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During foraging honeybees are always endothermic to stay ready for immediate flight and to promote fast exploitation of resources. This means high energetic costs. Since energy turnover of foragers may vary in a broad range, energetic estimations under field conditions have remained uncertain. We developed an advanced model, combining the benefits of mechanistic and correlative models, which enables estimation of the energy turnover of stationary foragers from measurements of body surface temperature, ambient air temperature and global radiation. A comprehensive dataset of simultaneously measured energy turnover (ranging from 4 to 85 mW) and body surface temperature (thorax surface temperature ranging from 33.3 to 45 °C) allowed the direct verification of model accuracy. The model variants enable estimation of the energy turnover of stationary honeybee foragers with high accuracy both in shade and in sunshine, with SD of residuals = 5.7 mW and R2 = 0.89. Its prediction accuracy is similar throughout the main range of environmental conditions foragers usually experience, covering any combination of ambient air temperature of 14–38 °C and global radiation of 3–1000 W m−2. [ABSTRACT FROM AUTHOR]

The worldwide distribution of honeybees and their fast propagation to new areas rests on their ability to keep up optimal 'tropical conditions' in their brood nest both in the cold and in the heat. Honeybee colonies behave like 'superorganisms' where individuals work together to promote reproduction of the colony. Social cooperation has developed strongly in thermal homeostasis, which guarantees a fast and constant development of the brood. We here report on the cooperation of individuals in reaction to environmental variation to achieve thermal constancy of 34–36 °C. The measurement of body temperature together with bee density and in-hive microclimate showed that behaviours for hive heating or cooling are strongly interlaced and differ in their start values. When environmental temperature changes, heat production is adjusted both by regulation of bee density due to migration activity and by the degree of endothermy. Overheating of the brood is prevented by cooling with water droplets and increased fanning, which start already at moderate temperatures where heat production and bee density are still at an increased level. This interlaced change and onset of different thermoregulatory behaviours guarantees a graded adaptation of individual behaviour to stabilise the temperature of the brood. [ABSTRACT FROM AUTHOR]

Honeybees need water for different purposes, to maintain the osmotic homeostasis in adults as well as to dilute stored honey and prepare liquid food for the brood. Water is also used for cooling of the hive. Foraging in endothermic insects is energy-intensive and the question arises how much energy bees invest in a resource without any metabolically usable energy. We investigated the energy demand of water collecting bees under natural conditions. The thermoregulation and energetic effort was measured simultaneously in a broad range of experimental ambient temperatures (Ta = 12-40 °C). The thorax temperature as well as the energetic turnover showed a great variability. The mean Tthorax was ranging from ~ 35.7 °C at 12 °C to nearly 42.5 °C at 40 °C. The energy turnover calculated from CO2-release was highest at a Ta of 20 °C with about 60 mW and lowest at 40 °C with about 22 mW per bee. The total costs during collection decreased from 10.4 J at 12 °C to 0.5 J at 40 °C. The energetic effort of the water collectors was comparable with that of 0.5 M sucrose foraging bees. Our investigation strongly supports the hypothesis that the bees’ motivational status determines the energetic performance during foraging. [ABSTRACT FROM AUTHOR]

The Western honeybees Apis mellifera carnica and A. m. ligustica are closely related subspecies living in neighbouring regions. Metabolism and the upper lethal thermal limits are crucial physiological traits, adapted in the evolutionary process to environment and climate conditions. We investigated whether samples from these two ecotypes differ in these traits. The standard metabolic rate was higher in the A. m. ligustica population only at a high temperature ( T ~ 40 °C; dVCO = 12 nl s; P < 0.05), probably due to a higher body temperature (dT = 1.5 °C; P < 0.01). The critical thermal maximum of activity and respiration was similar (difference activity CT = 0.8 °C, respiratory CT = 1.1 °C). The lethal temperature (LT) revealed higher tolerance and survival rates of the Ligustica bees (Carnica 50.3 °C; Ligustica 51.7 °C; P < 0.02). Results reveal the adaptation of the two subspecies to their historic climate conditions, possibly favouring Ligustica in a warming environment. [ABSTRACT FROM AUTHOR]

