A<unk>  is a chemical that triggers a natural behavioral response in another member of the same species. There are alarm<unk> s, food trail<unk> s, sex<unk> s, and many others that affect behavior or physiology. Their use among insects has been particularly well documented, although many vertebrates and plants also communicate using<unk> s.
Pheromone
Hymecromone
Theobromine
Octopamine
Dopamine
Thiotepa
Albitocin
Epinephrine 