Plant communication - why should plants emit volatile cues?

There are now approximately 10 documented examples of volatile plant communication that affect resistance to herbivores. For several of these cases, plants have been found to experience fitness benefits by responding to information (cues) released by experimentally damaged neighbors. However, it remains puzzling why plants might emit these cues following herbivore attack. One possibility is that release of cues is not adaptive for the emitter but rather cues leak out as a consequence of damage. Hypothetical benefits of emitting cues include: repelling herbivores; attracting predators of herbivores; suppressing germination of competitors; communicating with other branches of the same plant; and communicating with genetic relatives. Progress will be made in this field if we can find a system that is more tractable, allowing the nature of the cue to be identified and manipulated or allowing us to examine genetic constraints and influences on communication.