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Polistes paper wasps are a widespread taxon inhabiting various climates. They build nests in the open without a protective outer layer, which makes them vulnerable to changing temperatures. To better understand the options they have to react to environmental variation and climate change, we here compare the thermoregulatory behavior of Polistes biglumis from cool Alpine climate with Polistes gallicus from warm Mediterranean climate. Behavioral plasticity helps both of them to withstand environmental variation. P. biglumis builds the nests oriented toward east-south-east to gain solar heat of the morning sun. This increases the brood temperature considerably above the ambience, which speeds up brood development. P. gallicus, by contrast, mostly avoids nesting sites with direct insolation, which protects their brood from heat stress on hot days. To keep the brood temperature below 40–42 °C on warm days, the adults of the two species show differential use of their common cooling behaviors. While P. biglumis prefers fanning of cool ambient air onto the nest heated by the sun and additionally cools with water drops, P. gallicus prefers cooling with water drops because fanning of warm ambient air onto a warm nest would not cool it, and restricts fanning to nests heated by the sun.

Climate change is expected to produce shifts in species distributions as well as behavioural and physiological adaptations to find suitable conditions or to cope with the altered environment. The paper wasps Polistes dominula and Polistes gallicus are closely related species, native in the European Mediterranean region and North Africa. P. dominula has expanded its range to the relatively cooler climates of Northern and Eastern Europe, but P. gallicus remained in its original distribution area. In order to reveal their metabolic adaptation to the current climate conditions, and the impact on energy demand at future climate conditions, we investigated the respiratory metabolic rate (CO2 production) of P. dominula from Austria and P. gallicus from Italy. In contrast to the metabolic cold adaptation hypothesis their standard metabolic rate was nearly the same and increased in a typical exponential course with increasing ambient temperature. The metabolic rate of active wasps was higher than the standard metabolic rate and increased with the wasps' activity. There was no obvious difference in the active metabolism between the two species, with the exception that some P. gallicus individuals showed some extraordinary high values. A simultaneous measurement of metabolic rate and body temperature revealed that increased CO2 production was accompanied by endothermic activity. The two investigated populations of paper wasps are quite similar in their metabolic response to temperature, although they live in different climate regions. The spread of P. dominula into cooler regions did not have significant influence on their active and standard metabolic rate.

Holometaboly is a key evolutionary innovation that has facilitated the spectacular radiation of insects. Despite the undeniable advantage of complete metamorphosis, the female of some holometabolous species have lost the typical holometabolous development through neoteny. In Xenos vesparum Rossi (Strepsiptera: Stylopidae), a derived species of the holometabolous endoparasitic order Strepsiptera, neotenic females reach sexual maturity without the pupal and the imaginal stages, thus retaining their larval morphology (with the exception of the anterior part of the body or cephalothorax), while males undergo normal pupal-based metamorphosis. Expression of the “adult-specifier” E93 factor has been shown to be required for proper metamorphosis in holometabolous insects. Here, we investigated the involvement of E93 in female neoteny by cloning XvE93. Interestingly, while we detected a clear up-regulation of XvE93 expression in pupal and adult stages of males, persistent low levels of XvE93 were detected in X. vesparum females. However, a specific up-regulation of XvE93 was observed in the cephalothorax of late 4th female instar larva, which correlates with the occurrence of neotenic-specific features in the anterior part of the female body. Moreover, the same expression dynamic in the cephalothorax and abdomen was also observed for other two critical metamorphic regulators, the anti-metamorphic XvKr-h1 and the pupal specifier XvBr-C. The specific up-regulation of XvE93 and XvBr-C in the female cephalothorax seems to be the result of an increase in 20-hydroxyecdysone (20E) signaling in this region for we detected higher expression levels of the 20E-dependent nuclear receptors XvHR3 and XvE75 in the cephalothorax. Overall, our results detect a sex-specific expression pattern of critical metamorphic genes in X. vesparum, suggesting that neoteny in Strepsiptera results from the modification of the normal expression of E93, Br-C and Kr-h1 genes.

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. Electronic supplementary material The online version of this article (10.1007/s00359-018-1278-9) contains supplementary material, which is available to authorized users.

