The variation in number of European pine sawflies,Neodiprion sertifer(Geoffroy), caught in pheromone traps during 11 d of the peak flight period was in part explained by the weather, measured by a weather station at the study site. Daily average air temperature was the most important variable and was positively related to the log catch; it explained 86% of the variation. A threshold for flight was determined to be ≍+ 11°C. Rain during most of the day inhibited flight, but occasional showers did not. Wind velocity and humidity did not increase the explained part of the variation significantly in a multiple regression model after inclusion of air temperature. Trap sample and weather-recording intervals<1 d did not enhance the correlations. An all-season study showed low correlation between catch and temperature because of varying background population and a considerable distance to the meteorological stations where the temperature data were collected.