Plant responses to herbivore attack.

(a) Leaf damage induces local defensive responses, including the production of compounds that travel through the plant and cause defence responses elsewhere. In addition, insect mouth secretions and tissue damage may cause the attacked plant to release volatile compounds. These volatile compounds foster the development of defences in undamaged parts of the same plant. (b) Such volatile compounds may also induce defences in neighbouring plants, which then become less vulnerable to herbivores. Volatile compounds may also attract predators that feed on the herbivore attacker.