Inter-varietal interactions among plants in genotypically diverse mixtures tend to decrease herbivore performance
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Much research has explored the effects of plant species diversity on herbivore populations, but far less has considered effects of plant genotypic diversity, or how abiotic stressors, like drought, can modify effects. Mechanisms by which plant genotypic diversity affects herbivore populations remain largely unresolved. We used greenhouse studies with a model system of wheat (Triticum aestivum L.) and bird cherry-oat aphid (Rhopalosiphum padi L.) to determine whether the genotypic diversity of a plant’s neighborhood influences performance and fitness of herbivores on a focal plant and if drought changes the influence of neighborhood diversity. Taken across all varieties we tested, plant–plant interactions in diverse neighborhoods reduced aphid performance and generated associational resistance, although effects on aphids depended on variety identity. In diverse mixtures, drought stress greatly diminished the genotypic diversity-driven reduction in aphid performance. Neighborhood diversity influenced mother aphid size, and appeared to partially explain how plant–plant interactions reduced the number of offspring produced in mixtures. Plant size did not mediate effects on aphid performance, although neighborhood diversity reduced plant mass across varieties and watering treatments. Our results suggest inter-varietal interactions in genotypic mixtures can affect herbivore performance in the absence of herbivore movement and that abiotic stress may diminish any effects. Accounting for how neighborhood diversity influences resistance of an individual plant to herbivores will help aid development of mixtures of varieties for managing insect pests and clarify the role of plant genotypic diversity in ecosystems.
KeywordsAssociational resistance Drought Genotypic diversity Intraspecific diversity Stress
We would like to thank M.E. Barbercheck, J.P. Kaye, M.B. Thomas, and anonymous reviewers for comments that improved this manuscript. Thank you to A.M. Helms for assistance with the phytohormone component of this study. Funding was provided by a United States Department of Agriculture National Institute of Food and Agriculture Predoctoral Fellowship (Grant 11037855) to IMG.
Author contribution statement
IMG and JFT conceived and designed the experiments. IMG performed the experiment and analyzed the data. IMG and JFT wrote the manuscript.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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