I hope this link will be useful:

http://www.fspublishers.org/published_papers/28750_..pdf

Thank you very much for the link Germaine Cornet.

Kind Regards

Elton

I think there's no key which is especially for Pakistan hoverflies, but with the available keys for palearctic syrphids you'll have most or all of the species. Here you have a selection of keys: http://www.syrphidae.com/keys.php

On this website you also can find checklists e.g. from Iranian and Russian syrphids which should cover most of the species also in Pakistan (and there is also a forum for questions).

Two recommended books for identification: M. P. Van Veen (2010): Hoverflies of Northwest Europe: Identification Keys to the Syrphidae KNNV Publishing

and:

Van der Goot,V.S. (1981) De zweefvliegen van Noordwest - Europa en Europees Rusland, in het bijzonder van de Benelux. KNNV, Uitgave no.32: 275pp. Amsterdam. 

And surely there are several papers about Syrphidae from Pakistan their with their specialities (faunistic literature; but I don't have an overview about literature dealing with Pakistan). Finally there is a hoverfly mail discussion server where you can ask experts about identification problems: http://lists.nottingham.ac.uk/mailman/listinfo/syrphidae

Dear Peter

Thank you for the Guide. I will try to download them.

Kind Regards

Elton