Principles of Insect Low Temperature Tolerance

Abstract

It is well known that temperature has a pervasive effect on insects. Nearly every aspect of an insect's life is influenced by temperature, from direct effects on the kinetics of enzymatic reactions, to defining the limits of physiological function and behavior, and ultimately to shaping of evolutionary pathways. As a group, insects, more than any other eukaryotic taxon, have evolved not only to survive but to flourish in a wide variety of thennal environments. Low temperature is not precisely defined since it covers a wide variety of topics and temperature ranges, and includes the maintenance of nonnal activity at low temperature, tolerance of chilling during the summer versus survival of prolonged exposure to cold during the winter, and applied aspects including the cryopreservation of insects. The ranges of insect responses to low temperature are illustrated in Fig. 2.1. Insects respond to low temperature in essentially two ways: either they survive by entry into a domiant (diapause) or quiescent state (see review by Tauber et al., 1986; Danks, 1987) or they remain active. Insects that enter a donnant state exhibit tolerance to a greater range of low temperatures than those that do not. Some overwintering insects extend their limits of low-temperature survival to - 70°C or below, approximating the lowest reported temperatures for natural environments. When many insects and related terrestrial arthropods from temperate and tropical areas are exposed to temperatures between 0 and I0°C, they are immobilized and enter a state of chill coma that is reversible if the duration of exposure is not prolonged. Other active insects are lethally injured by cold shock even though their body water does not freeze. Some species, particularly those inhabiting alpine and polar regions, have evolved to function nonnally at low temperatures (see Chapter 14). A number of polar species are able to move at temperatures as low as -4°C (Lee and Baust, 1987), whereas a Himalayan midge remains