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°S, 37°W),Hydromedion sparsutumandPerimylops antarcticus(Coleoptera, Perimylopidae), were quantified. Respiration rates of individual insects (live weights, 11–21 mg) were measured at 10°C prior to chilling (−4°C) or freezing (SCP range −3.8 to −5.3°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 ofP. antarcticusandH. sparsutum,although mean levels were depressed by 6–15%. Freezing produced considerable enhancement of respiratory activity. Mean values increased postfreezing in larvae (+34%) ofH. sparsutumand in both larvae (+44%) (P< 0.01) and adults (77%) (P< 0.05) ofP. antarcticus.Chilling and freezing had different effects on respiration rates andP. antarcticusshowed the greatest metabolic response to freezing.