The diel periodicity of the mating flight activity ofLaspeyresia pomonella(L.) was studied by catches in timing sex pheromone traps operated over the 1972 season in pears at San Jose, California. Males (both released and wild) responded rhythmically in approximately the same way to bothtrans-8,trans-10-dodecadien-l-ol (1 mg dispenser) and to caged living virgin females (5 females per cage). The response was entrained to the light-dark cycle, but was not uniform over the season, because both low and high temperatures often limited flight. Temperatures at this location were relatively moderate and affected, for the most part, only the tails of the daily distributions, and the median catches usually occurred within one hour after sunset over the entire season. Compared with early season, initiation of daily flight was delayed in mid-late season because of high afternoon temperatures. Evening flight, on the other hand, was somewhat greater because limiting low temperatures were less often encountered during that period. Also, in the late period there appeared to be a slight tendency for more prolonged evening flight to the synthetic sex attractant than to females.