Herbivore- induced plant volatiles: targets, perception and unanswered questions

Plants respond to mechanical wounding, herbivore feeding or infection by pathogens with the release of volatiles. Small C-6 molecules termed green-leaf volatiles form a general element in most of these blends; however, the overall composition is usually sufficiently specific that other organisms are able to determine the nature of the attacker. Receivers of herbivore-induced volatile organic compounds (HI-VOCs) comprise distant parts of the same plant (within-plant signalling'), neighbouring plants (plant-plant signalling'), herbivores, and multiple carnivores that respond to the plant's cry for help', such as parasitoids and hyperparasitoids, entomopathogenic nematodes, and predatory mites, beetles, bugs and birds. In spite of intensive research efforts, many central questions still remain. How do plants perceive volatiles? What is the relative impact of each of the interactions with different receivers of HI-VOCs on the fitness of the emitting plant and that of the interacting organisms? How long can these compounds remain stable in the atmosphere? Why are VOC-mediated effects on herbivores and beneficial organisms not used as a common tool in sustainable agriculture? Here, I briefly summarize the ecological effects of HI-VOC perception and discuss the most pertinent questions raised by participants at the 32(nd)New Phytologist Symposium in Buenos Aires.