Riptortus pedestris is known to acquire their symbiotic bacteria, Caballeronia insecticola, from soil environments in every generation. The symbionts have been demonstrated to affect behavioral and physiological traits of the host insect such as the enhancement of development. In particular, symbiotic effects on female adults could directly entail changes in their population growth. Therefore, we investigated a suite of symbiotic effects of C. insecticola on behaviors and fitness-related parameters of female R. pedestris. Overall, symbiotic females showed an behavioral enhancement in both feeding efficacy and movement capacity including walking and flight. In addition, the survival rates under exposure to overwintering conditions and insecticide resistance level were significantly higher in symbiotic females than the aposymbiotic. Finally, although symbiotic females exhibited shorter longevity, their fecundity was found higher compared to the apo-symbiotic.

Nutrient acquisition by insect herbivores affect all aspect of the the lifespan of individauls. For seed-sucking insect herbivores, they face challenges with nutrient acquisition due to requirement for extra-oral digestion of seed contents into a readily-ingestible state. In this study, we demonstrated environmentally-transmitted Caballeronia insecticola allow seed-sucking R. pedestris to overcome challenges with extra-oral digestion. Through the evaluation, first, we found symbiotic insects exhibited enhanced feeding efficiency by consuming significantly larger amount of food per feeding attempt compared to apo-symbiotic insects (P<0.05). Then, we observed feeding behavior modification in the symbiotic insects from the behavior tracking evaluation. Symbiotic insects displayed dichotomic behavior which can be generally divided into early focused feeding and later subdued resting periods. By contrast, apo-symbiotic insects displayed unordered behavior by frequent switches between feeding and walking behavior.

Riptortus pedestris has established symbiotic interactions with specific bacteria from soil environment in every generations. The soil environment is extremely heterogeneous with microbial diversity, suggesting that bacterial composition of the R. pedestris can be affected by surrounding environments. Therefore, we investigated spatiotemporal variation of bacterial communities in wild R. pedestris collected from five mainland areas and Jeju Island in South Korea across insect generations. Among the 390 R. pedestris adults collected, we detected a total of 28 bacterial genera from the symbiotic region of insects. Among the bacterial genera, genus Caballeronia bacteria was the most abundantly detected regardless of sampling site and generation. Nevertheless, bacterial richness varied among the insect generations with 10 genera detected in overwintered generation, 15 genera in the 1st generation and 18 genera in the 2nd generation. Moreover, we found five bacterial genera that were exclusively detected from the Jeju island compared to the mainland areas surveyed.

The bean bug, Riptortus pedestris, is one of major hemipteran pests against the soybean, Glycine max in Korea. In previous study, it was suggested that water-taking in the first instar nymphal stage of R. pedestris is certainly necessary for successful ecdysis and their survival. To investigate water-taking behavior of the first instar nymphs of R. pedestris on plant, electrical penetration graphic patterns were analysed while R. pedestris fed on the napa cabbage leaf, Brassica rapa subsp. pekinensis by using EPG system. In the result, a X-waveform was dominantly observed for average 42.0 min out of total recording time (120 min). There was significant positive correlation (r = 0.457, P = 0.000452, n = 55) between body weight increase and cumulative durations of X-waveform. In addition, histological observation of cross-sections indicated that stylet tip in the plant tissue during X-waveform period is located nearby xylem cells, suggesting that X-waveform is closely related to xylem sap feeding behavior of R. pedestris in plant.

The bean bug is one of major hemipteran pests against the soybean, Glycine max in Korea. Gene expression regulation technologies such as RNA interference and gene editing have emerged as a next generation pest control strategy in agriculture. To search genes effective to feeding inhibition with exogenous dsRNA, a total of 26,761 transcripts were obtained from salivary glands of the bean bug and several target gene candidates such as GPCR, OBP, and CSP were profiled in this study. On the other hand, 1st instar nymphs of the bean bug after hatching were highly attracted to water and absorbed about 701.5 ± 137.72 ㎍/individual/day, suggesting that it could be a practical way for RNA interference by feeding exogenous dsRNA dissolved in water. These preliminary results are expected to be helpful to investigate novel pest control strategy of R. pedestris in the future.

Vertical transmission of symbiont is known as the most effective way to deliver their offspring. However, it has beenreported that the bean bug, Riptortus pedestris, acquires its gut symbiont, Burkholderia sp., from its environment (e.g.soil) during the 2nd instar nymphal stage. Nevertheless, it is not unknown how they locate their symbiont. For this reason,dual-choice experiments were conducted in both solitary (a nymph) and group conditions (100 nymphs) to investigatewhether or not R. pedestris has preference on Burkholderia sp. treated or untreated solution in laboratory conditions. Inthese experiments, there was no significant difference in the preference between the two treatments. We are testing inthe Y-tube olfactometer system to evaluate the response of R. pedestris on possible chemical cues from Burkholderia sp..

The bean bug, Riptortus pedestris (Hemiptera: Alydidae), is one of the major pests on leguminous crops especially in Korea and Japan. Because of its economic importance as crop pest, A large proportion of research on this species have focused on applied questions related to pest management tactics. In addition to the applied research, recent studies have also revealed an interesting relationship between R. pedestris and a gut symbiont Burkholderia sp. as an ideal model system for insect-microbe symbiotic interaction. Under this circumstance, our research group initiated a series of research projects to better understand behavioral ecology of R. pedestris and address its implications for both basic and applied questions. This presentation will cover various behavioral studies with R. pedestris including sublethal effects of insecticides, harmonic radar tracking, overwintering ecology, and symbiont acquisition mechanisms