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Overwintering insects are facing energetic challenges because of food shortage, low temperature, and desiccation stress. Paper wasps of the genus Polistes overwinter as mated adults (gynes) in hibernacula protecting them from predation, snow, and rain but barely from low environmental temperature. In different climates, they face differing overwintering temperature regimes, and therefore they may differ in their energy use. We investigated how much of energy resources built up until autumn is used during diapause dormancy in natural hibernacula by measuring lipid, glycogen, and free carbohydrate content in autumn and early spring in Polistes dominula from temperate European (Austrian) and warm Mediterranean (Italian) climate and Polistes gallicus from Mediterranean climate. Winter energy consumption amounted to ~ 339 and ~ 310 J per wasp in the Austrian and Italian Polistes dominula populations. The smaller Italian Polistes gallicus consumed ~ 247 J. This amounts to 2.62, 2.35, and 1.79 J per day. Of this, the energy demand was mainly fuelled by lipids (84%, 93%, and 90%, respectively), but glycogen stores contributed also considerably (16%, 6%, and 9%). Free carbohydrates decreased only by 0.7%, 1%, and 0.8%. While fat stores seem still sufficient in spring, the wasps depleted most of their carbohydrates. The energy reserves of 396, 400, and 147 J per wasp remaining in spring in the three populations seem sufficient to fuel rest or simple brood care activities for a whole summer but restrict foraging flights to a few hours (~ 3.5-6 h). Results suggest that energy supply might become challenging in expected future climate scenarios., (© 2024. The Author(s).)

The paper wasp Polistes dominula is a thermophilic species originating from the Mediterranean climate, but is now widely spread in Europe. They live in quite differing habitats; and as synanthropic species, they have been established in human settlement areas. They build a single small comb at protected places with a favorable microclimate. We measured the temperature of the wasps, the nests and their environment at typical nesting sides in Austria (Europe) in the temperate climate, in order to reveal relationships between nest and body temperature and the habitats' microclimate. The temperatures of the comb and of the wasps' body were in a wide range (~20-37 °C) above the ambient air temperature at the nest. This is an advantage as higher temperatures accelerate the development speed of the brood. However, the mean comb temperature did not exceed approximately 38.6 °C. This was managed by cooling efforts of the adult wasps. The ambient air temperature near the nest (~1-2 cm) was always clearly elevated above the ambient air temperature at a local standard weather station in the habitat. A comparison with climate-model-generated macroclimate data revealed the necessity of measuring microclimate data for a reliable description of the insects' thermal environment.

Gynes of paper wasps ( Polistes sp.) spend the cold season in sheltered hibernacles. These hibernacles protect against predators and adverse weather conditions but offer only limited protection against low temperatures. During overwintering diapause, wasps live on the energy they store. We investigated the hibernacles' microclimate conditions of species from the Mediterranean (Italy, P. dominula , P. gallicus ) and temperate (Austria, P. dominula ) climates in order to describe the environmental conditions and calculate the energetic demand of overwintering according to standard metabolic rate functions. The temperatures at the hibernacles differed significantly between the Mediterranean and temperate habitats (average in Austria: 3.2 ± 5.71 °C, in Italy: 8.5 ± 5.29 °C). In both habitats, the hibernacle temperatures showed variance, but the mean hibernacle temperature corresponded closely to the meteorological climate data. Cumulative mass-specific energetic costs over the studied period were the lowest for the temperate P. dominula population compared with both Mediterranean species. The lower costs of the temperate species were a result of the lower hibernacle temperature and acclimation to lower environmental temperatures. Model calculations with an increased mean temperature of up to 3 °C due to climate change indicate a dramatic increase of up to 40% in additional costs.

Ambient temperature is a main parameter that determines the thriving and propagation of ectothermic insects. It affects egg and larval development as well as adults' survival and successful overwintering. Pyrrhocoris apterus is a herbivorous bug species almost ubiquitous in Eurasia. Its distribution extends from the Atlantic Coast to Siberia, Northwest China and Mongolia. After introduction, it established successfully in the USA, Central America, India and Australia, which indicates a high invasive potential of this species. We determined the climatic conditions in Central Europe in a habitat where P. apterus has been continuously observed for decades. We conducted temperature measurements in the habitat and in the microhabitats where individuals could be found during the year and set them against freely available climate data commonly used to characterize habitat climate. Our temperature measurements were also compared to thermal limits (critical thermal minima and maxima). Although ambient temperatures outside the thermal boundaries of P. apterus can and do occur in the habitat, the bugs thrive and propagate. Microhabitat measurement in winter showed that individuals sought areas with favorable temperatures for hibernation. In particular, these areas are not (always) represented in large-scale climate tables, leading to possible misinterpretation of future patterns of spread of invasive species spread.

