THE CHEMISTRY OF EAVESDROPPING, ALARM, AND DECEIT

Arthropods that prey on or parasitize other arthropods frequently empl oy those chemical cues that reliably indicate the presence of their pr ey or hosts. Eavesdropping on the sex pheromone signals emitted to att ract mates allows many predators and parasitoids to find and attack ad ult insects. The sex pheromones are also useful signals for egg parasi toids since eggs are frequently deposited on nearby plants soon after mating. When the larval stages of insects or other arthropods are the targets, a different foraging strategy is employed. The larvae are oft en chemically inconspicuous, but when they feed on plants the injured plants respond by producing and releasing defensive chemicals. These p lant chemicals may also serve as ''alarm signals'' that are exploited by predators and parasitoids to locate their victims. There is conside rable evidence that the volatile ''alarm signals'' are induced by inte ractions of substances from the herbivore with the damaged plant tissu e. A very different strategy is employed by several groups of spiders that remain stationary and send out chemical signals that attract prey , Some of these spiders prey exclusively on male moths. They attract t he males by emitting chemicals identical to the sex pheromones emitted by female moths. These few examples indicate the diversity of foragin g strategies of arthropod predators and parasitoids. It is likely that many other interesting chemically mediated interactions between arthr opod hunters and their victims remain to be discovered. Increased unde rstanding of these systems will enable us to capitalize on natural int eractions to develop more ecologically sound, environmentally safe met hods for biological control of insect pests of agriculture.