Changes of cold hardiness of the overwintering larvae of Athetis lepigone (Lepidoptera: Noctuidae) at different overwintering stages.

【Aim】Athetis lepigone( Mschler) is a new insect pest of summer corn at seedling stage in North China. With the transformation of cultivation,the damage area of A. lepigone has been gradually expanding. In this study,the cold hardness of A. lepigone was measured to reveal its cold resistance mechanisms. 【Methods】We measured body weight,the supercooling point( SCP),the freezing point( FP) and the contents of water,fat and glycogen in mature larvae at different overwintering stages( the early overwintering stage,November 7th,2012; the overwintering stage,January,20th 2012; while the late overwintering stage,March 5th,2013). 【Results 】 The SCP values on different dates during overwintering were significantly different,the lowest SCP value(- 23. 16 ± 0. 38℃) appeared in January,while the highest(- 16. 24 ± 1. 24℃) appeared at the beginning of winter. The variation tendency of FP value was consistent with that of SCP. According to the quantitative detection,we found that the fresh body weight had no correlation with SCP( r = 0. 17,P = 0. 12). The highest fat content appeared at the beginning of winter,while the lowest appeared at the late overwintering stage. The lowest glycogen content appeared at the overwintering stage. Supercooling capability enhanced as the free water content decreased,while reduced as the free water content increased. However,the change of bound water content was opposite to that of the free water content. 【Conclusion】The cold hardiness of overwintering larvae of A.lepigone changes significantly at different overwintering stages,which gradually strengthens as temperature decreases in winter and weakens as temperature increases after overwintering.