The galls occur on several species of Helianthus, and their size and shape appears to vary with the species of sunflower...

The following are a few excerpts from Dr. Needham’s paper (cited above):
"[on H. agrestis] gall is a thickening of the walls of the stem, about an inch long and four-fifths as wide, and with a large oval cavity inside. It varies in form from oblong to almost round. It tapers a little more abruptly to the stem at the upper end." ... "Galls occur singly on the stems; very rarely two, and when two, one or both are imperfectly formed. They are generally located somewhat below mid-height of the plant." In contrast on Helianthus angustifolius, the irregular galls occur amongst the inflorescence, the peduncles of the flower heads branching out from the gall. The gall may be quite slender when on an individual peduncle and up to as large or larger than that of Gnorimoschema gallaesolidaginis (Riley), when several peduncles branch from it. Full-grown larvae pass the winter within the gall, leaving in the spring by a small circular opening.

- Annette F. Braun: (1963) The Genus Bucculatrix in America North of Mexico (Microlepidoptera)^©

Reference: https://www.biodiversitylibrary.org/page/38632234#page/58/mode/1up