Flight of the honey bee

Summary

Thorax surface temperature,T _ts, was measured by a thermistor glued to the scutum, and inner thorax temperature,T _ti, by a very fine thermoelement implanted in the scutellum (Fig. 1A, B). After implantation, exhaustion-flight experiments were made using an open jet wind tunnel (Fig. 1C) and previously exhausted, tethered bees fed on known quantities of glucose solution. Flights lasted up to 3 h at a wind velocity of 4.3 m s⁻¹ and at ambient temperatures,T _a, of 20, 25, 30 and 35°C.

T _ti was significantly (1–1.5°C) higher thanT _ts at all values ofT _a (Fig. 2A-C). Temperature differences ΔT _ts=T _ts−T _a, and ΔT _ti=T _ti−T _a, were constant for approximately 75% of flight time, usually diminishing in the final 25% (Fig. 2). Mean ΔT _ti was 1.12±0.48°C atT _a=20°C, and 1.94±0.59°C at 25°C≤T _a≤35°C (Fig. 3B). Regurgitation of liquid droplets did not reduceT _ti orT _ts. During flight,T _ti,T _ts and wingbeat frequency,F _w, followed similar courses.

After exhaustion-flights mean body mass,M _b, was 77.5±5.49 mg, independent ofT _a (Fig. 3A). Wingbeat frequency was 144.8±13.5 s⁻¹ atT _a=20°C, and 167.6±10.1 s⁻¹ at 25°C≤T _a≤35°C (differences significant; Fig. 3C). Mean flight time after feeding with 10 μl glucose solution (1.54 mol glucose l⁻¹) was 43.2±4.8 min atT _a=20°C, and 30.6±4.7 min at 25°C≤T _a≤35°C (differences significant; Fig. 3D). Under the same flight conditions, metabolic power,P _m, was 17.29±1.94 mW atT _a=20°C, and 24.69±3.60 mW at 25°C≤T _a≤35°C (differences significant). Mean thermal conductivity was 0.63±0.26 W m⁻² °C⁻¹, independent ofT _a (Fig. 2E).

AtT _a=20°C, ΔT _ti was proportional to wing stroke frequency,F _w, (Fig. 4A);P _m was porportional toF ^1.73_w (Fig. 4B). The exponent 1.73 is not significantly different (α=0.05) from 2.0. No correlation was found betweenP _m andM _b (Fig. 4C). Relative metabolic powerP _mrel=P _m M ⁻¹_b was proportional toM ^−1.48_b (Fig.4D).