To grow and reproduce, plants must have some defense against herbivores that eat them. One form of defense is to call for help from other insects. As stated in the ancient proverb, “The enemy of my enemy is my friend.” Herbivores that feed on plants can have many enemies, including parasitoid wasps.The majority of wasps (order Hymenoptera) are parasitoids. Parasitoids lay their eggs inside other insects. The parasitoid larvae consume the tissue of their host and kill it. Parasitoids must be able to find potential hosts in order to be successful. Finding small caterpillars or other hosts in a complex maze of plant foliage can be a daunting task. Many parasitoids rely on odors to locate hosts.
When caterpillars or other herbivores feed on plants, the feeding damage releases volatile chemicals. These chemicals benefit parasitoid wasps that use the odors to find hosts. The odors benefit the plant because they attract parasitoids that reduce damage from herbivores. Plants that release characteristic odors in response to insect feeding damage can get a little help from their parasitoid friends.