In endothermic wasps, foraging is an expensive activity. To maximise the benefit for the colony, wasps can optimise either the intake rate or energetic efficiency of a foraging trip. We investigated the foraging behaviour of Vespine wasps under variable environmental and reward conditions. We trained them to forage for 0.5 molar sucrose solution from an artificial flower in a flow-through respiratory measurement chamber, and simultaneously measured their body temperature using infrared thermography to investigate interactions between thermoregulation and energetics. Measurement of carbon dioxide release (for energetic calculations) and load weight enabled the direct determination of foraging efficiency. An unlimited reward increased the wasps’ energetic effort to increase the suction speed through high body temperatures. With reduced reward (limited flow), when an increased body temperature could not increase suction speed, the wasps decreased their body temperature to reduce the metabolic effort. Solar heat gain was used differently, either to increase body temperature without additional metabolic effort or to save energy. The foraging efficiency was mainly determined by the flow rate, ambient temperature and solar heat gain. In shade, an unlimited sucrose flow and a high ambient temperature yielded the highest energetic benefit. A limited flow reduced foraging efficiency in the shade, but only partly in sunshine. Solar radiation boosted the efficiency at all reward rates. Wasps responded flexibly to varying reward conditions by maximising intake rate at unlimited flow and switching to the optimisation of foraging efficiency when the intake rate could not be enhanced due to a limited flow rate.

Sexual displays of acoustically signalling insects are used in the context of mate attraction and mate choice. While energetic investment in sound production can increase the reproductive success of the sender, this entails metabolic costs. Resource allocation into sexually selected, reproductive traits can trade off against allocation to naturally selected traits (e.g., growth, immunity) when individuals' energy budgets are limited. Estimating the magnitude of the costs invested in acoustic signalling is necessary to understand this trade-off and its influence on fitness and life-history. To compare the costs associated with acoustic signalling for two ensiferan species, we simultaneously took respiratory measurements to record the rate of CO2 production and used infrared thermography to measure the increase in thorax temperature. Furthermore, to identify what combinations of acoustic parameters were energetically costly for the sender, we recorded the calling songs of 22 different cricket and katydid species for a comparative analysis and measured their thorax temperature while they sang.Acoustic signalling was energetically costly for Mecopoda sp. and Anurogryllus muticus, requiring a 12- and 16-fold increase over resting levels in the CO2 production rate. Moreover, calling increased thorax temperature, on average, by 7.6 and 5.8°C, respectively. We found that the song intensity and effective calling rate, but not simply the chirp/trill duty cycle or the pulse rate alone were good predictors for the thorax temperature increase in males.

In honeybees fast and efficient exploitation of nectar and pollen sources is achieved by persistent endothermy throughout the foraging cycle, which means extremely high energy costs. The need for food promotes maximisation of the intake rate, and the high costs call for energetic optimisation. Experiments on how honeybees resolve this conflict have to consider that foraging takes place in a variable environment concerning microclimate and food quality and availability. Here we report, in simultaneous measurements of energy costs, gains, and intake rate and efficiency, how honeybee foragers manage this challenge in their highly variable environment. If possible, during unlimited sucrose flow, they follow an 'investment-guided' ('time is honey') economic strategy promising increased returns. They maximise net intake rate by investing both own heat production and solar heat to increase body temperature to a level which guarantees a high suction velocity. They switch to an 'economizing' ('save the honey') optimisation of energetic efficiency if the intake rate is restricted by the food source when an increased body temperature would not guarantee a high intake rate. With this flexible and graded change between economic strategies honeybees can do both maximise colony intake rate and optimise foraging efficiency in reaction to environmental variation.

