Anton Stabentheiner

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.

Participation of nitric oxide in the mustard oil-induced neurogenic i inflammation of the rat paw skin

The possibility of nitric oxide (NO) participating in the neurogenic inflammatory reaction of the rat hindpaw skin to topical application of mustard oil was examined in anesthetized rats. Vasodilation was measured by contactless infrared emission thermography, plasma protein exudation was measured by the Evans blue leakage technique, and formation of oedema was determined by measurement of the paw volume. Topical administration of mustard oil increased the temperature of the paw skin by 2-3 degrees C, a response that was accompanied by plasma protein extravasation and followed by development of slight oedema amounting to a 7-8% increase in paw volume. That the mustard oil-induced increase in paw temperature and oedema formation was neurogenic was shown by the finding that both responses were absent in adult rats treated with a neurotoxic dose of capsaicin (0.16 mmol kg-1 s.c.) as neonates. NG-Nitro-L-arginine methyl ester (L-NAME, 43 mumol kg-1 i.v.) an inhibitor of NO formation, caused a significant increase in mean arterial blood pressure and a moderate decrease in cutaneous blood flow, whereas the same dose of the inactive enantiomer, D-NAME, was without effect. L-NAME, but not D-NAME, reduced the cutaneous hyperaemia caused by topical administration of mustard oil by about 50% but did not significantly diminish the exudative reaction to mustard oil. These findings indicate that endothelium-derived NO plays a mediator role in the vasodilator component of mustard oil-induced neurogenic inflammation in the rat paw skin whereas the increase in vascular permeability does not seem to involve NO directly as a mediator.

Variability of the thermal behavior of honeybees on a feeding place

SummaryThe thermoregulation of honeybees (Apis mellifera carnica) was investigated under field conditions, on a feeding place 335 m away from the hive, where 0.25M or 0.5M sucrose solution was offered. By means of real-time tele-thermography, contactless body surface temperature measurements of undisturbed animals were made.The foraging bees showed highly developed individual thermoregulatory abilities. Complex behavioral patterns such as food uptake, active body temperature regulation, and preparation for flight were performed simultaneously. However, body temperature was more variable than expected. When bees drank 0.5M sucrose solution, they generally had a higher thoracic surface temperature (TThs) and showed smaller temperature fluctuations (e.g., cooling down after landing) than with 0.25M solution. Given 0.5M sucrose they stayed for shorter periods at the feeding place. The highest (maximum)TThs during the stop was positively (linearly) correlated with the ambient temperature (Ta=18−30°C) for both 0.25M and 0.5M sucrose feeding. At aTa of 19°C the mean (interpolated) maximum values forTThs were 37.2°C (0.25M) and 38.5°C (0.5M); at aTa of 27°C they were 39.2°C (0.25M) and 40.9°C (0.5M). The minimumTThs was correlated withTa only with 0.5M feeding, whereas with 0.25M feeding a great variability was observed. Similarly as the maximumTThs,TThs upon landing and taking off were positively (linearly) correlated withTa and were higher during 0.5M feeding.The quality (concentration) of the food offered to the bees obviously influenced their thermal behavior at the feeding place.

Thermoregulation of dancing bees: thoracic temperature of pollen and nectar foragers in relation to profitability of foraging and colony need.

The thorax surface temperature of dancing honeybees (Apis mellifera carnica) recruiting nestmates to natural sources of nectar and pollen around Graz (Austria) was measured by real-time infrared thermography without touching them or disturbing social interactions. Thorax temperature during dancing was quite variable (31.4-43 degrees C). In the course of a foraging season it varied considerably and was always lower than in bees foraging from a highly profitable food source (2 molar sucrose 120 m from the hive). It averaged 38.0 degrees C (SD=2.24, n=224 dances) in the nectar foragers and 37.4 degrees C (SD=1.64, n=171) in the pollen foragers, resembling that of dancers foraging 0.5 molar sucrose from feeders with unlimited flow. Hive air temperature accounted only for about 3-8% of total variation. Foraging distance modulated dancing temperature in a way that, according to the decrease of the profitability of foraging with distance, maximum temperatures decreased and, in accordance with the increase of the dancing threshold with distance, minumum temperatures increased with distance, this way providing new support for the hypothesis that the dancing temperature is modulated by the profitability of foraging and the dancing and foraging motivation of the bees. Dancing temperature of both nectar and pollen dancers correlated with several parameters of the hive status, increasing with the amount of brood and decreasing with the amount of honey and pollen. These correlations are discussed with respect to literature reports on a colonys need for pollen and nectar, in particular the effect of brood and the amount of pollen on pollen foraging, and the effect of honey stores and demand for nectar on nectar foraging.

