D3044: 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 Popillia japonica is intercropping soybean with sorghum, which is claimed to disrupt movement and reduce abundance. However, the mechanism by which intercropping affects P. japonica behavior 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 aimed to identify whether plant volatiles play a key role in repellence of P. japonica from sorghum-intercropped soybean fields. We hypothesized that when soybean is intercropped with sorghum, plant volatiles would be unique compared to non-intercropped plants and negatively affect the behavior of Japanese beetle. To answer this, leaf samples were extracted with dichloromethane to obtain solvent-soluble volatile and semi-volatile organic compounds from individual soybean and sorghum plants in both intercropped and monoculture field plots. Orientation to single volatile extracts and the combined volatiles by P. japonica were assessed by tracking individual P. japonica with Ethovision (v.16.0). Dual-choice feeding assays were also conducted using release-recapture assays in large containers deployed in environmental chambers. We found no repellent effect of sorghum on Japanese beetle behavior in the extract assays. We also found no preference to any treatment within the feeding assays. This suggests that factors other than leaf volatile chemistry, such as plant structure or microhabitat differences, may underlie any deterrent effect of sorghum–soybean intercropping.