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I'd be surprised if they weren't, but they are still fruit flies. Well, of course they are. But that's just the same as saying that humans and dolphins are still mammals or that mammals and reptiles are still vertebrates.

No. Fruit flies can breed with fruit flies just as wolves and dogs (different species) can breed.

No. Fruit flies can breed with fruit flies

Gee, really?

Cryptic reproductive isolation in the Drosophila simulans species complex
Gametic incompatibilities between races of Drosophila melanogaster
Adaptive evolution drives divergence of a hybrid inviability gene between two species of Drosophila
Genetic dissection of hybrid incompatibilities between Drosophila simulans and D. mauritiana. I. Differential accumulation of hybrid male sterility effects on the X and autosomes
Genetic dissection of hybrid incompatibilities between Drosophila simulans and D. mauritiana. III. Heterogeneous accumulation of hybrid incompatibilities, degree of dominance, and implications for Haldane's rule
Early events in speciation: polymorphism for hybrid male sterility in Drosophila
A test of the chromosomal rearrangement model of speciation in Drosophila pseudoobscura
Association of Misexpression with Sterility in Hybrids of Drosophila simulansand D. mauritiana
The Genetics of Speciation by Reinforcement
Evolutionary novelties in islands: Drosophila santomea, a new melanogaster sister species from Sao Tome