Seasonal and geographical variations in the community structure of environmentally-transmitted symbiotic bacteria in Riptortus pedestris (Hemiptera: Alydidae)

Riptortus pedestris (Hemiptera: Alydidae) is an important agricultural pest acquiring symbiotic bacteria from soil in every generation. Thus, soil microbiota could directly affect the symbiotic bacterial community structures of R. pedestris. In this study, we investigated the symbiotic bacterial communities in R. pedestris across multiple seasons and regions in South Korea. Foraging R. pedestris adults were collected using pheromone traps from three distinct generations in 2022; visual inspection was employed to locate overwintering adults in 2022 and 2023. In foraging R. pedestris, a total of 26 bacterial genera were detected from the insect midguts. Among them, 16 bacterial genera have not been previously documented for their symbiotic associations with R. pedestris. Genus Caballeronia was the most dominant, accounting for 46.2% of the bacteria detection frequency across the foraging generations, followed by genus Yokenella. The number of symbiotic bacterial genera showed seasonal variations, yielding 10, 18, and 15 genera in overwintered, first, and second generations, respectively. A majority of R. pedestris in the overwintered generation harbored a single bacterial genus. However, this pattern was not the case especially in the first generation, from which 57.1% of R. pedestris harbored multiple bacterial genera. Geographically, Caballeronia was also the most dominant across the six sampling sites. However, the dominance of Caballeronia was substantially lower in Jeju Island than the mainland sites, and five genera were exclusively found in the island. From overwintering R. pedestris, five bacterial genera were detected with the dominance of Caballeronia with two genera exclusively found in the overwintering populations.