The description of mechanisms underlying biological diversity is a keystone of ecological research. It is well accepted that diversity can play fundamental roles determining the stability of natural systems as well as the trajectories of species interactions. For plant-herbivore interactions in particular, the relationship between host-plant diversity and their natural enemies has been extensively studied in all terrestrial ecosystems. Nonetheless, the diversity of chemical defenses and their effects on plant-herbivore interactions, whether at the species or the community level, is a dimension of diversity that has seldom been the focus of ecological research. Recently, interdisciplinary collaborations, modern analytical techniques, and a small number of groundbreaking studies have awakened greater interest on this topic. At this organized oral session speakers will present new findings and novel approaches of this promising new field of study that tackle classical ecological questions.