How many species?

I’ve got a little question to keep people busy over the long weekend.

There are three populations of an organism. The populations are physically separated from each other as a result of geographical factors. Geographically, they are arranged in a more or less linear fashion. The geographic details are as follows:

Population A is the northwestern population. Population B lies to the southeast, and is eparated from population A by a minimum of ~14km. Population C is southeast of population B, and separated by about 50km.

Populations A & B are identical to each other in appearance and in a key reproductive characteristic. Population C differs very slightly in appearance, but is substantially different in the reproductive characteristic.

The organisms (flying insects) were captured and bred in the laboratory. Experimental crosses were made for the different combinations of these three populations, with the following results:

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