The effect of photoperiod on nymphal development, growth and adult size was examined in a pentatomid bug, Dolycoris baccarum, collected in Osaka (a warm temperate region) and Hokkaido (a subfrigid region), Japan. When insects were reared from eggs at 25°C, the developmental period was long and adult size was large under photoperiods close to the critical photoperiod for the induction of adult diapause. Adults of the Hokkaido population were larger than those of the Osaka population. There was no significant correlation between developmental period and adult size. Insects also showed variation in their growth rate: growth rate was low under photoperiods a little longer than the critical photoperiod for the induction of diapause. The ecological significance of variation in development and growth is discussed.