Volatile-mediated interactions: Assessing the role of volatiles in sorghum and soybean intercropping for Japanese beetle management

Japanese beetle, Popillia japonica Newman (Coleoptera: Scarabaeidae) is an economically important invasive pest of over 300 plants, including soybean. One suggested integrated pest management strategy for reducing Popillia japonica damage is intercropping soybean with sorghum which appears to disrupt movement and reduce abundance of Japanese beetles. However the mechanism by which intercropping affects P. japonica colonization remains unknown. Previous studies found that P. japonica react to various undamaged plant volatiles and herbivore-induced volatiles, therefore intercropping might change volatile cues used by P. japonica for host plant selection. This study aims to identify whether plant volatiles play a key role in repellence of P. japonica from sorghum-intercropped soybean fields and identify volatiles that mediate this effect. We hypothesized that when soybean is intercropped with sorghum, volatile emissions would be unique compared to non-intercropped plants and negatively affect the behavior of Japanese beetle. To answer this, headspace volatiles from individual soybean and sorghum plants in field plots, both intercropped and in monoculture, were collected using mobile field aeration equipment and eluted with dichloromethane in the laboratory. Orientation to single volatile extracts and the combined intercropped volatiles by P. japonica was assessed individually with Ethovision (v.16.0) and in groups of 20 within release-recapture assays deployed in environmental chambers. We found unique emissions of volatiles in monocropped compared with intercropped plants. In addition, we found these volatile blends significantly affected the subsequent behavior of P. japonica. Our work suggests there is potential in manipulating the behavior of this important invasive species using intercropping.