Expecting the unexpected: Plant-mediated and indirect effects of biopesticides on arthropod pests and their natural enemies

While direct effects of biopesticides, such as those of plant and microbial origin, on various organisms have been extensively documented, the interactions between biopesticides and plants have been largely neglected. Plant-based (bio) pesticides can include metabolites that signal stress or imminent herbivore attack, activating plant signaling pathways and gene expression involved in antiherbivore defenses. Similarly, entomopathogenic microbes can adopt an endophytic lifestyle, colonizing or being recognized by crop plants and inducing a primed state that makes plants more resistant to subsequent arthropod pest infestations. Besides effects within the biopesticide-treated plants, we predict that biopesticides can influence multitrophic interactions in the agroecosystem due to their interactions between treated and neighboring nontreated plants, as well as indirect effects from volatile organic compounds released by biopesticides on the plant surface, which arthropod pests and their natural enemies use as cues for finding hosts or food resources. Here we review and interpret empirical studies examining plant-mediated effects and indirect effects of biopesticides on arthropod pests and their entomophagous biological control agents in the context of pest management. Unlike synthetic pesticides, most studies indicate conducive effects of biopesticides for pest management, considering the interactions among plants, pests, and natural enemies. However, further efforts to understand plant-mediated and indirect effects of biopes ticides on interactions with natural enemies and plant–plant communication are needed to optimize their use in sustainable pest management strategies.