Lethal temperature limits

Abstract

Temperature change has an effect on many physiological processes and insects frequently evolve strategies to overcome the rate, sub-lethal or lethal effects of temperature variation. This chapter examines the responses of insects to potentially lethal and sub-lethal temperatures. Estimates of stress tolerance are affected considerably by measurement protocols and these are dealt with in detail. High and low temperature responses take place over a variety of time scales, from hours (hardening) to days (acclimation) to longer periods (evolved response, which include the evolution of plasticity). The mechanisms underlying high temperature responses include heat shock protein production, membrane alterations, and the production of polyhydric alcohols. Similar alterations are made in response to cold, but upper and lower limits tend to be decoupled in insects. Cold hardiness strategies seem not to have a high temperature equivalent, and cover three major responses: freezing tolerance, freeze intolerance, and cryoprotective dehydration. The chapter ends with a focus on global patterns in thermal tolerance, demonstrating the limited variation in upper limits by comparison with lower limits.