We studied, over a 6-yr period, temporal dynamics of plum curculio, Conotrachelus nenuphar (Herbst.), immigration into an unsprayed section of a commercial apple orchard with the main aim of establishing the relationships between the timing of immigration, weather factors, and phenological tree stage. By using panel and pyramid traps baited with attractive synthetic odor and deployed near woods adjacent to orchard trees, we exploited the chemical cues potentially directing the spring immigration by plum curculios. On each of the 6 yr, traps were inspected on a daily basis over the entire period of plum curculio immigration, which ranged from 51 to 85 d. Across all 6 yr, most immigrant plum curculios (on average 57% of the total) potentially colonizing host trees were captured by traps by the time of petal fall. Based on our combined trapping and weather data, we propose the occurrence of pre- and postpetal fall periods of plum curculio immigration, each of which is influenced to a different extent by temperatures prevailing in spring. Only during the prepetal fall period, but not afterward, was there a strong influence of air temperature on captures by both panel and pyramid traps. Thermal constants (expressed in degree days) estimated reflected more accurately onset of plum curculio immigration than tree phenology. Our combined results indicate that the odor-baited traps evaluated can be used to predict initiation of plum curculio immigration using thermal constants and also to monitor accurately the magnitude of plum curculio immigration into orchard blocks. Findings are discussed with respect to the ecology and management of plum curculio.