INSECT COLD-HARDINESS - INSIGHTS FROM THE ARCTIC

Cold-hardiness and related adaptations of insects in the Arctic corres pond to characteristic climatic constraints. Some species are long-liv ed and are cold-hardy in several stages. In the Arctic, diapause and c old-hardiness are less likely to be linked than in temperature regions , because life-cycle timing depends as much on the need to coincide de velopment with the short summer as on the need to resist winter cold. Winter habitats of many species are exposed rather than sheltered from cold so that development in spring can start earlier. Several feature s of cold-hardiness in arctic species differ from the characteristics of temperate species: these include very cold-hardy insects with low s upercooling points that are not freezing tolerant; freezing-tolerant s pecies that supercool considerably rather than freezing at relatively high subfreezing temperatures; mitochondrial degradation linked with t he accumulation of cryoprotectants; and the possibly limited occurrenc e of thermal hysteresis proteins in winter. Several interesting relati onships between cold-hardiness and water have been observed, including different types of dehydration. Winter mortality in arctic insects ap pears to be relatively low. Adaptations to cold in summer include rete ntion of cold-hardiness, even freezing tolerance; selection of warm si tes; and behaviour such as basking that allows elevated body temperatu res. Studies especially on the high-arctic moth Gynaephora groenlandic a show that various factors including cold-hardiness and other summer and winter constraints dictate the structure of energy budgets and the timing of life cycles. Future work should focus on the biological and climatic differences between arctic and other areas by addressing hab itat conditions, life-cycle dynamics, and various aspects of cryoprote ctant production at different times of year. Even in the Arctic cold-h ardiness is complex and involves many simultaneous adaptations.