FURTHER OBSERVATIONS ON GLYCEROL AND COLD-HARDINESS IN INSECTS

Changes in glycerol content and supercooling points were studied in three overwintering species. In larvae of Hyponomeuta evonymellus L. and eggs of Acrolita naevana (Hb.), glycerol was accumulated and supercooling points were lowered during the fall. After diapause was broken, the glycerol content decreased, accompanied by an increase in supercooling points. Similar changes were observed in all larvae of Laspeyresia strobilella (L.), although some of them pupate after one winter, while others remain in diapause for at least 1 more year. The larvae that remain in diapause are able to accumulate glycerol during exposure to low temperatures, and in this way increase their cold-hardiness, Glycerol was lost at 20 °C in the fall when all larvae of L. strobilella were in diapause, whereas diapausing eggs of A. naevana retained their glycerol content at this temperature. Eggs of A. naevana from a location in eastern Norway accumulated more glycerol than did eggs from a location with a milder climate in western Norway, thus suggesting differences in adaptation to low temperatures, Larvae of H. evonymellus and eggs of A. naevana were killed by freezing, while larvae of L. strobilella were freezing-tolerant in the middle of the winter.