Now I think it is genalis, it is a more common species and the thorax is only weakly striped, while in variabilis the strpes are much more pronounced...as I said it is a difficult genus

I have some other images very similar to the one I posted. They show the three weak longitudinal stripes a bit better. I'll post them here. (Feel free to frass if it's basically redundant.)

After zooming in on the photos to 400% while trying to study thoracic bristles, it seems that the vague middle black strip at the anterior end of the mesonotum is the only true one. I think the vague lateral stripes are likely illusory artifacts of the the dorsocentral bristles and their shadows! (For whatever its worth.)

As a learning experience, I was planning to try to key this in "The Fruit Flies or Tephritidae of California", published in 1963 by Foote & Blanc (downloadable as a PDF at http://essig.berkeley.edu/CIS/cis07.pdf). I just checked the index of that work though, and the genus Campiglossa doesn't appear there...so I guess the names have changed. I'll try anyway, since going through a key helps me learn vocabulary and get a feel for characters & nuances to which I'd be largely oblivious otherwise.

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Seems the Essig Museum reorganized their pages...here's a link to a listing of all the California Insect Survey publications available free online:

http://essig.berkeley.edu/resources/cis_publications.shtml

Once at that page, you can text search "Foote" in your browser to find the paper you were looking for.

Good news. I'd feared the publication had been obsoleted.

I can send you a PDF if you want....

Currently, I have most, but not all of the document

ronhem949@yahoo.com

In this key the species are in the genus Paroxyna. (Try it again!).
There have been a few more species added to the California list, but this key is still very helpful.

After carefully comparing my photos with all the wing plates at the end of Foote & Blanc's monograph, it seemed to me the best fit was a toss up between their "Plates 59, 60 and 63", that is Paroxyna corpulenta, P. genalis, and P. variabilis (in their nomenclature). Of course, I'm a novice and have no real feel for the degree of variation in wing pattern here. I noted that their range map for P. corpulenta has a data point almost exactly where my photo was taken, while the map for P. genalis has a single data point in far-off San Diego. But they didn't seem to have much location data, so that may not mean much.

I did put a good effort into working through the keys, but found it quite difficult due to limitations of my photos and my confusion with some of their descriptive terminology (e.g. couplet 4 of their key to genera on pg 5). I definitely could not have confidently arrived at Paroxyna using the key without your hint. But with it, that genus certainly seemed plausible :-) Navigating the key to species seemed less clear to me (at least after the 1st couplet). Thanks for your input and guidance!

Good job! It is always very difficult to go through these keys and most of them are not very good... I is difficult t make a good key..
By the way corpulenta is a synonym of genalis, so they are the same..
It takes a while until you know where all these bristles are, but they are important and there is a good illustration in this book, which helps a lot..
This genus has typically lots of spots on the wings, and also in 90% a white spot in the black pterostigma, very important is that the proboscis is bent, in similar genera, the mouthparts are very short and always straight... There is a more modern book called the Fruitflies north of Mexico, by Foote somebody and Norrbom, this is a very nice book covering all species in the US with much better distribution maps and often better keys. And they have a pic of every species wing!

So Campiglossa genalis it is. Excellent!

And thanks for all the extra details. Next time I'll try to get a nice shot of the proboscis:-) While attempting to key from the photo, I did get a thrill from verifying presence of the characteristic "small, rounded, hyaline spot in the stigma" mentioned in the genus description of Foote & Blanc. I look forward to perusing the more recent book you mention at a good university library. Thanks again:-)