Males of the Nantucket pine tip moth,Rhyacionia frustrana, flew significantly earlier on cool than on warm nights in response to traps baited with either crude pheromone extract or live females. Moths were unable to sustain flight below 10°C. Initiation of flight appeared to be unrelated to light intensity.The early flight on cool nights increases the probability that sufficient numbers of the moths emerging from overwintering pupae will successfully mate and maintainR. frustranapopulations.