Effect of temperature on cold-hardiness and tissue ice formation in the adult chrysomelid beetle Melasoma collaris L.

The freeze-tolerant chrysomelid beetle Melasoma collaris overwinters in plant litter on windswept ridges or covered with snow for 8–9 months in the Norwegian alpine region. Lower lethal temperature, supercooling and melting point depression were correlated to accumulation of glycerol. The lower limit of freeze tolerance was associated with the freezing of 73–75% body water. About 23–15.5% of the body water was osmotically inactive, and the highest percentage was revealed in individuals depleted of glycerol at 21°C. A shift in cooling rate from 1°Cmin-1 to 1°C every 13.5min lowered nucleating temperature markedly. The alteration in nucleating activity probably arises from the structure of the haemolymph nucleating agent that functions to slow embryo growth at the slow cooling rate. An enhanced supercooling is particularly beneficial in autumn before M. collaris has accumulated glycerol, since supercooled individuals accumulate glycerol in higher concentrations than frozen ones. Freezing at higher temperatures is probably a better survival strategy during brief intervals with pronounced decrease in air temperature.