Flight of the honey bee

Summary

Using manometric and gas analytical methods oxygen consumption$\dot V_{O_2 }$, carbon dioxide production$\dot V_{CO_2 }$, respiratory quotientRQ, (Fig. 1A-C) and thorax surface temperature difference ΔT _ts (Fig. 3) were determined in single bees. The animals were either sitting in respiratory chambers or were suspended by the scutum, in which case they were resting, ‘walking’ (turning a small polystyrene ball) or flying in a closed miniature wind tunnel.

During resting (sitting in Warburg vessels) at an ambient temperatureT _a=10°C,RQ was 1.01±0.2 (n=905) with variations due to method (Fig. 1D, E).RQ values during walking were determined in single cases. In no case were they significantly different from 1.00. After the first 10 min of flight meanRQ was 1.00±0.04. It was significantly smaller than 1.00 (RQ=0.97) only during the last 5% of long-time flights (mean flight duration 58.8±28.8 min). With the exception of near-exhaustion conditions no signs of fuels other than carbohydrates were found.

Metabolic rateP _m was 19.71±21.38 mW g⁻¹ during ‘resting’ at 20°C≤T _a≤30°C indicating that many resting bees actively thermoregulate at higherT _a. After excluding bees which were actively thermoregulating, by an approximationP _m was 5.65±2.44 mW g⁻¹ at 20°C≤T _a≤30°C. ‘True resting metabolic rate’ for sitting bees atT _a=10°C was 1.31±0.53 mW g⁻¹ (Fig. 2A, B).

A significant negative correlation was found between relative (specific) oxygen consumption$\dot V_{O_2 }$rel and body massM _b at 85 mg≤M _b≤150 mg.

At 0°C≤T _ts≤16.5°C a significant (α-0.01) positive correlation was found between$\dot V_{O_2 }$ and ΔT _ts in single resting bees:$\dot V_{O_2 }$ ΔT _Ts+0.099, or betweenP _m and ΔT _ts:P _m=1.343 ΔT _ts+0.581 (Fig. 3D)$\dot V_{O_2 }$ in ml h⁻¹,P _m in mW,T in °C).

During walking (duration 13.15±5.71 min,n=13) at 12.5°C≤T _a≤21°C a stable ΔT _ts of 11.41±3.37°C, corresponding to 167 mW g⁻¹, was reached for 80 to 90% of the walking time (Fig. 4B).

During wind tunnel flights of tethered animals the minimal metabolic power measured in exhaustion experiments was 240 mW g⁻¹. Calculation of factors of increase inP _m is of limited value in poikilotherms, in which true resting conditions are not exactly defined.