The phasic influence of self-generated air current modulations on the locust flight motor

Summary

• 1. Using high speed film analysis (500 frames/s) to investigate the head nodding movement during tethered flight inLocusta shows that the position of the wind-sensitive head hairs with respect to the flight direction is altered by 5.5° in the rhythm of the wing beat (Fig. 2).

• 2. Wind measurements in the region of the hair fields demonstrate that the wind reaching the hairs during flight is modulated by the animal's own wing beat. The modulation has a peak-to-peak value of 0.6–1.0 m/s (Fig. 3).

• 3. An airstream with its speed modulated by these values was used to stimulate the wind-sensitive hairs to analyse the steady-state response during tethered flight in animals with the antennae removed (Fig. 1). In these entrainment experiments absolute coordination (a relation of locked phase) between the wind modulation and the flight oscillator is found in a range of about 3 Hz around the intrinsic flight frequency. At frequencies both above and below this range, relative coordination (a relation of preferred phase) is obtained (Figs. 4–7).

• 4. The dynamic response to step changes in the modulation frequency was tested. There is an immediate reaction, but it takes several wing beats to reach the new steady-state (Fig. 8).

• 5. When flight was elicited while a modulated wind stream was already blowing, the first wing beat occurred in a preferred phase with respect to the stimulus modulation (Figs. 10 and 11).

• 6. To understand the generation of the flight pattern, the whole flight oscillator must be considered as a cooperative system of central neuronal, sensory (proprioceptive) and mechanical components (Fig. 12).