Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to impact the behavior of the receiving individuals. Pheromones of certain pest insect species, such as the Japanese beetle, acrobat ant, and the gypsy moth, can be used to trap the respective insect for monitoring purposes, to control the population by creating confusion, to disrupt mating, and to prevent further egg laying.

Figure 1.1: (S)-Ipsdienol is a terpene alcohol and is one of the major aggregation pheromones of the bark beetle. It was first identified from Ips confusus, in which it is believed to be a principle sex attractant

When a female bark beetle produces and secretes a sex pheromone in order to attract a mate, the pheromone can be carried on currents of air to male bark beetles, whose antennae can intercept individual pheromone molecules, completely intact, still in the same form as when they were secreted by the female, no matter how far away she is. The male recognizes the structure of the molecule; it can clearly tell if it has just intercepted the proper pheromone or some subtle imposter that also happens to have the formula C₁₀H₁₆O.