As I remember it, the word "hormone" was coined from a Greek word for "messenger."

Hormones are found in plants as well as in animals. I remember reading over twenty years ago about resistance to Gypsy moth infestation arising in trees well removed from initial invaded tree, and apparently mediated by something in aerosols release from leaves being chewed by the moth larvae.Increased tannin in the leaves reached levels toxic to the larvae.

In the latest Discover magazine there is an article aboutmany different kinds of plants emitting aerosols that attract predators of the insects that are damaging them.No name is given to these agents.

Would "hormone" be appropriate in this case?