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Rest stop fauna - Silvius pollinosus - female

Rest stop fauna - Silvius pollinosus - Female
Powder River rest area, Johnson County, Wyoming, USA
July 14, 2015

How is this separated from qu
How is this separated from quadrivittatus?

Not sure
I might have placed this by comparison with the earlier photo. The wing pattern is a good match for the illustration of Silvius pollinosus jeanae Pechuman, 1960 except for the small dots along the outer veins. Those dots are mentioned in Williston's description. Williston did not know S. quadrivittatus so he did not distinguish it. Say's description is inadequate.

I do not have Philip's key to Silvius. I may try to get it through interlibrary loan but that will take a while. As far as I know 50+ year old issues of Revista Brasileira de Entomologia are not online.

In that case, you might be ab
In that case, you might be able to find solutions in The Horse and Deer Flies (Diptera: Tabanidae) of Texas. An updated link on the Bugguide page for this source was added.

Keys to quadrivittatus, but...
I have that file already, but I didn't get it until after I posted my photo.

My fly keys to Silvius quadrivittatus, but the key and redescription of pollinosus contradict Williston's description which says "also a number (4-8) of minute brown spots on all the veins beyond the discal cell."

If I go by the wing photos, then my fly has spots much smaller than pictured. If you consider the minute spots to be absent spots, then it doesn't fit well because of the lack of a spot at the end of R2+3. The species with elongate spots does not have a spot long enough to split into two widely separated spots.

Only S. gibsoni has spotting on M1 like my fly.

There definitely is some cont
There definitely is some contradiction in the literature. For example, a key by Middlekauff and Lane (1980) has quadrivittatus without a subapical spot on R4, but an earlier publication by just Middlekauff and the Texas one say that it does. That's two against one so I go with quadrivittatus having R4 with a spot.

Well what if they are considered to be spots? I'm not sure if thickness of the spots is terribly relevant.

If anything, this doesn't have to be placed in quadrivittatus and can be just left at genus.

Moved from Silvius.

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