Use of calorespirometry to determine effects of temperature on metabolic efficiency of an insect

Characterizing temperature responses of predatory insects is an important p art of understanding their life history, and is often necessary for predict ing their potential as bio-control agents of herbivorous insects. To illust rate the power of current methods of calorespirometry in determining the re sponse of energy metabolism to environmental variables, we used isothermal calorimetry to measure metabolic heat and CO2 production rates of convergen t lady beetles (Hippodamia convergens, Guerin-Meneville) as a function of t emperature. For comparison, CO., production rates were also measured with a n infrared gas analyzer. Anabolic rates and energy use efficiencies were ca lculated as functions of temperature from the calorespirometric data. For t his species, both heat and CO2 rates are small (approximate to1 muW/mg and 8 pmol/s/mg, respectively) and essentially constant below ITC, above which both rise approximately linearly up to approximate to 15 muW/mg and 50 pmol /s/mg at 40 degreesC. The anabolic rate is approximately zero below 0 degre esC, rises to a broad maximum of approximate to7 muW/mg around 20 degreesC, decreases above 25 degreesC, and then exhibits an increase due to stress a bove 35 degreesC. Energy use efficiency is roughly constant at approximate to 70% from 0 to 15 degreesC, above which it decreases to approximate to 25 % from 30 to 40 degreesC. The beetles are predicted to be most successful i n the temperature range from 10 to 35 degreesC, with an optimum from 15 to 25 degreesC. These conclusions agree with results from behavioral studies, but the calorespirometric methods are much faster, less labor intensive, an d can be applied to any stage of development.