NON-FREEZE SURVIVAL OF SPRUCE BUDWORM LARVAE, CHORISTONEURA-FUMIFERANA, AT SUBZERO TEMPERATURES DURING DIAPAUSE

Spruce budworm larvae, Choristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae), in early-, mid- and late-diapause (maintained at 2 degre es C), were exposed to various sub-zero temperatures, above the superc ooling point, for different periods to determine the insect's cold-har diness in terms of non-freeze survival. Larvae which were in the middl e of diapause showed the highest survival (percentage of larvae emergi ng from hibernacula after diapause), followed by larvae in late- and e arly-diapause respectively. When exposed to -23 degrees C, larvae whic h were acclimatized to outside air temperatures had a much higher surv ival than the larvae maintained at 2 degrees C. This survival was corr elated with a glycerol content that was ten times higher and a depress ed supercooling point in acclimatized larvae compared to lab-maintaine d larvae. Experiments also demonstrated that mortality of the larvae m aintained in an extended supercooled state at -23 degrees C was due to cold injury rather than freezing. The present study supports the hypo thesis that glycerol may have a cryoprotective role other than depress ing the supercooling point in freeze-intolerant insects and highlights the importance of investigating non-freeze mortality during insect di apause.