Activity of the direct downstroke flight muscles ofLocusta migratoria (L.) during steering behaviour in flight

Summary

The dynamics of the time shift reaction of the direct downstroke muscles following yaw, pitch and roll stimuli are examined using triangular, sinusoidal and rectangular time functions for the displacements.

In yaw, the time shifts are mainly proportional to the imposed yaw angle (Fig. 1a). Rectangular yaw movements reveal that the time shift responses follow the stimulus fast with a latency of 1 ... 2 wing beat periods or may develop slowly over several milliseconds (Figs. 1b, 4).

In triangular pitch and roll stimuli the reaction seems to be a mixed response to the momentary rotational angle and to the speed of the rotation (Figs. 2a, 3a). In rectangular pitch and roll stimuli, the reactions are obviously atypical: the directions of the (phasic) time shifts are independent of the direction of the rotation (Figs. 2b, 3d).

The burst length (Waldron, 1968) in the direct downstroke muscles may also change following imposed rotations. However, these changes are not so pronounced as the time shift responses (Fig. 6). Where the burst length changes, it is most often negatively correlated with the time shift, i.e., increase of burst length corresponds to earlier firing. However, many exceptions to this rule (Fig. 7) show that there is no strict functional relationship between time of occurrence of a unit and the length of burst which it fires.