Ecological modeling evaluates the potential impacts of symbionts on plant pathogen vectoring in field populations

Within the last decade, research into the use of insect microbial symbionts as a means of controlling populations of insect vectors and the pathogens they transmit has advanced substantially. Many microbes have been iden-tified that affect important epidemiological traits of vectors or pathogens in the laboratory, yet few have been tested in the field. Consequently, it remains unknown which effects of symbionts drive successful control. We investigated the relative importance of simultaneous effects caused by one such microbe, Caballeronia spp., on the potential of its squash bug host to vector phytopathogenic Serratia marcescens. Infection with Caballeronia, a beneficial symbiont of squash bugs, leads to reduced pathogen titers and rapid clearance of S. marcescens in bugs, reducing the vectoring potential of a significant pest in squash agriculture. Using simulation modeling and sensitivity analysis, we determined the relative impact that reducing the vector potential of symbiont-free (aposymbiotic) bugs and increasing population-level symbiont coverage would have on overall pathogen transmission in a field setting. In this system, we show that aposymbiotic insects contribute significantly to pathogen outbreaks even when they comprise a small portion of the population. While reducing the transmission rate of aposymbiotic insects shows promise in disease mitigation, maximizing symbiont prevalence in the vector population is likely to have the most impact on mitigating plant infections. We conclude that for symbiont-mediated interventions where disparities in transmission between aposymbiotic and symbiotic individuals are already high, ensuring high symbiont uptake in a population is critical for success.