WIND-EVOKED ESCAPE RUNNING OF THE CRICKET GRYLLUS BIMACULATUS

Spontaneous walking and escape running in response to wind puffs directed to the abdominal cerci were quantitatively studied in tethered walking crickets. 1. An apparatus for optically recording rotations of an air-supported sphere was developed to measure the intended locomotion of insects with high linear and temporal resolution but without mechanically imposed bias. 2. During spontaneous locomotion without sensory cues for orientation, alternate pauses of 0.35-2.2 s and walking phases of 0.5-6 s resulted in a highly variable pattern of locomotion on a meandering path. 3. A single air puff to one or both of the wind-sensitive cerci evoked a short run, whereas a continuous sequence of puffs caused sustained escape running with a tendency to turn away from the stimulus source. Escape running was characterized by a series of stereotyped running bouts and pauses, both significantly shorter than those recorded during spontaneous locomotion. 4. Forward speed and angular speed of escape running correlated linearly with the wind puff frequency between 5 and 10Hz. This was caused by a shortening of the standing phases, while the durations of the running bouts were constant. The reflex-like running bouts and the pattern of escape running were largely independent of the duty cycle of the wind puff series and the wind speed. Neither individual steps nor running bouts were synchronized with the stimulus pattern. 5. The behavioural modes of spontaneous walking and escape running were maintained with a minor reduction in general activity in partly dissected specimens during intracellular recording in the prothoracic ganglion. Each impaled local interneurone with locomotion-related activity generated action potentials in the actual step rhythm of walking and running bouts, but did not show specific activity during escape running. Some of these local neurones, however, showed modu-lations of spike frequency before or during intended turns and may participate in the coordination of the prothoracic legs