Supercooling and survival of the beech leaf mining weevil Rhynchaenus fagi L. (Coleoptera: Curculionidae)

The relationship between supercooling and survival of the beech leaf mining weevil, Rhynchaenus fagi was examined in exposures at constant temperatures between +10 and −15 °C, and in cycling regimes. Similar observations were made on naturally overwintering field populations. No weevil survived cooling to, or below the supercooling point. The mean supercooling point of weevils exposed to temperatures at, or below +2 °C, or sampled from the field, was consistently below −21 °C. When exposed to a constant +2 or −5 °C, mortality was low, at 10 and 12% after 168 and 126 days respectively. Mortality increased rapidly in weevils exposed to temperatures below −10 °C, with 48% survival after 112 days at −10 °C and only 25% after 84 days at −15 °C. None of the dead weevils had frozen. Periods spent at +2 °C in cycling treatments which included exposure at −10 or −15 °C, extended the duration of survival at the lower temperatures compared to constant exposures at these temperatures, but mortality was still more rapid than at a constant +2 °C. Survival of naturally overwintering insects was consistently high over three winters.