Plants have developed a sophisticated defense system. They can not only directly fend off herbivores by producing toxins, but also do so indirectly by emitting odorant molecules into the atmosphere that are perceived by predatory insects; these predators are lured to the attacked plant and feed on the herbivore or parasitize it – thereby providing a benefit for the plant.
Scientists at the Max Planck Institute for Chemical Ecology have discovered that saliva from tobacco hornworm larvae (Manduca sexta) activates a substance in tobacco leaves, producing an odorous attractant. The attractant is picked up by carnivorous insects that feed on the hornworm larvae and eggs.
(Via) Press release PDF at Max Planck Institute for Chemical Ecology
