Winter survival of an adult bark beetle Ips acuminatus Gyll

Freezing-susceptible adult Ips acuminatus hibernate underneath bark of Scots pine. The beetles lower their supercooling points from ?20 to ?34°C due to accumulation of low molecular weight antifreezes. The capability of specimens to supercool to about ?20°C in the absence of cryoprotective solutes during winter, seemed to be at least partially attributable to the presence of a thermal hysteresis factor at 3–4°C.Using a GC-MS-COM technique, a unique combination of accumulated solutes present only in specimens demonstrating supercooling points below ?20°C was identified as ethylene glycol, mannitol, sorbitol and dulcitol. Not previously found in nature, ethylene glycol was the major solute (90%) synthesized at sub-zero temperatures. Exposure to ?10°C was an effective cue to accumulation of ethylene glycol and nearly 5 times as effective in promoting sorbitol synthesis than was ?5°C. When low molecular weight substances were lost at high temperatures, they were not re-synthesized in beetles re-exposed to sub-zero temperature. The supercooling point was closely related to both the concentration of ethylene glycol and to the haemolymph melting point. Attempts to correlate changes in sorbitol concentrations to changes in supercooling points were not conclusive.Proliferation of thermal hysteresis was observed in the beginning of November. A melting-hysteresis freezing point differential of about 3.6°C was demonstrated in the haemolymph of beetles during December. No thermal hysteresis was demonstrated in the haemolymph of positive phototactic beetles or in the outdoor beetles in May. The combination of high temperature and long photoperiod appeared to be a more effective cue to the final loss of thermal hysteresis than was high temperature alone.