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Temnostoma alternans ? - Temnostoma excentrica

Temnostoma alternans ? - Temnostoma excentrica
Allison Park, Allegheny County, Pennsylvania, USA
June 6, 2012

Moved from Temnostoma.

Moved from Syrphid Flies.

I'd like to see another opinion, and this is a neat fly!

BOLD has an entry for Temnostoma excentrica
with a few photos and geographic data for North America.

Temnostoma nomenclature
Hi folks,

BOLD is not a great resource to use for nomenclature. I sent them an update a few months ago but I have not checked to see if it has been implemented. Even if it has been, is the most up-to-date Diptera nomenclatural database. Temnostoma excentrica has been resurrected as a valid species in this database as a result of morphological research by the Russians and molecular data that I have collected. Temnostoma vespiforme is now considered exclusively an Old World taxon.

Sorry that I have not updated my field guide pages in so long. We are working to finish our field guide this year and will put the pages up when it is completed if the publisher will allow it.

Jeff Skevington

Thank you Jeff
Do you agree that this is Temnostoma excentrica, we've been waiting for expert confirmation to make a new page for it.

Temnostoma excentrica
Yes, I agree that it is Temnostoma excentrica.

Thanks Kelsey
I'm glad I posted it I wasn't going to because T. alternans was already represented for PA but this one seemed a bit different. I'll post the one I think is T. alternans and another one I believe is this species.

Hi John - definitely do! You
Hi John - definitely do! You have nice photos here and we aren't overflowing with Temnostoma the way we are with some other more common syrphids. If you're curious to key the species out, here are the two keys I used:

Curran 1939

Shannon 1939

One other point about alternans - although it's not in the keys, the images we have here on BG and on Jeff Skevington's page show alternans as having the thoracic suture spots divided in two (as in venustum) rather than joined as in this fly. So that may be another helpful character to consult, in addition to the abdominal markings.

It actually looks a lot like...
...Temnostoma vespiforme (do a Google search)--but there seems to be some disagreement as to whether that species occurs in North America or not.

Eagerly awaiting an expert opinion. :)

Not alternans - that species
Not alternans - that species has three black markings on the fourth abdominal segment, one central, and I only see two on the sides in this photo.

I keyed it out in both Shannon 1939 and Curran 1939, and in both cases got Temnostoma excentrica - in Curran this is separated from T. vespiforme by the all-yellow femora (at least the anterior femora black on the basal third or more for vespiforme).

Skevington's page is somewhat confusing - the 2013 Key to the Genera of Nearctic Syrphidae doesn't list vespiforme as a species in the Nearctic, but the Skevington pages here do. Systema Dipterorum lists T. excentrica as a valid species name found in your region, and vespiforme as European.

Shall I make a new guide page for T. excentrica, or shall we wait for another opinion?

Curran - scutellum not yellow pollinose; not marked as alternans; thoracic suture spots not distinctly separated as in venustum; more than 4 yellow fasciae on abdomen; scutellum yellow pilose; femora wholly yellow.

Shannon - (skipped 2-3 based on overall appearance); two crossbands on each abdominal segment; yellow markings on thoracic suture not separated; femora yellow. (note that Shannon doesn't list vespiforme)

Diptera catalog
Temnostoma excentricum (Harris) is listed as a valid species, for what its worth. (1)

I would move it to genus...
...and wait for additional, hopefully expert, opinions--but you may be bolder than I. :)

If you feel confident of the ID, go ahead and create the page. If not, it doesn't hurt to be cautious.

I think you may be right
I initially thought that might be the case when looking at the one sample here but it lacks the two posterior marks on the thorax that mine has. I see that others on the web do have those marks. I have other photos of Temnostoma alternans that look like the ones here.

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