INOCULATIVE FREEZING IN OVERWINTERING TENEBRIONID BEETLE, BOLITOPHAGUS-RETICULATUS PANZ

Adults of the tenebrionid beetle Bolitophagus reticulatus are able to endure prolonged sub-zero temperatures both as freeze-tolerant and freeze-avoiding. The switch between the two strategies is linked to the moisture content of the hibernaculum. Accumulation of low molecular weight substances parallels depression of haemolymph melting points down to -6.5-degrees-C. The supercooling point is lowered to -30-degrees-C during winter, and enhanced supercooling below -20-degrees-C was closely correlated to the depression of haemolymph melting points. Thermal hysteresis-producing antifreeze proteins, however, were not present. Spontaneous freezing at the supercooling point proved fatal, whereas initiation of freezing by contact with external ice ensured protective extracellular freezing. At temperatures 4-5-degrees-C above mean supercooling point, survival was always poorer in the inoculated frozen specimens than in the extensively supercooled specimens. Thus, the present study does not imply that freeze tolerance is more efficient than freeze avoidance in promoting cold hardiness.