Tephritis baccharis (Coquillett) is a bivoltine and monophagous on Baccharis salicifolia (Ruiz & Pavon) Persoon in southern California... First instar larvae hatch and tunnel into the pith just basad to the apical bud where they initiate gall formation. Gall and larval growth continue slowly into the fall, where pupation occurs. (p.86)

T. baccharis has been reared only from bud galls on B. salicifolia. The young larva settles, molts, and initially excavates a small ellipsoidal cell about 3 mm long and <2 mm wide in the juvenile gall, evidenced externally as only a slight swelling of a branch terminal... Twenty of 23 fully formed F2 galls of the previous year’s overwintering generation sampled at Oriflamme Canyon were fusiform; the remaining galls, subovoidal. The former shape resulted from continued growth of the bud at each gall apex; whereas, the latter shape resulted from death of the terminal bud from larval feeding by T. baccharis... The galls of T. baccharis, like those of T. stigmatica, are shortened, thickened, succulent terminal parts of main or axillary branches. The 23 mature galls incorporated an average of 3.8 +- 0.3 (range, 1-6) nodes, and were smooth surfaced, light green and longitudinally striped or unilaterally colored red-purple when occupied. When empty, the galls turned tan, shriveled, and dehisced, or became woody and persisted as branch swellings. Externally, the 23 galls averaged 13.1 +- 0.5 (range, 8-9) mm in length, and 5.6 +- 0.2 (range, 4-7) mm in width. (p. 94)

Twenty of 30, F1 galls collected on Santa Cruz Island were fusiform; the remainder, subovoidal. These 30 galls incorporated 3.8 +- 0.1 (range, 3-5) axils and externally measured 20.4 +- 1.0 (range, 12-33) mm long by 8.3 +- 0.3 (range, 6-13) mm wide. (p.95)

[Tephritis baccharis was described in Coquillett, 1894, as being from a "irregular oval gall... on tender twigs of Baccharis viminea". T. baccharis has been reared from San Diego County and Los Angeles County.]