Abstract
Insects that tolerate severe cold during winter may either supercool or tolerate ice forming within the tissues of the body. To compare the relative advantages of freezing and supercooling, we measured rates of CO~2~ production and water loss in frozen and supercooled goldenrod gall fly larvae (Eurosta solidaginis). As an important first step, we measured the time required for ice content and metabolic rate to stabilize upon freezing. Ice content stabilized after only three hours of freezing at β5Β°C, whereas CO~2~ production required 12 hours to stabilize. Subsequent experiments found that freezing greatly reduced both water loss and metabolic rate. Comparisons of supercooled and frozen larvae at β5Β°C indicated that CO~2~ production fell 47% with freezing and water loss decreased 35%. As temperature decreased to β10 and β15Β°C, CO~2~ production fell exponentially and was no longer detectable at β20Β°C with our measurement system. Our results demonstrate that freezing significantly reduces energy consumption during the winter and may therefore improve winter survival and spring fecundity. The advantages of freezing over supercooling would drive selection toward insect freeze tolerance and also toward higher supercooling points to increase the duration of freezing each winter. J. Exp. Zool. 292:345β350, 2002. Β© 2002 WileyβLiss, Inc.