Re: Mosquito Evolution in London's Underground?

I recall reading that mosquitos, thought to have evolved into a different species after years of confinement, had been discovered in the London Undeground railway tubes. I have been unable to locate the source, or any further information. If true, is this the first observed example of a change in species?

Yes, your recollection is correct. I found the original journal article describing the "molestus" mosquitoes of the London Underground:

Byrne, K. and Nichols, R.A. (1999), "Culex pipiens in London Underground tunnels: differentiation between surface and subterranean populations." Heredity 82: 7-15

According to Byrne and Nichols, attempts at mating the underground "molestus" mosquitoes with their aboveground Culex pipiens ancestors were unsuccessful, suggesting that the two had diverged into separate species (I would suggest reading their paper for a better description of their findings).

No, this is not the first (or only) example of a recent speciation event. In fact, the Talk-Origins Archives has an ongoing (if not comprehensive) list of other recent speciation events, while our own archives have several posts defining speciation and giving examples of adaptation events on the verge of speciation.