Species diversity of environmentally-transmitted bacteria colonizing Riptortus pedestris (Hemiptera: Alydidae) and symbiotic effects of the most dominant bacteria.

Riptortus pedestris (Hemiptera: Alydidae) establish endosymbiosis with specific bacteria from extremely diverse microbiota in soil. To better understand ecology and evolution of the symbiosis, it is important to characterize bacterial species diversity colonizing R. pedestris and evaluate their symbiotic effects. Nonetheless, previous research was limited to a few bacteria strains such as Caballeronia insecticola. In this study, second-instar nymphs were provided with field soils and reared to adult. Then, bacteria colonizing the midgut M4 region of R. pedestris were analyzed for bacterial species identification based on the 16S rRNA gene. First, a total of 15 bacterial species were detected belonging to Burkholderiaceae. Most of R. pedestris were found to harbor single bacterial species, whereas several insects harbored at most two bacterial species simultaneously. Among the total insects harboring single bacterial species, 91.2% harbored genus Caballeronia. The most dominant species was C. jiangsuensis, not previously documented for symbiotic associations with R. pedestris. Second, in laboratory conditions, C. jiangsuensis significantly enhanced the development, body size, and reproductive potentials of R. pedestris, compared to individuals with no symbiotic bacteria. These results add novel information to better understand symbiotic bacteria community establishing in R. pedestris and symbiotic effects on the host insects.