An analysis of dispersal and movement in Phaulacridium vittatum (Sj÷st.) (Acrididae)

Abstract

Marked adults of Phaulacridium vittatum dispersed rapidly for the first few days after mass release at a point, irrespective of the terrain or the vegetation surrounding the release point. Their displacement resulted in an elliptical spatial distribution with the major elliptical axis running north-south. Thus dispersal was non-random, the movements of the grasshoppers apparently being oriented by reference to the sun's position or to the plane of polarized light in the sky. After a period of from 2 days to 1 week, dispersal ceased although movement continued. From the seventh day after release the grasshoppers always moved non-randomly in such a way as to avoid further net displacement. Estimates were made by a multiple regression method of the rates of movement between cells in grids of different scales. The grids were superimposed on maps showing the successive distributions of the marked groups after the maximum dispersal had occurred. This analysis, combined with observations on the movements of characteristically marked individuals, indicated that each individual of P. vittatum moved about in such a way as to remain within a limited ambit for relatively long periods. The significance of site attachment shown by individuals of this species is discussed.