Predatory mites learn to discriminate between plant volatiles induced by prey and nonprey herbivores

Abstract

Many carnivorous arthropods can use chemical information from plants to locate their herbivorous prey. The composition of blends of herbivore-induced plant volatiles can vary with plant and herbivore species and thus carnivores are confronted with variable information about the presence of their prey. Such environmental variation is expected to favour learning. We investigated the learning ability of the predatory mite Phytoseiulus persimilis, a specialized natural enemy of polyphagous spider mites. We reared mites on different plant species, and subsequently tested their preference for volatiles from lima bean plants infested with either the prey herbivore Tetranychus urticae or the nonprey caterpillar Spodoptera exigua in a Y-tube olfactometer. Predators reared on lima bean preferred the volatiles induced by T. urticae, whereas predators reared on cucumber did not. We also investigated the foraging behaviour of mites after a nonrewarding experience during the adult phase (i.e. food deprivation in the presence of S. exigua-induced volatiles from lima bean) or after a rewarding experience (i.e. feeding in the presence of T. urticae-induced volatiles). The rewarding experience had a much larger impact on the foraging responses. Predatory mites with multiple experiences (i.e. a nonrewarding experience followed by a rewarding experience) had the strongest preference for T. urticae-induced versus S. exigua-induced volatiles. We conclude that these learning abilities enable the predatory mites to forage in an environment where their prey can feed on a different plant species than the one on which the predator developed, and where nonprey caterpillars are also present.