[NatureNS] Tachinid guesswork.

Date: Mon, 11 Sep 2006 01:18:19 -0300
From: Stephen Shaw <srshaw@dal.ca>
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Hi Angus,  There's not enough info in the either image to definitively 
identify
either of your specimens on appearance alone, unless someone recognizes either
one explicitly as a locally-known species, apparently what Chris and Dave were
doing.
   Tachinids are the largest family of recently evolved flies (perhaps largest
of all in terms of numbers of species), close to blowflies and their kin,
difficult to identify as to species. If you see a very bristly fly like yours,
it's likely a tachinid unless it's a robberfly (Asilidae), but asilids 
are more
ancient and have a much different antennal tip (this antenna is 
"modern"). This general group of "calyptrates" including tachinids is 
distinguished by a
fleshy lobe at the base of the wing, the calypter, clearly visible as a white
area in the photo, so this rules out most of the other modern groups (the
acalyptrates). The calypter has been suggested to increase flight
manoeuvrability.  So, bristly calyptrate = it's likely a tachinid.  The third
segment of the antenna (funiculus, or 3rd flagellomere) is the main olfactory
organ in these flies, much studied recently in _Drosophila_.  In your specimen
it is more prominent than often found, another feature sometimes seen in
tachinids.
This is loose stuff from me as none of these features are cast-iron 
identifiers,
but I'd still vote Tachinidae.

For an informative professional site on the latest phylogeny of Diptera try
googling Flytree.  One link from there will get you to a useful Atlas site run
from CSIRO in Canberra, Australia, which has a strong Diptera group.  This has
a very detailed listing of named external parts of flies (which light up when
you type 'calypter' etc.), particularly the various unmemorable groups of body
bristles that are often used in detailed run-downs of species in keys.  It
covers several levels of fly phylogeny -- four, I think.  Direct link for the
Atlas is
www.ento.csiro.au/biology/fly/fly.html#
Pick the Musca example for your tachinid(?) fly. It's in the sister group.
Steve
*************************************

Quoting Angus MacLean <angusmcl@ns.sympatico.ca>:
> I appreciate you calling me on this one, Stephen, as I know virtually 
> nothing about the differences. This other photo shows the wing(s) 
> clearly and I thought the clear vein (on the right) was the spurious 
> vein of the mimic.
> http://www.flickr.com/photo_zoom.gne?id=239985082&size=o
> Which features of the other image leads you to believe it is a 
> "tachinid" fly. In this pic I have difficulty seeing the features 
> mentioned in the NAS Guide.
> Thanks,
> Angus
-- 

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