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Hi,
Sometimes when I try to identify diptera, I compare wings veins to match another species's photo.
my method is to create two layer in photoshop, one on top the other. The top layer is partial opaque so I can match the veins exactly to the other photo.

My question is when can I use this method?
1. Does different diptera sp. could have the same wing pattern?
2. Does the same diptera sp. (let say from different part of the wourld) could have the different wing pattern?

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1. Yes! There are some cases where different families can show a very similar wing venation! In this case you should use other features to get 100% sure. The best rule is to play with some features and never ONLY one! There are many exceptions to almost all thumb rules. :)


2. The same species in any local of the world is virtually the same (it can be some very tiny variations - remember that the individuals can have variation! as it happens with human species or any another species!! Populations are dynamic!) .

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Jorge is right of course about using more than one set of characters to arrive at an ID, but if you have the skills in Photoshop to do this sort of comparison quickly and easily, then I think it would work very well as a guide.

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Jorge,
Of course some families can have a very similar wing venation. but with my photoshop technic I can check for similar venation or identical venation. So I was wondering if it's possible to have two completely identical venation in two diffrent species?

Susan,
It's not complecated to create layers in photoshop. just create a new layer and copy the second image above it.

Does anyone want a tutorial?

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The problem with relying on wing venation is that it is usually slightly variable even within the same species, so even if it was slightly different between genera it wouldn't help you much. If it was easy to identify flies using wing venation alone then someone would have done it already - but instead we have keys and we use other features too, like bristles :)

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I must echo Chris's views strongly:- wing veins are useful but you waste your time using them unless you use other characters as well.
Even within a species there can be considerable variation
Even within an individual there is often variation:- the two wings being different:- this is a consequence of the fluctuating assymmetry that can be important in how flies evolve.
Re use of photoshop:- I have played with image computational approaches to quantifying morphometric characters. :- creating layers will not help you unless each image is exactly in the same plane, even using Montage , FDR and other image tools there are image registration issues which are only fixed by applying algorhythmic fakery.
Its fun playing with these things but don't take them too seriousely. I recently used an FDR approach to merge wings from a group of empidid species and so come up with a 'ground plan' for the group. The results were visually interesting but scientifically irrelevant!

In summar, use a key and forget about the computer

cheers
Adrian

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Although I agree with what Chris and Adrian have said, wing venation can still be a very useful tool in identifying genera and (sometimes) species. One of the early keys to British Tachinidae genera (by C.D.Day) was largely based on wing venation, and although it wasn't 100% accurate, it was MUCH easier to use than the subsequent key (by van Emden). One of the reasons that wing venation is not used more is that describing the relative lengths and angles of the veins can be very tedious - often there are other characters that are easier to describe using words in a key!

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Yes, though Day's key takes a lot of getting used to and van Emden really shot himself in the foot by having the "prosternum bare or hairy?" feature (one ofthe most difficult to check) in couplet 1 :p