The biophysical ecology and heat exchange of insects have been reviewed by Casey (1988, 1992). Heat transfer routes of convection and radiation are the most important, because conduction will be negligible when only tarsi are in contact with the substrate, metabolic heat production (MHP) is insignificant in small insects, and evaporation is costly and generally assumed to play a minor role. Hence, the importance of behaviour that takes advantage of air temperature, air movement, and solar radiation (which are integrated in measurements of Te). All behavioural mechanisms depend on the availability of solar radiation to provide thermal diversity in the environment in both time and space (Stevenson 1985). In this landmark paper, Stevenson constructed a series of heat-transfer models to provide quantitative estimates of the relative importance of various behavioural and physiological mechanisms in changing body temperature in ectotherms. He concluded that behavioural mechanisms were easily dominant and, of these, the times of seasonal and daily activity have the greatest impact on Tb, followed by microhabitat selection and then postural adjustments. Usually a complex interplay between these factors is involved, as the examples below will demonstrate.
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