The European corn borer, an important pest of maize in Southern Germany was found in Northern Germany in 1983 and 1984. A light infestation was recorded in the area of Osnabrück feeding on mugwort. In the area of Recklinghausen it was found with a high population in mugwort and also at low population levels in maize. The appearance in maize was correlated with the degree of infestation in nearby mugwort. Tests in the field and in the laboratory have shown that the borer has adapted to the climate in Northern Germany and formed a lowtemperature- race. Therefore, a complete development of the larvae in maize before harvesting is possible. These results indicate that the borer may spread throughout maize crops in Northern Germany. Possible prophylactic control-mefsures are discussed.