Characterizing temperature responses of predatory insects is an important part of understanding their life history, and is often necessary for predicting their potential as bio-control agents of herbivorous insects. To illustrate the power of current methods of calorespirometry in determining the response of energy metabolism to environmental variables, we used isothermal calorimetry to measure metabolic heat and CO2 production rates of convergent lady beetles (Hippodamia convergens, Guérin-Méneville) as a function of temperature. For comparison, CO2 production rates were also measured with an infrared gas analyzer. Anabolic rates and energy use efficiencies were calculated as functions of temperature from the calorespirometric data. For this species, both heat and CO2 rates are small (≈1 μW/mg and 8 pmol/s/mg, respectively) and essentially constant below 10°C, above which both rise approximately linearly up to ≈15 μW/mg and 50 pmol/s/mg at 40°C. The anabolic rate is approximately zero below 0°C, rises to a broad maximum of ≈7 μW/mg around 20°C, decreases above 25°C, and then exhibits an increase due to stress above 35°C. Energy use efficiency is roughly constant at ≈70% from 0 to 15°C, above which it decreases to ≈25% from 30 to 40°C. The beetles are predicted to be most successful in the temperature range from 10 to 35°C, with an optimum from 15 to 25°C. These conclusions agree with results from behavioral studies, but the calorespirometric methods are much faster, less labor intensive, and can be applied to any stage of development.
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