The Reactions of the Desert Locust,Schistocerca gregaria(Forsk.), (Orthoptera, Acrididae) to Physical Factors, with special Reference to Relative Humidity

Abstract

Reactions of 3-day-old first- and fourth-instar hoppers of Schistocerca gregaria (Forsk.) of phase gregaria, to three physical factors, namely to relative humidity, temperature and light have been studied in an alternative chamber apparatus designed to give an enclosed space with gradients of humidity. The responses to each factor independent of the others, and to the interactions of these factors, were considered.It was found that both the first- and the fourth-instar hoppers respond strongly to humidity. They are agitated by low, and even more by very high, humidities, but become more quiescent within a zone of 60–70 per cent. R.H., where they spend more time. Within this zone they hop and turn less and this decrease in activity appears to be a response which is independent of both temperature and of light intensity. This zone of decreased agitation has been called “the zone of minimum activity”. However, the speed of walking in contrast to the other types of activity, increased progressively with humidity.Increase in light intensity raises the level of activity at all humidities, i.e., it increases the duration of activity within the limits of experimental time and the speed of walking. With rise in temperature there is an increase in hopping, in klinokinesis and orthokinesis.