No‐choice oviposition preferences predict neighborhood effects among host plants in a model system

Abstract

Abstract Neighbouring plant species can indirectly affect each other's fitness through insect herbivores. For instance, the number of eggs an insect deposits on a focal plant can be influenced by the presence of a neighbouring plant species because of the herbivore's relative host plant preferences. Yet, the relationship between oviposition preferences (measured in no‐choice tests) and the strength and direction of such indirect effects among neighbouring plants remains poorly understood. We performed a lab experiment using bean beetles (Callosobruchus maculatus) and five species of beans to determine if beetles' no‐choice preferences for a neighbouring bean species correlated with the number of eggs laid on a focal species in two‐species environments (diculture). We predicted that as the preference for the neighbouring beans increased compared to the focal host, beetles would lay fewer eggs on the focal bean host. Across all pair‐wise combinations, our prediction was supported: as the relative no‐choice preference of neighbouring beans increased, the number of eggs laid on focal beans decreased. However, this relationship was relatively weak. We also found that beetles tended to lay more eggs in diculture compared to arenas with one bean species. These results provide empirical evidence linking herbivores' no‐choice preferences to the strength of neighbourhood effects and suggest that even within a relatively controlled environment, neighbourhood effects can be weak. Our results also highlight that unexpected changes to the total number of eggs laid by herbivores in mixed‐plant patches relative to monoculture can complicate predictions.