EFFECTS OF GLYCEROL ON COLD-HARDINESS IN INSECTS

Abstract

The effects of glycerol on cold-hardiness in insects and seasonal changes in glycerol concentrations were investigated. The presence of this polyhydric alcohol was demonstrated in overwintering stages of 10 species. Larvae of one species also contained sorbitol, and eggs of two species another polyhydric alcohol, probably mannitol.Evidence gathered from various diapausing species showed that glycerol accumulated during the fall. This increase in concentration was observed in eggs of one species at temperatures ranging from −5° to 20 °C. No decrease in glycerol content was observed in any species as long as it was in diapause. After diapause was broken glycerol was lost in all species, in some even at temperatures down to −5 °C. Increase in concentration was never found in postdiapause insects. In two species, which do not have a diapause, the glycerol content increased below a certain temperature and decreased at higher temperatures.Three species were freezing-tolerant, although one contained less than 3% and another no glycerol, whereas eight species, most of which contained more than 15%, were killed by freezing. Thus glycerol alone cannot protect against freezing injuries.In several species the cold-hardiness was increased by the presence of glycerol because supercooling points were depressed. These depressions were more than those of the corresponding melting points. The regression of amount of supercooling on concentration of glycerol was linear in five species.