Eggs are inserted into apical and axillary buds. From one to six larvae feed gregariously within an open cavity within the expanded pith parenchyma of galls ... The galls are elongate-obclavoidal, sometimes bear axillary branches and flower heads, and are covered by a wooly investiture ... adults emerge ... through a common channel by pushing aside a thin, pre-formed, apical, "gall cap" ...
larvae feed ... on proliferating pith parenchyma (callose tissue), shallowly pitting the walls, and continually expanding ... the cavities [which] remained free of frass and solid waste, except for [discarded skeletons of early instars]
Galls were ... covered with a whitish tomentum [and were 6-41 mm long by 1.7-7.8 mm in widest width] ...

Foote et al. (1993) reported Anaphalis sp. and Gnaphalium stramineum Kunth as hosts, besides G. luteo-album ... Accordingly, T. signata is oligophagous on certain species of Anaphalis and Gnaphalium ...

[click below for photos]

- Richard D. Goeden & Jeffrey A. Teerink: (1997) Life History and Description of Immature Stages of Trupanea signata Foote (Diptera: Tephritidae) on Gnaphalium luteo-album L. in Southern California^©

Reference: https://www.biodiversitylibrary.org/page/16213423#page/771/mode/1up