Trirhabda larvae on Coyote Brush - Trirhabda flavolimbata
San Bruno Mountain, San Mateo County, California, USA
February 28, 2015
These caterpillar-like beetle larvae were spotted by Tim Forsell on a recent field trip to San Bruno Mountain. They were munching on a bush within a group of unusually large-leaved coyote brush (Baccharis pilularis), which is a dominant shrub in the coastal scrub community of much of central California. The distinctive metallic-green larvae, and the host plant here indicate Trirhabda flavolimbata. Looks to me like at least two instars are present in the photo.
Tim saw large numbers of these on many nearby plants. They appeared to be substantially defoliating this bush. Coyote brush tends expand its coverage and colonize choice habitat if not checked, and herbivory by Trirhabda presumably plays a role in maintaining the overall ecological balance here.