Physiological consequences of supercooling and freezing for overwintering insects

LAYNE, J. R. JR.; KUHARSKY, D. K.: Physiological consequences of supercooling and freezing for overwintering insects.

Freeze tolerance and enhanced supercooling ability (freeze avoidance) are distinct adaptations in insects facilitating survival of subfreezing temperatures. It has been suggested that freeze tolerance has advantages over freeze avoidance with respect to certain aspects of insect ecophysiology. Third instars of the goldenrod gall fly (Eurosta solidaginis Fitch) were kept either frozen or supercooled at -5 C for 10 weeks. Supercooled larvae lost 26% of their wet weight (-15.2 mg) and frozen larvae lost 14% of wet weight (-8.3 mg), mostly as a result of water loss during the treatments. Moreover, although supercooled larvae lost more water than did frozen larvae (-13.5 mg vs. -7.9 mg), lipid content was stable throughout both treatments (approximately 10 mg per larva). Freeze-treated larvae were more likely to survive to pupariation (92% vs. 65%) and adult emergence (73% vs. 50%) than were supercool-exposed larvae. This insect species copes better with prolonged freezing than it endures prolonged supercooling. However, it remains to be clarified whether or not this effect can be attributed to differences in water retention.

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