Genus Trirhabda? - Trirhabda confusa

Moved

… Aaron Schusteff, 10 January, 2012 - 2:06am

Almost certain about your beetle now

Hi Elinor...I've been fairly confident that your post here was T. confusa for a while now, especially since running into a similar beetle on Chrysothamnus nauseosus in the Western Tranverse Range, which abuts the southernmost reaches of the mountain chain that includes your locale on Mt. Hamilton. But I was still unsure about the distribution and degree of likeness for the alternate possibility of T. manisi. So I was waiting until I could review a copy of the definitive reference by Hogue(1) to clarify the T. manisi issue.

But today I visited the Cal. Academy of Science...the only major CA museum with holdings of the apparently hard-to-come-by T. manisi. To my eye, it does look significantly different than the beetles you and I found. And all the specimens were from the Siskiyou Mountains, at the far north (actually, just over the border) of CA and into Oregon. I'm not 100% sure, but I'm guessing that T. manisi doesn't make it anywhere near as far south as Mt. Hamilton. So from appearance, and my inference on range...I'm confident we can move your post to T. confusa at this point. I'll let you know if I find out anything of further interest once I actually get a hold of Hogue's work.

I also looked at a number of T. confusa specimens. The CAS collection had many specimens from Inyo Co, and some from the arid inner coast ranges (where one might find Chrysothamnus)...up to the New Idria area. As far as I saw, seems Mt. Hamilton may be a northern outlier for T. confusa. So now you have a (modest) terrestial "discovery" to add to your (more substantial) celestial discoveries :-)

… Aaron Schusteff, 10 January, 2012 - 2:05am

MCZ type database

. . . was available again, and perhaps brought the solution. Compare under image in my former post, please.

… Boris Büche, 31 May, 2007 - 5:21am

Trirhabda flavolimbata?

Hi Neighbor, I have photographed this insect on Coyote Brush (Baccharis pilularis) which is plentiful in Alum Rock Park and possibly Mt. Hamilton. See discussions under images #39115 and #133728. So, you apparently have Trirhabda flavolimbata--no common name. My images are in a natural setting; but, not otherwise better. Thanks to everyone for their identifications. I greatly appreciate your collaborative efforts.

… Barry Grivett, 27 August, 2007 - 3:22pm

I didn't know about the MCZ d

I didn't know about the MCZ database. A very useful resource! Thanks!

… Elinor Gates, 31 May, 2007 - 1:56pm

Thanks!

Hostplant named gets us one step further. Google search turned up rabbitbrush is foodplant of at least 2 spp. of Trirhabda (none of which seems to be yours).

By the way, this species seems to be in the guide already:

and choice again limited by the information present there.

… Boris Büche, 30 May, 2007 - 5:37am

What other info could pin dow

What other info could pin down which species this beetle is? There are lots of these beetles around and I can get more info easily, if I knew what would be useful.

… Elinor Gates, 30 May, 2007 - 10:57am

What remains is species ID

. . . which is specialist´s business, so I can´t tell what else is needed. Perhaps nothing. Genus I think is sure by now.

… Boris Büche, 31 May, 2007 - 1:12am

Welcome, I also say!

And please, what are the plants your many beetles were sitting on? To know this, can be of great help in herbivore insects (as leaf beetles).

… Boris Büche, 29 May, 2007 - 4:16am

Rabbitbrush

The beetles were mostly on rabbitbrush. Mt. Hamilton is the only place in Santa Clara county
that rabbitbrush grows in profusion.

… Elinor Gates, 29 May, 2007 - 1:36pm

We don't know the beetles either!

but just wanted to welcome you to bugguide. A lovely image, we hope to see more from you!

… john and jane balaban, 28 May, 2007 - 5:15pm

Trirhabda flavolimbata?

… Barry Grivett, 27 August, 2007 - 3:24pm

On top of Mt. Hamilton we don

On top of Mt. Hamilton we don't have Coyote Brush (or if we do, very little). However, rabbitbrush (chrysothamnus nauseosus ssp. mohavensis) is extemely common up here and was the only plant on which I saw these beetles. Will trirhabda flavolimbata feed on both coyote brush and rabbitbrush?

