Intercropping alters phytochemicals associated with insect herbivory

Authors: FYIE, JARROD - The Land Institute; STRATTON, CHASE - The Land Institute; Morrison Iii, William; MURRELL, EBONY - The Land Institute

Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/5/2024
Publication Date: 3/21/2025
Citation: Fyie, J.Q., Stratton, C.A., Morrison III, W.R., Murrell, E.G. 2025. Intercropping alters phytochemicals associated with insect herbivory. Journal of Chemical Ecology. https://doi.org/10.1007/s10886-025-01555-9.
DOI: https://doi.org/10.1007/s10886-025-01555-9

Interpretive Summary: Plants produce natural chemicals called phytochemicals to protect them against pathogens and insect feeding. Many environmental factors can influence the abundance and types of phytochemicals produced by plants, including a practice called intercropping in which two or more crops are grown together in a single field. This is often done to improve resilience of the crops against insect pests. Despite the importance of phytochemicals and intercropping in crop production and protection, it is not known specifically how phytochemical production is impacted by intercropping and how that relates to resistance against insect feeding. To address this, we studied volatile compounds produced by wheat and sweetclover when they were was intercropped with silflower, a crop that has resistance against several insect pests. We also studied volatiles before and after challenge with fall army worm, a notorious pest of many crops in the Great Plains region. In wheat, we discovered a novel compound that was present only when it was intercropped with silflower that was produced regardless of insect feeding. When grown alongside silflower and exposed to fall army worm, sweetclover produced volatiles that resemble compounds produced by silflower. Specifically, these volatiles included terpenes, a class of chemicals that is linked to plant defenses and may be linked to resistance to insect feeding. Altogether, these results support the role of intercropping in influencing volatile compounds, particularly those that can inhibit insect feeding, which can increase agricultural sustainability without the input of pesticides.

Technical Abstract: Given the multiple mechanisms for interspecific chemical interaction between adjacent or common mycorrhizal network (CMN)-connected plants, phytochemical defenses of pest-susceptible crop species may be enhanced or altered by intercropping with phytochemically diverse neighbors. We assessed the influence of belowground connection (mediated by arbuscular mycorrhizal fungi [AMF] or root-based allelopathy) between phytochemically diverse plants on aerial volatile organic compound (VOC) emission profiles by intercropping Melilotus alba and Triticum aestivum with Silphium integrifolium in AMF-inoculated soil. To assess the impact of belowground connection on herbivorous pest performance, we conducted an in-situ, no-choice bioassay with Spodoptera frugiperda. This study shows evidence for communication between silflower and neighboring sweetclover and wheat in a way that may influence in-field pest dynamics. The presence of a novel bioactive compound in wheat grown with silflower suggests belowground chemical interactions occur between these plant species, and aboveground biomass growth demonstrates modest facilitation when they are grown in biculture. Sweetclover grown in biculture with silflower responds to fall armyworm infestation in a way that more closely approximates the volatile profile of silflower, which is a poor host plant for fall armyworm. Furthermore, the overall volatile profile in biculture plants shifted toward terpenes that are more prominent in silflower than sweetclover or wheat. These results support further research into the role of belowground plant-plant interactions on pest dynamics in agroecological systems as a means to improve agricultural sustainability.