Flight of the honey bee

Summary

From measurements of gas exchange of single tethered bees flying in a closed-circuit miniature respiration wind tunnel atRQ=1.0, a relative metabolic power (relative metabolic rate) ofP _mrel=0.515±0.1W g⁻¹ was calculated based on a body mass of 80 mg for an ‘empty’ bee. This did not vary significantly over the temperature range 25.3°C≤T _a≤34.0°C, but was significantly lower atT _a=20°C. Over the range 22°C≤T _a≤26°CP _mrel was 0.379±0.07 W g⁻¹.

Relative metabolic powerP _{m rel} was calculated from round-about or wind tunnel post-flight thorax cooling rates (exponentially rising from 1 to 5.5°C min⁻¹ per °C temperature difference at wind velocities from 0 to 4.3 m s⁻¹) and from differences between thorax surface temperature and ambient temperature (exponentially decreasing from 6 to 1°C over the same range of wind velocities). A value ofP _mrel=0.195±0.09W g⁻¹ was found, independent of wind velocity.

From measurements of exhaustion flights of defined fed bees executing prolonged flights (30.6±4.7 min) in front of an open-jet wind tunnel, a relative metabolic power of 0.309±0.05 W g⁻¹ was calculated, which did not vary significantly over the temperature range 25°C≤T _a≤35°C, but was significantly lower atT _a=20°C.

Our data from 3 experimentally different determinations ofP _mrel are compared to data from a number of literature sources. A critical discussion suggests probable values of approximately 0.3 W g⁻¹ for tethered flights (round-abouts, wind-tunnels), 0.4 W g⁻¹ for medium speed free-foraging flights, and 0.5 W g⁻¹ for hovering flight. Probable mechanical flight power for a muscle efficiency of 0.2 in medium speed free-foraging flight is approximately 70 mW g⁻¹ body mass (equivalent to 5.6 mW for an ‘empty’ 80 mg bee) and 230 mW g⁻¹ flight muscle mass. This is in the upper range of theoretical calculations, but not excessively high.