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Trirhabda Revisited - Trirhabda flavolimbata

Trirhabda Revisited - Trirhabda flavolimbata
Sweeney Ridge, Golden Gate National Recreation Area, San Bruno, San Mateo County, California, USA
May 29, 2009
Size: ~6mm
A little under 2 years ago I became fascinated with this species, which inspired me to make my first BugGuide post.

Recently, I noticed their larvae on many Coyote Brush plants all along a hike of a few miles. So I thought I'd get some photos to complement the earlier adult Trirhabda images of many BugGuide contributors.

Checking out the guide page today, I found there have been recent contributions of larval images from Santa Barbara, CA on 3/29/09 and Santa Clara, CA on 4/25/09. Here are two more from San Bruno, CA on 5/29/09. As would be expected, the phenology is moving northward as the season progresses. Another two images of a paler larva from the same locale on 6/4/09 appear here.

Trirhabda species are known to be restricted in their host plants, with the larva of different species typically associated with one (or a few) host(s) in a given genus. The host plant of Trirhabda flavolimbata is Coyote Brush (Baccharis pilularus) in the composite family (Asteraceae). Coyote Brush is a dominant shrub in coastal scrub communities along much of the length of California.

Since first getting to know Trirhabda flavolimbata, I've almost always seen it on Coyote Brush...with the exception of one time late in the season (Septermber) when 10+ adults were cavorting on branches of Aster chilensis, another composite. (I don't know what they were doing there, the leaves seemed uneaten on the plant.)

Images of this individual: tag all
Trirhabda Revisited - Trirhabda flavolimbata Trirhabda Revisited - Trirhabda flavolimbata

Great images of the larva, Aaron!
Did you try to raise these?
I took some larvae of another sp. at Liebre Mountain, late May(possibly eriodictyonis, or diducta, considered sister taxa), on Eriodictyon crassifolium var. nigrescens. They pupated ~3 weeks ago, then turned into the same beetles I had photographed on the same plants. I've also observed them on Eriodictyon in other areas, but haven't had time to post any of the photos yet.
Currently I'm busy working on 4 different spp. of the pollen-collecting wasp Pseudomasaris found in the San Gabriels; fascinating wasps with their bee-like provisioning habits.

Well...I did *try*
But, unfortunately, I didn't succeed. The poor guys/gals (three of them) didn't survive long enough to pupate (after which I had planned to return them to their original Coyote Brush home). Don't know what I did wrong...I included some leafy twigs and a dash of potting soil in a pint-size plastic container, with holes poked in the lid for air. But apparently my rearing skills need improvement.

As I recall, eriodictyonis and diducta are among the few Trirhabda species that use non-asteraceous host plants. How long did your larva take to pupate? (In case I dare try again.)

I (unwittingly) saw my first Psuedomasaris last spring in your general area. Wonderful creatures, and your BugGuide posts are helpful in learning about them. My travelling is in limbo right now -- as my mechanics search for a hard-to-find part for my van. Else I'd volunteer to head down and assist with your Masarine efforts. They're fascinating, and I feel a certain gratitude towards a group presumably ancestral to the huge and wonderful clade of bees :-)

Have a great 4th!
Yes, you'd certainly enjoy observing those pollen-collecting wasps if you were down here. Not considering P. vespoides, I found four different spp. in the San Gabriels, & just observed them again yesterday: wheeleri, coquilletti, edwardsii, and zonalis. I'm still evaluating all, sorting through many (you can imagine) photos, and will post them some time soon. Will head up at least a couple more times next week.

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