Experiments were conducted in a growth chamber, greenhouses, and orchards to determine the level of infestation, behavior, and survival of larvae from European corn borer, Ostrinia nubilalis (Hübner), races and a population on apple cultivars. Field infestations of apple shoots with either eggs or first instars of three races yielded no establishment. In a greenhouse test with potted scions, however, a bivoltine race responding to a predominately E pheromone mix, produced significantly more dead shoots than other infestations. Greatest shoot mortality in the greenhouse was caused by infestations with fourth instars. In growth-chamber tests, neonate larvae displayed a low degree of establishment on fruits, but where there was establishment, fruit entry increased proportionately with instar. Cultivars in both the orchard and the growth chamber were not equally susceptible to larval entry into fruits. Bivoltine races responding to E or Z pheromone blends entered orchard fruits to a greater degree and caused more damage than did a univoltine race responding to a Z pheromone blend.