Body temperature and thermoregulation in two species of yellowjackets,Vespula germanica and V. maculifrons

In spite of the abundance and broad distribution of social wasps, little information exists concerning thermoregulation by individuals. We measured body temperatures of the yellowjackets Vespula germanica and V. maculifrons and examined their thermoregulatory mechanisms. V. germanica demonstrated thermoregulation via a decreasing gradient between thorax temperature and ambient temperature as ambient temperature increased. V. maculifrons exhibited a constant gradient at lower ambient temperatures but thorax temperature was constant at high ambient temperatures. Head temperature exhibited similar patterns in both species. In spite of low thermal conductances, a simple heat budget model predicts substantial heat loads in warm conditions in the absence of thermoregulation. Both species regurgitated when heated on the head. A smaller volume of regurgitant was produced at lower head temperatures and a larger volume at higher head temperatures. Small regurgitations resulted in stabilization of head temperature, while large ones resulted in 4°C decreases in head temperature. Regurgitation was rare when wasps were heated upon the thorax. Abdomen temperature was 3–4°C above ambient temperature, and approached ambient temperature under the hottest conditions. No evidence was found for shunting of hot hemolymph from thorax to abdomen as a cooling mechanism. The frequency of regurgitation in workers returning to the nest increased with ambient temperature. Regurgitation may be an important thermoregulatory strategy during heat stress, but is probably not the only mechanism used in yellowjackets.Abbreviations M _b body mass - M _th thorax mass - T _a ambient temperature - T _ab abdomen temperature - T _b body temperature - T _h head temperature - T _th thorax temperature - C _t thermal conductance     

Thermoregulation of foraging honeybees on flowering plants: seasonal variability and influence of radiative heat gain

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.     

City-Scale Expansion of Human Thermoregulatory Costs

The physiological maintenance of a stable internal temperature by mammals and birds – the phenomenon termed homeothermy – is well known to be energetically expensive. The annual energy requirements of free-living mammals and birds are estimated to be 15–30 times higher than those of similar-size ectothermic vertebrates like lizards. Contemporary humans also use energy to accomplish thermoregulation. They are unique, however, in having shifted thermoregulatory control from the body to the occupied environment, with most people living in cities in dwellings that are temperature-regulated by furnaces and air conditioners powered by exogenous energy sources. The energetic implications of this strategy remain poorly defined. Here we comparatively quantify energy costs in cities, dwellings, and individual human bodies. Thermoregulation persists as a major driver of energy expenditure across these three scales, resulting in energy-versus-ambient-temperature relationships remarkably similar in shape. Incredibly, despite the many and diversified uses of network-delivered energy in modern societies, the energy requirements of six North American cities are as temperature-dependent as the energy requirements of isolated, individual homeotherms. However, the annual per-person energy cost of exogenously powered thermoregulation in cities and dwellings is 9–28 times higher than the cost of endogenous, metabolic thermoregulation of the human body. Shifting the locus of thermoregulatory control from the body to the dwelling achieves climate-independent thermal comfort. However, in an era of amplifying climate change driven by the carbon footprint of humanity, we must acknowledge the energetic extravagance of contemporary, city-scale thermoregulation, which prioritizes heat production over heat conservation.     

Leptin Signaling Is Required for Adaptive Changes in Food Intake,but Not Energy Expenditure,in Response to Different Thermal Conditions

Survival of free-living animals depends on the ability to maintain core body temperature in the face of rapid and dramatic changes in their thermal environment. If food intake is not adjusted to meet the changing energy demands associated with changes of ambient temperature, a serious challenge to body energy stores can occur. To more fully understand the coupling of thermoregulation to energy homeostasis in normal animals and to investigate the role of the adipose hormone leptin to this process, comprehensive measures of energy homeostasis and core temperature were obtained in leptin-deficient ob/ob mice and their wild-type (WT) littermate controls when housed under cool (14°C), usual (22°C) or ∼ thermoneutral (30°C) conditions. Our findings extend previous evidence that WT mice robustly defend normothermia in response to either a lowering (14°C) or an increase (30°C) of ambient temperature without changes in body weight or body composition. In contrast, leptin-deficient, ob/ob mice fail to defend normothermia at ambient temperatures lower than thermoneutrality and exhibit marked losses of both body fat and lean mass when exposed to cooler environments (14°C). Our findings further demonstrate a strong inverse relationship between ambient temperature and energy expenditure in WT mice, a relationship that is preserved in ob/ob mice. However, thermal conductance analysis indicates defective heat retention in ob/ob mice, irrespective of temperature. While a negative relationship between ambient temperature and energy intake also exists in WT mice, this relationship is disrupted in ob/ob mice. Thus, to meet the thermoregulatory demands of different ambient temperatures, leptin signaling is required for adaptive changes in both energy intake and thermal conductance. A better understanding of the mechanisms coupling thermoregulation to energy homeostasis may lead to the development of new approaches for the treatment of obesity.     

