CHANGES IN SORBITOL CONTENT AND SUPERCOOLING POINTS IN OVERWINTERING EGGS OF THE EUROPEAN RED MITE (PANONYCHUS ULMI (KOCH))

Abstract

Overwintering eggs of the European red mite (Panonychus ulmi (Koch)), stored at 6 °C in the laboratory, were found to accumulate sorbitol during the fall, while a decrease in concentrations took place from January to March. A linear correlation suggests that increased sorbitol content causes a depression of the supercooling points. Significant changes in supercooling points during storage were found in eggs from two locations in eastern Norway, while only small changes took place in eggs from a location in western Norway. Changes in sorbitol content were significant in eggs from all locations. Maximum concentrations of sorbitol were observed at the time diapause terminated. Judging from the supercooling points, eggs collected in eastern Norway were slightly more cold-hardy than were eggs from milder climates in western Norway.