Major physiological adjustments in freezing-tolerant grey tiger longi-corn beetle (Xylotrechus rusticus) during overwintering period

摘要

1Xylotrechus rusticus (Linnaeus) is one of the most destruc-tive woodborers in northeast China;it damages poplar and is listed as a domestic forestry quarantine pest. Overwintering larvae were collected during October 2012 and March 2013 in Harbin, China, to quantify indi-cators related to the insect’s overwintering strategy and the major cryo-protectants. The supercooling points (SCPs), which ranged from-14.7°C to -2.9°C, were higher than the lethal temperatures of LT50 (-33.64°C) and LT99 (-40.17°C) after 24 h exposure. , also the minimum mean daily temperature (-24.5°C) and mean monthly temperature (-18.0°C) at the sampling site in January during 2008-2012. Thus, X. rusticus is a typical freezing-tolerant insect. Glycerol serves as a major cryoprotectant for overwintering larvae , because it was the only polyol accumulated during the winter and it also had a significant negative correlation with the SCP (p=0.033, R=0.907). The glycogen and lipid are major sources of ener-gy and their levels decreased substantially in the middle of overwintering, when glycogen had a significant correlation with the SCP (p= 0.006, R=0.971) whereas the lipid contents did not. Moreover, inter-conversions between glycerol and glycogen, as well as mannose and glycogen, were suggested by their negative correlations. The water content did not change obviously during the winter and was not correlated with the SCP. The free amino acids in the hemolymph and the total protein contents of the bodies of larvae changed significantly during winter, although both had no correlations with the SCP.