) controlled by a self-written Excel VBA-macro (Microsoft Corporation). Values of the body temperature during foraging were taken in regular intervals of about 3 s immediately after the landing of the insects until their take off. The surface temperatures of head (Thd), thorax (Tth) and abdomen (Tab) were calculated with an infrared emissivity of 0.97, determined Protease Inhibitor Library solubility dmso for the honeybee cuticle ( Stabentheiner and Schmaranzer, 1987 and Schmaranzer and Stabentheiner, 1988). Because the ThermaCam is working in the long-wave infrared range (7.5–13 μm) the reflected radiation from the bees’ cuticle produced only a small measurement

error (0.2 °C for 1000 W m −2) which was compensated for. In this way we reached an accuracy of 0.7 °C for the body surface temperature of the bees at a sensitivity of <0.1 °C. The temperature gradient between the thorax and the ambient air (thorax temperature excess = Tthorax − Ta) is often used as a measure to judge the endothermic capability of insects. In sunshine, however, this is not a reliable measure of the endogenously generated temperature excess because of additional heating of the bees’ body by the solar radiation. Therefore, we compared the living bees’ temperature excess of thorax, head and abdomen with that of this website the dead bees (endothermic temperature excess = [Tbody − Ta]living − [Tbody − Ta]dead).

The relationship between body temperature, temperature excess, crop loading and Ta or solar radiation was described

by simple linear, sigmoidal or exponential regression functions and tested with ANOVA. Data analysis aminophylline and statistics were performed by using the Statgraphics package (Statistical Graphics Corporation) and ORIGIN software (OriginLab Corporation). Fig. 1 shows a thermogram of a water foraging honeybee (Apis mellifera carnica) and of 2 dead bees fixed at the foraging site on a wooden grate. We analyzed 879 foraging stays of bees at the water barrel. From 12,377 thermograms we evaluated body surface temperatures of head (Thd, n = 11,290), thorax (Tth, n = 11,340) and abdomen (Tab, n = 11,334) of water foragers, of all body parts of dead bees (n = 1037 each), and of the water surface (Twater, n = 4957). Fig. 2 shows representative body temperature curves of bees at low, medium and high ambient temperature (Ta). From these curves the mean value of each body part for each foraging stay was calculated and plotted in Fig. 3. It contains 3–45 measuring points per stay (including arrival and departure values) depending on the duration of foraging. We investigated the body temperature regulation of water foraging honeybees (Apis mellifera carnica) in the whole range of ambient temperatures (Ta = ∼3–40 °C) and solar radiation (50–1200 W m−2) they are likely to be exposed in their natural environment.