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Abstract

1. The wing beat of Calliphora was observed stroboscopically in tethered flight. Two synchronized video cameras filmed the macroscopic wing movements and the microscopic events in the wing articulation. 2. The radial stop (RS) never contacts the pleural wing process (PWP) during the upper turning of the wing. This is in contradiction to Pfau's models (1973, 1985, 1987) of the gear change mechanism. 3. The contact of the RS and the PWP during the lower half of the wing cycle occurs only rarely. To describe normal flight (no contact at all), the novel models of dipteran wing beat (Miyan and Ewing 1985 a, b, 1988; Ennos 1987) have to be modified. 4. Three basic operating modes of the wing articulation were observed during the lower half of the wing cycle (Fig. 2): The RS engages in the posterior (mode 1) or in the anterior (mode 2) groove of the PWP, or the RS moves into a cleft anterior of the PWP without touching the latter (mode 3). A fourth mode (mode 0: The RS stays behind the PWP) is seldomly observed and seems to be rather unphysiological. The correlation of the modes with the peaks in the downstroke amplitude distribution (Fig. 5) indicates that in modes 1 and 2 the PWP acts as a wing stop during downstroke. 5. The amplitude can also be reduced during mode 3 (variant mode 3h). The contact with the PWP is not necessary for the reduction of the downstroke amplitude (Fig. 7). 6. In most spontaneous maneuvres observed, unilateral mode change to mode 3h, 2, or 1 resulted in reduced downstroke amplitudes and delayed supination at the lower turning point (Figs. 3d, 6). The possible involvement of the different modes in the separation of roll- and yawtorque production is discussed. 7. It is discussed which muscles and sclerites might produce the mode changes.