Trirhabda Sp? - Xanthogaleruca luteola

Making sense of comments thread below (6+ yrs later)

This post originally consisted of the 6 images thumbnailed below (3 adult Xanthogaleruca luteola, and 3 Trirhabda larvae)...all found on rabbitbrush at the same time & locale:

Rose's comment at the bottom of this comments thread prompted the sensible separatation of the Xanthogaleruca luteola images from the Trirhabda images.

… Aaron Schusteff, 30 May, 2021 - 12:07am

Very unusual host plant transfer?

It's interesting that these were found on rabbitbrush (genus Chrysomthmnus/Ericameria) in the sunflower family, Asteraceae. That is a very different plant from the elm tree host (genus Ulmus, family Ulmaceae) usually associated with Xanthogaleruca luteola!!

Note that rabbitbrush is also a host plant for a number of Trirhabda species native to Colorado (e.g. T. niticollis, T. lewisii, and T. pilosa). Species in the genus Trirhabda are considered quite "picky" in their choice and use of host plants (e.g. see Swigoňová & Kjer(1) ). And if the same goes for Xanthogalerua then feeding on rabbitbrush by adults, let alone larvae, is noteworthy and would likely be of interest to researchers in this group. It may also have significant implications for range managers, considering the abundance of rabbitbrush in the west and its role as a dominant or sub-dominant shrub in a number of plant communities and ecosystems.

… Aaron Schusteff, 26 October, 2014 - 2:04am

Second thoughts & questions

Van, do you remember whether you saw more than one adult X. luteola on the rabbitbrush when you took the photos in this series?

And might you have seen other adult Trirhabda (lewisii/nitidicollis) among the larvae?

Perhaps the adult X. luteola in your post here simply flew from a nearby elm tree to this patch of rabbitbrush...which was previously occupied by a population of native Trirhabda larvae?

I just searched for images of X. luteola larvae and found the following:

Natural Resources Canada
Oklahoma State University
Galerie du Monde des Insectes
Bugwood.org

Though the appearance of the larvae changes with instars, I couldn't find images for X. luteola that were as uniformly dark metallic green as those in the post here (which do look like Trirhabda larvae). It seems the larvae may not be X. luteola.

Guess the best way to ID those larvae would be to collect some late instars right before they drop to the ground to pupate in the litter...and see what you get after they emerge! (Along with beetles, you may get some interesting parasitoids...looks like an egg was laid on the larvae in the 3rd image of your series.)

… Aaron Schusteff, 26 October, 2014 - 2:08pm

As I remember, there were mor

As I remember, there were more than 10 adults on the rabbitbrush. That's what confused me. I've seen numerous X. luteola in my yard, since we have very large Siberian elms and they are attracted to UV lights when mothing, and their larvae on the elm leaves. I only observed the metallic blue larvae on the rabbitbrush, thus thought Trirhabda sp. and were adults since their description is similar.

X. luteola are very common here and there were elms in the area where the rabbitbrush photos were taken.

I will check the photos that I shot that day and another day that I had Trirhabda sp. larvae at another location and see if there might be an adult. I will forward any, if I find one.

… Van Truan, 26 October, 2014 - 4:46pm

Moved

Moved from Trirhabda.

… Aaron Schusteff, 26 October, 2014 - 12:45am

Xanthogaleruca luteola, rather

… roar, 7 September, 2014 - 4:06pm

Yes

The 3rd antennal segment is a bit longer than the 4th here, as in genus Xanthogaleruca. The 3rd antennal segment is significantly shorter than the 4th in Trirhabda.

And the two short, dark medial stripes at the bases of the elytra are an even more conspicuous clue that this is Xanthogaleruca luteola...as is the "hour-glass" shape of the medial spot on the pronotum.

Also, the "Pueblo City Park" habitat is consistent with an introduced species like this one...as opposed to the wild-lands habitat commonly associated with nearctic Trirhabda, which are all native species.

Note that Van has an earlier 2012 post of the same species from the same area that he placed correctly at that time:

… Aaron Schusteff, 26 October, 2014 - 12:38am

Thanks for the correction. I

Thanks for the correction. I think there may have been a Siberian elm within the area. I was kind of confused myself.

… Van Truan, 26 October, 2014 - 7:13am

images should be separated

The beetle is an Elm Leaf, but the larvae are Trirhabda. The Elm leaf beetle larvae do not eat rabbitbrush, and they're not metallic blue-green. I'd get these pics separated to avoid confusion.

… Rose L, 29 May, 2021 - 7:56pm

Good Point, Rose

I agree: unlinking the current 6 images of the series; then relinking the 3 adult images under Xanthogaleruca luteola:

...and the 3 larval images under Trirhabda:

...seems a good resolution here. Nearly 7 years on now, I'm not sure why that didn't occur to us back then, and the issue was apparently lost in the shuffle of time up to now. So thanks for your comment Rose.

… Aaron Schusteff, 29 May, 2021 - 11:54pm