Fruit flies are in a taxonomic family (Drosophilidae) within the class Insecta. So you want something to "speciate" out of its whole family, not just out of its species, before you'll believe in speciation?
Ah! This would be the promising new science of Pig-Ignorantism now battering at schoolhouse doors all around the country. It could only be that.
<troll_mode> What's the big deal? It's still a fly! Evilution won't be proved until they turn a fly into an aardvark or something! </troll_mode>