This species is bivoltine and induces morphologically different bud galls in spring (April–May) and summer (August–September), which are very similar on all three host plants. The spring generation galls ... are inconspicuous and difficult to locate due to the minor difference between galled and normal shoots, although the growth of galled ramets is sometimes stunted and they therefore appear shorter than ungalled ramets. ... The apical leaves of a galled ramet appear splayed, and the base of the gall from which they originate is slightly thickened. Each gall usually contains only one conical, white chamber in the middle of the apical meristem (Fig. 76), ca. 3 mm long, and containing a single larva that is usually found deep at the bottom of the chamber with its head facing downwards. Occasionally 2–3 chambers are found in the same gall and may be attached to each other longitudinally. The chamber is surrounded by approximately 10 leaves that are much shorter and thinner than normal leaves. ... On S. altissima, these modified leaves are lighter in color, especially along their mid vein. These are surrounded in turn by a whorl of leaves of normal shape and size. Galls contained pupae already in early May, suggesting rapid development of the spring generation soon after the plants sprout.