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 R 2  = 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 ., (© 2023. The Author(s).)

Paper wasps are widely distributed in Europe. They live in the warm Mediterranean, and in the harsh Alpine climate. Some species are very careful in their choice of nesting sites to ensure a proper development of the brood. We investigated microclimate conditions at the nests of three species ( P. dominula, P. gallicus, P. biglumis ) from differing climates, in order to characterize environmental conditions and conduct energetic calculations for an entire breeding season. The mean ambient nest temperature differed significantly in the Mediterranean, temperate, and Alpine habitats, but in all habitats it was about 2 to 3 °C above the standard meteorological data. The energetic calculations of adult wasps' standard and active metabolic rate, based on respiratory measurements, differed significantly, depending on the measured ambient temperatures or the wasps' body temperatures. P. gallicus from the warm Mediterranean climate exhibited the highest energetic costs, whereas P. biglumis from the harsh Alpine climate had the lowest costs. Energetic costs of P. dominula from the temperate climate were somewhat lower than those in the Mediterranean species, but clearly higher than those in the Alpine species. Temperature increase due to climate change may have a severe impact on the wasps' survival as energetic costs increase., Competing Interests: The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

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., (© 2022. The Author(s).)

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.

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 (CO 2 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 CO 2 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., (Copyright © 2020 The Authors. Published by Elsevier Inc. All rights reserved.)

Heteroptera, or true bugs populate many climate zones, coping with different environmental conditions. The aim of this study was the evaluation of their thermal limits and derived traits, as well as climatological parameters which might influence their distribution. We assessed the thermal limits (critical thermal maxima, CT max , and minima, CT min ) of eight seed bug species (Lygaeidae, Pyrrhocoridae) distributed over four Köppen-Geiger climate classification types (KCC), approximately 6° of latitude, and four European countries (Austria, Italy, Croatia, Bulgaria). In test tubes, a temperature ramp was driven down to -5 °C for CT min and up to 50 °C for CT max (0.25 °C/min) until the bugs' voluntary, coordinated movement stopped. In contrast to CT min , CT max depended significantly on KCC, species, and body mass. CT max showed high correlation with bioclimatic parameters such as annual mean temperature and mean maximum temperature of warmest month (BIO5), as well as three parameters representing temperature variability. CT min correlated with mean annual temperature, mean minimum temperature of coldest month (BIO6), and two parameters representing variability. Although the derived trait cold tolerance (TC = BIO6 - CT min ) depended on several bioclimatic variables, heat tolerance (TH = CT max - BIO5) showed no correlation. Seed bugs seem to have potential for further range shifts in the face of global warming.

European Polistine wasps inhabit mainly temperate and warm climate regions. However, the paper wasp Polistes biglumis represents an exception; it resides in mountainous areas, e.g., in the Alps and in the Apennines. In these habitats, the wasps are exposed to a broad temperature range during their lifetime. We investigated whether they developed adaptations in their metabolism to their special climate conditions by measuring their CO 2 production. The standard or resting metabolic rate and the metabolism of active wasps was measured in the temperature range which they are exposed to in their habitat in summer. The standard metabolic rate increased in a typical exponential progression with ambient temperature, like in other wasps. The active metabolism also increased with temperature, but not in a simple exponential course. Some exceptionally high values were presumed to originate from endothermy. The simultaneous measurement of body temperature and metabolic rate revealed a strong correlation between these two parameters. The comparison of the standard metabolic rate of Polistes biglumis with that of Polistes dominula revealed a significantly lower metabolism of the alpine wasps. This energy saving metabolic strategy could be an adaptation to the harsh climate conditions, which restricts foraging flights and energy recruitment.

