When the long hard northern winter sets in, insect larvae have two options: beat the ice or perish. Some insects tolerate ice formation while others avoid freezing and cheat death by stuffing themselves full of antifreeze compounds. However, insects that live in the extreme latitudes may have to go to even greater lengths to survive; their supercooled body fluids may transform into a viscous glass (vitrify) at extremely low temperatures to avoid freezing. Todd Sformo and colleagues from the University of Alaska Fairbanks, the University of Notre Dame and 21st Century Medicine, Inc., explain that larvae from some Alaskan populations of the red flat bark beetle seem to remain unfrozen at temperatures as low as –80°C, and they wondered whether the larvae may have opted for the vitrification option. Curious to find out how overwintering larvae survive, Sformo and his colleagues measured the antifreeze protein activity, water and glycerol contents as well as the change in heat capacity of the larvae's bodies as they cooled to find out if their body fluids were transformed into a glass (p. 502).
Amazingly, the larvae did not freeze, even at temperatures as low as –150°C; instead of forming ice crystals, their body fluids vitrified to protect them from damage. They also found that the larvae lost body fluids as the temperature fell, increasing their glycerol levels to an impressive 4–6 mol l–1.
The team explains that as summer turns into autumn the larvae begin producing antifreeze proteins to protect them down to –20°C, before beginning to dehydrate, which raises their glycerol and antifreeze concentrations even further for protection down to –40°C. Finally, as the winter temperatures fall even further, they lose more body fluids, raising their glycerol concentrations to such an extent that their body fluids turn into a viscous glass at –58°C, protecting them all the way down to –150°C.