Male spruce budworm moths were kept in a wind tunnel for 4 days and assayed each day to determine their ability to locate calling females that were surrounded by rubber septa loaded with synthetic pheromone, a 95:5 blend of E:Z-11-tetradecenal. As the concentration of synthetic pheromone increased, the numbers of males successfully locating females decreased, the latency of response increased, and the speed of flight decreased. At release rates from the septa close to those of a calling female, 6–60 ng/h per septum, most disrupted males flew to a septum instead of the females. At the highest release rate tested, 600 ng/h, many males were inactive or flew to the sides of the tunnel, which indicates sensory fatigue. This effect was more pronounced among males that were continuously exposed to the synthetic pheromone for the 4 days than among males kept in pheromone-free air between assays. About a quarter of the males died or became unable to fly after the 4 days, but there was no change in the proportions of the different responses of males, or in their response times, with increasing age, nor was there evidence that males were conditioned by their experience on previous days. The results led to the conclusion that time-averaged atmospheric concentrations of the synthetic pheromone as high as 20 ng/m3 are necessary to achieve effective disruption of the orientation of male spruce budworm moths to calling female moths.