The two paper wasps, Polistes dominula and Polistes gallicus, are related species with strongly differing distribution ranges. We investigated thermal tolerance traits (critical thermal limits and metabolic response to temperature) to gain knowledge about physiological adaptations to their local climate conditions and to get evidence for the reasons of P. dominula’s successful dispersion. Body and ambient temperature measurements at the nests revealed behavioural adaptations to microclimate. The species differed clearly in critical thermal minimum (P. dominula −1.4 °C, P. gallicus −0.4 °C), but not significantly in critical thermal maximum of activity (P. dominula 47.1 °C, P. gallicus 47.6 °C). The metabolic response did not reveal clear adaptations to climate conditions. At low and high temperatures, the metabolic rate of P. dominula was higher, and at intermediate temperatures, we determined higher values in P. gallicus. However, the species exhibited remarkably differing thermoregulatory behaviour at the nest. On average, P. gallicus tolerated a thoracic temperature up to ~41 °C, whereas P. dominula already tried at ~37 °C to keep the thorax below ambient temperature. We suggest this to be an adaptation to the higher mean ambient temperature we measured at the nest during a breeding season. Although we determined for P. dominula a 0.5 °C larger thermal tolerance range, we do not presume this parameter to be solely responsible for the successful distribution of P. dominula. Additional factors, such as the thermal tolerance of the queens could limit the overwintering success of P. gallicus in a harsher climate.

Graphical abstract . Highlights ► We demonstrate the benefits of a combined use of infrared thermography with respiratory measurements in insect ecophysiological research. ► Infrared thermography enables repeated investigation of behaviour and thermoregulation without behavioural impairment. ► Comparison with respirometry brings new insights into the mechanisms of energetic optimisation of bee and wasp foraging. ► Combination of methods improves interpretation of respiratory traces in determinations of insect critical thermal limits., Endothermic insects like honeybees and some wasps have to cope with an enormous heat loss during foraging because of their small body size in comparison to endotherms like mammals and birds. The enormous costs of thermoregulation call for optimisation. Honeybees and wasps differ in their critical thermal maximum, which enables the bees to kill the wasps by heat. We here demonstrate the benefits of a combined use of body temperature measurement with infrared thermography, and respiratory measurements of energy turnover (O2 consumption or CO2 production via flow-through respirometry) to answer questions of insect ecophysiological research, and we describe calibrations to receive accurate results. To assess the question of what foraging honeybees optimise, their body temperature was compared with their energy turnover. Honeybees foraging from an artificial flower with unlimited sucrose flow increased body surface temperature and energy turnover with profitability of foraging (sucrose content of the food; 0.5 or 1.5 mol/L). Costs of thermoregulation, however, were rather independent of ambient temperature (13–30 °C). External heat gain by solar radiation was used to increase body temperature. This optimised foraging energetics by increasing suction speed. In determinations of insect respiratory critical thermal limits, the combined use of respiratory measurements and thermography made possible a more conclusive interpretation of respiratory traces.

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 (T(th)) was regulated at a high and rather constant level over a broad range of ambient temperatures (T(th) = 33.7-35.7°C, T(a) = 10-27°C). However, at a certain T(a), T(th) showed a strong variation, depending on the plants from which the bees were foraging. At warmer conditions (T(a) = 27-32°C) the T(th) increased nearly linearly with T(a) to a maximal average level of 42.6 °C. The thorax temperature excess decreased strongly with increasing T(a) (T(th)-T(a) = 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 T(th) in the spring than in the summer. An anova revealed that season had the greatest effect on T(th), followed by T(a) and radiation.4. It was presumed the foragers' motivational status to be the main factor responsible for the variation of T(th) between seasons and different plants.

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) of11 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.

We report here on the interrelationship of aggressive behaviour and thermoregulation in honeybees. Body temperature measurements were carried out without behavioural disturbance by infrared thermography. Guard bees, foragers, drones, and queens involved in aggressive interactions were always endothermic, i.e. had their flight muscles activated. Guards made differential use of their endothermic capacity. Mean thorax temperature was 34.2-35.1°C during examination of bees but higher during fights with wasps (37°C) or attack of humans (38.6°C). They usually cooled down when examining bees whereas examinees often heated up during prolonged interceptions (maximum >47°C). Guards neither adjusted their thorax temperature (and thus flight muscle function and agility) to that of examined workers, nor to that of drones, which were 2-7°C warmer. Guards examined cool bees (

