Abundance and diversity of gut-symbiotic bacteria, the genus Burkholderia in overwintering Riptortus pedestris (Hemiptera: Alydidae) populations and soil in South Korea.

Riptortus pedestris is a major agricultural pest on leguminous plants in South Korea and Japan. Recent studies have revealed that R. pedestris can form beneficial symbiosis with bacteria belonging to genus Burkholderia acquired from soil newly for every generation. Although their physiological interactions are relatively well-understood, infection rate and abundance of the Burkholderia in overwintering natural populations of R. pedestris remain unknown. Therefore, the objective of this study was to characterize Burkholderia infection ratio and clade composition of overwintering R. pedestris populations as well as prevalence and diversity of the genus Burkholderia in soil by conducting a two-year field survey. From the field survey, we found 29 overwintering R. pedestris adults in forested areas nearby soybean fields. Diagnostic PCR analysis revealed that overall infection rate of the symbiotic Burkholderia was 93.1% from overwintering adults. Among the Burkholderia-infected R. pedestris, 70.4% of individuals harbored unclassified Burkholderia clades whereas 22.2% and 7.4% of R. pedestris harbor stinkbug-associated beneficial and environmental (SBE) group and Burkholderia cepacia and complex (BCC), respectively. All R. pedestris were infected with a single clade of Burkholderia. In soil, 56.2% of soil samples were Burkholderia positive, and unlike R. pedestris, multiple Burkholderia clades were detected from 62.2% of those samples. Clade composition of the genus Burkholderia in the samples with the bacteria was 91.1%, 60.0%, 31.1% and 8.8% for plant-associated beneficial and environment (PBE), BCC, SBE and unclassified clade, respectively.