4). This passive effect in nest thermoregulation is considerably higher in wasps than in honeybees (see insert of Fig. 4; compare also Kovac et al., 2007). A wasp RQ below 1 would shift the curve of wasp metabolism in terms of O2 consumption to even higher values, and this way increase the difference in energy turnover between bees and wasps. In phases of regulated nest temperature, therefore, a certain number of ectothermic wasps produce a higher amount of heat than the same number of ectothermic individuals in honeybee colonies at a certain ambient temperature.

This has also the consequence that fewer wasps are needed for active (endothermic) Z-VAD-FMK supplier heat production. Relatively few thermally active wasps may take away much burden from other individuals which can stay

passive. At the upper range of selleck chemical experimental temperatures (from ∼35 °C upwards) the wasps showed rest only sparsely. Both, number and duration of resting periods decreased with rising Ta and agitated movement predominated. Furthermore, many individuals showed cooling behavior, an indication that the individuals were not comfortable under these circumstances, and mainly wanted to escape the hostile environment. From 39.7 °C onwards only 37.5% (3 of 8 individuals) of the wasps could be measured in a true resting state ( Fig. 4, crossed boxes), all other individuals were measured during “rest” in their “deleterious range” ( Klok et al., 2004) or heat stupor ( Fleurat-Lessard and Dupuis, 2010), right after cyclic respiration had ceased (see Fig. 6, after stage 4). Other individuals tested did not show rest at all at these high temperatures PAK5 and therefore were not included in this study. As a consequence, one could reason that Vespula generally does not show resting behavior at ambient temperatures above Ta ≈ 40 °C ( Fig. 4, dashed line). In any case occasional rest (observed only for one or two minutes) at these temperatures is at a very high energetic level. With rising ambient temperatures, an increasing number of individuals did not survive the experiments (see Fig. 4, mortality

in %) in spite of Ta being way under their CTmax (see Table 1). The time of exposure obviously plays a considerable role in the wasps’ thermal tolerance when Ta reaches the upper edge of viability (compare e.g. Terblanche et al., 2011 and Willmer et al., 2004). Activity CTmax (“knockdown temperature” as defined by Klok et al., 2004) and respiratory CTmax (“mortal fall”, ( Lighton and Turner, 2004)) of V. vulgaris were proved to be within narrow thermal margins (average 0.4 °C, Table 1). This has to be expected under normobaric conditions ( Stevens et al., 2010). The use of the residual of the absolute difference sum of CO2 production (rADS residual, see Fig. 6) proved eligible in determining the end point of cyclic respiration and respiratory CTmax.