Abstract: 【Aim】 Galeruca daurica (Joannis) is a new pest outbreaking seriously in the Inner Mongolian grasslands in recent years and overwinters as eggs under cow pats, stones and grass clusters. Understanding the cold hardiness of the overwintering eggs of G. daurica is helpful to forecast its distribution and population dynamics. 【Methods】 We measured the survival rates and developmental durations of overwintering eggs of G. daurica exposed to different low temperatures (-18--39℃) for 12 and 24 h and exposed to -30℃ for different periods (0-60 d), respectively, in the laboratory. 【Results】 Low temperature intensity and exposure time significantly affected the survival rates of overwintering eggs of G. daurica. The survival rates declined with the decrease of exposure temperature and the extension of exposure time. After the overwintering eggs were exposed to the temperatures ≤-33℃ for 12 h or the temperatures ≤-30℃ for 24 h, their survival rates were significantly lower than the corresponding controls (25℃). The lower half lethal temperatures (LT₅₀) after 12 and 24 h exposure were -33.08 and -32.13℃, respectively, and the half lethal time (Lt₅₀) at -30℃ was 33.33 d. The developmental duration of surviving eggs prolonged significantly after exposure to -36℃ for 12 h or the temperatures ≤-33℃ for 24 h, but had no significant change after exposure to -30℃ for 30 days. 【Conclusion】 The overwintering eggs of G. daurica have strong cold hardiness, and low temperature in winter may usually not cause mass mortality of overwintering eggs.

Key words: Galeruca daurica, cold hardiness, overwintering egg, survival rate, lower lethal temperature, lower lethal time, developmental duration