Trirhabda sp. (perhaps T. diducta?) - Trirhabda diducta

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Home » Guide » Arthropods (Arthropoda) » Hexapods (Hexapoda) » Insects (Insecta) » Beetles (Coleoptera) » Polyphaga » Series Cucujiformia » Longhorn and Leaf Beetles (Chrysomeloidea) » Leaf Beetles (Chrysomelidae) » Skeletonizing Leaf Beetles and Flea Beetles (Galerucinae) » Galerucini » Section Coelomerites » Trirhabda » Trirhabda diducta

Photo#140988

Copyright © 2007 Aaron Schusteff

Trirhabda sp. (perhaps T. diducta?) - Trirhabda diducta

Chews Ridge Area, Los Padres National Forest, Monterey County, California, USA
June 17, 2007

This definitely looks like a Trirhabda, noting overall shape/color/markings of head, pronotum (w/ characteristic three spots) and elytra; form of antennae (w/ 3rd segment < than 4th); form of legs/tarsi, etc.

It was found on a stem of the shrub Eriodictyon tomentosum, which led me to speculate it might be species diducta, which is one of only two species of Trirhabda known to use Eriodictyon species as host plants. The images of the (lecto)type specimen for T. diducta seem to match the beetle in the above photo fairly well (whereas the type image for E. eriodicyonis does not, as it has smaller pronotal spots, a much narrower occipital marking, and lacks any elytral vittae).

However, in the references I've seen, the specific host of T. diductum is recorded as E. californicum rather than E. tomemtosum, and these two plant species are quite distinct in vestiture, form, and flower. E. tomentosum is abundant in the area where the photos were taken, whereas E. californicum could very well grow in the area, but I do not recall seeing it nearby. Anyone have insights? I'd appreciate input/feedback.

Addendum 11/16/07: About two weeks after posting this, I found out that Eriodictyon tomentosum is indeed cited as a host plant for Trirhabda diducta in "Table 1" of Swigoňová & Kjer(1)

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Trirhabda sp. (perhaps T. diducta?) - Trirhabda diducta

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Contributed by Aaron Schusteff on 29 August, 2007 - 3:53am
Last updated 22 May, 2023 - 12:01am

Moved

Moved from Trirhabda.

… john and jane balaban, 12 September, 2007 - 6:38pm

thank you

thanks for allways paying attention

… Rob Westerduijn, 13 September, 2007 - 8:47am

I second that!

Thanks to you too Rob :-)

… Aaron Schusteff, 13 September, 2007 - 1:00pm

within variation

Great find, Aaron. What are the other species you mention known from Eriodictyon? Is there no way to exclude those. At first glance I thought your beetle was different from the type. However your beetle seems to have more black on all its markings than the type, but as it is found on the same places in the same form I think this could well be within variation. Especially note the presence of a very faint stripe which is very well visible on the elytra of your specimen. Also the marking on the head are the same form and there is a spot behind the eye on both specimens. Concerning the host. If you found it on a species in the same genus I think it is very likely to be able to feed on both. A species of a closely related genus here in Peru, Dircema marginatum, feeds on several species in the genus Cecropia and also on a species of the closely related genus Pourouma from the same plantfamily. Allmost all of these beetles are oligophagous (found on several closely related species). In conclusion I think it could very well be T. diducta.

… Rob Westerduijn, 29 August, 2007 - 11:40am

The one other species...

...I'm aware of that feeds on Eriodictyon is (you'll like this :-) Trirhabda eriodictyonis (for background, see "Thank you Boris" entry in the thread here). However images of the type specimen for E. eroidictyonis don't appear to have elytral stripes (vittae?), so T. diducta seems the better guess to me at this point. Still haven't got to the UC Berkeley library to look at this reference:

Blake, D.H. 1931. Revision of the species of beetles of the genus Trirhabda north of Mexico. Proc. U.S. Nat. Mus. 70:1-36.

But I hope to soon. Maybe that will help, though its quite old. Thanks for your comments:-)

… Aaron Schusteff, 29 August, 2007 - 1:16pm

Trirhabda diducta

I think you can make a speciespage for Trirhabda diducta

… Rob Westerduijn, 3 September, 2007 - 4:10pm

Thanks Rob....

....I agree. I got to the UC Berkeley library yesterday and was able to read the article "Phylogeny and host-plant association in the leaf beetle genus Trirhabda LeConte (Coleoptera: Chrysomelidae)" by Zuzana Swigo and Karl M. Kjer [Molecular Phylogenetics and Evolution 32 (2004) 358–374]. It has a very complete list of host-plant data for all Trirhabda species, and it includes Eriodictyon tomentosum as a recorded host plant for Trirhabda diducta. I also went through the key in A Synopsis of the North American Galerucinae (Coleoptera: Chrysomelidae) which led to T. diducta.

As far as making a new species page for T. diducta...I don't know how to do so (or if I'm authorized?).

… Aaron Schusteff, 12 September, 2007 - 1:28am

editors

yes, you need to have the editor version to do that. Maybe Boris or somebody else will see this and make the page.

… Rob Westerduijn, 12 September, 2007 - 8:51am

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