The Riptortus pedestris-Burkholderia symbiotic system is a promising model for understanding molecular mechanism of symbiosis. In previous studies, the Burkholderia symbiont has been shown to play important biological roles in the growth and fitness of host R. pedestris. The Burkholderia symbiont, one of bacteria found in the soil, is the only bacterium that can colonize the symbiotic midgut region of R. pedestris. However, the molecular mechanism of host selectivity for the Burkholderia symbiont remains unknown. To determine where the selection occurs, we firstly compared initial infectivity of different mid-gut regions after oral infection of Escherichia coli and Burkholderia. Interestingly, E. coli were not detected in any regions of mid-gut, while Burkholderia could reach to the posterior region of mid-gut. Therefore, we hypothesized that host selectivity for the Burkholderia symbiont is occurred in the salivary gland. To address this hypothesis, we treated E. coli and Burkholderia with lysate of salivary gland and examined their survival by estimation of colony forming unit (CFU) on the plate. We found that E. coli, but not Burkholderia, was susceptible to the lysate of salivary gland. To determine molecular basis of the selective mechanism in the salivary gland, we analyzed antimicrobial proteins (AMPs) from lysate of salivary gland. we identified three AMPs, namely rip-trialysin1, rip-trialysin2 and lysozyme and further purified rip-trialysin1 and rip-trialysin2. When E. coli and Burkholderia were treated with rip-trialysin1 and rip-trialysin2, rip-trialysin1 exhibited little antimicrobial activity, but rip-trialysin2 exhibited antimicrobial activity. Furthermore, we found that E. coli was susceptible, but Burkholderia is resistant to commerciallypurchased egg white lysozyme. Our results suggest that R. pedestris salivary gland provides a chance of selection for the Burkholderia symbiont and lysozyme in salivary gland seems to play an important role for the selection of gut symbiont.