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Posted by thijsdegraaf on 17-09-2013 16:47

A tachinid fly. Small. I think about 5 mm. I hope you can help me.
Bergen, The Netherlands. Photos 17-9-2013.
Regards, Thijs

Posted by thijsdegraaf on 17-09-2013 20:25

Ah ... In October 2009 I had photographed a Bessa selecta. This is my second fly of this genus. ;)
Thanks Theo.

Posted by sd on 18-09-2013 10:29

Hi Theo,

Are there no other means of distinguishing B. selecta and B. parallela other than presence of discals on T3, T4 ( selecta) and the host ( Symphyta for selecta, Microlepidoptera for parallela)?

I have 2 specimens of Bessa from here in Suffolk. One is certainly selecta
(http://www.dipter...d_id=40319 )
but the other has discals on T4 but not T3.
(Sand Dunes are a few km away, so dune type diptera turn up from time to time, eg Villa modesta ).

regards,
Steve

Edited by sd on 18-09-2013 10:29

Posted by thijsdegraaf on 18-09-2013 16:31

Hi Steve.
I've tried to find the topic about my Bessa selecta, but did not succeed. To long ago I think.
You can find this fly on my website. (The eighth fly.) http://www.tuin-t...engels.htm It was determined by Jaakko
When somebody asked why, was this his commen: Just a combination of features: sharp kink in the m-vein, white hairs behind the head, low "short-legged" sitting position and small size.
I hope he was right, for the only difference i can find is indeed Terites 3 and 4 with discal bristles for selecta and Tergite 3 without, tergite 4 almost always without discal bristles for parallela.

Regards, Thijs

Edited by thijsdegraaf on 19-09-2013 07:17

Posted by Zeegers on 18-09-2013 16:48

#10

@Steve,
No,there are only 2 features
* host (Yponomeuta / other)
* discal setae

Indeed, 1 out of 100 is intermediate in discal setae.

I always got away with this, because I had series of just 1 species.

If it is only 1 specimen, you are in trouble !

[ I expect those to be selecta, but that is not very scientific !]

Theo

Posted by thijsdegraaf on 18-09-2013 19:36

#11

I think I change my website. I change the "Bessa selecta" for this Bessa paralllela. With a discription of both species.
Thijs :|

Edited by thijsdegraaf on 18-09-2013 19:37

Posted by sd on 18-09-2013 20:13

#12

Hi, Thanks to both of you for helpful comments. I should also have noted that parallela is much rarer than selecta in the UK.

regards,
Steve

Posted by thijsdegraaf on 19-09-2013 07:57

#13

I found the topic of the B. selecta in 2009. ;) It's http://www.dipter...ost_114393

Edited by thijsdegraaf on 19-09-2013 07:58