Respiration of resting honeybees

The relation between the respiratory activity of resting honeybees and ambient temperature (T(a)) was investigated in the range of 5-40 degrees C. Bees were kept in a temperature controlled flow through respirometer chamber where their locomotor and endothermic activity, as well as abdominal ventilatory movements was recorded by infrared thermography. Surprisingly, true resting bees were often weakly endothermic (thorax surface up to 2.8 degrees C warmer than abdomen) at a T(a) of 14-30 degrees C. Above 33 degrees C many bees cooled their body via evaporation from their mouthparts. A novel mathematical model allows description of the relationship of resting (standard) metabolic rate and temperature across the entire functional temperature range of bees. In chill coma (<11 degrees C) bees were ectothermic and CO(2) release was mostly continuous. CO(2) release rate (nls(-1)) decreased from 9.3 at 9.7 degrees C to 5.4 at 5 degrees C. At a T(a) of >11 degrees C CO(2) was released discontinuously. In the bees' active temperature range mean CO(2) production rate (nls(-1)) increased sigmoidally (10.6 at 14.1 degrees C, 24.1 at 26.5 degrees C, and 55.2 at 38.1 degrees C), coming to a halt towards the upper lethal temperature. This was primarily accomplished by an exponential increase in gas exchange frequency (0.54 and 3.1 breaths min(-1) at 14.1 and 38.1 degrees C) but not in released CO(2) volume per respiratory cycle (1487 and 1083 nl cycle(-1) at 14.1 and 38.1 degrees C). Emission of CO(2) bursts was mostly (98%) accompanied by abdominal ventilation movements even in small CO(2) bursts. Larger bursts coincided with a longer duration of active ventilation. An increased amount of CO(2) expelled per unit time of ventilation indicates a higher efficiency of ventilation at high ambient temperatures.