Flies and species change

[icantlogoff]

Hi, and an apology at the outset for my ignorance.

I am trying to find a reference on the net or book for something i saw some time ago regarding flies.

They had slowly changed some parameters of the flies environment ,and i believe got the flies to change the diet to salt and not sugar anymore, this also made the 'new' flies unable to breed with the original flies (whos diet was still sugar based)
Showing in effect that a fly can be forced by natural selection to become a species no longer able to exist within in original species?

Any pointers will help

Thank you al in advance

Steve