Herbivory by multiple arthropods does not hinder the attraction of natural enemies to plant volatiles: insights from a meta-analysis.

Abstract

Plants under herbivore attack emit herbivore-induced plant volatiles (HIPVs) that recruit natural enemies (NEs) of the herbivores for defense. The composition of HIPVs is often specific to the herbivore species, and infestation by multiple herbivore species produces a distinct volatile blend compared to single infestations, potentially influencing tritrophic interactions. Although two decades of research have investigated how multiple herbivory can affect chemically-mediated tritrophic interactions, a comprehensive understanding on this topic remains elusive, as studies have shown varying results depending on the system examined. We performed a quantitative synthesis of 29 studies, extracting effect sizes from 94 experiments that assessed the olfactory preferences of NEs for HIPVs emitted from multiple-infested and single-infested plants. Our analysis revealed that multiple infestations do not affect the attractiveness of HIPVs to NEs, regardless of whether the plant is infested by nonhosts, hosts from different or the same feeding guild, the NE dietary specialization, or guild. However, specialist NEs prefer HIPVs emitted from plants with hosts even if they are infested by multiple herbivores over those infested by only a single non-host herbivore. Our meta-analysis provides valuable insights into the complexity of chemically-mediated tritrophic interactions, demonstrating that the co-infestation with nonhosts or multiple hosts do not affect attractiveness of HIPVs to NEs.