Raspberry cane midge (Resseliella theobaldi) is widespread in Europe on raspberries, both in field grown crops and under protected cultivation. Eggs laid in natural splits or wounds in the bark of primocanes result in larvae that feed on the newly exposed periderm layer. These feeding sites are colonized by a range of pathogenic fungi causing the disease complex 'midge blight'. Yield losses frequently exceed 50%, often making the crop unprofitable to harvest. Effective control of midge blight relies on accurate timing of sprays of insecticides directed against the first generation midge eggs and resultant larvae laid by overwintered females in the spring. Previous research has shown that start of egg laying is influenced by many factors including topography, altitude and aspect. One objective of a 2-year project (1998-99), 'Reduced Application of Chemicals in European Raspberry production (RACER)', funded by EU-Craft and BBW (Switzerland) was to test a model previously developed in the United Kingdom of midge emergence at other locations in Europe. In the UK, the date of emergence and oviposition by overwintered females is dependent on accumulated 10 cm soil temperatures. Based upon research at the Scottish Crop Research Institute, it has been calculated that midge eggs are first observed once a total of 326 Degree Days above a base of 4?C from 1 February has been achieved. Observation elsewhere in Europe suggests that this empirical model required modification to accommodate local climatic conditions. The methodology used to determine the thermal time requirements for a range of geographical locations is discussed.