Fig. 3. Virtual-reality arena and flight data plotted as a function of open spiracles in Drosophila. (A) Set-up as described (Lehmann and Dickinson, 1997). To elicit maximum locomotor performance of the animal, a 30° stripe drum (BP) displayed in the electronic flight arena was oscillated under open-loop conditions in a vertical direction around the tethered flying fly. IRD, infrared diode; PSD, position detector of flight force laser balance; L, laser; WSA, wing stroke analyser. (B) Wing stroke amplitude, (C) wing stroke frequency, (D) maximum normalized flight force production, (E) mean lift coefficient , and (F) mean drag coefficient , based on a quasi-steady aerodynamic approach, plotted against the number of open thoracic spiracles (grey). Abdominal spiracles remained unsealed in all experiments. Data represent mean values of all data points within a flight sequence that fell within the top 1% of flight force (equal to maximum locomotor capacity of the fly). Number of tested flies: N=5 (0), N=23 (1), N=43 (2), N=26 (3) and N=10 (4 open thoracic spiracles). To distinguish the changes resulting from the modifications of local spiracle gas conductance from those associated with alterations in total flight force production, we estimated kinematic and aerodynamic parameters in unmanipulated animals (see text) within a ±2% range of flight forces that match the maximum values shown in D (red). Red area in B,C, E,F indicates ±s.d. N=10 flies. See text for details.