The European paper wasp, Polistes dominulus Christ, is an abundant wasp species in South and Central Europe which dispersed to the north in recent times. Polistes dominulus exhibits an energy-extensive mode of life, spending much time resting at the nest, which should be reflected in adaptations regarding gas exchange and standard metabolism. We analysed the resting metabolism (CO2 emission) of Polistes dominulus workers in the ambient temperature range an individual may be exposed to during a breeding season (Ta = 2.4–40.6 °C) via flow through respirometry. Behaviour and endothermic activity were assessed by infrared thermography. With rising Ta, CO2 release followed an exponential increase from 27 to 149 and 802 nl g−1 min−1 at Ta = 3, 20 and 35 °C, respectively. Measurements of the thermal regime at the nest showed that resting P. dominulus are most of the time in the lower range of their standard metabolic curve. A comparison with a “highly energetic” wasp like Vespula sp. revealed that Polistes dominulus not only optimises behaviour but also reduces metabolism to save energy. The CO2 emission patterns changed with ambient temperature, from discontinuous (≤25 °C) to cyclic (25–36 °C) and continuous gas exchange at higher temperatures. A pronounced break appeared in the data progression regarding cycle frequency and CO2 emission per gas exchange cycle between 15 and 10 °C. This striking change in gas exchange features indicates a physiological adaptation to special respiratory requirements at low temperatures. Electronic supplementary material The online version of this article (doi:10.1007/s00360-015-0915-7) contains supplementary material, which is available to authorised users.

The body temperature of honeybees (Apis mellifera carnica Pollm.) was determined by infrared measuring instruments without touching the animals. From spring until summer the insects were observed on 13 different species of plants while foraging nectar and pollen within their natural environment. In this way it was possible for the first time to measure the body surface temperatures of all three parts of the body continuously and often simultaneously without disturbing the animals in their activity. It was remarkable that in spring at an ambient temperature from 12–20 °C on average the thorax was warmer by 6.4 °C and the head by 4.1°C than in summer (ambient temperature: 20–26 °C). The temperatures of all three parts of the body always exceeded ambient temperature. The thorax was the warmest part of the body. Concerning caput and abdomen, which were distinctly cooler, a slight dependence on the ambient temperature could be observed. The temperature of the abdomen, the coolest part of the body, never fell below 20.6 °C. It was obvious that heat was exchanged between the thorax and the two other parts of the body. The average thoracic temperature amounted to 35.7 °C in spring and to 29.3 °C in summer. The mean temperature of the head was 30.9 °C in spring and 26.8 °C in summer, that of the abdomen 25.2 °C and 23.1 °C. The higher body temperatures in spring possibly protect the bees against cooling at the lower ambient temperature.

Honeybee larvae and pupae are extremely stenothermic, i.e. they strongly depend on accurate regulation of brood nest temperature for proper development (33-36 degrees C). Here we study the mechanisms of social thermoregulation of honeybee colonies under changing environmental temperatures concerning the contribution of individuals to colony temperature homeostasis. Beside migration activity within the nest, the main active process is "endothermy on demand" of adults. An increase of cold stress (cooling of the colony) increases the intensity of heat production with thoracic flight muscles and the number of endothermic individuals, especially in the brood nest. As endothermy means hard work for bees, this eases much burden of nestmates which can stay ectothermic. Concerning the active reaction to cold stress by endothermy, age polyethism is reduced to only two physiologically predetermined task divisions, 0 to approximately 2 days and older. Endothermic heat production is the job of bees older than about two days. They are all similarly engaged in active heat production both in intensity and frequency. Their active heat production has an important reinforcement effect on passive heat production of the many ectothermic bees and of the brood. Ectothermy is most frequent in young bees (< approximately 2 days) both outside and inside of brood nest cells. We suggest young bees visit warm brood nest cells not only to clean them but also to speed up flight muscle development for proper endothermy and foraging later in their life. Young bees inside brood nest cells mostly receive heat from the surrounding cell wall during cold stress, whereas older bees predominantly transfer heat from the thorax to the cell wall. Endothermic bees regulate brood comb temperature more accurately than local air temperature. They apply the heat as close to the brood as possible: workers heating cells from within have a higher probability of endothermy than those on the comb surface. The findings show that thermal homeostasis of honeybee colonies is achieved by a combination of active and passive processes. The differential individual endothermic and behavioral reactions sum up to an integrated action of the honeybee colony as a superorganism.

