Overwintering of the boreal butterfly Colias palaeno in central Europe.

Background: Colias palaeno (Linnaeus, 1761) (Lepidoptera: Pieridae) is a butterfly with boreal distribution with declining populations in peat bogs and subalpine habitats in Central Europe.
Objective: We investigated the cold tolerance of overwintering caterpillars from one mountain population from Czech Republic (960m a.s.l.) and one alpine population from Italy (2000m a.s.l.).
Methods: We measured supercooling point (SCP), lower lethal temperature (LLT) and content of cryoprotectants.
Results: The caterpillars were freeze-avoiding, with lower LLT close to their very low SCP (-25 to -27 degree C). The mountain population accumulated high concentrations of glycerol (5% fresh mass) and sugars (trehalose 0.8%, glucose 0.2%), while the Italian alpine population only moderate amounts of glycerol (0.3%) and sugars (trehalose 0.5%, glucose 0.3%) without effect on their cold hardiness. Larvae that overwintered at +5 degree C had a lower body mass than those overwintering in natural conditions, indicating a metabolic weight loss, but both groups survived equally well.
Conclusion: We hypothesize that the high concentration of glycerol contributes to the high desiccation tolerance.