This causes a drop in the total intratracheal pressure (Buck and Keister, 1955, Buck and Keister, 1958, Buck and Friedman, 1958 and Hetz et al., 1994). In the following flutter phase single spiracles open and close rapidly. Gas exchange works here due to convection and CHIR-99021 chemical structure diffusion. Small amounts of O2 are inhaled to sustain a certain low level of PO2 for a minimum O2 delivery to the insect’s metabolizing tissues (Hetz and Bradley, 2005 and Lighton, 1996). The CO2 level keeps rising in the hemolymph during the flutter phase, as only small amounts of CO2 are exhaled (Buck,

1958). As accumulated CO2 reaches a trigger threshold, a massive amount exits from the tracheal system to the environment in the open-spiracle phase (Lighton, 1996 and Schneiderman and Williams,

1955). CO2 is assumed to act directly at the spiracular muscles, with little central nervous control (Hoyle, 1961); however, Bustami and Hustert, 2000, Bustami et al., 2002 and Woodman et al., 2008 found contrary evidence. Discontinuous Maraviroc clinical trial gas exchange was hypothesized to be an adaptation aimed at minimizing water loss from the tracheae (hygric model, Chown, 2002, Chown et al., 2006a, Dingha et al., 2005, Duncan et al., 2002b, Hadley, 1994, Kivimägi et al., 2011, Williams and Bradley, 1998, Williams et al., 1998 and Williams et al., 2010), though findings by Contreras and Bradley, 2009, Gibbs and Johnson, 2004 and Sláma et al., 2007 call into question the universal validity of this model. Other explanations suggest that it developed to allow sufficient gas exchange in subterranean, CO2 rich environments (chthonic model, Lighton and Berrigan, 1995). A combination of these two models is the hygric-chthonic hypothesis (Lighton, 1998). An alternative explanation suggests that it minimizes old oxygen toxicity (Bradley, 2000 and Hetz and Bradley, 2005). The variation of respiration patterns has been well investigated

in different species (Basson and Terblanche, 2011, Chown et al., 2006a, Groenewald et al., 2012, Klok and Chown, 2005, Kovac et al., 2007, Nespolo et al., 2007, Terblanche et al., 2008a and Williams et al., 2010). Such an analysis is lacking in vespine wasps. This is especially interesting because Vespula sp. show an overall higher level and a steeper incline in resting metabolism with increasing ambient temperature (high Q10) than many other insects (see Käfer et al., 2012). In this paper, therefore, we investigated the characteristics of the respiration patterns of vespine wasps, Vespula sp., over their entire viable temperature range. We compare the specific features of their gas exchange patterns with other flying and nonflying insects. Respiration of adult insects is accomplished by a combination of passive diffusive gas exchange and active convective ventilation (Jõgar et al., 2011, Lighton, 1996 and Terblanche et al., 2008b). Ventilatory movements are usually observed via automated optical activity detection.