The thorax temperature and energy expenditure of sucrose foraging honeybees varies markedly in direct response to the richness of food rewards and distance (e.g. Stabentheiner and Schmaranzer, 1986, Stabentheiner and Schmaranzer, 1987, Stabentheiner and Schmaranzer, 1988, Dyer and Seeley, 1987, Schmaranzer and Stabentheiner, 1988, Waddington, 1990, Stabentheiner and Hagmüller, 1991, Underwood, 1991, Balderrama et al., 1992, Stabentheiner et al., 1995, Moffatt and Núñez, 1997, Moffatt, 2001, Stabentheiner, 1996 and Stabentheiner, 2001). Highly motivated bees foraging concentrated sucrose solution increase body temperature with increasing energy gain from the food source. However, water does

not provide a gain of energy. Rather, bees have to invest a lot of energy, especially to forage at low Ta. The high body temperatures observed CAL-101 molecular weight (means ∼35–38 °C) are comparable with bees foraging 0.25–0.5 molar sucrose solution ( Schmaranzer and Stabentheiner, 1988). Usually, honeybees avoid foraging at a Ta below about 12 °C. To MK-2206 datasheet our knowledge only Heinrich (1979a) reported foraging

of a few bees on flowers at a Ta below 10 °C. In spring, when our colonies had to provide already a lot of brood, the bees collected water at very low and for them critical temperatures (down to 5 °C). At these very extreme conditions they exhibited thoracic temperatures of 33.5 °C above the ambient air on average. In some cases, mean Tth per stay was kept 36 °C above Ta. This extreme energetic investment for thermoregulation, therefore, emphasizes the water foragers’ highly motivated state despite the fact that water contains no usable energy. This is a good hint at the high importance of water for the survival of the colonies. The temperature of the abdomen was below MG-132 mouse that of the head at low Ta ( Fig. 3). However, Fig. 7C shows that at low Ta still a considerable amount

of the thoracic heat production reached the abdomen. Heinrich, 1980b and Heinrich, 1993 suggested that bees use a series of aortic loops in the petiole as a counter-current heat exchanger to prevent heat leakage to the abdomen. The heat still reaching the abdomen would be an inevitable result of the remaining hemolymph circulation. However, we presume that bees, beside the necessity to save energy, have to provide the abdomen with enough heat for proper function of physiological processes involved in energy supply and respiration. Concerning the temperatures of head and abdomen, the head was the better-regulated body part (Fig. 2 and Fig. 3). Even at very low Ta the hemolymph circulation from the warm thorax ( Heinrich, 1979b, Heinrich, 1980a and Coelho, 1991b) was kept at a level preventing the Thd from falling below 20 °C (mean per stay), which seems to bee necessary for a proper function of physiological and neural processes (see below).