Plant Volatile Signals in Response to Herbivore Feeding

A surge in release of volatiles by several plant species can be observed in response to insect feeding. Oral secretions from these feeding herbivores provide the initial chemical signal that triggers the release of plant volatiles; one or more elicitors from the oral secretion allow the plant to identify and differentiate herbivore feeding from mere mechanical wounding. Elicitor(s), in combination with mechanical wounding, trigger the release of compounds both locally and systemically. These volatiles, which may be a blend of constitutive and induced compounds, vary in their relative and absolute concentration over time. They serve as easily detectable and distinctive chemical cues for predators and parasitoids of the herbivores feeding on the plants. Volatile compounds released from herbivore infested plants include the monoterpenes and sesquiterpenes of the isoprenoid pathway, green leaf volatiles of the fatty acid/lipoxygenase pathway and aromatic metabolites, such as indole and methyl salicylate, of the shikimic acid/tryptophan pathway.