Trade-offs between activity and thermoregulation in a small carnivore,the least weasel Mustela nivalis

We studied factors influencing daily energy expenditures (DEE) of male least weasels (Mustela nivalis) using the doubly labelled water technique. The relationship between ambient temperature and DEE formed a triangular pattern, characterized by invariance of the maximum DEE and an inverse relationship between minimum DEE and temperature. A simple energetic model relating the DEE of male weasels to activity time (AT) and ambient temperature predicted that, across seasons, less than 10 per cent of measurements approach the upper bound of observed DEE. Male weasels were able to maintain a relatively constant maximum energy output across varying temperatures by adjusting their AT to changes in temperature. They achieved maximum energy expenditures in winter due to high thermoregulatory costs, and in spring and summer due to high levels of physical activity. This pattern exemplifies a ‘metabolic niche’ of a small mammal having extremely high energy expenditures primarily driven by ambient temperature.     

Thermoregulation of water foraging honeybees—Balancing of endothermic activity with radiative heat gain and functional requirements

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.     

Conceptual learning by miniature brains

Concepts act as a cornerstone of human cognition. Humans and non-human primates learn conceptual relationships such as ‘same’, ‘different’, ‘larger than’, ‘better than’, among others. In all cases, the relationships have to be encoded by the brain independently of the physical nature of objects linked by the relation. Consequently, concepts are associated with high levels of cognitive sophistication and are not expected in an insect brain. Yet, various works have shown that the miniature brain of honeybees rapidly learns conceptual relationships involving visual stimuli. Concepts such as ‘same’, ‘different’, ‘above/below of’ or ‘left/right are well mastered by bees. We review here evidence about concept learning in honeybees and discuss both its potential adaptive advantage and its possible neural substrates. The results reviewed here challenge the traditional view attributing supremacy to larger brains when it comes to the elaboration of concepts and have wide implications for understanding how brains can form conceptual relations.     

Radiant heat affects thermoregulation and energy expenditure during rewarming from torpor

The high expenditure of energy required for endogenous rewarming is one of the widely perceived disadvantages of torpor. However, recent evidence demonstrates that passive rewarming either by the increase of ambient temperature or by basking in the sun appears to be common in heterothermic birds and mammals. As it is presently unknown how radiant heat affects energy expenditure during rewarming from torpor and little is known about how it affects normothermic thermoregulation, we quantified the effects of radiant heat on body temperature and metabolic rate of the small (body mass 25 g) marsupial Sminthopsis macroura in the laboratory. Normothermic resting individuals exposed to radiant heat were able to maintain metabolic rates near basal levels (at 0.91 ml O(2) g(-1) h(-1)) and a constant body temperature down to an ambient temperature of 12 degrees C. In contrast, metabolic rates of individuals without access to radiant heat were 4.5-times higher at an ambient temperature of 12 degrees C and body temperature fell with ambient temperature. During radiant heat-assisted passive rewarming from torpor, animals did not employ shivering but appeared to maximise uptake of radiant heat. Their metabolic rate increased only 3.2-times with a 15- degrees C rise of body temperature (Q(10)=2.2), as predicted by Q(10) effects. In contrast, during active rewarming shivering was intensive and metabolic rates showed an 11.6-times increase. Although body temperature showed a similar absolute change between the beginning and the end of the rewarming process, the overall energetic cost during active rewarming was 6.3-times greater than that during passive, radiant heat-assisted rewarming. Our study demonstrates that energetic models assuming active rewarming from torpor at low ambient temperatures can substantially over-estimate energetic costs. The low energy expenditure during passive arousal provides an alternative explanation as to why daily torpor is common in sunny regions and suggests that the prevalence of torpor in low latitudes may have been under-estimated in the past.     

