Insect Pest Control by Manipulating Insect’s Symbiont - Insights from Studying the Bean Bug Symbiosis

Symbiotic bacteria are common in insects. Because symbiotic bacteria are known to intimately affect the various aspects of insect host biology, ideally insects can be controlled by manipulating their symbiont. However, the attempts to control insects through their symbiont have been very limited. The paucity of the insect pest control using their symbiont is most likely due to the poor understanding of the symbiotic interactions between host insect and symbiont, which is attributed to the difficulty in cultivation of insect symbionts. However, the recently established bean bug, Riptortus pedestris, symbiotic system provides good opportunities to study insect’s symbiont in molecular level through their cultivable symbionts. Bean bugs acquire genus Burkholderia cells from environment and harbor them as their gut symbionts in the specialized posterior midgut. The genome of the Burkholderia symbiont was sequenced, and the genomic information has been used to generate the genetically manipulated Burkholderia symbiont strains. After orally administering the mutant Burkholderia symbionts into bean bugs for symbiotic association, the bacterial colonization levels in the host gut and host phenotypes were analyzed. As a result, we have identified novel symbiotic factors necessary for establishing successful association with host. Our recent understandings on the bacterial symbiotic factors demonstrate a great possibility to control the bean bug pest using genetically modified Burkholderia symbiont.