Semiochemical parsimony in the Arthropoda.

A wide variety of arthropods have adapted their own semiochemicals to subserve multiple functions in diverse contexts. Semiochemicals, the pheromones and allomones, have been detected in arthropod species in six orders, and it has been clearly established that these compounds are used with great parsimony. The versatility of these invertebrates in using these natural products for an incredible diversity of functions emphasizes the significance of semiochemicals in the evolutionary biology of Arthropoda. Multifunctional pheromones have proved to be especially characteristic of the queens of eusocial species. Compounds such as the queen substance of the honey bee, Apis mellifera, possess unrelated primer and releaser functions for the workers and act as a sex attractant for drones. Females of other hymenopterous species exploit the secretions of sting-associated glands as sex pheromones, whereas a variety of nonhymenopterous species have adapted components in diverse defensive secretions to function as sex pheromones. The alarm pheromones of many arthropods are also used as defensive allomones, activity inhibitors, cryptic alarm pheromones, aggregative attractants, robbing agents, digging agents, trail pheromones, and antimicrobial agents. Defensive allomones also possess some of these parsimonious roles; in addition, however, some of these compounds possess highly distinctive roles, such as functioning as lethal attractants for prey, or, in he aquatic milieu, cuticular wetting agents. Clearly, the availability of a variety of pheromones and allomones has enabled arthropods to evolve an elegant semiochemical parsimony with which to exploit the biological milieu.