One for all and all for one: the energetic benefits of huddling in endotherms

Huddling can be defined as “an active and close aggregation of animals”. It is a cooperative group behaviour, permitting individuals involved in social thermoregulation to minimize heat loss and thereby lower their energy expenditure, and possibly allowing them to reallocate the saved energy to other functions such as growth or reproduction. Huddling is especially important in the case of animals faced with high heat loss due to a high surface‐to‐volume ratio, poor insulation, or living in cold environments. Although numerous experimental studies have focused on the huddling behaviour of a wide range of species, to our knowledge, this is the first attempt to review the various implications of this widely used behavioural strategy. Huddling allows individuals to maximise energy savings by (1) decreasing their cold‐exposed body surface area, (2) reducing their heat loss through warming of ambient temperatures surrounding the group, and (3) eventually lowering their body temperature through physiological processes. Huddling provides substantial energy savings and is estimated to reduce energy expenditure by between 6 and 53%. Broad variations in the energetic benefits of huddling depend on the number of individuals and species involved in huddles, the ambient temperatures to which individuals are exposed and the density of the aggregations. It has been shown that huddling individuals have increased survival, a lower food intake, a decreased body mass loss, increased growth rate, reduced water loss, and/or a more constant body temperature together with a significant reduction in metabolic rate. Though huddling has been studied widely, this review reveals the intricacies of this adaptive behaviour.     

Honeybee Colony Thermoregulation – Regulatory Mechanisms and Contribution of Individuals in Dependence on Age,Location and Thermal Stress

Honeybee larvae and pupae are extremely stenothermic, i.e. they strongly depend on accurate regulation of brood nest temperature for proper development (33–36°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 ∼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 (<∼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.     

Honeybees prefer warmer nectar and less viscous nectar,regardless of sugar concentration

The internal temperature of flowers may be higher than air temperature, and warmer nectar could offer energetic advantages for honeybee thermoregulation, as well as being easier to drink owing to its lower viscosity. We investigated the responses of Apis mellifera scutellata (10 colonies) to warmed 10% w/w sucrose solutions, maintained at 20–35°C, independent of low air temperatures, and to 20% w/w sucrose solutions with the viscosity increased by the addition of the inert polysaccharide Tylose (up to the equivalent of 34.5% sucrose). Honeybee crop loads increased with nectar temperature, as did the total consumption of sucrose solutions over 2 h by all bees visiting the feeders. In addition, the preference of marked honeybees shifted towards higher nectar temperatures with successive feeder visits. Crop loads were inversely proportional to the viscosity of the artificial nectar, as was the total consumption of sucrose solutions over 2 h. Marked honeybees avoided higher nectar viscosities with successive feeder visits. Bees thus showed strong preferences for both warmer and less viscous nectar, independent of changes in its sugar concentration. Bees may benefit from foraging on nectars that are warmer than air temperature for two reasons that are not mutually exclusive: reduced thermoregulatory costs and faster ingestion times due to the lower viscosity.     

Energy budget of the chicken foot

1. 1.|A mathematical model predicts the energy loss from a chicken foot provided the following variables are known: body temperature, air temperature, wind velocity, blood flow to the foot, and the relative partitioning of blood flow via two distinct venous returns.

2. 2.|Chickens are capable of keeping their feet from freezing at temperatures as low as −30°C ambient, but at a high energy cost.

3. 3.|Chickens can modulate blood flow to their feet at thermoneutral temperatures enough to vary heat loss to environment by about one-fourth metabolic heat production.

Exogenous insulin enhances humoural immune responses in short-day,but not long-day,Siberian hamsters (Phodopus sungorus)

Many animals experience marked seasonal fluctuations in environmental conditions. In response, animals display adaptive alterations in physiology and behaviour, including seasonal changes in immune function. During winter, animals must reallocate finite energy stores from relatively costly, less exigent systems (e.g. reproduction and immunity) to systems critical for immediate survival (e.g. thermoregulation). Seasonal changes in immunity are probably mediated by neuroendocrine factors signalling current energetic state. One potential hormonal candidate is insulin, a metabolic hormone released in response to elevated blood glucose levels. The aim of the present study was to explore the potential role of insulin in signalling energy status to the immune system in a seasonally breeding animal, the Siberian hamster (Phodopus sungorus). Specifically, exogenous insulin was administered to male hamsters housed in either long ‘summer-like’ or short ‘winter-like’ days. Animals were then challenged with an innocuous antigen and immune responses were measured. Insulin treatment significantly enhanced humoural immune responses in short, but not long days. In addition, insulin treatment increased food intake and decreased blood glucose levels across photoperiodic treatments. Collectively, these data support the hypothesis that insulin acts as an endocrine signal integrating seasonal energetic changes and immune responses in seasonally breeding rodents.     

