ABSTRACT.In an ambient temperature (Ta) range of 18–28°C, thoracic temperatures (Tth) of individual maleLymantria dispar(L.), caught at flight in the field, ranged from 21 to 36.5°C, with a correlation coefficient of 0.63 betweenTthand ambient temperature (Ta). Ambient temperature (and insolation) altered the insect's body temperature and the probabilities, latencies, and durations of preflight responses to pheromone. In a wind tunnel at 16 and 20°C, quiescent males exposed to pheromone raised theirTthby sustained wing fanning from 17 and 21°C, respectively, toc.24°C before takeoff. At 24 and 28°C ambient,Tthrose by takeoff to 28 and 31°C, respectively. The latencies of male wing fanning in response to pheromone decreased from 1.44 min at 16°C ambient, to 0.58 min at 20°C, to 0.26 min at 24°C, and to 0.16min at 28°C. The components of behaviour (antennal twitch, body jerk, step and wing tremor) that occurred between quiescence and wing fanning were more frequent at ambients of 16 and 20°C than a