AbstractIn 1975, 19.4% of 6950 marked apple maggot adults,Rhagoletis pomonella, which were released in the center of a 7 × 7 array of unsprayed apple trees were recaptured on Pherocon®AM traps. The distribution of the marked flies was not uniform as most of the flies were recaptured near the release point. The distribution of native flies which migrated into the test area from adjacent infested apple trees was also non-uniform.