DISSERTATION RESEARCH: Predicting the Combined Effects of Plant Resistance and Natural Enemies on Plant Fitness

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ABSTRACTPlants often produce chemical defenses that reduce herbivore feeding, but those chemicals may also have a negative effect on predators which, by attacking herbivores, also reduce herbivore damage to plants. This research asks whether the negative effect of plant defense on predators is sufficient to cause more chemically defended plants to grow less well or to produce fewer seeds; in addition, the PIs will detect whether the degree of interference between chemical defense and predators differs for different types of plants, herbivores, and predators. Using beetles feeding on soybean plants, earlier work found that a predator was more effective in decreasing herbivore damage and increasing seed production on plants with few resistance chemicals than on heavily defended plants. In this research, we will explore whether the negative effect of soybean defense on predators is influenced by the type of chemical defense (permanent vs. transient), the diet breadth of the herbivore (a single vs. multiple plant species), and the predator's feeding method (consuming the prey externally vs. as an internal parasite). These experiments may help to explain why some plant species produce defenses only after they receive herbivore damage, while other plants are always defended. The results of these experiments should improve our understanding of when plant chemical defense will enhance or detract from the positive benefits plants receive when predators attack herbivores, and could also could help to determine when releasing predators to control insect pests on soybeans and other agricultural plants may be more or less effective.