Polistine wasps collect nectar for their energetic demand and for the provision of the brood. They are mainly ectothermic during different behavioral tasks. We investigated the body temperature of two species living in differing habitats and climate regions, in order to reveal the environmental influence on their thermoregulatory behavior. The species were Polistes dominula in the temperate climate of Central Europe, and Polistes gallicus in the warm Mediterranean climate of Southern Europe. The wasp's body temperature was measured during foraging on lovage ( Levisticum officinale ) and fennel ( Foeniculum vulgare ) by infrared thermography in the entire ambient temperature range they are usually exposed to (T a ~ 20-40 °C). The temperature of all body parts increased nearly linearly with ambient temperature, with the thorax as the warmest part. To achieve optimal foraging temperatures, they preferably use solar radiation. An "operative temperature model" enabled the evaluation of the endothermic effort. Polistes dominula foraging on lovage exhibited no endothermic activity. However, while foraging on fennel they had a weak and almost constant endothermic performance of about 1 °C. Polistes gallicus , by contrast, exhibited mostly no or only minor endothermy during foraging. Both wasps avoid a high energetic effort and this way reduce their foraging costs.

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 (T a  = 12-40 °C). The thorax temperature as well as the energetic turnover showed a great variability. The mean T thorax was ranging from ~ 35.7 °C at 12 °C to nearly 42.5 °C at 40 °C. The energy turnover calculated from CO 2 -release was highest at a T a 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.

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 mol l -1 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 mass 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., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2018. Published by The Company of Biologists Ltd.)

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.

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.

Vespine wasps (Vespula sp.) are endowed with a pronounced ability of endothermic heat production. To show how they balance energetics and thermoregulation under variable environmental conditions, we measured the body temperature and respiration of sucrose foragers (1.5 M, unlimited flow) under variable ambient temperature (T a = 20-35 °C) and solar radiation (20-570 W m(-2)). Results revealed a graduated balancing of metabolic efforts with thermoregulatory needs. The thoracic temperature in the shade depended on ambient temperature, increasing from ~37 to 39 °C. However, wasps used solar heat gain to regulate their thorax temperature at a rather high level at low T a (mean T thorax ~ 39 °C). Only at high T a they used solar heat to reduce their metabolic rate remarkably. A high body temperature accelerated the suction speed and shortened foraging time. As the costs of foraging strongly depended on duration, the efficiency could be significantly increased with a high body temperature. Heat gain from solar radiation enabled the wasps to enhance foraging efficiency at high ambient temperature (T a = 30 °C) by up to 63 %. The well-balanced change of economic strategies in response to environmental conditions minimized costs of foraging and optimized energetic efficiency.

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 (T a = 2.4-40.6 °C) via flow through respirometry. Behaviour and endothermic activity were assessed by infrared thermography. With rising T a, CO2 release followed an exponential increase from 27 to 149 and 802 nl g(-1) min(-1) at T a = 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.

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 a ~40 °C; dVCO 2 =12 nl s -1 ; P <0.05), probably due to a higher body temperature (dT thorax =1.5 °C; P <0.01). The critical thermal maximum of activity and respiration was similar (difference activity CT max =0.8 °C, respiratory CT max =1.1 °C). The lethal temperature (LT 50 , 8h ) 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.

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.

We investigated the respiration patterns of wasps (Vespula sp.) in their viable temperature range (2.9-42.4°C) by measuring CO2 production and locomotor and endothermic activity. Wasps showed cycles of an interburst-burst type at low ambient temperatures (Ta<5°C) or typical discontinuous gas exchange patterns with closed, flutter and open phases. At high Ta of >31°C, CO2 emission became cyclic. With rising Ta they enhanced CO2-emission primarily by an exponential increase in respiration frequency, from 2.6 mHz at 4.7°C to 74 mHz at 39.7°C. In the same range of Ta CO2 release per cycle decreased from 38.9 to 26.4 μl g(-1)cycle(-1). A comparison of wasps with other insects showed that they are among the insects with a low respiratory frequency at a given resting metabolic rate (RMR), and a relatively flat increase of respiratory frequency with RMR. CO2 emission was always accompanied by abdominal respiration movements in all open phases and in 71.4% of the flutter phases, often accompanied by body movements. Results suggest that resting wasps gain their highly efficient gas exchange to a considerable extent via the length and type of respiration movements., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