A comparison of the thermoregulation of water foraging wasps (Vespulavulgaris, Polistesdominulus) 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 degrees C) the regression lines revealed mean thorax temperatures (T(th)) of 35.5-37.5 degrees C in Vespula, and of 28.6-33.7 degrees C in Polistes. At high T(a) (30-39 degrees C) T(th) was 37.2-40.6 degrees C in Vespula and 37.0-40.8 degrees C in Polistes. The thorax temperature excess (T(th)-T(a)) increased at moderate T(a) by 1.9 degrees C (Vespula) and 4.4 degrees C (Polistes) per kW(-1)m(-2). At high T(a) it increased by 4.0 degrees 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 degrees C) Vespula exhibited distinct endothermy in contrast to Polistes, which showed only a weak endothermic activity. At high T(a) (30-39 degrees 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.

In addition to honeybee workers, drones also contribute to colonial thermoregulation. We show the drones' contribution to thermoregulation at 5 different experimental temperatures ranging from 15-34 °C. The frequency and the degree of endothermy depended on the drones' local ambient temperature and age. Location on brood or non-brood areas had no influence. The frequency of endothermic drones and the intensity of endothermy increased with decreasing temperature. 30% of drones of 8 days and older heated their thorax by more than 1 °C above the abdomen. The youngest drones (0-2 days) did not exceed this level of endothermy. Though young drones were less often engaged in active heat production, their contribution to brood warming was not insignificant because their abundance on the brood nest was 3.5 times higher than that of the oldest drones (≥13 days). Results suggest that the stimulus for the drones' increased frequency of heating at low experimental temperatures was their low local ambient air and/or comb temperature.

Body surface temperature of individually marked wasps (Paravespula vulgaris, Vespidae, Hymenoptera) was measured by infrared thermography during repeated visits to a feeding bowl without injuring them or disturbing their behavior. Wasps were fed 0.5, 1 and 2 mol/l sucrose solution at two ambient temperatures.Thoracic temperature varied significantly in dependence on food quality (sucrose concentration of solution). At the higher ambient temperatures of 26.1-30.2 degrees C mean thoracic surface temperatures from different experiments were 35.3 and 38.0 degrees C when the wasps took a 0.5 mol/l sucrose solution, 37.0, 38.7 and 38.7 degrees C when they took a 1 mol/l solution, and 39.1 degrees C when they took a 2 mol/l sucrose solution. At the lower ambient temperatures of 17.6-21.0 degrees C thoracic temperatures were lower but the effect of different sucrose concentrations was similar: 34.7 degrees C with a 0.5 mol/l and 36.1 degrees C with a 1 mol/l sucrose solution. The concentration effect amounted to about 10-25% of the whole variability of thorax temperature. By contrast, the temperatures of the head and abdomen did not follow the changes in thorax temperature according to changes in sucrose concentration closely, which suggests that the pattern of haemolymph circulation may have changed after landing, during the wasps' stay at the feeder. At initial landing at the feeders thoracic temperatures where equal to (three of eight tests) or lower (five of eight tests) than at final departure.The correlation of thorax temperature with food quality probably reflects the wasps' level of excitement and motivation to collect the food, which allows them to balance energetic investment with profitability of foraging and the needs of flight muscle performance and motility.

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 microl O(2) min(-1) at 15 degrees C ambient temperature to 81.1 microl min(-1) at 25 degrees C, and reached a minimum of 29.9 microl min(-1) at 40 degrees C. In bees with low activity, it decreased from 89.3 microl O(2) min(-1) at 15 degrees C to 47.9 microl min(-1) at 25 degrees C and 14.7 microl min(-1) at 40 degrees 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 degrees 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 microl O(2) min(-1) at 10 degrees C to 0.38 microl min(-1) at 15 degrees C, 1.12 microl min(-1) at 25 degrees C, and 3.03 microl min(-1) at 40 degrees C. At 15, 25 and 40 degrees C, this was 343, 73 and 10 times below the values of the highly active bees, respectively. The Q(10) 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 degrees C to 1.35 in the range 21-31 degrees C, and increased again to 2.49 in the range 30-40 degrees C. We conclude that attempts to describe the temperature dependence of the resting metabolism of honeybees by Q(10) 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 Q(10) according to the exponential function (V(O(2))=0.151 x 1.0784(T(a))) (interpolated Q(10)=2.12).

