Photoperiodically controlled adult diapause in the bean bug, Riptortus clavatus (Thunberg) (Heteroptera: Alydidae) was due to suppression of corpus allatum activity under short-day conditions. The mechanical extensibility of the cuticle of the pronotum was significantly higher in nondiapause adults reared under long-day conditions than in diapause adults reared under short-day conditions. Furthermore, diapause adults accumulated significantly larger amount of lipids than nondiapause ones. It was then examined whether these two characteristics of adult diapause also depend on activity of the corpus allatum, by removal of the corpus allatum and transection of the nervi corporis allati. Even after these two kinds of surgery, adults responded to photoperiod and showed similar differences both in mechanical properties of the cuticle and in lipid content between long-day and short-day conditions. Therefore, inactivity of the corpus allatum is not responsible for the stiffer cuticle or higher lipid accumulation in diapause adults.