at least I got the genus right. :)

Incidentally, if xerene is not in CA, then we seem to have a couple of misidentified images in the Guide (here).

a species isnt recorded from a particular area doesnt mean it isn't there :-). It might be good to have a chrysomelid specialist double-check the CA records of M. xerene, though. I can try running some through the key, if the images show the right characters. Thanks!

I was just doing a bit of reading to see if I could figure out how one distinguishes M. rubrolineata from M. xerene. Ron and I found a few of these guys on a recent outing -- see his photos here. Now, I'm really curious about Blaine's comment that some of the literature doesn't seem to support there being a range for M. xerene within CA, especially after finding this page which does reference a range within our state. Curious to know whether any further information has come to light on this issue or whether a chrysomelid specialist could indeed be consulted on the matter...

I'm going to encounter one of these sooner or later, would like to know what details need to be photographed.

...than I was 7 years ago on the question of this tricky ID, except that I have now seen several sources corroborating records of M. xerene in CA.

I haven't done so myself, but if you register for a free account with JSTOR, you can read "A REVISION OF THE GENUS MICRORHOPALA (COLEOPTERA: CHRYSOMELIDAE) IN AMERICA NORTH OF MEXICO" online for free. From looking at the preview, I'm guessing it probably has some nuggets of wisdom regarding what distinguishes M. xerene from M. rubrolineata. Here's the link:
https://www.jstor.org/stable/41712020?seq=1#fndtn-page_scan_tab_contents

https://archive.org/details/cbarchive_121887_arevisionofthegenusmicrorhopal1983

Details:

-Interstriae 9 undulate to slightly serrate; lateral profile angled; tarsal segment 3 cleft ventrally to about half length of segment; eye margined behind by a double row of punctures ...xerene

-Serrations on interstriae 9 conspicuous; lateral profile of frons not prominent or angulate; tarsal segment 3 cleft ventrally to about 2/3 length of segment; punctures behind eye arranged in a single row, less often confused or arranged in a double row
... 9 (leading to rubrolineata)

Another mention:

[M. rubrolineata] differs from M. vittata and xerene, which are similarly marked with red or orange, by the frons that does not appear prominent, angled, or carinate in profile.

I have Staines' Hispines of North America and can try to run it through the keys later tonight, if someone doesn't get to it first.

How about M. rubrolineata?