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Nectaring (and picking up a lot of pollen!) on flowers of buttercup (Ranunculus californicus).

The last picture shows the tip of its proboscis tucked under a fold/flap of tissue at the base of the petal that seems to represent a nectary-structure of R. californicus that I wasn't previously aware of.

I'm posting 4 observations of what I think are the same species of tiny fly (~3 mm from wingtips to tips of antennae). The others are iNat obs 166971508, 166975556, and 166975589. All were found lingering on flowers of Lithophragma affine along the same stretch of trail (< 1/2 mile long) on two days (4/18/23 and 4/22/23)..and I didn't notice any of these on other plants.

The photos are not as sharp & diagnostic as I'd like, but I think they're members of an under-represented genus Microphor...of which there is currently only one nearctic post on iNat (which also appears on BugGuide along with one additional post.)

When I first saw these in the field I presumed were "micro bee flies" in the family Mythicomyiidae (and that's what iNat's "computer vision" model suggested ;-)

But after carefully scrutinizing the photos and reviewing various ID resources (e.g. the 1981 Manual of Nearctic Diptera and the recent revision Brooks & Cumming(2022)), I concluded they're likely what was previously referred to as Microphorus in the MND (therein considered a genus in the family Empididae). However, per the revision Brooks & Cumming(2022), the genus name has reverted to an earlier spelling, Microphor...and the genus is treated as part of the subfamily Microphorinae, currently placed in family Dolichipodidae sensu lato.

My best guess for the species ID at this point is M. obscurus, based on the following criteria gleaned from Brooks & Cumming(2022):

• "distal section of vein M1 (beyond base of M2) longer than preceding section (between r-m and base of M2)"...see their Figs 29, 30, 85–90, 169–176 (and also Fig 23 for venation labelling reference). The clearest (though still somewhat vague) wing venation photo I got was the dorsal view of the male in 166975589)
• "Antennae with stylus distinctly shorter than postpedicel"...see their Figs 59, 61, 62. [Note that from the many relevant figures in Brooks & Cumming, the relatively-short stylus here seems to exclude members of Schistostoma, the other genus in Microphorinae...and also perhaps M. skevingtoni (Fig 37) and M. discalis (Figs. 17, 19, 20)]
• Seta relatively short and inconspicuous on head, thorax, and abdomen...see their Figs 59, 61, 62
• Haltere dark (as opposed to pale in bilineatus, which is in addition extralimital to CA)

However, note that the one passably-interpretable photo I got of the wing venation (i.e. the male in 166975589) seems to fit better with their diagrams for M. skevingtoni (Fig 26) or M. discalis (Fig 23), than with M. obscurus (Fig 26)...and all three of these species are recorded in the general area here. Also, the head of that male in 166975589 appears appreciably more elongate, and with post-pedicel more basally-swollen, than does the male in the BugGuide post here...which is currently (and I think correctly) placed under M. obscurus (perhaps differences are due to intraspecies variation?). Thus I'm not entirely confident in the species ID of M. obscurus...and am only placing the posts to genus for now. I'm hoping someone familiar with the group may eventually be able to confirm or correct my species hypothesis.

PS: Presuming these are indeed Microphor, the observed association w/ Lithophragma affine would constitute a new species for the list of plants visited by nearctic Microphorinae in Table 1, pg. 15 of Brooks & Cumming(2022).

Found growing on the trunk of a Coast Live Oak (Quercus argrifolia). The first photo is the individual as found (dried), while the second photo is after being splashed with water. The third photo is showing the underside of a small section of the lichen.

Under a dissecting scope, a torn piece appeared to have a distinct upper cortex layer which is how I differentiated it from the very similar genus Collema. (Piece was collected under NPS permit for the 2023 Pinnacles Bioblitz).

Ran onto stone on west exposed hillside above dry creek, in Baccharis-Artemisia scrub.
The last three images were taken by Dr. Marshal Hedin (@mhedin), and show the adult male that molted 20-23 February 2023. These photos have been used with permission.
https://bugguide.net/node/view/2224186