Seasonal changes in supercooling capacity and major cryoprotectants of overwintering Asian longhorned beetle (Anoplophora glabripennis) larvae

1 The Asian longhorned beetle is a destructive trunk borer in forests and urban landscape trees. 2 Dynamic changes in the supercooling capacity of Anoplophora glabripennis larvae in a natural population and the mechanism of cold hardiness during different overwintering periods at physiological and biochemical levels were explored. 3 The results showed that the supercooling point of overwintering larvae decreased initially before increasing subsequently with seasonal changes in ambient temperature. Fresh mass and glycogen tended to decrease initially and then reached their minimum levels in January. Total amounts of low molecular weight substances and free amino acids in the haemolymph increased gradually as the ambient temperature decreased. Glycerol (779.80 +/- 29.10 mu m/mL) and trehalose (104.35 +/- 12.38 mu m/mL) concentrations were always higher than those of glucose and mannitol. All low molecular weight substances (besides trehalose) were almost metabolized by early spring. The concentrations of serine, phenylalanine, valine, leucine, proline, glutamic acid and alanine all reached their highest level in the colder winter months. 4 The results of the present study suggest that A. glabripennis larvae accumulate cryoprotectants to improve their supercooling capacity, and enhance cold hardiness by reducing the supercooling point with respect to a decrease in ambient temperature until freezing temperatures appear. Anoplophora glabripennis larvae are a freeze-tolerant insect.