I suggest that you reread the genetic studies on races of bees.
Every carefully-performed study that I've read demonstrates a continuum of
gene transfer from one race to the next.

I think we are talking about two different things. At present, the so-called races lack barriers to gene flow but when they arose, they arose in isolation. Otherwise they likely would not have formed into distinct subspecies, as they did. Additionally, some regional types have barriers to gene flow, such as the differential brood rearing patterns discovered by Jamie Strange in France. 

> Conservation of geographic races of A. mellifera was proposed by Ruttner et al. (1990) in response to observed hybridization of local bee stocks with imported stock. However, to date little has been done to further this goal. 

> Despite the importation of non-native honey bee colonies into the Landes region, annual colony cycle data from our study demonstrate the persistence of the Landes ecotype. 

Strange, James P., Lionel Garnery, and Walter S. Sheppard. "Persistence of the Landes ecotype of Apis mellifera mellifera in southwest France: confirmation of a locally adaptive annual brood cycle trait." Apidologie 38.3 (2007): 259-267.

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