Overwintering of the boreal butterfly Colias palaeno in central Europe

Colias palaeno (Linnaeus, 1761) (Lepidoptera: Pieridae) is a butterfly with boreal distribution with declining populations in peat bogs and subalpine habitats in Central Europe.

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.).

We measured supercooling point (SCP), lower lethal temperature (LLT) and content of cryoprotectants.

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.

We hypothesize that the high concentration of glycerol contributes to the high desiccation tolerance.