B. Schricker

Thermal investigations of a honey bee colony: thermoregulation of the hive during summer and winter and heat production of members of different bee castes

SummaryThe temperature at the centre, the periphery and the entrance of a honey bee colony (Apis mellifera carnica) was continuously determined during the summer season and the broodless time in winter. During the summer season the temperature in the brood nest averages 35.5°C with brief excursions up to 37.0°C and down to 33.8°C. Increasing environmental temperatures resulted in linear increases in the temperature of the hive entrance, its periphery and its centre. The temperature in the centre of an overwintering cluster is maintained at an average value of 21.3°C (min 12.0°C, max 33.5°C). With rising ambient temperatures the central temperature of a winter cluster drops whereas the peripheral temperature increases slightly. With decreasing external temperatures the peripheral temperature is lowered by a small amount while the clusters centre temperature is raised. Linear relationships are observed between the central and the ambient temperature and between the central temperature and the temperature difference of the peripheral and the ambient temperatures. The slopes point to two minimum threshold values for the central (15°C) and the peripheral temperature (5°C) which should not be transgressed in an overwintering cluster. Microcalorimetric determinations of the heat production were performed on the three castes of the honey bee: workers, drones and queens of different ages. Among these groups single adult workers showed the highest heat production rates (209 mW·g−1) with only neglectible fluctuations in the heat production rate. Juvenile workers exhibited a mean heat production rate of 142 mW·g−1. The rate of heat production of adult workers is strongly dependent upon the number of bees together in a group. With more than 10 individuals weight-specific heat dissipation remains constant with increasing group sizes at a level approximately 1/17 that of an isolated bee. Differences are seen between the rates of virgin (117 mW·g−1) and laying (102 mW·g−1) queens. Laying queens showed less thermal fluctuations than virgin queens. High fluctuations in heat production rates are observed for drones. In both groups (fertile, juvenile) phases of high and extremely low activity succeed one another. The heat production of juvenile drones was 68 mW·g−1, that of fertile drones 184 mW·g−1 due to stronger locomotory activities.

Nestmate recognition in social wasps: manipulation of hydrocarbon profiles induces aggression in the European hornet

Abstract. The influence of individual cuticular hydrocarbons on nestmate recognition in the European hornet, Vespa crabro L., was investigated. We observed the behavioural response of workers towards differently treated dead conspecifics in a bioassay. Dummies were extracted with dichloromethane and extracts were spiked with microgram amounts of synthetic hydrocarbons naturally occurring on the cuticle of V. crabro. These modified extracts were reapplied to extracted workers that were subsequently tested in the bioassay. Non-spiked nestmate dummies (negative control) and untreated non-nestmate dummies (positive control) were tested in control experiments. The addition of only heneicosane or a mixture of heneicosane, tricosane, and (Z)-9-tricosene to the extracts led to a significant increase of agonistic behaviour in workers leaving the nest for foraging flights. Returning workers reacted much less aggressively than those leaving. This is one of the first behavioural proofs that manipulation of cuticular hydrocarbon profiles can be perceived by a social insect species. The results support the hypothesis that colony-specific cuticular hydrocarbon profiles are involved in the phenomenon of nestmate recognition among social insects.

Calorimetric investigations of the different castes of honey bees, Apis mellifera carnica

SummaryHoney bees of different age and castes were investigated calorimetrically at 20, 25 and 30 °C. Experiments were completed by endoscopic observation of the insects in the visible and the near infrared range and by acoustical monitoring and subsequent frequency analysis of various locomotor activities. Direct calorimetric results of this paper are compared with data of indirect calorimetry from the literature using a respiratory quotient of 1.00 and 21.13 J consumed. Agreements between both methods are generally good. The results show that weight-specific heat production rates increase with age of worker bees by a factor of 5.6 at 30 °C, 3.7 at 25 °C and 40.0 at 20 °C. In groups of foragers the heat production decreases with growing group size to around 6% of the value for an isolated bee. The presence of a fertile queen or of brood reduces the heat output of a small worker group significantly. Adult drones exhibit a much higher metabolic rate (up to 19.7-fold at 20 °C) than juveniles with strong fluctuations in the power-time curves. Fertile queens show a less pronounced heat production rate than virgin queens (54% at 30 °C, 87% at 25 °C and 77% at 20 °C). Calorimetric unrest is much higher for young than for adult queens. Heat production is very low in both uncapped and capped brood and less than 30% of that of a newly emerged worker. In most cases temperature showed a significant influence on the metabolic level, although its sign was not homogeneous between the castes or even within them. Locomotor activities are easily recorded by the acoustic frequency spectrum (0–7.5 kHz) and in good agreement with endoscopic observations and calorimetric traces.

Role of cuticular lipids in nestmate recognition of the European hornet Vespa crabro L. (Hymenoptera, Vespidae)

Summary: In order to elucidate nestmate recognition in the European hornet Vespa crabro L. (Hymenoptera, Vespidae) the behavioral response of workers towards dead nestmates and non-nestmates was tested in a bioassay. The testing arena was integrated in a socially and physically intact nest, in an effort to ensure natural behavior of the extremely sensitive wasps. The hornets responded to dead non-nestmates with aggressive behavior, whereas dead nestmates were tolerated or ignored. Solvent extraction of non-nestmate dummies resulted in significant decrease of agonistic behavior of the responding workers. Their behavior towards extracted non-nestmate dummies was no longer statistically distinguishable from the behavior towards nestmate dummies treated in the same way. Treatment of extracted nestmate dummies with cuticular extracts of non-nestmates induced aggressive behavior in the responding workers, whereas treatment of the extracted non-nestmate dummies with cuticular extracts of nestmates lead to a significant decrease of agonistic behavior, when compared with untreated non-nestmates. ¶A statistical comparison of the two colonies with regard to the chemical composition of the cuticular extracts revealed that relative peak areas of 5 monoenes, 4 methyl branched alkanes, 1 terpenoid ester, and 2 n-alkanes differed significantly. The chemical analysis of the Dufours gland revealed that all 16 compounds identified in the gland were also present in the cuticular extracts. ¶The results strongly indicate that particular mixtures of cuticular lipids play an important role in nestmate recognition of V. crabro.

