Have we ever observed two drosophila lineages that evolved reproductive isolation in labs?
Rice and Salt$^1$ bred fruit flies for 35 generations and from one line of flies created two groups that were isolated from each other reproductively. They could not interbreed because they no longer bred in the same environment. Depending on one's definition of 'species' this could be a case of artificial speciation.

$^1$Rice WR, Salt GW (1988), Speciation via disruptive selection on habitat preference: experimental evidence". The American Naturalist 131 (6): 911–917.