Respiratory responses to chilling and freezing in two sub-antarctic insects.

The effects of chilling (to temperatures above the supercooling point, SCP) and freezing on respiration of adults and larvae of two coleopterans living on sub-Antarctic South Georgia (54 degrees S, 37 degrees W), Hydromedion sparsutum and Perimylops antarcticus (Coleoptera, Perimylopidae), were quantified. Respiration rates of individual insects (live weights, 11-21 mg) were measured at 10 degrees C prior to chilling (-4 degrees C) or freezing (SCP range -3.8 to -5.3 degrees C) and posttreatment. The species possess a small amount of freeze tolerance in both adults and larvae. Chilling had no significant effects on respiration rates of P. antarcticus and H. sparsutum, although mean levels were depressed by 6-15%. Freezing produced considerable enhancement of respiratory activity. Mean values increased postfreezing in larvae (+34%) of H. sparsutum and in both larvae (+44%) (P < 0.01) and adults (77%) (P < 0.05) of P. antarcticus. Chilling and freezing had different effects on respiration rates and P. antarcticus showed the greatest metabolic response to freezing.