A method for continuous direct calorimetric measurements of energy metabolism in intact hornet (Vespa crabro) and honeybee (Apis mellifera) colonies

Abstract The heat production rates of an intact hornet ( Vespa crabro ) colony and a honeybee ( Apis mellifera ) winter cluster were measured by means of direct calorimetry. Two camping cold boxes with Peltier elements as cooling systems were used as simple and inexpensive differential calorimeters. The boxes had a volume of 24 I and sensitivities of between 6.8 mV W −1 and 14.8 mV W −1 , depending on the experimental setup. They They were modified in such a way that the foragers had free access to the outdoor environment. The average daily heat production rate of the hornet colony ranged from 1.2 W at the end of the season in October up to 12.5 W at the stage of maximum biomass in August. The heat production rates of a honeybee winter cluster were measured in the following winter at ambient temperatures of 0–5°C. The maximum heat production rate was attained at 0°C (20.5 W) and the minimum heat production rate at 5°C (11.5 W). These results are compared with data for energy metabolism obtained respirometrically and by artificial heating of empty nests, respectively.

Calorimetric investigations on social thermogenesis in the hornet Vespa crabro L. (Hymenoptera: Vespinae)

Abstract Heat production rates of individual hornets were measured at 10, 15, and 20°C by means of direct calorimetry in order to investigate endothermic behaviour and capabilities to contribute to nest heat. Hornet workers showed heat production rates of 49 mW per g wet weight (w.w.) (SD = ±8 mW g −1 ) at 20°C; drones have lower heat production rates at the same temperature (36 mW g −1 , SD = ±5 mW g −1 ). Nevertheless, the latter may contribute significant portions of heat to the nest at the end of season. The heat production of the whole colony was assessed at 1.8 W at the state of maximum biomass and at 1.3 W later, after the appearance of the reproductive forms, i.e. the drones and queens. The fact that drones and workers lowered their heat production rates with decreasing ambient temperatures in our experiments is discussed.

Microcalorimetric investigation of the action of propolis on Varroa destructor mites

Abstract Treatment of Varroa destructor (Anderson and Trueman) mites with propolis has displayed both narcotic and lethal effects. The length of narcosis and rate of mortality showed dependence on the concentration of propolis used, the duration of contact time and the extraction procedure. Investigation of the action of propolis on the heat production rate of Varroa mites was performed by means of a Biocalorimeter (BCP 600). Calorimetric results point to the fact that even weak propolis concentrations with feeble lethal effects have a strong influence on the specific heat production rate. Thus, treatment with a 20% propolis solution in 40% ethanol resulted in a mortality rate of only 34% but dropped the heat production rate by 75%, a corresponding 5% propolis solution had no lethal effect but reduced the specific heat production rate still by 37% and treatment with a 0.5% propolis solution in 55% ethanol resulted in a non-significant mortality rate of 7% but reduced the specific heat production rate by 29%. Propolis showed a strong impact on the structure of the calorimetric power–time (p–t) curves. The usually highly structured p–t curves were smoothed due to treatment even with weak propolis concentrations.

Direct Carousel Flight Calorimeter for Metabolic Investigations of Small Insects

An isoperibolic heat flow calorimeter is described for the determination of heat production rates during the tethered flight of small insects such as flies, honeybees or hornets. The insects are fixed with their thoraces to one arm of a low-friction carousel. A sensor counts the number of revolutions per time and determines the speed of flight. Wing sound is monitored by a microphone with an audio recorder, so that wing beat frequencies and hence locomotor activities can be determined. Different illumination means are incorporated to guarantee the illumination levels necessary for flight.

Microcalorimetric investigations of the energy metabolism of honeybee workers, apis mellifera carnica

Abstract Heat production measurements were performed for individual workers of different age and for worker groups of the honeybee Apis mellifera carnica by means of a 100-ml-Calvet-calorimeter. Individual worker bees show a strong positive correlation of the weight specific heat production rate with age. Increasing numbers of workers together in a group reduce the heat production drastically, so that a group of 12 bees dissipate less heat than one isolated animal. Addition of a queen or of bee brood to a group of 6 workers lowers the heat output, too. These effects could be described as socially conditioned by the use of an endoscope or a microphone incorporated into the calorimetric vessel. Endoscopie observations have been performed in the visible and the infrared region of the spectrum.

Heat Dissipation of Flying Wax Moths (Galleria Mellonella) Measured by Means of Direct Calorimetry

Heat production rates and flight speed of adult wax moths (Galleria mellonella) were investigated by means of direct calorimetry at TA=20 and 30°C. Specific heat production rates were not significantly different between males and females at TA=20°C (pTH=747±123.7 mW g-1, n=5 for males and pTH=791±169 mW g-1, n=5 for females) even with females having a higher body mass (MB=83.8±21.6 mg, n=9 for males and MB=146.4±25.7 mg, n=11 for females) and wing load. In females, heat production rates were dependent on temperature with higher heat production rates at TA=20°C (pTH=791±169 mW g-1, n=5) than at TA=30°C (pTH=441±74 mW g-1, n=6). Flight speed was also clearly correlated with TA. Both males and females flew more slowly at TA=20 than at 30°C.