Further, the thorax is thermally isolated from the abdomen by an insulating air sac. Recall that the insulating properties of air sacs is another adaptive role of these structures. At low temperature the heart and ventral diaphram beat at fairly low rates and relatively little of the thoracic heat is transferred to the abdomen by hemolymph flow. At the other extreme, at high thoracic temperatures the rates of heart beat and ventral diaphram action increase, and the hemolymph flows between thorax and abdomen much faster. A much increased rate of heat transfer between the thorax and abdomen follows.
Heat is radiated from the virtually uninsulated abdomen to the environment.
This last is shown by the rapid drop in temperature in the ventral section of the abdomen. The figure also shows an important anatomical feature of thermoregulation. The aorta loops between the left and right dorsal longitudinal muscles, thereby allowing substantial heat exchange between flight muscles and hemolymph. First we want to look at the business of measuring temperature. A fever thermometer is a little largish for this kind of research on insects.