Ice nucleation and freezing tolerance in New Zealand alpine and lowland weta, Hemideina spp. (Orthoptera; Stenopelmatidae)

The alpine tree weta Hemidiena maori Pictet et Saussure (Orthoptera: Stenop elmatidae) is a large, flightless insect found above the treeline on many o f the mountain ranges of the South Island of New Zealand. The population fo und on the Rock and Pillar Range, Central Otago has been identified as free zing tolerant with a haemolymph ice nucleating agent. The ability of H. mao ri to survive freezing is compared to the lowland weta Hemideina thoracica Walker and H. crassidens Blanchard, both of which are able to survive the f ormation of some ice in their bodies. Mortality is associated with time spe nt frozen in H. thoracica, and it is hypothesized that this species is kill ed when a critical proportion of its body water is frozen. All five subalpi ne and alpine populations of H. maori surveyed were found to be freezing to lerant. Comparison of temperatures of first nucleation and mean supercooling point of haemolymph droplets suggest that haemolymph ice nucleating activity vari es between populations of H. maori. Hemideina maori collected from the Mt C ook region appear to lack a haemolymph ice nucleator. This population is ne vertheless freezing tolerant, suggesting that the haemolymph ice nucleating agent described in H. maori is not essential for freezing tolerance. Hemid eina crassidens and H. ricta Hutton, both of which are found in lowland hab itats, also had high mean supercooling point and temperatures of first nucl eation of haemolymph droplets, suggesting that these species also have a ha emolymph ice nucleator. Comparison of ice nucleation characteristics of haemolymph and faecal mater ial (representing gut contents) suggests that gut nucleators in H. maori ma y be at least as efficient as the haemolymph nucleator. It is concluded tha t freezing tolerance is probably not an adaptation to the alpine environmen t. This highlights the need for inter- and intraspecific comparative studie s if physiological data are to be used to draw evolutionary conclusions.