5 to 3 °C) than honeybees if measured at the same food Ponatinib chemical structure source and under the same ambient conditions ( Kovac and Stabentheiner, 1999, Kovac and Stabentheiner, 2011, Kovac et al., 2009, Kovac et al., 2010 and Schmaranzer and Stabentheiner, 1988). According to the life-style hypothesis ( Reinhold, 1999) we had expected that this would result also in a lower resting metabolism. However, it was a surprising result that Vespula stands out not only with a considerably higher resting metabolism compared to A. mellifera ( Fig. 4, insert, wasp CO2 production at 15 °C 41%, at 25 °C 63%, at 35 °C 57% higher than in bees, respectively) but also with a much steeper increase

(higher mean Q10 value) with rising ambient temperature. The wasps’

CO2 production ( Fig. 4) follows basically an exponential course. Slight deviations of single data points have been well documented in similar investigations on resting insects ( Kovac et al., 2007, Lighton and Bartholomew, 1988, Lighton, 1989 and Stabentheiner et al., 2003) and could be regarded as slight plateaus in an otherwise exponential increase. While the CO2 curve of honeybee resting metabolism follows a sigmoidal progression with the inflection point at around 37 °C Cyclopamine clinical trial ( Kovac et al., 2007), the wasps’ curve is described best by an adapted exponential function (see Fig. 4) with an assumed sudden drop-off at the wasps’ upper critical thermal maximum. Honeybee foragers feed on a diet consisting predominantly of carbohydrates, which results in a respiratory quotient (RQ) of 1 (Rothe and Nachtigall, 1989). As the wasps were caught on an artificial feeding station provided with sucrose solution and were also supplied with carbohydrates during the experiment (1.5 M sucrose solution not ad libitum), also a RQ = 1 could be assumed. So, as the wasp and bee RQ should show minimal – if any – differences under these experimental conditions, a direct comparison of their resting metabolism seems to be possible from the CO2 recordings. A comparison of the resting metabolism of Vespula with that of honeybees ( Kovac et al., 2007) and Polistes ( Weiner et al.,

2009 and Weiner et al., 2010) shows that the metabolism of Vespula is not optimized to save energy in the resting state. Their unexpected high basal metabolic rate and the steep incline with ambient temperature surely have consequences for their social thermoregulation. Similar as was reported in honeybees ( Stabentheiner et al., 2010), nest temperature regulation in Vespine wasps ( Himmer, 1962, Klingner et al., 2005, Klingner et al., 2006 and Steiner, 1930) can be assumed to be the result of behavioral measures, active (endothermic) heat production “on demand” and “passive effects”. An important passive effect is the reinforcement of passive heat production (in the ectothermic state) of resting individuals due to social nest temperature homeostasis ( Stabentheiner et al., 2010).