Herbivore-induced plant volatiles specificity

Variability in induced plant volatiles complicates the reliance of natural enemies on these cues. One way of dealing with variability is through associative learning, which may allow parasitoids to learn which cues are most likely to lead them to suitable hosts at a particular time in a particular area. Moreover, recent studies suggest that plant volatile blends alone carry specific information on the herbivores by which they are attacked. For example, predatory mites can distinguish between the blends of apple trees infested by two herbivores species (20). Du et al. (21) showed that different aphid species elicit different volatile blends in bean plants and that the aphid parasitoid, Aphidius ervi, can use these differences to distinguish plants infested by its host. Aphis pisum from those infested by a nonhost. Aphis fabae... 

As yet, there is no specific pattern in how induced volatiles affect the attractiveness of plants to herbivores. Obviously, the responses will be correlated with fitness consequences. Insects vulnerable to natural enemies and induced plant toxins are, therefore, expected to avoid induced plants, whereas those that are adapted to plant defenses and/or benefit from aggregating are likely to be attracted. Comparative studies could test such hypotheses. 

This rather unspecific induction of nectar secretion in cotton was surprising in light of the fact that the induction of volatile emission by this plant had been demonstrated to be specific. Herbivore-damaged plants show a higher rate of volatile emission compared with mechanically damaged plants (McCall et al, 1994), and herbivore feeding induced de novo synthesis of various terpenoids (Pare and Tumlinson, 1997), which resulted in a quantitative as well as a qualitative response to herbivory. The specificity of the plant response is not restricted to the differentiation between mechanical damage and herbivory. The composition of the induced volatile blend also varies between (even closely related) herbivore species (De Moraes etal, 1998). 

Ozawa, R., Arimura, G., Takabayashi, J., Shimoda, T. and Nishioka, T. (2000). Involvement of jasmonate- and salicylate-related signaling pathways for the production of specific herbivore-induced volatiles in plants. Plant and Cell Physiology 41 391-398. 

Plants respond to the mechanical or insect herbivore damage of their tissues." During herbivorous attacks, some plants emit a specific blend of volatiles, which may result in defense responses retarding development of the herbivores or attraction of herbivore enemies to feed upon them. In lima bean leaves, the spider mite-induced volatiles, as well as infestation and artificial wounding, activate the ethylene and JA signaling pathways. ... 

Plants respond to herbivory by producing volatiles that in turn attract carnivorous natural enemies of the herbivores. These volatiles are produced by the plants as a specific response to herbivore damage or mainly as a result of mechanical damage. These so-called HIPVs attract carnivores, which in turn reduce the damage caused by herbivorous arthropods. These chemical alarm calls thus represent an example of induced indirect... 

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