Adults of a natural population of Rhagoletis pomonella (Walsh) were labeled with strontium 89 by spraying apple and other foliage with an enzymatic soy hydrolysate bait solution containing radioactive strontium chloride. By subsequent capture of labeled and unlabeled adults on sticky-board traps it was estimated that about 5% of the natural population was marked by this method. The capture of labeled and unlabeled adults indicated short dispersal flights and the tendency for the population to remain with the orchard. Distribution of adults within the orchard was influenced by tree variety and the presence or absence of fruit; they were more prevalent in early- and mid-season-bearing varieties than in later varieties. Labeling experiments in 1969 showed that the adults do some feeding in areas adjacent to orchards and that some of these return to the orchard.