Tephritis stigmatica overwinters in southern California at least partly as immature larvae in F2* galls formed mostly in low auxillary branches on S. douglasii [an older synonym for Senecio flaccidus var. douglasii] ... In contrast, F1 galls usually were isolated on upper parts of aerial stems ...

All but one of [50 F2 galls collected] were spindle-shaped. These galls either were sessile or born on pedicels of various lengths, up to 5 mm long. [They] tapered apically ... Branch and stem galls are formed from expanded pith tissue, the branches and stems swelling to about three times normal diameter ... F2 galls collected at Pearblossom ... averaged 2.4 ... cm in length and 6.5 ... mm in greatest diameter. These galls incorporated as many as six nodes ... The fully grown larva extends its feeding tunnel distally and outward to, but not through, the epidermis leaving a round, thin, 2-mm dia., translucent window to the outside ...

[* Article repeatedly refers to F(subscript)1 galls and F(subscript)2 galls.
Click below for monochrome photos of galls. Scroll up slowly to read article.]

- Richard D. Goeden: (1988) Gall Formation by the Capitulum-Infesting Fruit Fly, Tephritis stigmatica (Diptera: Tephritidae)^©

Reference: https://www.biodiversitylibrary.org/item/54696#page/47/mode/1up