Periploca ceanothiella

[N]ewly hatched larvae move directly into the terminal growth where they penetrate the buds and inflorescences to cause the swellings or galls ... Before pupation begins, the larva cuts an exit hole partially through the side of the gall to leave only a thin film of bark which covers the entrance ... The galls may vary greatly in abundance, ranging from only an occasional gall to 20 or more lineal foot of branch and twigs in heavy infestation ... [T]he gall is somewhat spindle-shaped and averaged about 13 mm in length by 6 mm diameter. This is about three times the diameter of the twig ... 

Examination of Ceanothus collections at [several Southern California arboreta and botanic gardens] showed varying degrees of non-susceptibility to the stem galls. [Table 2 shows] Heavy occurrence [on] Ceanothus griseus [and] C.g. horizontalis  ... Moderate occurrence [on] C. cyaneus, C. thyrsiflorus [and two cultivars] and Light occurrence [on] C. arboreus, C. oliganthus, C. diversifolius, C. lemmonii, C. integerrimus, C. leucodermis, C. lobbianus [and several cultivars].

[click below to see several grayscale photos] 

Biology of the Ceanothus Stem-Gall Moth, Periploca Ceanothiella (Cosens), with Consideration of Its Control