Effects of environmentally-acquired gut symbionts on fitness and behavior of adult female host, Riptortus pedestris (Hemiptera: Alydidae)

Bean bug, Riptortus pedestris (Hemiptera: Alydidae), acquires its symbiotic bacteria belonging to family Burkholderiaceae from soil environments in every generation. Beneficial effects of its symbiotic bacteria have been demonstrated mainly with immature stages of R. pedestris, while remaining their effects on adult biology largely unexplored. In this study, we investigated effects of the gut symbiont, Caballeronia insecticola, on fitness and behavior traits of female R. pedestris adults. First, the symbiotic bacteria exerted adverse effects on survivorship, with which survival rates decreased to 86.7 % and 56.7 % in apo-symbiotic and symbiotic females, respectively, at 60 days after adult emergence. Despite a reduced longevity of symbiotic females, the fecundity of symbiotic insects was on average 2.0-fold greater than that of apo-symbiotic ones during this period. We also evaluated overwintering survivorship in laboratory conditions and found that symbiotic females exhibited significantly higher survivorship than that of apo-symbiotic ones. Second, behavioral assays demonstrated that symbiotic R. pedestris displayed enhanced feeding efficiency by consuming higher amounts of soybean per feeding attempt. For both walking and flight capacity, symbiosis yielded significant increases in mobility than apo-symbiotic ones. In particular, symbiotic females flew on average 1.3 km over 4 h, which was 138.1-fold greater than apo-symbiotic ones. Finally, symbiotic females were less susceptible to an organophosphate insecticide, fenitrothion, yielding the lethal concentrations for 50 % (LC₅₀) at 72.4 ppm and 92.4 ppm for apo-symbiotic and symbiotic groups, respectively. Taken together, our study demonstrates that the symbiotic effects on female R. pedestris would favor the host population growth.