The vibrational startle response of the desert locust Schistocerca gregaria.
Substratum vibrations elicit a fast startle response in unrestrained quiescent desert locusts (Schistocerca gregaria). The response is graded with stimulus intensity and consists of a small, rapid but conspicuous movement of the legs and body, but it does not result in any positional change of the animal. With stimuli just above threshold, it begins with a fast twitch of the hindlegs generated by movements of the coxa-trochanter and femur-tibia joints. With increasing stimulus intensity, a rapid movement of all legs may follow, resulting in an up-down movement of the whole body. The magnitude of both the hindleg movement and electromyographic recordings from hindleg extensor and flexor tibiae muscles increases with stimulus amplitude and reaches a plateau at vibration accelerations above 20 m s(-)(2) (peak-to-peak). Hindleg extensor and flexor tibiae muscles in unrestrained animals are co-activated with a mean latency of 30 ms. Behavioural thresholds are as low as 0. 47 m s(-)(2) (peak-to-peak) at frequencies below 100 Hz but rise steeply above 200 Hz. The response habituates rapidly, and inter-stimulus intervals of 2 min or more are necessary to evoke maximal reactions. Intracellular recordings in fixed (upside-down) locusts also revealed co-activation of both flexor and extensor motor neurones with latencies of approximately 25 ms. This shows that the neuronal network underlying the startle movement is functional in a restrained preparation and can therefore be studied in great detail at the level of identified neurones.
Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK. tf203@hermes.cam.ac.uk
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D000818:Animals; D001522:Behavior, Animal; D004576:Electromyography; D004594:Electrophysiology; D006110:Grasshoppers / Q000502:physiology*; D006185:Habituation, Psychophysiologic; D009046:Motor Neurons / Q000502:physiology; D013216:Reflex, Startle / Q000502:physiology; D014732:Vibration