Eggs of Riptortus clavatus parasitized by Ooencyrtus nezarae were placed in an outdoor cage in Osaka City from early September to late October at intervals of about 10 days. The female adults of O. nezarae emerging from these hosts were transferred to 25°C and 16L-8D at intervals of about 30 days and their oviposition was recorded. Female adults did not enter diapause until November or December, and therefore they were capable of parasitizing eggs even in late autumn. The preoviposition period after transfer to 25°C and 16L-8D was longer from January to March, even though the median value was only 4 or 5 days. We concluded, therefore, that diapause in female adults of O. nezarae was most intense during these periods. The changes in intensity of diapause are considered to be an adaptation to avoid untimely termination of diapause on warm days in winter or early spring.