The thermal behavior of round and wagtail dancing honeybees (Apis mellifera carnica) gathering sucrose solutions of concentrations between 0.5 and 2 mol·l-1 was investigated under field conditions by infrared thermography (30–506 m flight distance). During the stay inside the hive thoracic surface temperature ranged from 31.4 to 43.9 °C. In both round and wagtail dancing honeybees the concentration of sucrose in the food influenced dancing temperature in a non-linear way. Average dancing temperature was 37.9 °C in foragers gathering a 0.5 mol·l-1 sucrose solution, 40.1°C with a 1 mol·l-1, 40.6°C with a 1.5 mol·l-1 and 40.7°C with a 2 mol·l-1 solution. The variability of thoracic temperature was highest with the 0.5 mol·l-1 and lowest with the 1.5 and 2 mol·l-1 concentrations. Thoracic temperatures during trophallactic contact with hive bees were similar to dancing temperature at 1.5 mol·l-1 but lower at the other concentrations. During periods of distribution of food to hive bees (trophallactic contact >2.5s) the dancers' thorax cooled down by more than 0.5°C considerably more frequently with the 0.5 mol·l-1 solution (65% of cases) than with the 1.5 mol·l-1 solution (26%). By contrast, heating the thorax up by more than 0.5°C was infrequent with the 0.5 mol·l-1 solution (2%) but occurred at a maximum rate of 26% with the 1.5 mol·l-1 solution. Bees gathering the 1 or 2 mol·l-1 solutions showed intermediate behavior. Linear model analysis showed that at higher concentrations the dancers compensated better for variations of hive air temperature: per 1 °C increase of hive temperature dancing temperature increased by 0.34, 0.22, 0.12, and 0.13 °C with 0.5, 1, 1.5, and 2 mol·l-1 sucrose solutions, respectively. The results furnish evidence that dancing honeybees follow a strategy of “selective heterothermy” by tuning their thermal behavior to the needs of the behavior performed at the moment. Thoracic temperature is regulated to a high level and more accurately when fast exploitation of profitable food sources is recommended. Thoracic temperature is lowered when the ratio of gain to costs of foraging becomes more unfavorable.

SummaryLongevity, duration of hive-bound period, and foraging period, of worker bees, infested or not infested during their pupal development, were investigated during the whole year. Shortening of lifespan depended on the extent of infestation and on season. Influence of infestation on lifespan could be shown during hive-bound and foraging periods; no influence could be shown on flight activity. Drastic differences occurred during winter; in 4 observation hives, only 4–18% of the infested bees that had emerged in September, survived until the following March.

Graphical abstract Highlights ► Vespine wasps have a very high mass-specific resting metabolic rate. ► They exhibit a steep increase of resting metabolism with ambient temperature. ► Wasp thermolimit was considerably below that of honeybees (44.9 vs. 48.9 °C). ► Infrared thermography allowed accurate estimation of the respiratory thermolimit., 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

Graphical abstract . Research highlights ▶ Thorax temperature was regulated from 37.0–45.3 °C (ambient temperature: 3–39 °C). ▶ Solar heat gain was used to increase thorax temperature by about 1–3 °C. ▶ High thorax temperature allowed regulation of an optimal head temperature. ▶ Flexible thermal strategy enabled foraging in a broad ambient temperature range., 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 (Ta) and solar radiation they are likely to be exposed in their natural environment in Middle Europe. The mean thorax temperature (Tth) during foraging stays was regulated at a constantly high level (37.0–38.5 °C) in a broad range of Ta (3–30 °C). At warmer conditions (Ta = 30–39 °C) Tth increased to a maximal level of 45.3 °C. The endothermic temperature excess (difference of Tbody − Ta of living and dead bees) was used to assess the endogenously generated temperature elevation as a correlate of energy turnover. Up to a Ta of ∼30 °C bees used solar heat gain for a double purpose: to reduce energetic expenditure and to increase Tth by about 1–3 °C to improve force production of flight muscles. At higher Ta they exhibited cooling efforts to get rid of excess heat. A high Tth also allowed regulation of the head temperature high enough to guarantee proper function of the bees’ suction pump even at low Ta. This shortened the foraging stays and this way reduced energetic costs. With decreasing Ta bees also reduced arrival body weight and crop loading to do both minimize costs and optimize flight performance.