Response of a Phytoseiid Predator to Herbivore-Induced Plant Volatiles: Selection on Attraction and Effect on Prey Exploitation

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Bean plants infested with herbivorous spider mites emit volatile chemicals that are attractive to P. persimilis, a predator of spider mites. In Y-tube olfactometer tests we evaluated involvement of a genetic component in predator response to herbivore-induced plant volatiles. Replicated bidirectional selection resulted in a significant increase in attraction after one generation of selection, but no decrease even after three generations of selection, indicating significant, but unbalanced, additive genetic variation in predator perception of, or response to, herbivore-induced plant volatiles. Selected lines responded differently than an unselected population to food deprivation, pointing to an interaction between their internal state and response to plant volatiles. Selected lines also differed from unselected ones in behaviors associated with local prey exploitation, such as residence time, prey consumption, and reproduction. At lower prey densities, P. persimilis from both "+" lines left spider mite-infested leaves more rapidly and consumed fewer prey eggs than an unselected population. Defining olfactory components of predator search behavior is one step in understanding the effect of plant volatiles on predator foraging efficiency. By selecting lines differing in their attraction to herbivore-induced plant volatiles we may experimentally investigate the link between this behavior, predator foraging efficiency, and local and regional predator-prey population dynamics. The impact of significant additive genetic variation in predator response to plant volatiles on evolution in a tritrophic context also remains to be uncovered.

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