Low temperature and insect activity

Abstract Insects are cold blooded, and their metabolism and activity is very greatly influenced by the temperature of their bodies, which temperature is almost entirely dependent on that of the surrounding environment. A low temperature inhibits activity, and a higher temperature usually stimulates the animal. The range over which any species can survive is limited above and below by lethal temperatures, and within this range lies the much narrower zone of normal activity. Most insects can for instance survive exposure to a much lower temperature than that at which activity ceases. Certain terms used for conciseness in this paper require definition. The “chill-coma temperature” (Belehradek 1935) is the temperature at which the insect is immobilized by the cold. The “cold-death point” is the temperature below which exposure is lethal. It appears that if there is one single factor more than any other which controls the distribution of an insect, it is the temperature below which activity never normally takes place. Insect distribution and survival is no doubt greatly affected by such factors as lethal high and low temperatures and unfavourable atmospheric humidity, but if, in any region, the temperature does not rise sufficiently often above that at which the normal activity of a species begins, that species will cease to exist although all other conditions are favourable to life. In temperate regions climatic conditions are seldom sufficiently extreme actually to kill many insects, but numerous species are unable to live actively or breed successfully there.