I will put a very tentative toe in the water and suggest that, in addition to added protection from parasites/disease, it might also be a function of weather/climate, and northern races are adapted to producing more propolis to seal up cracks and holes.  I have noticed that my Carniolan stock will use propolis to reduce the size of the entrance hole in the shim I use in the winter for spacing and top entrance, I am assuming (always dangerous) to cut down on wind intrusion and heat loss.  My Italian stock don't seem to do that.  My Russian stock don't seem to do it either, but they are so efficient with their winter stores that they stay pretty far down in the three-deep stack, and I rarely see them poke their heads out all winter.  Tough little critters.

Bill
Claremont, NH

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