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Pipiza bimaculata?

 
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NickU



Joined: 21 Apr 2010
Posts: 11

PostPosted: Thu May 06, 2010 8:08 am    Post subject: Pipiza bimaculata? Reply with quote

Is it ever possible to identify Pipiza spp.. from photos? I took a shot of a Pipiza (see http://www.diptera.info/forum/viewthread.php?thread_id=29747) which I didn't even realise was a syrphid at first..) but now I've been pointed in the right direction and am checking the right genus, it looks closest to P. maculata from online photos (based on wing markings and extent of white marks on the abdomen), but are these characters too variable to rely on?

Near Box, Wiltshire, 4.5.2010

NickU
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conopid



Joined: 03 Sep 2005
Posts: 342
Location: Shrewsbury, Shropshire

PostPosted: Fri May 07, 2010 6:17 pm    Post subject: Reply with quote

Pipiza are difficult with specimens and sometimes impossible. There is very little chance of ID from photos, which is a shame as they are a nice varied genus (too varied in fact!)
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Nigel Jones
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NickU



Joined: 21 Apr 2010
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PostPosted: Fri May 07, 2010 6:28 pm    Post subject: Reply with quote

OK, many thanks. Pipiza sp. it is then..... Photographed another one today, very similar but with no hint of the white marks. Maybe the same or a different species, but only the Pipizas will ever know I guess!
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Roger K.A. Morris



Joined: 06 Nov 2005
Posts: 1652

PostPosted: Fri May 07, 2010 9:28 pm    Post subject: Reply with quote

Hello Nick

The features you are using don't work. The main features relate to colours of feet, colours of hairs on the face and 4/5 tergites. My guess, and it is only a guess, is P. noctiluca for the following reasons:

1. Front and mid-taris look to have yellow sections (dark in bimaculata).
2. Wings have slight cloud but not well defined as in P. lugubris.
3. Shape and jizz does not feel right for P. austriaca.

P. noctiluca is very much a dump species with several distinct forms known and many others lurking.

This is an illustration of the need to hold on to specimens - numbers of Pipiza records have declined markedly in recent years, but my own recording suggests that they are actually no rarer in the field.

Regards

Roger
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NickU



Joined: 21 Apr 2010
Posts: 11

PostPosted: Sat May 08, 2010 2:12 pm    Post subject: Reply with quote

Hello Roger

Many thanks for this detailed, helpful feedback. As a generalist, not a specialist, it takes this kind of feedback before I know which characters to focus on while taking pics and seeking IDs of different genera/species.

As a photographer, I don't usually collect specimens, but I have a scientific background and so try to seek the most accurate ID's I can. I do have a sweep net, though, and if collecting specimens for some groups could prove very useful for gathering distributional data, I'd consider doing some.

I did get another Pipiza (I'm pretty sure!) photo yesterday in my garden and based on your feedback, suspect it's of a different species with all black legs: http://www.diptera.info/forum/viewthread.php?thread_id=29822

I realise that with photos alone Pipiza sp. maybe the only safe ID, and gather from Nigel Jones that even with specimens and keys, sure identification is not guaranteed, and it sounds like the taxonomy needs to be refined. I suspect the lack of recording may well be due to the difficulty of identification.
Nick
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Roger K.A. Morris



Joined: 06 Nov 2005
Posts: 1652

PostPosted: Sat May 08, 2010 9:42 pm    Post subject: Reply with quote

Hi Nick

your new one is a Cheilosia - face has a nose and is not flat and shaggy.

I'm afraid that hovers require a fair bit of microscopy so collecting specimens is an inevitability if you want to get useful ID. One of the biggest problems we now have is that people don't like collecting and consequently the numbers of records of difficult taxa are declining - this has possible issues in the long run for conservation measures.

I have an article on this due out with British Wildlife soon I think.

If you want specimens checked I'd be delighted.

