STUDIES ON ECOPHYSIOLOGICAL ASPECTS OF TH E HIBERNATION OF THE SPRUCESAWFLY, PRISTIPHORA-ABIETINA CHRIST (HYM, TENTHREDINIDAE)

Pristiphora abietina survives the winter as a nymph in a cocoon restin g in the upper layer of soil litter. In order to understand the causes of doubtful nymph mortality, the cold resistance and some features re lated to it were tested by experiments. During the period from July to March, the nymphs exhibit poor supercooling abilities, in the range f rom -3.6 to -7.7C. The mean supercooling points show seasonal changes, with the lowest temperatures in November/December. The nymphs usually survived freezing at temperatures a few degrees beyond the supercooli ng point in dry and wet environments. Thus, Pristiphora abietina nymph s appear to be tolerant to freezing, as well as to inoculative freezin g. Because the cocoon is permeable to water it does not protect the ny mphs from superficial wetting. The cocoons represent an efficient shel ter against transpiration, but even naked nymphs lose water very slowl y in dry air. Therefore, a negative correlation between sensitivity to desiccation and tolerance to inoculative freezing is presumed. Physio logical and ecological aspects of this feature are discussed within th e context of hibernation.