Herbivore population dynamics can be influenced significantly by heterogeneity in plant quality. Birth and death rates of herbivores are influenced by plant-induced changes in parameters such as growth, survival, and fecundity. Variation in plant quality can also have a profound influence on herbivore populations through changes in rates of movement, mortality due to natural enemies, and rates of competition. We should also expect that the strength of density dependence, and herbivore population dynamics, will vary with host plant quality. This thesis examines the impact of variable plant quality on the dynamics of an insect herbivore population. This is done using both aphid population data collected from a common garden of six different species of Asclepias plants and some simple models of hypothetical populations to further explore the consequences of variable plant quality.