Abstract: Diapause inducement, super-cooling point, and mortality under low temperature environment and physiological index in relation to cold-hardiness in Chilo suppressalis populations from different geographical locations were studied in the laboratory. The results showed that the critical photoperiods of Beijing population at 22℃, 25℃ and 28℃ were 13 h and 55 min, 13 h and 44 min, and 13 h and 6 min, respectively, which were significantly longer than those of Fuzhou population at the same temperature. The super-cooling point of -15.13℃ for the diapause larvae collected from field in Beijing was drastically lower than both lab populations from Beijing and Fuzhou, indicating that there was a close relationship between larval cold hardiness and regulation from natural environment. During the test range from - 25℃ to -10℃, the mortality of diapause larvae increased as the temperature dropped, but there was a significant difference between two geographical populations, in which the high latitude population (Beijing) possessed a stronger cold hardiness. The weight of the diapausing larvae was significantly higher than non- diapausing ones developed under similar condition, and the water content in the diapause larvae was much lower. However, the protein and sugar contents in the diapause larvae were all higher than those in the non-diapause ones, suggesting that there were positive relationships between larval cold hardiness and the contents of protein and sugar.

Key words: Rice stem borer, geographic population, diapause, cold-hardiness, super-cooling point, Freezing point