PEFFER, Ben J.; LAYNE, JR., Jack R.; Slippery Rock University, PA; Slippery Rock University, PA: Effects of tissue freezing on hemolymph K concentration and water distribution in caterpillars of Pyrrharctia isabella.

Tissue freezing causes substantial osmotic flux of water from cells and reduces aerobic-based production of ATP. These events could disturb ion homeostasis inside the bodies of insects. The magnitude of this disturbance may vary with the severity of the freeze conditions and with the ability of a particular species to cope with freezing. We investigated freezing-induced changes in extracellular K levels and body water distribution in caterpillars (woolly bears) of the Isabella tiger moth (Pyrrharctia isabella), a moderately freeze-tolerant species. Woolly bears were frozen at � 6 C for up to 6 weeks at a time. Short-term survival of caterpillars following this treatment was very high (92%) but only 17% of caterpillars completed metamorphosis. Woolly bears had stable (P > 0.05) body water contents during the initial 3 weeks of the freeze; however, there was a significant (P < 0.05) reduction in water content by 6 weeks. The latter change matched a significant (P < 0.05) rise in hemolymph osmolality. Hemolymph K rose nearly 33% (P < 0.05) by 3 weeks into the freeze but no further rise was detected (P > 0.05). Woolly bears have been previously reported to cope well with freezes lasting one week or less in duration. Here they experienced some dehydration after freezing for 6 weeks and recovery was very low. It is uncertain whether this ultimately caused their deaths but dehydration has been linked to winter mortality in other insects. A rise in K hemolymph preceded body water loss in woolly bears, and it most likely originated from the intracellular compartment. Hemolymph hyperkalemia may be due to a reduction in membrane pump activity in order to conserve ATP reserves. Homeostatic regulation of this ion was not abandoned altogether since dehydration did not result in further elevation of hemolymph K.