6.1. Flow-through respirometry
Honey bees are, as honey bee scientists know quite well, extremely social insects. This means that their behaviour may change considerably if they are separated from the community to be put into a respiratory or energetic measurement chamber. In such situations individuals want nothing but find an exit out of the chamber to fly home. This may not matter (much) in experiments where flight energetics (Wolf et al., 1989; Harrison et al., 1996; Woods et al., 2005) or the interrelation of thermoregulation and heat production are under investigation (Stabentheiner et al., 2003a, 2012). Respiratory and energetic measurements also resemble a natural situation quite well if the bees have freely entered the measurement chamber because they expected a reward therein (Balderrama et al.,1992; Moffatt, 2000; Stabentheiner et al., 2012). It is not possible – and this has always to be kept in mind –, however, to determine the energy turnover of hive bees directly from respiratory measurements of isolated individuals. Energy turnover may change by more than a 100-fold due to an unpredictable degree of endothermy. In research on insect respiration and energetics, flow-through respirometry is the state of the art (Lighton, 2008). Its great advantage is that the bees are supplied with fresh air throughout the experiment, which makes possible measurements over extended time periods (Kovac and Stabentheiner, 2007). If necessary, the atmospheric composition may be changed artificially, for example to investigate the impact of tracheal mites on flight capability (Harrison et al., 2001) or of increased hive CO2 levels on respiration and energy turnover. Modern equipment provides high sensitivity, down to the ppm (O2 sensors) or sub-ppm range (CO2 sensors). With appropriate calibration and care measurement accuracy of a few ppm is possible.