Hot Desert Arthropods at Low Temperatures

Abstract

As mentioned previously, insects can be considered as containers in which the physical conditions for supercooling are favourable (Sømme 1982). Although they may not be exposed to freezing tropical regions and summer-acclimated specimens from temperate regions have SCPs in the range of −7 to −12 °C (Zachariassen 1985). Due to the ability of terrestrial arthropods to supercool, Cloudsley-Thompson (1973) and Constantinou and Cloudsley-Thompson (1986) pointed out that they are partly pre-adapted to inhabit cold environments. For this reason, species living in hot deserts may have the supercooling capacity to tolerate freezing temperatures of their environments. Cold hardiness, however, is not merely a question of supercooling, but also involves the maintenance of vital physiological and biochemical processes at low temperatures (Duman et al. 1991a). In fact, some insects such as the summer-acclimated aphids described by Bale et al. (1988), are killed in a few minutes at subzero temperatures before their SCPs are reached. Very little is known about the harmful effects of exposure to cold above freezing temperatures. Summer--acclimated temperate insects and tropical insects usually succumb within a short time, and offer a striking contrast to overwintering stages of temperate, polar and alpine species that survive for several months at temperatures below zero. Cold hardiness in terrestrial arthropods from hot deserts offers an interesting example of how species primarily adapted to warm climates may also be able to survive periods of freezing conditions in their natural habitats.