Thermoregulation of water foraging wasps (Vespula vulgaris and Polistes dominulus)

A comparison of the thermoregulation of water foraging wasps (Vespula vulgaris, Polistes dominulus) under special consideration of ambient temperature and solar radiation was conducted. The body surface temperature of living and dead wasps was measured by infrared thermography under natural conditions in their environment without disturbing the insects’ behaviour. The body temperature of both of them was positively correlated with T_a and solar radiation. At moderate T_a (22–28 °C) the regression lines revealed mean thorax temperatures (T_th) of 35.5–37.5 °C in Vespula, and of 28.6–33.7 °C in Polistes. At high T_a (30–39 °C) T_th was 37.2–40.6 °C in Vespula and 37.0–40.8 °C in Polistes. The thorax temperature excess (T_th–T_a) increased at moderate T_a by 1.9 °C (Vespula) and 4.4 °C (Polistes) per kW⁻¹ m⁻². At high T_a it increased by 4.0 °C per kW⁻¹ m⁻² in both wasps. A comparison of the living water foraging Vespula and Polistes with dead wasps revealed a great difference in their thermoregulatory behaviour. At moderate T_a (22–28 °C) Vespula exhibited distinct endothermy in contrast to Polistes, which showed only a weak endothermic activity. At high T_a (30–39 °C) Vespula reduced their active heat production, and Polistes were always ectothermic. Both species exhibited an increasing cooling effort with increasing insolation and ambient temperature.     

蜜蜂体内王浆主蛋白基因mrjp9的转录表达研究

蜜蜂体内有9种王浆蛋白基因(major royal jelly protein,MRJPs1～9),其中MRJPs1～5在蜂王浆中含量较高,是蜂王浆生物学功能的基础。MRJPs6～9在王浆中没有或含量极少,且功能未知。为研究非王浆蛋白组分的MRJP9的生物学功能,本研究用RT-PCR的方法对意大利蜜蜂Apis mellifera ligustica Spinola不同组织,不同部位,不同级型样本中mrjp9的转录水平进行检测和定量。结果发现mrjp9在蜜蜂的幼虫、蛹和成年蜜蜂的各组织部位均广泛转录表达,但其在幼虫、蛹和刚出房的成年蜜蜂体内表达水平较低,而在成年采集蜂体内表达水平则较高,其表达与蜜蜂的发育时期有关。通过对在成年蜜蜂体内各组织部位的表达水平进行检测的结果显示该基因主要在蜜蜂的头、胸和王浆腺等组织部位的表达较高,其他组织部位表达较少。此外,该基因也在雄蜂和蜂王体内广泛表达,不受蜜蜂性别和级型的影响。这些结果说明mrjp9是一与蜜蜂发育有关的基因,可能与蜜蜂的行为发育和分工调控有关。     

Kleptothermy: an additional category of thermoregulation,and a possible example in sea kraits (Laticauda laticaudata,Serpentes)

Lacking the capacity for thermogenesis, most ectotherms inhabiting thermally heterogeneous environments rely instead upon exploiting that ambient heterogeneity. In many cases they maintain body temperatures within a narrow range despite massive spatial and temporal variation in ambient conditions. Reliance on diverse thermal opportunities is reflected in specific terms for organisms that bask in sunlight to regulate their temperature (heliotherms), or that press their bodies against warm substrates to facilitate heat flow (thigmotherms), or that rely on large body mass to maintain thermal constancy (gigantothermy). We propose an additional category of thermoregulators: kleptotherms, which regulate their own temperature by ‘stealing’ heat from other organisms. This concept involves two major conditions: the thermal heterogeneity created by the presence of a warm organism in a cool environment and the selective use of that heterogeneity by another animal to maintain body temperatures at higher (and more stable) levels than would be possible elsewhere in the local area. Kleptothermy occurs in endotherms also, but is usually reciprocal (rather than unilateral as in ectotherms). Thermal monitoring on a small tropical island documents a possible example of kleptothermy, based on high stable temperatures of a sea snake (Laticauda laticaudata) inside a burrow occupied by seabirds.     

