Objectives Tolerance and adaptability to and outbreak potential in winter of Ectropis grisescens Warren, one of the most widespread and destructive pests at tea plantations in northern China, were studied.

Method Overwintering ability of E. grisescens at various life stages was determined by measuring the supercooling capacity and low-temperature survival of the moth. Effects of cold hardening the tea geometrids on mortality and contents of moisture, fats, and glycerol as well as the activities of antioxidative catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) were analyzed.

Result The lowest supercooling point (SCP) and freezing point (FP) of E. grisescens pupae were −18.66 ℃ and −10.56 ℃, respectively. The cold hardiness of the moth at various developmental stages ranked pupae ＞4^th instar ＞3^rd instar ＞5^th instar larvae. Under acute exposure to −4 ℃, the median lethal times (LT₅₀) for 3^rd to 5^th instar larvae were 3.643 h, 4.573 h, and 3.671 h, respectively, whereas the pupae could sustain a temperature as low as −7 ℃ with a significantly higher LT₅₀ of 15.513 h. In addition, the survival of the larvae and pupae were significantly enhanced by a 5 ℃ cold hardening treatment. A 6h treatment could result in a 40% reduction in mortality rate from 60%-80% to 20%-40%. The contents of glycerol, a cryoprotectant that increased their tolerance to low temperatures, in the 4^th instar, 5^th instar, and pupae varied significantly by the hardening as well. Meanwhile, the activities of CAT, POD, and SOD rose under the treatment. That the coordinated enhancement mitigated the cytotoxic effect of cold stress on the moth suggested the antioxidant defense system actively participated in the cold hardiness augmentation in E. grisescens.

Conclusion Even though the tolerance to coldness in winter of E. grisescens larvae was low, the moth could, nonetheless, survive in a plastic-sheltered tea plantation in northern China through cold hardening to emerge in the following spring.