32 kPa = 760 Torr). All gas exchange referred to as respiration in the following chapters is strictly speaking
CO2 emission, as O2 uptake was not measured in this setup. To evaluate the wasps’ behavior and to determine the periods when the tested individuals were at rest we applied state of the art infrared thermography techniques that particularly enabled us to distinguish between rest and activity without disturbing the wasps in their natural behavior (Käfer et al., 2012, Kovac et al., 2007 and Stabentheiner et al., 2012). The top of the measurement chamber was transparent to infrared (IR) radiation (covered with plastic film permeable in the range of 3–13 μm). It enabled us to record both the wasps’ body surface temperature and activity with an infrared thermography camera (ThermaCam SC2000 NTS, 17-AAG order FLIR Systems Inc., Wilsonville, USA; for details see Kovac et al., 2007, Schmaranzer and Stabentheiner, 1988, Stabentheiner and Schmaranzer, 1987 and Stabentheiner et al., 2012). Not only visual clues (e.g. body movements), but also the thermal state of the individual (ectothermic or endothermic) could be evaluated. This this website thermal state was determined by the difference in thoracic and abdominal surface temperature (Tth − Tab). An individual
was assessed as resting when it was ectothermic (Tth ≈ Tab) and showed no or only scarce body movements for a minimum timespan of 10 min (see classification according to Crailsheim et al., 1999, Stabentheiner and Crailsheim, 1999 and Stabentheiner et al., 2003); single flips of legs or antennae were allowed (compare Kaiser, 1988). At higher Ta
(>27.6 °C) the duration was reduced to 5 min if no 10 min sections were available. In the course of evaluation we had to redefine “rest” in such a way that individuals not moving for a longer period of time were allowed to show weak endothermy (Tth − Tab < 2 °C, usually <1 °C) over a few periods in the experiment (see Käfer et al., 2012 and Kovac et al., 2007). IR sequences were recorded on hard disk at 3, 5 or 10 Hz. triclocarban Analysis of the yellow jackets body surface temperatures was conducted with AGEMA Research software (FLIR Systems Inc., Wilsonville, USA) controlled by a proprietary Excel (Microsoft Corporation, Redmond, USA) VBA macro. A respiration cycle was determined from one minimum in CO2 emission just before the open phase to the next one. For discontinuous gas exchange cycles (DGCs) this included a closed and a flutter phase. In cyclic respiration at higher temperatures the same scheme applied. From minimum emission to minimum emission, every CO2 peak was assumed to be a respiration cycle. Abdominal ventilation movement (pumping, etc.) was assessed from IR video sequences recorded at a frequency of 10 Hz. A minimum of 10 respiration cycles were assessed in the evaluation of respiration movements, resulting in time spans of 13 min at the highest Ta (36.3 °C) and 287 min at the lowest Ta (5.9 °C) tested.