Abstract:In this study, overwintering larvae of Chilo suppressalis was divided into higher, middle and lower instars, cold hardiness of which was investigated in terms of supercooling point and freezing point, and the biochemical mechanism of cold hardiness was also studied. The results showed that the supercooling point of higher instar was maximum in February (-9.81℃) and that of middle instar larvae increased gradually from January to March (-13.35℃, in February). On the contrary, the supercooling point of lower instar was minimum in February (-15.64℃) and significantly lower than that of higher instar. In the same month, contents of water and glycerol of lower instar were the highest, follow by middle instar, and those of higher instar were the lowest.