Gall.-Length 1.5 cm., width I cm. This deformity consists of irregularly thickened, partly unfolded opposite leaflets, the swelling being confined mostly to the basal half of the midrib. The upper leaflets are usually affected and the central shoot arrested or destroyed ...

Thomasia [Resseliella] californica Felt ... [L]arvae produc[e] midrib galls on the leaflets of Symphoricarpos

Symphoricarpus (snowberry)
...
Swollen leaf midrib or margin...Resseliella californica (Felt)

Galls first appear in May. Larvae are full-grown in July and drop to the ground to pupate. Adults were reared in August. Host: S. albus. Distr.: Oregon and California. Ref.: Larew and Capizzi (1983)