Burton Mesa Management Area, near Vandenberg Village, Santa Barbara County, California, USA
April 28, 2003
Landed on my clothing, near a vernal pool.
This looks similar to the image of Galerucella nymphae by Terry Thormin,
, save for the color of the elytra.
G. calmariensis and G. pusilla (also not green as far as I've seen), native to Europe and Asia, have been used to control Purple Loosestrife (Lythrum salicaria).
P.S. I should have moved this to the genus page some time ago. Candidates for species are luteocincta, labrata, and possibly flavolimbata. Their colors may vary from green to metallic blue, and may differ only in male genitalia. According to Michael Catarino (Santa Barbara Museum of Natural History, & California Beetle Project), both T. labrata and luteocincta have been collected in coastal Santa Barbara county.