Oral secretions: A key molecular interface of plant–insect herbivore interactions

The oral secretions of insect herbivores are complex mixtures of organic and inorganic solutes and enzymes that are deposited onto plant tissues during the feeding process. Some specific components of insect oral secretions have been shown to confer important functions in mediating plant-insect interactions at the molecular level. In this review, we examined the biochemical studies of insect oral secretions to summarize the current knowledge of their compositions. We then moved beyond the functional studies of components of oral secretions, and focused on the literature that pinpointed specific molecular targets of these compounds. Finally, we highlighted the investigations of oral secretion components in the context of insect physiology, which shed light on the potential evolutionary trajectory of these multi-functional molecules.