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.

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.

A viral genome was assembled de novo from next-generation sequencing (NGS) data from bean bugs, Riptortus pedestris, infected with an entomopathogenic fungus, Beauveria bassiana (Bb), and was further confirmed via the RACE method. Based on the phylogenetic analysis of the RdRp sequences, RiPV-1 was clustered in the unassigned insect RNA viruses with two other viruses, APV and KFV. These three viruses were suggested to constitute a new group of insect RNA viruses. Interestingly, RiPV-1 replication was increased dramatically in bean bugs 2 to 6 days after fungal infection. In conclusion, a novel insect RNA virus was found by NGS data assembly. This virus can provide further insight into the interaction between virus, fungus and the host.

A novel insect-infecting positive sense single-stranded RNA virus, Riptortus pedestris virus-1 (RiPV-1), was found in the Riptortus pedestris transcriptome data by de novo assembly and further confirmed by RACE method. The genome of RiPV-1 consists of 10,554 nucleotides (nt) excluding the poly(A) tail and contains a single large open reading frame (ORF) of 10,371 nt encoding a 3,456 aa polyprotein and flanked by 71 and 112 nt 5' and 3' noncoding regions, respectively. RiPV-1 genome contains the consensus genome organization of picorna-like RNA helicase, cysteine protease, and RNA-dependent RNA polymerase (RdRp) array in that order from the 5' to the 3' end. From the phylogenetic analysis, RiPV-1 was clustered with unassigned insect RNA viruses, APV and KFV, which suggests that these three insect picorna-like viruses might constitute a novel group of insect-infecting RNA viruses. Tissue tropism analysis revealed that RiPV-1 was relatively abundant in the thorax, abdomen, midgut and fat body. Interestingly, RiPV-1 replication was enhanced by Beauveria bassiana JEF-007 infection that was quantified using qRT-PCR. This study identified a novel insect-infecting virus and provided further insight into the relationship between virus, fungus and host.