COLLABORATIVE RESEARCH: What makes a generalist herbivore? The interplay between top-down and bottom-up forces on herbivore diet breadth

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One-third of all species on Earth are insects that eat plants (herbivores) and they are key to environmental health. For example, insect herbivores are food for other animals, such as birds, snakes, and mammals. Insect herbivores pollinate flowering plants, however they can also be pests of food crops which can reduce our food supply. Thus, to conserve natural habitats and our food supply, we must know how insect herbivores are affected by their food plants and by the animals that eat them. After decades of research, we still do not know why insect herbivores feed on particular plants. Even though very few insect herbivores are generalists which feed on many different types of plants, generalists are the most damaging pests of crops. This research will study a common generalist herbivore to answer: What allows generalist herbivores to use new plants or to feed on many different types of plants? Answering this question is key for knowing when and how pests spread onto different crops. This project will educate elementary, middle, high school, and college students. A science camp for middle school girls from low income families will be established by this project.One of the major unresolved questions in biology is to understand why there are so many different species. Insect herbivores are an ideal study group for this question because they are so diverse. Host plant use is an important driver of insect herbivores’ diversification, however, most studies examining the link between diet breadth and insect herbivore evolution focus on specialist herbivores. Focusing on specialists does not tell us which factors lead herbivores to specialize or to maintain generalism. By focusing on generalists, this project will study how selective forces from host plant use and natural enemies can lead to diet expansion or contraction, and thereby affect the evolution and diversification of insect herbivores. Using a generalist herbivore (fall webworm, Hyphantria cunea) that feeds on over 400 plant species across a wide geographic range, this project will: 1) Determine whether diet breadth is a population or individual-level trait, and test for the genetic basis of diet breadth using a candidate gene approach; 2) Investigate if local adaption to host plants is predicted by diet breadth; 3) Test how natural enemy composition and abundance affect herbivore diet breadth; 4) Test if escape from natural enemies explains diet expansion to poor quality hosts; and 5) Examine how the interplay of selective forces from host plants and natural enemies may change over time. This research will provide critically needed tests of how selective forces influence generalist herbivores and diet breadth evolution.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.