Heterothermic insects like honeybees, foraging in a variable environment, face the challenge of keeping their body temperature high to enable immediate flight and to promote fast exploitation of resources. Because of their small size they have to cope with an enormous heat loss and, therefore, high costs of thermoregulation. This calls for energetic optimisation which may be achieved by different strategies. An ‘economizing’ strategy would be to reduce energetic investment whenever possible, for example by using external heat from the sun for thermoregulation. An ‘investment-guided’ strategy, by contrast, would be to invest additional heat production or external heat gain to optimize physiological parameters like body temperature which promise increased energetic returns. Here we show how honeybees balance these strategies in response to changes of their local microclimate. In a novel approach of simultaneous measurement of respiration and body temperature foragers displayed a flexible strategy of thermoregulatory and energetic management. While foraging in shade on an artificial flower they did not save energy with increasing ambient temperature as expected but acted according to an ‘investment-guided’ strategy, keeping the energy turnover at a high level (∼56–69 mW). This increased thorax temperature and speeded up foraging as ambient temperature increased. Solar heat was invested to increase thorax temperature at low ambient temperature (‘investment-guided’ strategy) but to save energy at high temperature (‘economizing’ strategy), leading to energy savings per stay of ∼18–76% in sunshine. This flexible economic strategy minimized costs of foraging, and optimized energetic efficiency in response to broad variation of environmental conditions. [ABSTRACT FROM AUTHOR]

1. During nectar and pollen foraging in a temperate climate, honeybees are exposed to a broad range of ambient temperatures, challenging their thermoregulatory ability. The body temperature that the bees exhibit results from endothermic heat production, exogenous heat gain from solar radiation, and heat loss. In addition to profitability of foraging, season was suggested to have a considerable influence on thermoregulation. To assess the relative importance of these factors, the thermoregulatory behaviour of foragers on 33 flowering plants in dependence on season and environmental factors was investigated. 2. The bees ( Apis mellifera carnica Pollman) were always endothermic. On average, the thorax surface temperature ( Tth) was regulated at a high and rather constant level over a broad range of ambient temperatures ( Tth = 33.7-35.7°C, Ta = 10-27°C). However, at a certain Ta, Tth showed a strong variation, depending on the plants from which the bees were foraging. At warmer conditions ( Ta = 27-32°C) the Tth increased nearly linearly with Ta to a maximal average level of 42.6 °C. The thorax temperature excess decreased strongly with increasing Ta ( Tth− Ta = 21.6 − 3.6°C). 3. The bees used the heat gain from solar radiation to elevate the temperature excess of thorax, head, and abdomen. Seasonal dependance was reflected in a 2.7 °C higher mean Tth in the spring than in the summer. An anova revealed that season had the greatest effect on Tth, followed by Ta and radiation. 4. It was presumed the foragers' motivational status to be the main factor responsible for the variation of Tth between seasons and different plants. [ABSTRACT FROM AUTHOR]

Abstract: Foraging honeybees are subjected to considerable variations of microclimatic conditions challenging their thermoregulatory ability. Solar heat is a gain in the cold but may be a burden in the heat. We investigated the balancing of endothermic activity with radiative heat gain and physiological functions of water foraging Apis mellifera carnica honeybees in the whole range of ambient temperatures (T a) and solar radiation they are likely to be exposed in their natural environment in Middle Europe. The mean thorax temperature (T th) during foraging stays was regulated at a constantly high level (37.0–38.5°C) in a broad range of T a (3–30°C). At warmer conditions (T a =30–39°C) T th increased to a maximal level of 45.3°C. The endothermic temperature excess (difference of T body − T a of living and dead bees) was used to assess the endogenously generated temperature elevation as a correlate of energy turnover. Up to a T a of ∼30°C bees used solar heat gain for a double purpose: to reduce energetic expenditure and to increase T th by about 1–3°C to improve force production of flight muscles. At higher T a they exhibited cooling efforts to get rid of excess heat. A high T th also allowed regulation of the head temperature high enough to guarantee proper function of the bees’ suction pump even at low T a. This shortened the foraging stays and this way reduced energetic costs. With decreasing T a bees also reduced arrival body weight and crop loading to do both minimize costs and optimize flight performance. [ABSTRACT FROM AUTHOR]

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]

In honeybee colonies, guards protect their nest from various robbers including bees from other colonies. Infrared thermography showed that the guards and the bees examined by them (examinees) differ considerably in their thermal behaviour according to their particular role in the nestmate recognition process. The thorax surface temperature was on average higher and more variable in the examinees (36.1°C, S.D. = 4.14, N = 1545, 303 bees) than in the guards (34.0°C, s.n. = 2.00, N = 1681, 772 bees). During thorough examinations lasting longer than 30s, more than 60% of the examinees showed phases of intense thoracic heating of more than 2°C (maximum temperature 48.5°C), whereas most guards cooled down. Our data suggest that these examinees heat up their surface to enhance chemical signalling during examinations. [ABSTRACT FROM AUTHOR]

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]