Indirect cost of a defensive trait: variation in trichome type affects the natural enemies of herbivorous insects on Datura wrightii

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Abstract
The costs and benefits of defensive traits in plants can have an ecological component that arises from the effect of defenses on the natural enemies of herbivores. We tested if glandular trichomes in Datura wrightii, a trait that confers resistance to several species of herbivorous insects, impose an ecological cost by decreasing rates of predation by the natural enemies of herbivores. For two common herbivores of D. wrightii, Lema daturaphila and Tupiocoris notatus, several generalized species of natural enemies exhibited lower rates of predation on glandular compared to non-glandular plants. Lower rates of predation were associated with reductions in the residence time and foraging efficiency of natural enemies on plants with glandular trichomes, but not with direct toxic effects of glandular exudate. Our results suggest that the benefit of resistance to herbivores conferred by glandular trichomes might be offset by the detrimental effect of this trait on the natural enemies of herbivores, and that the fitness consequences of this trichome defense might depend on the composition and abundance of the natural-enemy community.