Regards

Roger
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NickU



Joined: 21 Apr 2010
Posts: 11

PostPosted: Sun May 09, 2010 11:58 am    Post subject: Reply with quote

Hi Roger
OK, many thanks again. Am now tuning in more to the head shape, how the antennae are positioned as well as leg colour, but appreciate your point that with difficult genera, collecting and careful keying is the only way to be sure what's what. And of course, that's crucial for knowing what lives where, what's declining, and what habitats need conserving. I'd be interested to see your article when it comes out; I'm sure for some genera/ species that can be identified form photos the growing number of photographers submitting shots to various websites is helping to track distribution (and I've had some positive feedback to my postings of rarely reported species), but for some genera that clearly just doesn't cut it... If collecting would really help, and I knew which genera were most of interest in that regard, maybe I could start doing some, and send you some for definitive ID, though it is usually a odds with photography! I'd have to stalk some targets twice; once with a camera, and again with a net and they're not always that accommodating!.
best wishes, Nick
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brianh



Joined: 23 Oct 2008
Posts: 150

PostPosted: Mon May 10, 2010 9:41 pm    Post subject: Reply with quote

I went out today with both camera and net with the hope of having both pictures and specimens which I could match up. As was mentioned you have to stalk your targets twice which was not easy.
Unfortunately most of my pictures were of Cheilosia. At one site I collected three specimens and subsequently took three pictures of others nearby. They all looked the same, but under the microscope I keyed out three species.
Previously I have photographed and collected Syrphus which usually key out to S. ribesii, but a small proportion are either torvus or vitripennis.
I have now come to the conclusion that I cannot rely on identification from pictures unless the species has a very distinctive feature that cannot be confused, or you do manage to get several views of head, legs, etc with the defining characters. This may be a minority of species as even the most common species have near identical lookalikes.
I think that usually you can only give the most likely (but not certain) identification.
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NickU



Joined: 21 Apr 2010
Posts: 11

PostPosted: Tue May 11, 2010 8:51 pm    Post subject: Reply with quote

Hi Brian
Some good points and I'm sure you're right that for many, many syrphids, keying out with specimens may be the only way to get to a definitive ID. Having said that, there do seem to be a number of genera and species which can be IDd from photos (with help from this and other forums I'm very confident of the IDs on many of my hover photos), and I'm slowly learning which key features are need to help with different genera (Eg the all important feet/leg colours in Eristalis spp).

I guess one problem is that keys were written assuming specimens are available for microscopic examination and fewer people are actually collecting and doing this now, as has been mentioned in this thread. While I accept that this will remain necessary for the trickiest genera, I wonder if at some stage new keys that are more "photographic evidence oriented" might be devised (maybe some are already out there...) as there are more and more people - like me - gathering photographic records and we're quite capable of getting the required angles and views once we're know what to focus on. If they're too subtle or hidden, then the microscope would remain the only way, still. Field observing and photography can also gather good behavioural and ecological info. Photographic evidence, supported by traditional keying of specimens where needed, should be a good combination.

A respondee on another forum pointed out to me that a hundred years ago it was assumed that identification of many bird species could only be done from shot specimens, but the advent of good field guides with accurate drawings and pointers on what characters to look for (and better optics to view them with) revolutionised the approach to bird identification. Digital photos are now commonly used to confirm sighting records instead of detailed field notes, so things have changed for birds at least. Diptera are maybe a tad trickier with so many more species, but I'm sure there's still plenty of scope for photo ID in many cases, even among the tricky Syrphidae and more photo-evidence friendly keys might help in the future!
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conopid



Joined: 03 Sep 2005
Posts: 342
Location: Shrewsbury, Shropshire

PostPosted: Tue May 11, 2010 9:23 pm    Post subject: Reply with quote

Another idea, you can capture, inspect and release specimens. Use a handlens to try and view key features of the insect kept inside a clear tube, which will increase the range you can identify in the field. Time consuming however, but if you are resolute in your resistance to collecting, this would be worth a try. You'd need to keep a simplified key with you in the field.

However for the majority of species a specimen is essential. You may just ocassionally get the right angles to do difficult species form photos, but the failure rate would almost certainly be very high. Sad

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Nigel Jones
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NickU



Joined: 21 Apr 2010
Posts: 11

PostPosted: Wed May 12, 2010 8:25 pm    Post subject: Reply with quote

Thanks Nigel; interesting idea, and I might just do that. I do find myself squinting at odd angles to check leg colours, how far markings stretch around the abdomen, etc and a specimen in a bottle might save me some contortions... ! and I'd rather not collect as a first option.

I may have mostly photographed the easier / most distinctive hoverfly species so far and will continue to submit records when l'm sure of them/ when I read that their distribution is patchy/under-reported (as I did recently for Criorhina ranunculi and Didea fasciata), but absolutely take your point that many genera are very tough to be sure of in the field/from photos and need careful keying.
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