14.4. Chemical defenses
Chemicals play vital roles in many aspects of insect behavior. In Chapter 4 we considered the use of pheromones in many forms of communication, including alarm pheromones elicited by the presence of a predator. Similar chemicals, called allomones, that benefit the producer and harm the receiver, play important roles in the defenses of many insects, notably amongst many Heteroptera and Coleoptera. The relationship between defensive chemicals and those used in communication may be very close, sometimes with the same chemical fulfilling both roles. Thus, a noxious chemical that repels a predator can alert conspecific insects to the predator’s presence and may act as a stimulus to action.
In the energy—time dimensions shown in Fig. 14.1, chemical defense lies towards the energetically expensive but time-efficient end of the spectrum. Chemically defended insects tend to have high apparency to predators, i.e. they are usually non-cryptic, active, often relatively large, long-lived, and frequently aggregated or social in behavior. Often they signal their distastefulness by aposematism — warning signaling that often involves bold coloring (see Plates 5.6 & 6.2) but may include odor, or even sound or light production.
(After Malcolm 1990)