Standard methods for physiology and biochemistry research in Apis mellifera

Summary Despite their tremendous economic importance, and apart from certain topics in the field of neurophysiology such as vision, olfaction, learning and memory, honey bees are not a typical model system for studying general questions of insect physiology. The reason is their social lifestyle, which sets them apart from a “typical insect” and, during social evolution, has resulted in the restructuring of certain physiological pathways and biochemical characteristics in this insect. Not surprisingly, the questions that have attracted most attention by researchers working on honey bee physiology and biochemistry in general are core topics specifically related to social organization, such as caste development, reproductive division of labour and polyethism within the worker caste. With certain proteins playing key roles in these processes, such as the major royal jelly proteins (MRJPs), including royalactin and hexamerins in caste development, and vitellogenin in reproductive division of labour and age polyethism, a major section herein will present and discuss basic laboratory protocols for protein analyses established and standardized to address such questions in bees. A second major topic concerns endocrine mechanisms underlying processes of queen and worker development, as well as reproduction and polyethism, especially the roles of juvenile hormone and ecdysteroids. Sensitive techniques for the quantification of juvenile hormone levels circulating in haemolymph, as well as its synthesis by the corpora aliata are described. Although these require certain instrumentation and a considerable degree of sophistication in the analysis procedures, we considered that presenting these techniques would be of interest to laboratories planning to specialize in such analyses. Since biogenic amines are both neurotransmitters and regulators of endocrine glands, we also present a standard method for the detection and analysis of certain biogenic amines of interest. Further questions that cross borders between individual and social physiology are related to energy metabolism and thermoregulation. Thus a further three sections are dedicated to protocols on carbohydrate quantification in body fluid, body temperature measurement and respirometry.

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

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.

Aggressive and Docile Colony Defence Patterns in Apis mellifera. A Retreater-Releaser Concept

Colony defence in Apis mellifera involves a variety of traits ranging from ‘aggressive’ (e.g. entrance guarding, recruitment of flying guards) to ‘docile’ (e.g. retreating into the nest) expression. We tested 11 colonies of three subspecies (capensis, scutellata, carnica) regarding their defensiveness. Each colony was selected as reportedly ‘aggressive’, ‘intermediate’ or ‘docile’ and consisted of about 10,000 bees. We applied three stimulation regimes (mechanical disturbance, exposure to alarm pheromones, and the combination of both) and measured their behaviours by tracking the rates of outflying bees at the entrance sites of the test hives. We provided evidence that for mechanical disturbances the test colonies resolved into two response types, if the ‘immediate’ defence response, assessed in the first minute of stimulation, was taken as a function of foraging: ‘releaser’ colonies allocated flying guards, ‘retreater’ colonies reduced the outside-hive activities. This division was observed irrespective of the subspecies membership and maintained in even roughly changing environmental conditions. However, if pheromone and mechanical stimulation were combined, the variety of colony defensiveness restricted to two further types irrespective of the subspecies membership: six of nine colonies degraded their rate of flying defenders with increasing foraging level, three of the colonies extended their ‘aggressiveness’ by increasing the defender rate with the foraging level. Such ‘super-aggressive’ colonies obviously are able to allocate two separate recruitment pools for foragers and flying defenders.

Correlations between hearing and sound production in piranhas

SummaryIn order to determine whether correlations exist between hearing and the known soundproduction abilities in piranhas (Serrasalmus nattereri), behavioral auditory thresholds were obtained with continuous tones and tone pulses. A new avoidance conditioning method was developed, where fin movements of caged animals were taken as response to a tone. The mean values of the far-field audiogram ranged from −26 dB re. 0.1 Pa at 80 Hz to a low point of about −43 dB between 220–350 Hz and rose to −14 dB at 1500 Hz. The frequency spectrum of typical drumming sounds (barks) covers the range of best hearing (100–600 Hz).Piranhas are able to integrate temporally acoustic signals: in threshold investigations with repeated tone pulses, the thresholds rose approximately exponentially with decreasing pulse duration and repetition rate; thresholds of single pulses were higher with shorter pulses. The temporal patterning of the calls and the temporal integration ability are well correlated in piranhas, optimizing intraspecific detectability and total length of sound production with respect to the fatigue characteristics of drumming muscles and habituation of the neural pacemaker.The lagenae of the piranhas were found to face laterofrontally; this is thought to be a morphological adaptation to sound production, saving the lagenae from excessive strain during activation of the drumming muscles.

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.

Role of nitric oxide in the vasodilator but not exudative component of mustard oil-induced inflammation in rat skin

The participation of nitric oxide (NO) in the neurogenic inflammatory reaction of the rat hindpaw skin to topical application of mustard oil was examined by the use ofNG-nitro-l-arginine methyl ester (l-NAME, 43 μmol kg−1 i.v.), an inhibitor of NO formation. Control rats received the same dose of the inactive enantiomerd-NAME. Vasodilatation was recorded by contactless infrared emission thermography, and plasma protein exudation was measured by the Evans Blue leakage technique and by measurement of the paw volume in anaesthetized rats.l-NAME reduced the cutaneous hyperaemia caused by topical administration of mustard oil by about 50% but did not change the exudative reaction to mustard oil. These findings indicate that NO plays a mediator role in the vasodilator component of neurogenic inflammation in the rat paw skin, whereas the increase in vascular permeability does not appear to depend on NO.