Larvae of this moth (Cosmopterigidae) cause spindle-shaped swellings on stems of wild lilac, Ceanothus spp. This galling may slow plant growth and reduce blooming.
Identification
The small, brown to dark gray adults (moths) have a wingspan of about 2/5 inch. The white eggs are about 1/50 inch in diameter. The pale, segmented larvae grow up to about 1/4 inch long.
Life cycle
The moths emerge from galls during spring and early summer and mate. The females lay eggs on buds and flowers. The larvae tunnel and feed in shoot terminals through fall, then overwinter in the galls.
Before pupating in late winter or spring, the larva cuts an exit hole partially through the side of the gall, leaving a thin cover of plant tissue. After pupating into an adult, the moth emerges through the hole covering. There is one generation per year.
Damage
Each stem swelling, or gall, is about 1/2 inch long and 1/4 inch in diameter. The galls vary in abundance from only an occasional gall to 20 or more per linear foot of branch and twigs in heavy infestations. Some twigs may be killed by the larval feeding injury. Where gall moth larvae feed in inflorescences, the flower clusters can be reduced to about 25% of their normal size.
Solutions
Prune and dispose of galled shoots before the moths emerge in spring. Where galling cannot be tolerated, plant less-susceptible ceanothus species and consider replacing shrubs most susceptible to the ceanothus stem gall moth.
