Volatile organic compounds diversity mediates tree diversity–insect herbivory relationships

The effects of plant diversity on insect herbivory are inconsistent in the literature, highlighting the need for further mechanistic understanding. Plant volatile organic compounds (VOCs) are influenced by plant diversity and related to insect herbivory. However, the role of VOCs in mediating plant diversity effects on insect herbivory remains poorly explored. Here, we investigated chewing insect herbivory of 128 818 leaves from 2606 trees, measured leaf VOCs from 137 tree individuals and assessed tree growth across a tree species richness gradient in a biodiversity–ecosystem functioning experiment in southern China. We aimed to explore the mechanisms underlying tree diversity effects on insect herbivory by examining the roles of plant VOCs. Results showed that tree species richness had overall negative effects on insect herbivory. These negative effects were partially offset by an indirect positive pathway in which increased community‐level VOC diversity heightened herbivory. However, the effects were also reinforced by an indirect negative pathway in which VOCs inhibited tree growth and consequently reduced herbivore damage. Overall, VOC‐mediated pathways were driven primarily by community‐level VOC diversity rather than by emissions of individual compounds. Our study pioneers the integration of VOCs into the well‐established framework of associational effects, demonstrating the critical role of VOC diversity in mediating the relationship among plant diversity, plant growth and insect herbivory. These findings underscore the significant contribution of phytochemical diversity to plant–herbivore interactions.