In insect groups with the ability of endothermy, the thermoregulatory capacity has a direct relation to body mass. To verify this relationship in vespine wasps, we compared the thermoregulation of hornets (Vespa crabro), the largest species of wasps in Central Europe, with two smaller wasps (Vespula vulgaris and Vespula germanica) in the entire range of ambient temperature (T(a): ~0-40°C) where the insects exhibited foraging flights.Despite the great difference in body weight of Vespula (V. vulgaris: 84.1±19.0 mg, V. germanica: 74.1±9.6 mg) and Vespa (477.5±59.9 mg), they exhibited similarities in the dependence of thorax temperature on T(a) on their arrival (mean T(th) = 30-40°C) and departure (mean T(th) = 33-40°C) at the nest entrance. However, the hornets' thorax temperature was up to 2.5°C higher upon arrival and up to 3°C lower at departure. The thorax temperature excess (T(th)-T(a)) above ambient air of about 5-18°C indicates a high endothermic capacity in both hornets and wasps. Heat gain from solar radiation elevated the temperature excess by up to 1°C. Results show that hornets and wasps are able to regulate their body temperature quite well, even during flight. A comparison of flight temperature with literature reports on other vespine wasps revealed a dependence of the T(th) on the body mass in species weighing less than about 200 mg.

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' CO(2) 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 CO(2) production rate of resting wasps increased steeply according to an exponential function, from 5.658 μl g(-1) min(-1) at 8.3°C to 8.504 μl g(-1) min(-1) at 20.2°C, 58.686 μl g(-1) min(-1) at 35.3°C and 102.84 μl g(-1) min(-1) at 40°C. The wasps' respiratory critical thermal maximum (CT(max)), marking the upper edge of their viable temperature range, was 45.3°C. The respiratory CT(max) did not differ significantly from the activity CT(max) of 44.9°C. CT(max) 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 © 2012 Elsevier Ltd. All rights reserved.)

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 (O(2) consumption or CO(2) 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.

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., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

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.

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.

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 (<33°C) longer than warmer ones, supporting the hypothesis that heating of examinees facilitates odour identification by guards, probably because of vapour pressure increase of semiochemicals with temperature. Guards in the core of aggressive balls clinged to the attacked insects to fix them and kill them by heat (maximum 46.5°C). Bees in the outer cluster layers resembled normal guards behaviourally and thermally. They served as active core insulators by heating up to 43.9°C. While balled wasps were cooler (maximum 42.5°C) than clinging guards balled bees behaved like examinees with maximum temperatures of 46.6°C, which further supports the hypothesis that the examinees heat up to facilitate odour identification.

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).

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 degrees C, S.D.=4.14, N=1545, 303 bees) than in the guards (34.0 degrees C, S.D.=2.00, N=1681, 772 bees). During thorough examinations lasting longer than 30 s, more than 60 % of the examinees showed phases of intense thoracic heating of more than 2 degrees C (maximum temperature 48.5 degrees C), whereas most guards cooled down. Our data suggest that these examinees heat up their surface to enhance chemical signalling during examinations.

The vasoconstrictive response to hyperbaric oxygen (HBO2) therapy was non-invasively quantified in eight healthy volunteers at 1.95 and 2.5 atm abs (197.5 and 253.2 kPa; multiplace chamber, air environment) by laser-Doppler flowmetry (LDF). The sensors for continuous measurement of microvascular perfusion (flux) and skin temperature were localized on the thenar eminence. Transcutaneous oxygen (tcPO2) and carbon dioxide (tcPCO2) tensions, blood pressure, heart rate, respiration rate, peripheral oxygen saturation, and temperature of the hyperbaric chamber were recorded at five conditions: 1) baseline--air breathing at 1.0 atm abs, 2) after 15 min of HBO2 at 2.5 atm abs, 3) after 15 min of HBO2 at 1.95 atm abs, 4) 1 min after decompression with oxygen breathing at 1.0 atm abs, and 5) after 15 min of breathing air at 1.0 atm abs. Flux decreased continuously at conditions 2 (76.5%), 3 (50.6%), and 4 (37% of baseline, P < 0.05; Tukey test). Skin temperature fell below baseline at conditions 2, 3, 4 (P < 0.01, Tukey test), and 5 (P < 0.05, Tukey test, P < 0.001, analysis of variance). Range of correlation between inspired gas PO2 (PIO2) and alteration of flux 0.91 to 0.72, median -0.41. Correlation between PIO2 and tcPO2, r = 0.98. Chamber temperature and tcPCO2 remained stable. HBO2 reduced dermal microcirculation and temperature disproportionate to PIO2. LDF is suitable for use under hyperbaric conditions.