Effect of cryoprotectants on the activity of hemolymph nucleating agents in physical solutions.

‘Many insects accumulate polyhydric alcohols, particularly glycerol, sorbitol, and carbohydrates during fall and winter. In the larval hymenopteran Brachon cephi, Salt (11) found glycerol concentrations as high as 5 m and supercooling points as low as -47°C. The production of these substances is correlated with increased cold hardiness in both freezing tolerant and freezing intolerant species. The mode of action of these substances remains partly unclear, but they are believed to promote cold hardiness in a number of ways. In freezing intolerant insects, which have a high capacity for supercooling, increasing polyol levels have been shown to depress the supercooling points by more than twice the corresponding melting point depression (13), by a mechanism which at least in part must be noncolligative. The low supercooling points of these insects have also been interpreted as a result of a complete removal of all nucleating particles from their body fluid (12, 15). In addition, Baust and Morrissey (1, 2) suggested that the cryoprotectants may serve to “mask” potential ice nucleation loci. Preliminary studies with the freezing intolerant lady beetle Coleomegilla maculata provided support for this hypothesis when it was found that glucose appeared to “mask” nucleators during cyclical temperature fluctuations. For freezing intolerant forms this “masking” would allow for extensive supercooling and the avoidance of freezing,