...and I seem to have missed most of the excitement. But what wonderful news to come back home to!! My most sincere thanks, Martin, for confirming this one. I was actually quite studiously attempting to key this out myself last night and felt pretty hopeful that it was indeed Dalmannia. I finally decided to go to bed before managing to figure out if it was likely D. picta or D. vitiosa.

I am quite pleased to have been able to spend some time documenting this lovely fly and even more pleased that I was able to rescue it from the chlorinated depths of the pool.

Oops! Forgot to ask... Am I correct in my observation that this is a female?

yes, it shows the large ovipositor with which it inject eggs into small bees...

Mystery solved!

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I meant to call attention to the proboscis in the last photo, but I forgot. I guess that feature did turn out to be pretty important. I started poking around in the conopid image comments and came across this interesting statement by Paul Beuk. Would you say that the proboscis on my specimen is "doubly bent"?

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...but then I found this comment from Keith Bayless about the eye to gena ratio and now I'm not sure... Help! I fear I'm in way over my head.

I've been studying Conopidae off-and-on recently, reading up in "The Manual of Nearctic Diptera (Vol II))(1)", and the "Conopid Flies of California" by Camras & Hurd (PDF here), and attempting to key various conopid posts on BugGuide for practice. So, I think I can see how you may have been derailed in trying to key your Dalmannia...if I were only using the key in Camras & Hurd, I'm pretty sure I would have been derailed!!

The first couplet, in both the keys to genera, concerns the position of the arista on the antenna (terminal vs. dorsal). From your photos, it's clear the arista is dorsal. The next couplet (that is, couplet 3 on pg 21 of "Conopidae of California"; and couplet 6 on pg. 54 of "Manual of Nearctic Diptera (Vol II)(1)") is the potentially perilous one! In both references it separates out Dalmannia by comparing the length of the anal cell of the fore-wing with the length of the adjacent basal medial cell. (What are the anal and basal medial cells? For figures illustrating them, see the cells labelled "Cu" and "M" in Figure 2B on pg 22 of Camras & Hurd; or the cells labelled "cup" and "bm" in Figure 67 at the top of pg 30 in the "Manual of Nearctic Diptera (Vol I)(2)").

Unfortunately, the "Conopidae of California" key potentially confuses the issue (at least for your particular species) by stating their couplet 3 as:

3A "Anal cell (Cu) much longer than second basal (M) (Myopinae) (fig. 2a) . . . . 4 "
3B "Anal cell (Cu) about equal to second basal (M)". . . . . . . . . . . . . . . . . . . . . 7 "

The 2nd chioce leads to Dalmannia...where we ought to end up here. But it turns out that in your species (and photos) the anal cell is much shorter that the second basal cell. That's because, as Camras & Hurd state in their description of D. vitiosa on pg 47,

"This small distinctive species lacks the crossvein between the second basal and discal cells." (Emphasis mine)

So in your species (and photos), what looks like "the second basal cell" is actually much longer than the anal cell, which makes is seem that neither of the alternatives in Camras & Hurd's couplet 3 work. So I can see how one might erroneously be led to consider the next couplet...asking whether the specimen has a "doubly-bent" proboscis.

All Conopidae have at least one "forward bend' at the base of the proboscis. Some genera also have a second "backward bend" around the middle of the proboscis. With this understanding, the "doubly-bent" proboscis of Myopa is clearly visible here:
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From your photos (and Paul Beuk's comment), it appears that Dalmannia also have a "doubly-bent" proboscis ...even though the keys in both references mentioned above separate out Dalmannia before their couplet referring to the "doubly-bent" proboscis character. (And neither reference indicates that Dalmannia has a doubly-bent proboscis, as far as I could tell.) So I can see how you might have thought you had Myopa...and then when the "eye to gena ratio" character didn't jibe, you might have felt lost in the wilderness.

At any rate, here's the sequence of key steps if you want to practice keying your conopid to genus in either or both references:

In the key on pg 751 of the "Manual of Nearctic Diptera (Vol II)": Couplets 1B, 6B(!), 7B;

In the key on pg 21 of the "Conopidae of California": Couplets 1A, 3B(!), 7A.

As indicated by Martin, once you have the correct genus, it keys readily to species vitiosa, using the key on pg 47 of Camras & Hurd.

Sorry to respond so late on your most excellent comment. I kept meaning to sit down and direct my full attention to processing all the great info in your detailed post, but I didn't get around to it until just now. My memory of where I got lost in trying to key this one originally is a little hazy, but I do think it's likely that it was evaluating the anal vs. basal cells that probably threw me for a loop.

I've got some other unidentified conopids (which I think might all be the same species)... I'll try to sit down with your notes and the pertinent references and keys to see if I can figure out the correct species. I'll be sure to take full advantage of all your recent studying by submitting my results for your review. :-)

I really wasn't sure, just taking a stab at it. I should look up the distinguising characteristics.

For what it's worth, leafminers are a pretty common sight around my place, so you're right on that count.