As part of a project on the movements of D. tryoni at an orchard near Wilton, N.S.W., llnes of cuelure traps were placed out in the shape of a cross with the orchard In the centre. The nearest traps were situated 0.5 mile (0.8 km) and the most distant traps 15 miles (24 km) from this orchard. Both newly emerged and mature flies were marked and released into the orchard; the rates at which they dispersed and the distance and direction they travelled were estimated from the recapture of marked males in the traps. Both newly emerged and mature adults dispersed over an area of several hundred square miles within a few weeks of being released in the orchard. Emigrants were caught in the outer ring of traps, 14-15 miles (22.4-24 km) from the orchard, within 3 weeks of being released. Overall, the mean distances flown by emigrants, for flies released when immature and when mature, were approximately the same. It is suggested that this was because of the absence of host trees in the area surrounding the orchard. Whereas the immature flies have a post-teneral dispersive phase during which movements are largely independent of host trees, the movements of mature flies are more directly related to the availability of fruiting hosts. The absence of host trees near the orchard therefore encouraged the long-distance dispersal of the mature flies. In urban areas where fruitlng hosts are plentiful, the dispersive movements of mature flies are likely to be less than those of immature flies.