INTERACTIONS BETWEEN DESICCATION RESISTANCE, HOST-PLANT CONTACT AND THE THERMAL BIOLOGY OF A LEAF-DWELLING SUB-ANTARCTIC CATERPILLAR, EMBRYONOPSIS-HALTICELLA (LEPIDOPTERA, YPONOMEUTIDAE)

During May 1997 thermal tolerance, supercooling point (SCP), low and h igh temperature survival, and desiccation resistance were examined in field-fresh Embryonopsis halticella Eaten larvae from Marion Island. S CPs were also examined in acclimated larvae, larvae starved for seven days, larvae within their leaf mines, and in larvae exposed to ice cry stals. Field-fresh larvae had a critical minimum temperature (CTMin) a nd critical maximum temperature (CTMax) of 39.7 degrees C and 39.7 deg rees C, respectively. Mean SCP of field-fresh caterpillars was -20.5 d egrees C and this did not change with starvation. Field-fresh larvae d id not survive freezing and their lower lethal temperatures (70% morta lity below -21 degrees C) and survival of exposure to constant low tem peratures (100% mortality after 12 hrs at -19 degrees C) indicated tha t they are moderately chill tolerant. SCP frequency distributions were unimodal for field-fresh larvae, but became bimodal at higher acclima tion temperatures. Contact with ice-crystals caused an increase in SCP (-6.5 degrees C), but contact with the host plant had less of an effe ct at higher subzero temperatures. It appears that the remarkable desi ccation resistance of the larvae is selected for by the absence of a b oundary layer surrounding their host plant, caused by constant high wi nds. This suggests that the low SCPs of E. halticella larvae may have evolved as a consequence of pronounced desiccation resistance. (C) 199 8 Elsevier Science Ltd. All rights reserved.