… Elinor Gates, 29 August, 2007 - 10:23am

Host Plant and Character Info

Hello neighbor(s) :-) A very useful resource for Trirhabda is the article: "Phylogeny and host-plant association in the leaf beetle genus Trirhabda LeConte (Coleoptera: Chrysomelidae)" by Zuzana Swigo and Karl M. Kjera in the journal MOLECULAR PHYLOGENETICS AND EVOLUTION, vol 32 (2004) pp 258--274. It lists four Trirhabda species whose range includes Mt Hamilton and that have Chrysothamnus nauseosus as a host, namely:

T. confusa, T. lewisii, T. manisii, and T. nitidicollis

According to the table of character traits on pg 371 of the Swigo & Kjera article, T. manisii should have pale femora without dark markings which (from Elinor's photo) seems to eliminate that option. The same table indicates that T. lewisii and T. nitidicollis have striped elytra (also see the hyper-linked images from MCZ in the list above) which seems to eliminate them, while T. confusa can have striped or non-striped elytra. (In fact, a photo of T. confusa appears in Evans & Hogue(1), which looks quite different than your beetle, but it's presumably the striped variety, so doesn't necessarily eliminate it.) Your photo does look a lot like Trirhabda flavolimbata, and one stated character that may visually help in separating T. confusa and T. flavolimbata is that the pronotal spots on T. confusa are supposed to be (non-metallic) black, whereas they're listed as (metallic) green for T. flavolimbata. Appears to work in your photo, though that character seems a bit fuzzy to my eye. Coyote Brush (Baccharis pilularis) is the only plant cited in Swigo and Kjera as a host for Trirhabda flavolimbata. Even so, I seem to recall mention of some incidental observations on other plants (at Jasper Ridge near Stanford) in the article: Tilden, J.W., 1953. Biological notes on Trirhabda flavolimbata. Coleopt. Bull. 7, 20–23. And I have seen groups of adult T. flavolimbata on Aster chilensis, though I'm not sure if they were feeding, let alone if the larvae feed on that plant. I'm just a enthusiatic amateur without enough field or curatorial experience or expertise to give authoritative answers. If host plant and other data appearing in the Swigo and Kjera article can be dependably used at face value, it seems that you may have T. confusa. But perhaps that's a big "if" in the sometimes fuzzy realm of taxonomy :-) And I also wonder if there just may not be enough expert entomological field data available, and perhaps you witnessed something that hasn't been seen or noted before...a population of T. flavolimbata which was munching on rabbitbrush?

… Aaron Schusteff, 17 November, 2007 - 1:27am

Thanks for the excellent info

Thanks for the excellent info and references (though I had to look up most of the technical terms). The pronotal spots on this beetle were definitely black, not metallic green, which seems to indicate T. confusa rather than T. flavolimbata. Does anyone know what time of year the different species are active? The beetles here on Mt. Hamilton were incredibly common May-June and mostly gone by July.

… Elinor Gates, 17 November, 2007 - 8:03pm

You're welcome

Re: technical terms...yeah, I'm admittedly enamored of precise (and perhaps arcane) terminology, but I did restrain myself a bit when I used the phrase "striped elytra" instead of "elytra vittate" :-)

I know Trirhabda flavolimbata was active and relatively abundant this year from late July to mid-August at Sweeney Ridge (above SFO) and Pt Reyes. (Also found one along side of Hwy 1, south of Half Moon Bay). I don't know about T. confusa.

… Aaron Schusteff, 20 November, 2007 - 4:41pm

Rabbitbrush, not Coyote Brush

Rabbitbrush is the common name for what used to be all considered Chrysothamnus, but have been moved into other genera as well. These are quite different from Baccharis- in the same family (Asteraceae/Compositae), but that's about it.

… Chuck Entz, 28 August, 2007 - 11:12pm