Roberts SP, Harrison JF
Department of Biology, Arizona State University, Tempe, AZ 85287-1501, USA.
J Exp Biol. 1999 Jun;202 (Pt 11):1523-33. doi: 10.1242/jeb.202.11.1523.
Thermoregulation of the thorax allows honeybees (Apis mellifera) to maintain the flight muscle temperatures necessary to meet the power requirements for flight and to remain active outside the hive across a wide range of air temperatures (Ta). To determine the heat-exchange pathways through which flying honeybees achieve thermal stability, we measured body temperatures and rates of carbon dioxide production and water vapor loss between Ta values of 21 and 45 degrees C for honeybees flying in a respirometry chamber. Body temperatures were not significantly affected by continuous flight duration in the respirometer, indicating that flying bees were at thermal equilibrium. Thorax temperatures (Tth) during flight were relatively stable, with a slope of Tth on Ta of 0.39. Metabolic heat production, calculated from rates of carbon dioxide production, decreased linearly by 43 % as Ta rose from 21 to 45 degrees C. Evaporative heat loss increased nonlinearly by over sevenfold, with evaporation rising rapidly at Ta values above 33 degrees C. At Ta values above 43 degrees C, head temperature dropped below Ta by approximately 1-2 degrees C, indicating that substantial evaporation from the head was occurring at very high Ta values. The water flux of flying honeybees was positive at Ta values below 31 degrees C, but increasingly negative at higher Ta values. At all Ta values, flying honeybees experienced a net radiative heat loss. Since the honeybees were in thermal equilibrium, convective heat loss was calculated as the amount of heat necessary to balance metabolic heat gain against evaporative and radiative heat loss. Convective heat loss decreased strongly as Ta rose because of the decrease in the elevation of body temperature above Ta rather than the variation in the convection coefficient. In conclusion, variation in metabolic heat production is the dominant mechanism of maintaining thermal stability during flight between Ta values of 21 and 33 degrees C, but variations in metabolic heat production and evaporative heat loss are equally important to the prevention of overheating during flight at Ta values between 33 and 45 degrees C.
胸部的体温调节使蜜蜂（西方蜜蜂）能够维持飞行肌肉的温度，以满足飞行的功率需求，并在广泛的气温（Ta）范围内在蜂巢外保持活跃。为了确定飞行中的蜜蜂实现热稳定性的热交换途径，我们在呼吸测量室中，测量了温度在21至45摄氏度之间飞行的蜜蜂的体温、二氧化碳产生速率和水汽损失速率。呼吸测量仪中蜜蜂的体温不受连续飞行持续时间的显著影响，这表明飞行中的蜜蜂处于热平衡状态。飞行过程中胸部温度（Tth）相对稳定，Tth随Ta变化的斜率为0.39。根据二氧化碳产生速率计算的代谢产热，随着Ta从21摄氏度升至45摄氏度，线性下降了43%。蒸发散热呈非线性增加，增加了七倍多，在Ta高于33摄氏度时蒸发迅速上升。在Ta高于43摄氏度时，头部温度比Ta下降了约1至2摄氏度，这表明在非常高的Ta值下，头部发生了大量蒸发。飞行蜜蜂的水分通量在Ta低于31摄氏度时为正，但在较高的Ta值时越来越负。在所有Ta值下，飞行中的蜜蜂都经历了净辐射散热。由于蜜蜂处于热平衡状态，对流散热被计算为平衡代谢产热与蒸发散热和辐射散热所需的热量。随着Ta升高，对流散热大幅下降，这是因为体温高于Ta的差值减小，而不是对流系数的变化。总之，在21至33摄氏度的Ta值之间飞行时，代谢产热的变化是维持热稳定性的主要机制，但在33至45摄氏度的Ta值之间飞行时，代谢产热和蒸发散热的变化对防止过热同样重要。