Hummingbird foraging and the relation between bioenergetics and behaviour

Because of their small size and expensive mode of flight, hummingbirds display some of the highest known mass-specific rates of aerobic metabolism among vertebrates. High enzymatic flux capacities through pathways of carbohydrate and long-chain fatty acid oxidation indicate that either substrate can fuel flight. Although hummingbirds are known to rely on fat to fuel migratory flight, short foraging bouts are fueled by the oxidation of carbohydrate, not fat. This allows birds refueling at meadows during migration to deposit fat at higher rates and avoids the energetic inefficiency that results from synthesizing fat from dietary sugar, and then breaking down the fat to fuel foraging flight. On cold mornings in subalpine meadows, refueling hummingbirds achieve net energy gain despite the high energetic costs of thermoregulation and flight. In doing so, they sustain the highest known time-averaged metabolic rates among vertebrates. However, low sucrose concentrations, provided in volumes large enough to allow the maintenance of energy balance at low temperature, result in energy deficit and mass loss. The problem of disposing of dietary water at low ambient temperature when intake rates are elevated suggests that the kidneys may be involved in establishing the upper limit to intake rates and, therefore, maximum sustained metabolic rates. It is suggested that hummingbird behaviour and metabolism have coevolved to maximize net energy gain. Further, the energetics of hummingbird thermoregulation and flight may have influenced the evolution of sucrose content in floral nectar.     

The Free Energy Profile of Tubulin Straight-Bent Conformational Changes,with Implications for Microtubule Assembly and Drug Discovery

αβ-tubulin dimers need to convert between a ‘bent’ conformation observed for free dimers in solution and a ‘straight’ conformation required for incorporation into the microtubule lattice. Here, we investigate the free energy landscape of αβ-tubulin using molecular dynamics simulations, emphasizing implications for models of assembly, and modulation of the conformational landscape by colchicine, a tubulin-binding drug that inhibits microtubule polymerization. Specifically, we performed molecular dynamics, potential-of-mean force simulations to obtain the free energy profile for unpolymerized GDP-bound tubulin as a function of the ∼12° intradimer rotation differentiating the straight and bent conformers. Our results predict that the unassembled GDP-tubulin heterodimer exists in a continuum of conformations ranging between straight and bent, but, in agreement with existing structural data, suggests that an intermediate bent state has a lower free energy (by ∼1 kcal/mol) and thus dominates in solution. In agreement with predictions of the lattice model of microtubule assembly, lateral binding of two αβ-tubulins strongly shifts the conformational equilibrium towards the straight state, which is then ∼1 kcal/mol lower in free energy than the bent state. Finally, calculations of colchicine binding to a single αβ-tubulin dimer strongly shifts the equilibrium toward the bent states, and disfavors the straight state to the extent that it is no longer thermodynamically populated.     

Context-dependent ‘safekeeping’ of foraging tools in New Caledonian crows

Several animal species use tools for foraging, such as sticks to extract embedded arthropods and honey, or stones to crack open nuts and eggs. While providing access to nutritious foods, these behaviours may incur significant costs, such as the time and energy spent searching for, manufacturing and transporting tools. These costs can be reduced by re-using tools, keeping them safe when not needed. We experimentally investigated what New Caledonian crows do with their tools between successive prey extractions, and whether they express tool ‘safekeeping’ behaviours more often when the costs (foraging at height), or likelihood (handling of demanding prey), of tool loss are high. Birds generally took care of their tools (84% of 176 prey extractions, nine subjects), either trapping them underfoot (74%) or storing them in holes (26%)—behaviours we also observed in the wild (19 cases, four subjects). Moreover, tool-handling behaviour was context-dependent, with subjects: keeping their tools safe significantly more often when foraging at height; and storing tools significantly more often in holes when extracting more demanding prey (under these conditions, foot-trapping proved challenging). In arboreal environments, safekeeping can prevent costly tool losses, removing a potentially important constraint on the evolution of habitual and complex tool behaviour.     

Bees get a head start on honey production

Nectar concentration is assumed to remain constant during transport by honeybees between flowers and hive. We sampled crop contents of nectar foragers on Aloe greatheadii var. davyana, a major winter bee plant in South Africa. The nectar is dilute (approx. 20% w/w), but the crop contents of bees captured on flowers are significantly more concentrated. In returning foragers, the concentration increases further to 38–40%, accompanied by a volume decrease. The doubling of sugar concentration suggests that nectar is regurgitated onto the tongue and evaporated during foraging and on the return flight. Processing of the dilute nectar into honey thus begins early, aided by low ambient humidities. This has implications for honeybee thermoregulation, water balance and energetics during foraging, and for the communication of nectar quality to recruits.