AVOIDANCE OF INTRACELLULAR FREEZING BY THE FREEZING-TOLERANT NEW-ZEALAND-ALPINE-WETA HEMIDEINA-MAORI (ORTHOPTERA, STENOPELMATIDAE)

Calorimetric analysis indicates that 82% of the body water of Hemidein a maori is converted into ice at 10 degrees C, This is a high proporti on and led us to investigate whether intracellular freezing occurs in H. maori tissue, Malpighian tubules and fat bodies were frozen in haem olymph on a microscope cold stage, No fat body cells, and 2% of Malpig hian tubule cells froze during cooling to -8 degrees C, Unfrozen cells appeared shrunken after ice formed in the extracellular medium, There was no difference between the survival of control tissues and those f rozen to -8 degrees C, At temperatures below -15 degrees C (lethal tem peratures for weta), there was a decline in survival, which was strong ly correlated with temperature, but no change in the appearance of tis sue, It is concluded that intracellular freezing is avoided by Hemidei na maori through osmotic dehydration and freeze concentration effects, but the reasons for low temperature mortality remain unclear, The fre ezing process in H. maori appears to rely on extracellular ice nucleat ion, possibly with the aid of an ice nucleating protein, to osmoticall y dehydrate the cells and avoid intracellular freezing, The lower leth al temperature of H. maori (-10 degrees C) is high compared to organis ms that survive intracellular freezing, This suggests that the categor y of 'freezing tolerance' is an oversimplification, and that it may en compass at least two strategies: intracellular freezing tolerance and avoidance. (C) 1997 Elsevier Science Ltd.