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To examine the possibility that mating continues in the winter in Okinawa, we observed the effects of adult temperature on male mating success in Euscepes postfasciatus. Males kept at 15℃ for the first 30 or 60 days of adulthood had much lower mating rates than those kept at 25℃ when paired with females at 25℃. However, when males were first kept at 25℃ for 30 days and then exposed to 15℃ for the next 30 days, they showed a high mating rate even when paired with females at 15℃, although the rate rapidly decreased with time. This indicates that 1) mating activity itself was not inhibited at 15℃ and that 2) sexually mature males retained the inseminating ability even after a period of cool conditions. The possibility that sperm is quickly depleted after several matings at a spermiogenesis-suppressing temperature was pointed out to explain the present results. This and other laboratory studies suggest the occurrence of mating in the winter highly likely on Okinawa Island, and point out the importance of release of sterile insects in all seasons including winter in eradicating this pest.