E54 Metabolism and heat production

Topic

An insect's metabolism generally scales allometrically with its body mass—following Kleiber's law, which is established by another model in this set—implying that a small insect possesses a significantly higher specific metabolic rate per unit of mass than a much larger insect.

Conversely, the insect's metabolic energy is derived primarily from the oxidation of lipids or carbohydrates during flight; the specific respiratory quotient—a parameter defined by another model in this set—depends on which of these two substrates the insect oxidizes.

The metabolic thermal effect—described by another model in this set—characterizes how the rate of the insect's enzymatic reactions accelerates with its body temperature; consequently, this ectothermic insect (the subject of yet another model in this set) becomes more active and consumes more oxygen at higher temperatures.

An insect's flight muscle constitutes the tissue that consumes the most energy per unit of mass in the entire animal kingdom—comparable to the best engines built by humans—reflecting the flight power output defined by another model in this set.

Thus, this model—incorporating the allometric scaling of metabolism relative to body mass introduced at the start—enables the use of indirect calorimetry (another model in this set) to estimate the insect's metabolic power output by measuring its oxygen consumption and carbon dioxide production, without requiring direct calorimetry. The fact that this indirect calorimetry of the insect measures oxygen consumption and carbon dioxide production with even greater precision means that the final estimate of the insect's metabolic power—based on the allometric scale relating to body mass upon which the model was built—is consequently also rendered even more precise.

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