1A; Hetz, 2007, Käfer et al., 2012 and Moerbitz and Hetz, 2010). Nevertheless, spiracle control functioned well at this lowest experimental ambient temperature. Honeybees, in comparison, fall into chill coma at Ta ∼ 10 °C and, losing control over their spiracles, emit CO2 continuously ( Kovac et al., 2007 and Lighton Linsitinib mouse and Lovegrove,

1990; compare Free and Spencer-Booth, 1960). With rising Ta, wasp DGC had closed phases and distinct flutter phases as found in many other resting insects (e.g. Chown and Davis, 2003, Hadley, 1994, Hetz and Bradley, 2005, Lighton, 1996, Lighton and Lovegrove, 1990, Sláma, 1999, Vogt and Appel, 1999 and Vogt and Appel, 2000). Open phases consisted of consecutive merging and in amplitude diminishing peaks at Tas of about 6–16 °C (Figs. 1B and 2A). The typical DGC pattern with closed, flutter and open phase appeared more and more distinctly ( Fig. 2B). With rising Ta, the DGC patterns changed Metformin in a way that the closed and flutter phases diminished in duration and then successively vanished entirely ( Fig 3). This result was in accordance to the findings of Contreras and Bradley (2010) in Rhodnius prolixus and Gromphadorhina portentosa, which showed that metabolic rate affects spiracle activity, which may be an explanation for the different patterns of gas exchange in one

species at different temperatures. At Ta ∼ 27.5 °C, 50% of the cycles showed flutter and closed phases (see Supplementary material, Table & Fig. S5). Closed phases ceased between 26.2 and 31.1 °C (i.e. at Ta = 31.1 °C no closed phases were detectable; see Fig. 3; Supplementary material, Table & Fig. S5). In R. prolixus, Contreras and Bradley (2010) still observed closed phases Amrubicin at Ta = 35 °C. It has to be kept in mind that they determined this relationship in a different experimental procedure, exposing insects to a temperature ramp while our insects were exposed to constant temperatures. A rough estimation of the cease temperature of closed phases can be done by determining the quotient of cycle to open phase duration (QC/O). We calculated a best fit curve of the QC/O from

the quotients of the original cycle and open-phase duration values. At a QC/O of 1, the open phase was as long as the respiration cycle, and the closed phase had vanished. This occurred at a temperature of 36.8 °C. This value corresponded almost exactly with the one determined from the best-fit curves for cycle and open phase duration in Fig. 3, which was 36.7 °C. Flutter phases ceased between 35.8 and 39.7 °C (see Fig. 3, Supplementary material S6). The fusion frequency of cycles should depend to a considerable degree on the relation between (basal) metabolic rate and CO2 buffer capacity of an insect. A prediction of Hetz (2007) suggests that DGCs should mainly occur in insects with large differences in metabolic rate due to changing temperatures or in insect species with huge spiracular conductance due to short-time high metabolic demands (e.g.