SUMMARY

1. The pleuroaxillary muscle of a forewing (M85) or hindwing (M114) in the locust is supplied by two motor neurones. Each of the two motor neurones innervates a different part of the muscle. Single impulses in these motor neurones produce small twitches in the muscle which tetanize at about 30 Hz. At the wingbeat frequency they show considerable tonic tension upon which ripples are super-imposed, 1:1 for each stimulus pulse. 2. During sustained, straight, tethered flight, the motor neurones spike rhythmically, producing one (leas often two) spike(s) per wingbeat in the first half of each downstroke. At the end of flight, when the wing is folded, a high-frequency, unpatterned burst of spikes occurs. 3. During flight-like motor activity where rhythmic sensory feedback is reduced, the pleuroaxillary muscle of a hindwing spikes throughout the 'wingbeat ' cycle, with little sign of rhythm. 4. The forewing muscle, M85, responds to imposed rolling during flight by advancing the timing of its spike, increasing the number of spikes at each wingbeat