Abstract: 【Aim】  Galeruca daurica Joannis began to outbreak seriously since 2009 and has caused great losses in the Inner Mongolian grasslands. Its occurrence region has expanded constantly and the damage has become more and more severe, which greatly influenced the sustainable development of grassland animal husbandry and ecological safety in Inner Mongolia. Low temperature is a key factor that affects the development and survival of insects, and their overwintering survival mainly depends on their tolerance to low temperature in winter. Understanding the supercooling point (SCP) and cold hardiness of G. daurica is helpful to forecast its distribution and population dynamics. 【Methods】  We measured the supercooling points in various developmental stages in the laboratory and determined the survival rates of larvae exposed to different low temperatures (-6℃--14℃) for 2 h or exposed to -5℃ for different periods (0.5-8 d) with the thermocouple method. 【Results】  The supercooling points had obvious differences among various developmental stages of G. daurica in the following order from low to high: egg (-29.8℃), 1st instar larva (-14.6℃), 2nd instar larva (-13.3℃), pupa (-12.1℃), 3rd instar larva (-10.2℃) and adult (-9.0℃). The SCPs of eggs were the lowest in December and January, and the highest in February. The survival rates of larvae declined with the decrease of treatment temperature and the extension of treatment time.  For 1st instar, 2nd instar and 3rd instar larva, the half lethal time of individuals (Ltime₅₀) at -5℃ was 3.84 d, 3.80 d and 2.28 d, respectively, while the lower lethal temperature needed to kill 50% of individuals (Ltemp₅₀) after 2 h exposure was -10.1, -9.1 and -8.5℃, respectively, higher than the corresponding SCPs. 【Conclusion】  The larvae of G. daurica can be considered as chillintolerant.

Key words:  Galeruca daurica, cold hardiness, supercooling point, survival rate, lower lethal temperature, lower lethal time