The influence of flight noise on behaviour in the Desert Locust Schistocerca gregaria (Forsk.)

Abstract

The paper describes experiments carried out in Africa to investigate the possibility that the flight noise of the Desert Locust influences the gregarious behaviour observed in swarms and plays a part in such behaviour as mass take-off. The sensitivity of the tympanal organs to pure tones in the range 0–20 kc/s was determined, and the methods used to record and analyse the sounds produced by single tethered flying locusts and also swarms of locusts in the field are described. It was found that under certain conditions a single flying locust emitted a noise due to impact between the wings and hind legs; this noise is termed “the wing-beat noise” and occurs at the frequency of the wing beat, that is at between 17–20 c/s. This noise apparently does not occur during level flight but appears during landing and take-off, when it may have behavioural significance. Behaviour experiments involving playback of recorded flight noise to locust swarms and the release of deafened locusts into settled and flying swarms are described. From the data on tympanal sensitivity and the acoustic power generated by portions of flying swarms it was possible to form estimates of the distances over which locusts can hear the flight noise of other locusts and of swarms. The principal behaviour patterns of flying swarms are discussed in relation to the data derived from the acoustic and behaviour experiments.