Flight of the honey bee

Summary Using manometric and gas analytical methods oxygen consumption, carbon dioxide production, respiratory quotientRQ, (Fig. 1A-C) and thorax surface temperature difference T_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°CT_a30°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°CT_a30°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 consumptionrel and body massM_b at 85 mgM_b150 mg.At 0°CT_ts16.5°C a significant (-0.01) positive correlation was found between and T_ts in single resting bees: T_Ts+0.099, or betweenP_m and T_ts:P_m=1.343 T_ts+0.581 (Fig. 3D) in ml h^–1,P_m in mW,T in °C).During walking (duration 13.15±5.71 min,n=13) at 12.5°CT_a21°C a stable T_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.