THE INFLUENCE OF ENVIRONMENTAL MICROSTRUCTURE ON THE BEHAVIORAL PHASESTATE AND DISTRIBUTION OF THE DESERT LOCUST SCHISTOCERCA-GREGARIA

In previous studies we used logistic regression analysis to quantify t he change in behavioural phase state of Schistocerca gregaria (Forskal ) nymphs subjected to variations in population density. Such work invo lved restricting insects in small containers either alone or in a crow d. In the present paper we have shown that the fine-scale distribution of food plants, perches and favourable microclimatic sites influences the spatial distribution of locusts, both in the laboratory and under semi-field conditions. When multiple resource sites were provided, so litarious locusts tended to disperse and behavioural gregarization was inhibited. However, provision of only a single site promoted congrega tion, overcoming the tendency of solitarious insects to avoid each oth er, and led to behavioural gregarization. The time-course and extent o f this response was fully consistent with our earlier experiments usin g enforced crowding. We suggest that such quantitative, experimental s tudies of the effects of environmental microstructure on behaviour may yield fundamental insights into the dynamics of plague formation in t he desert locust.