Multifunctionality of plant VOCs in agroecological systems: perspectives for biological pest control

Plant volatile organic compounds (VOCs) convey chemical information that mediates ecological interactions in plant-insect and plant-plant communication. Plant VOCs are important for biological pest control, as such chemical compounds have an ecological role in regulating pests either by deterring herbivores from feeding or oviposition, or indirectly by attracting natural enemies of herbivores. Plants that receive VOCs from herbivore-infested neighbours may also enter into an "alarmed" state in which they are primed and prepared to respond more strongly to future herbivore attacks. In this review, we focus on the role of plant VOCs as mediators of ecological multitrophic interactions in agroecological systems. We argue that-to fully elucidate the ecological role of VOCs and to effectively design biological control programs targeting plant VOCs-it is crucial to consider the multifunctional role of such volatile compounds. In fact, the same compound may serve different functions depending on the specific interplay of interacting organisms. We propose three different strategies for implementing plant VOCs in biological pest control: 1) breeding for plant VOCs to enhance recruitment of natural enemies; 2) using companion plants to promote crop resistance and biological control; 3) delivering VOCs into agroecosystems using novel technological advances. We conclude that plant VOCs hold promising potential for the development of sustainable control practices, although their current applications remain limited. We also identify important knowledge gaps, and the research needed to facilitate the implementation of plant VOCs in biological pest control.