The Posture of the Abdomen during Locust Flight: Regulation by Steering and Ventilatory Interneurones

1. Tethered flying locusts (Locusta migratoria) make correctional steering movements with the abdomen when stimulated with a moving artificial horizon and integrated wind jet, simulating deviation from a straight course. 2. Neurones in the metathoracic and first abdominal neuromeres of the metathoracic ganglion have been characterized morphologically and physiologically. The selective stimulation of these cells causes movements of the abdomen. 3. One group of neurones responds directionally to visually perceived horizon movements and is excited by wind on the head. Some of these neurones are rhythmically activated at the flight frequency while others receive tonic drive from the flight oscillator. Electrical depolarization results in bending of the abdomen; the direction of this movement is always compatible with compensatory steering. 4. Interneurones which are active during the expiration phase of ventilation also contribute to the posture of the abdomen in flight. They are not visually responsive but their selective inhibition at the onset of flight activity helps to bring the abdomen into flight posture. Some of these interneurones are modulated at the flight frequency. 5. The efficiency of cooperation between different sets of interneurones in producing behavioural patterns and the signficance of single neurone stimulation are discussed.