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Abstract: The relation between the respiratory activity of resting honeybees and ambient temperature (T a) was investigated in the range of 5–40°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°C warmer than abdomen) at a T a of 14–30°C. Above 33°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°C) bees were ectothermic and CO2 release was mostly continuous. CO2 release rate (nls−1) decreased from 9.3 at 9.7°C to 5.4 at 5°C. At a T a of >11°C CO2 was released discontinuously. In the bees’ active temperature range mean CO2 production rate (nls−1) increased sigmoidally (10.6 at 14.1°C, 24.1 at 26.5°C, and 55.2 at 38.1°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 3.1breathsmin−1 at 14.1 and 38.1°C) but not in released CO2 volume per respiratory cycle (1487 and 1083nlcycle−1 at 14.1 and 38.1°C). Emission of CO2 bursts was mostly (98%) accompanied by abdominal ventilation movements even in small CO2 bursts. Larger bursts coincided with a longer duration of active ventilation. An increased amount of CO2 expelled per unit time of ventilation indicates a higher efficiency of ventilation at high ambient temperatures. [Copyright &y& Elsevier]

We measured the energy turnover (oxygen consumption) of honeybees (Apis mellifera carnica), which were free to move within Warburg vessels. Oxygen consumption of active bees varied widely depending on ambient temperature and level of activity, but did not differ between foragers (>18 d) and middle-aged hive bees (7–10 d). In highly active bees, which were in an endothermic state ready for flight, it decreased almost linearly, from a maximum of 131.4 μl O2 min−1 at 15 °C ambient temperature to 81.1 μl min−1 at 25 °C, and reached a minimum of 29.9 μl min−1 at 40 °C. In bees with low activity, it decreased from 89.3 μl O2 min−1 at 15 °C to 47.9 μl min−1 at 25 °C and 14.7 μl min−1 at 40 °C. Thermographic measurements of body temperature showed that with increasing activity, the bees invested more energy to regulate the thorax temperature at increasingly higher levels (38.8–41.2 °C in highly active bees) and were more accurate.Resting metabolism was determined in young bees of 1–7 h age, which are not yet capable of endothermic heat production with their flight muscles. Their energy turnover increased from 0.21 μl O2 min−1 at 10 °C to 0.38 μl min−1 at 15 °C, 1.12 μl min−1 at 25 °C, and 3.03 μl min−1 at 40 °C. At 15, 25 and 40 °C, this was 343, 73 and 10 times below the values of the highly active bees, respectively. The Q10 value of the resting bees, however, was not constant but varied in a U-shaped manner with ambient temperature. It decreased from 4.24 in the temperature range 11–21 °C to 1.35 in the range 21–31 °C, and increased again to 2.49 in the range 30–40 °C. We conclude that attempts to describe the temperature dependence of the resting metabolism of honeybees by Q10 values can lead to considerable errors if the measurements are performed at only two temperatures. An acceptable approximation can be derived by calculation of an interpolated Q10 according to the exponential function VO2=0.151×1.0784Ta (interpolated Q10=2.12). [Copyright &y& Elsevier]