Generalist and sticky plant specialist predators suppress herbivores on a sticky plant
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Glandular trichomes are conventionally viewed as a type of direct defense against herbivores that carry indirect costs associated with the exclusion of numerous predators. We tested the hypothesis that predators are ineffective on sticky plants using a predator that is adapted to sticky plants, the harpactorine assassin bug Pselliopus spinicollis Champion, and a common surrogate generalist predator in analogous studies, the coccinellid Hippodamia convergens Guerin. We tested their top–down effects on herbivores using sticky and non-sticky races of common madia plants (Asteraceae: Madia elegans) and their native herbivores, a noctuid moth (Noctuiidae: Heliothodes diminutiva Hodges) and an aphid (Aphididae: Uroleucon madia Swain). We report that both predators were effective at reducing herbivore abundances on sticky and non-sticky plants, with greater efficacy on sticky plants.
KeywordsEnemy-free space Glandular trichomes Indirect defense Natural enemies Sticky plant specialist Tritrophic
We thank Clara LaPeyre, George Zaragoza, Ashley Adams, and Lindsey Hack for assistance in the field and laboratory, Virginia Boucher and Stebbins Cold Canyon UC Reserve for access to natural tarweed and arthropod populations, Jay Rosenheim, Louie Yang, and Rick Karban for helpful comments on the manuscript, an anonymous reviewer for careful and thoughtful comments that improved the manuscript, and Briggs Hall Janitorial staff for letting us use the courtyard for the experiment. This project was supported by a Robert van den Bosch Scholarship for Biological Control to BAK.
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