Investigating a Semiochemical-Based Mechanism for the Beneficial Activity of Sorghum Intercropped with Soybeans on Management of Popillia Japonica.

Japanese beetle, Popillia japonica Newman, is an invasive species that attacks many field and ornamental crops. Intercropping soybean with sorghum is suggested as a strategy to reduce the abundance of P. japonica throughout soybean fields. The mechanism by which this affects P. japonica is unknown but may arise from a difference in the host plant compounds emitted by the intercropped plants because P. japonica responds to olfactory cues. In this study, we investigated a semiochemical-based mechanism for the behavioral response of P. japonica to intercropping soybean with sorghum by (1) evaluating P. japonica behavioral responses to solvent extracts from monocropped soy, intercropped soy, and a mixture of soy and sorghum extracts in no-choice video-tracking and preference in a release-recapture dual-choice assay to host stimuli from plants; and (2) applying solid-phase microextraction (SPME) in conjunction with gas chromatography coupled with mass spectrometry (GC-MS) to characterize the semiochemical profiles of each extract. We found unique semiochemical profiles among our treatments, with 1-octen-3-ol and 1-octanol characteristic of monocropped soybean and dodecane-1-iodo primarily in sorghum extracts. Nevertheless, our treatments did not significantly affect movement or orientation by P. japonica compared to controls, nor did conspecifics exhibit a significant preference for any of the treatments in a dual-choice assay at a local scale. Therefore, if intercropping soybean with sorghum significantly affects the behavior of P. japonica in the field, it may occur at a different scale, or in response to non-olfactory stimuli (e.g., visual, habitat, or landscape cues) rather than semiochemical cues.