacterium for normal growth and development, but do not transmit it to their offspring; instead, young nymphs must re-acquire <i>Caballeronia</i> from soil every generation. This decoupling of the life history of host and microbe allowed us to measure the effect of host association on the microbe’s population. First, we quantified free-living <i>Caballeronia</i> in soil microcosms in the presence and absence of leaffooted bugs (<i>Leptoglossus phyllopus</i>) over a seven-month period using quantitative PCR. Second, we tested whether higher host density is correlated with increased abundance of <i>Caballeronia</i> in soil. We found that <i>Caballeronia</i> has a larger population in the presence of leaffooted bug and that its abundance is positively correlated with bug density, confirming that this relationship is, in fact, a mutualism.