It's not a new species because it's a new species?!?
Two strains of Drosophila paulistorum developed hybrid sterility of male offspring between 1958 and 1963. Artificial selection induced strong intra-strain mating preferences. (Test for speciation: sterile offspring and lack of interbreeding affinity.) Dobzhansky, Th., and O. Pavlovsky, 1971. "An experimentally created incipient species of Drosophila", Nature 23:289-292
Rapid speciation of the Faeroe Island house mouse, which occurred in less than 250 years after man brought the creature to the island. (Test for speciation in this case is based on morphology. It is unlikely that forced breeding experiments have been performed with the parent stock.) Stanley, S., 1979. Macroevolution: Pattern and Process, San Francisco, W.H. Freeman and Company. p. 41
Formation of five new species of cichlid fishes which formed since they were isolated less than 4000 years ago from the parent stock, Lake Nagubago. (Test for speciation in this case is by morphology and lack of natural interbreeding. These fish have complex mating rituals and different coloration. While it might be possible that different species are inter-fertile, they cannot be convinced to mate.) Mayr, E., 1970. Populations, Species, and Evolution, Massachusetts, Harvard University Press. p. 348
page 22 of the February, 1989 issue of Scientific American. It's called "A Breed Apart." It tells about studies conducted on a fruit fly, Rhagoletis pomonella, that is a parasite of the hawthorn tree and its fruit, which is commonly called the thorn apple. About 150 years ago, some of these flies began infesting apple trees, as well. The flies feed an breed on either apples or thorn apples, but not both. There's enough evidence to convince the scientific investigators that they're witnessing speciation in action. Note that some of the investigators set out to prove that speciation was not happening; the evidence convinced them otherwise.