Literature currently available on the population dynamics of insect herbivores tends to favour top-down regulation of abundance by the action of natural enemies. This unique volume challenges this paradigm and shows that tree dwelling species of aphids, through competition for resources, regulate their own abundance. The biology of tree dwelling aphids is examined, particularly their adaptation to the seasonal development of their host plants. When host plant quality is favourable aphids, by telescoping generations, can achieve prodigious rates of increase, which their natural enemies are unable to match. Using analyses from long-term population studies and experiments, this book introduces students and research workers to insect herbivore-host dynamics using the interaction between aphids and trees as a model.