Sweeney Ridge, Golden Gate National Recreation Area, San Bruno, San Mateo County, California, USA
July 30, 2007
Size: Body 7-9mm; Antennae ~5mm
A number of these beetles were crawling on my clothes as I rested on the ground (in coastal scrub/chaparral). I was able to tentatively ID to genus Trirhabda
using Evans and Hogue's "Field Guide to Beetles of California" (1)
. I had also seen many the previous week (July 26, 2007) along the Abbotts Lagoon trail (coastal dune, prairie and chaparral habitat) at Pt Reyes National Seashore.
When I got home, I checked BugGuide and found the post below:
The comments there, indicated knowing the host plant is crucial for an ID. From what I could gather, there are (at least?) three good candidate species of Trirhabda
in coastal California for this beetle, and each uses a different host plant:
* T. flavolimbata: host plant Coyote Brush (Baccharis pilularis); * T. luteocincta: host plant California Sage (Artemesia californica); and * T. diducta: host plant Yerba Santa (Eriodictyon californicum).
All three plants occur at Sweeney Ridge, Coyote Brush being by far the most adundant, followed by Artemisia
. Both these plants also occur at Abbotts Lagoon. I went back the next day and checked the plants. I found very
large numbers of the beetles on many Baccharis
plants and none on Artemisia
. So I believe this to be T. flavolimbata