Critical thermal limits, temperature tolerance and water balance of a sub-antarctic caterpillar, Pringleophaga marioni (Lepidoptera: Tineidae)

Thermal tolerance, supercooling point, water balance and osmoregulatory ability of Pringleophaga marioni Viette (Lepidoptera: Tineidae) are investigated in this study. Field-fresh larvae had a mean CT(Min) (cold stupor) of - 0.6°C and a mean CT(Max) (heat coma) of 38.7°C. The mean supercooling point of field-fresh individuals was - 5.0°C. Caterpillars showed 100% survival of freezing to - 6.5°C, but at - 12°C mortality rose to 100%. Survival of a 30 h exposure to - 6.0°C was 80%, but declined to 30% in the 6-12 h interval at - 7.5°C. No caterpillars survived for longer than 12 h at - 9.0°C. Survival of high temperatures (35°C and above) was poor. Tolerance of water loss (46% of fresh mass) and rates of water loss (1% fresh mass h ^-1) were similar to those found in other mesic insects. P. marioni larvae were incapable of metabolizing lipids to replenish lost water and showed no haemolymph osmoregulatory ability. It is suggested that the preponderance of freeze tolerance in high-latitude southern hemisphere species may be associated with their occurrence in moist habitats, and that the 'freeze tolerance' category be re-examined in the light of the range of strategies adopted by such arthropods.