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Abstract: Vespine wasps are known for their high endothermic capacity. Endothermic activity is directly linked to respiration. However, knowledge on wasp respiration is sparse and almost nothing is known about their resting metabolism. We investigated the yellowjackets’ CO2 production in a flow-through respirometer chamber overnight. Endothermic and behavioral activity was observed by real-time infrared thermography. Most resting wasps were ectothermic or only slightly endothermic (thoracic temperature excess against abdomen <0.6°C). In the investigated temperature range (T a =2.9–42.4°C) mean CO2 production rate of resting wasps increased steeply according to an exponential function, from 5.658μlg−1 min−1 at 8.3°C to 8.504μlg−1 min−1 at 20.2°C, 58.686μlg−1 min−1 at 35.3°C and 102.84μlg−1 min−1 at 40°C. The wasps’ respiratory critical thermal maximum (CTmax), marking the upper edge of their viable temperature range, was 45.3°C. The respiratory CTmax did not differ significantly from the activity CTmax of 44.9°C. CTmax values were considerably below that of honeybees (48.9 and 49.0°C for respiration and activity, respectively). This allows honeybees to kill wasps by heat-balling. Comparison with other arthropods showed that vespine wasps are among the insects with the highest mass-specific resting metabolic rate and the steepest increase of metabolism with ambient temperature. [Copyright &y& Elsevier]

Abstract: A comparison of the thermoregulation of water foraging wasps (Vespula vulgaris, Polistes dominulus) under special consideration of ambient temperature and solar radiation was conducted. The body surface temperature of living and dead wasps was measured by infrared thermography under natural conditions in their environment without disturbing the insects’ behaviour. The body temperature of both of them was positively correlated with T a and solar radiation. At moderate T a (22–28°C) the regression lines revealed mean thorax temperatures (T th) of 35.5–37.5°C in Vespula, and of 28.6–33.7°C in Polistes. At high T a (30–39°C) T th was 37.2–40.6°C in Vespula and 37.0–40.8°C in Polistes. The thorax temperature excess (T th–T a) increased at moderate T a by 1.9°C (Vespula) and 4.4°C (Polistes) per kW−1 m−2. At high T a it increased by 4.0°C per kW−1 m−2 in both wasps. A comparison of the living water foraging Vespula and Polistes with dead wasps revealed a great difference in their thermoregulatory behaviour. At moderate T a (22–28°C) Vespula exhibited distinct endothermy in contrast to Polistes, which showed only a weak endothermic activity. At high T a (30–39°C) Vespula reduced their active heat production, and Polistes were always ectothermic. Both species exhibited an increasing cooling effort with increasing insolation and ambient temperature. [Copyright &y& Elsevier]

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]