Species interact in a complex system with many relationships among them. However, a single species is often studied with respect to only one other species. This project will conduct field and laboratory experiments to examine how a second herbivore species affects the interactions in a plant-herbivore-parasite system. It will examine the role of aphids, which are plant sap feeders, on tobacco-caterpillar-wasp interactions, and examine how the presence of aphids change plant chemistry, which may alter the way a caterpillar and parasitic wasp interact. The growth rates of parasites and herbivores, parasite preference, egg-laying decisions of moths, and parasite infestation rates will be measured. Lastly, this project will examine how spatial scale alters the outcome of these interactions. This work will broaden our understanding of how community composition alters the outcomes of multi-species interactions, support the disseration research of a doctorate student, and provide undergraduate research experience in the field of ecology.