Abstract:Cold hardiness of the beet armyworm, Spodoptera exigua (Hübner), was investigated by measuring the supercooling points and freezing points of three geographical populations (Longyao, Hebei Province; Hengyang, Hunan Province and Nanjing, Jiangsu Province) and the field overwintering test. The results showed that supercooling points of pupae were the lowest, followed by adults, eggs and larvae. Moreover, pupae have the most obviously supercooling phenomenon, so it was the most feasible stage for overwintering. Cold hardiness of the population from Hengyang, Hunan Province was the most powerful, followed by Longyao population (Hebei Province) and Nanjing population (Jiangsu Province). Overwintering mortality were 100%, estimated by field trials in Nanjing with pupae burying in 2001 and 2002. And the winter temperature analysis also showed that the beet armyworm did can not survive the winter in some years. These results illustrate that the beet armyworm can possibly not overwinter in Nanjing during a chilly winter. So it is suggested that the northern limit of permanent overwintering regions for the beet armyworm be probably at the areas in the south of Nanjing.