The banded woolly bear caterpillar, Pyrrharctia isabella (Lepidoptera: Erebidae) overwinters in leaf litter and survives freezing under natural conditions. Following 18 weeks of cold acclimation at 5°C, all caterpillars could survive one week of continuous freezing at −20°C or 7 cycles of freezing-thawing at −20°C, but none survived freezing at −80°C. Field-collected caterpillars had a Tc (temperature of crystallization) of −7.7±0.5°C that decreased significantly to −9.5±0.6°C after 12 weeks of acclimation at 5°C. Hemolymph levels of free proline, total amino acids and proteins reached a peak during the first four weeks of acclimation; concomitantly, hemolymph osmolality increased markedly during this interval (from 364 to 1282 mosmol/kg). In contrast, hemolymph pH decreased during the first four weeks of acclimation before this trend reversed and pH values gradually returned to initial values. However, pH reached its peak value following one week at −20°C but decreased after longer periods of freezing. During cold acclimation, cholesterol levels decreased in the hemolymph and the membrane fraction of fat body but not in other tissues. Lethal freezing at −80°C, reduced cell survival in foregut tissue and caused leakage of free proline, total amino acids and proteins from tissues into the hemolymph. The addition of glycerol to the bathing medium reduced freezing injury in fat body cells as evidenced by reduced leakage of amino acids and proteins.

This content is only available via PDF.

Article PDF first page preview

Article PDF first page preview