Abstract
Insects often accumulate sugars and/or polyols at various concentrations only in winter. Glycerol is the most common polyols in both freeze-intolerant and freeze-tolerant insects, but other sugars and polyols such as trehalose, sorbitol, mannitol, inositol and glucose have been also found. Accumulation or loss of these cryoprotectants is effectively regulated by temperature-dependent activity in various enzymes. The capacity for polyol synthesis is also often linked to the developmental stage and diapause status. In freeze-intolerant insects, polyol accumulation provides colligative depression of SCP depending on the concentration and stabilizes the supercooling state of the hemolymph, although it may be less effective in many cases because the polyol content is often relatively low. On the other hand, in freeze-tolerant insects, the colligative action of polyols would regulate cell volume during extracellular ice formation to prevent excessive freeze concentration of cell. In addition, polyols could stabilize the native state of cell membrane and proteins under non-freezing and freezing low temperature conditions. Thus, winter polyol accumulation would have an important role on cold hardiness in both freeze-intolerant and freeze-tolerant insects.
