Flight of the honey bee

Summary

In round-about experiments (rate of success 40%) 80% of the bees began flying after thorax surface temperature had increased toT _ts=34.1±1.8°C (warming). The starting temperature difference ΔT _ts(=T _ts−T _a)=6.7±3.06 °C at an ambient temperature of 18.0°C≤T _a≤29.6°C (‘normal starts’). The latter decreased to 2.80±0.83°C after 2–5 min and remained constant during 85% of the flight time (42.5±29.2 min) (Fig. 1A). 20% of the bees began flying at ΔT _ts=1.6±0.3°C and continued to warm up during the first third of their flight (‘emergency starts’) (Fig. 1 B).

During slowT _a changes ΔT _ts remained constant. Immediately after a flight stop, temperature increased by 6.2–18.7% during the following 30–60 s (‘out effect’) (Fig. 1C). Dangling the legs resulted in a pronounced temperature loss ofT _ts≤1°C (Fig. 1 D).

ΔT _ts was negatively correlated withT _a at the start (ΔT _ts (°C)=88.32e^{−0.0926 Ta(°C)}; Fig. 2A), but not correlated toT _a during the flight at 20.5°C≤T _a≤26.7°C andv=0.72 ms⁻¹ (Fig. 2B). Individual variation was high (Fig. 2C). Flight duration was not correlated toT _a (Fig. 2D).

During wind tunnel flights (rate of success 16–38%) ΔT _ts reached a steady value after 2–5 min, remained steady during two thirds of the flight, and was not dependent onT _a (Fig. 3C). The mean value of ΔT _ts was 2.16±0.30°C at 19°C≤T _a≤34°C andv=1.8 ms⁻¹.

Heating constants in still air before short walks, longer walks (t≥4 min) and round-about flights were 2.28±0.86 min⁻¹, 3.55±1.33 min⁻¹ and 3.64±0.73 min⁻¹, respectively, but only 1.04±0.26 min⁻¹ under wind tunnel conditions (resting, but exposed to a wind speed of 1.8 m s⁻¹). Cooling constants after flight stop averaged 0.87±0.24 min⁻¹ in still air, 2.8±0.2 min⁻¹ in animals rotated at 0.72 m s⁻¹, and 1.32±0.22 min⁻¹ in animals exposed to a wind speed of 1.8 m s⁻¹. No statistical difference in heating and cooling constants were found in the temperature range 18°C≤T _a≤34°C.

A significant positive correlation was found between ΔT _ts and$\dot V_{O_2 }$ in resting bees exposed to a wind speed of 1.8 m s⁻¹ (Fig. 4A-C).