Injury caused by larvae of this fly resembles that of certain leaf spot fungi. It creates a yellow to greenish-yellow spot with a small dark center surrounded by a red ring (Fig. 70). The circular gall is 0.3 to 0.4 inch (8 to 10 mm) in diameter. It is visible on the upper surface of the leaf from mid-June until the foliage changes color in the fall. The small fly maggot feeds in a depression on the underside of the leaf at the center of the circle (Fig. 70). By the time leaf spots are evident, most maggots have fallen off the leaf.