Aster yellows is a disease of vegetable crops that is caused by a phytoplasma and vectored by the aster leafhopper. The phytoplasma invades the cells of both the insect and the plant host. The aster leafhopper has a very broad plant host range, and the plant host range of the phytoplasma is equally broad. Therefore, this phytoplasma requires adaptation to two kingdoms and a wide range of species, environments and ecosystems. Molecular analysis of the phytoplasma genome has provided new insights into the evolutionary history and adaptation of this pathogen to both insects and plants. The phytoplasma genome is small and rich in repeated DNA sequences, which appear to provide a mechanism for recombination and adaptability to the diverse environments in which they reproduce. Molecular detection of the phytoplasma has greatly facilitated research at the population and ecosystem scales. Rates of pathogen reproduction in both insects and plants leads to the observed pattern of disease in vegetable crops, with lettuce being the most susceptible to loss. Under typical Ohio environmental conditions, the development rate of the pathogen is such that the disease cycle takes place just once in any given lettuce field, but aster leafhopper dispersal between fields and multiple plantings throughout the growing season can lead to increasing proportions of infected plants over a growing season and production area-wide epidemics. Research on leafhopper dispersal behavior and rates led to an ecosystem level simulation of the epidemiology of the disease. Based on these simulations, the spatial pattern of fields, detection of the phytoplasma in immigrating aster leafhoppers and timing of control of the vectors are the key elements of an integrated approach to managing aster yellows.