Robert Brenchly compares two attitudes, that of importing bees to contribute
to variability in the gene pool and that of using local strains of bees.  As
he suggests they can both be right in the correct circumstances.

In a place where there are no native bees then all the genes are imported.
None is acclimatised at first to local conditions.  Therefore it makes sense
to import genes from as many places as possible and then leave them alone to
select themselves locally to suit local conditions.

Where there are native bees then this selection process can be assumed to
have been achieved naturally aeons ago.  Without imports you will find local
strains suited to local conditions with enough variability to cope with most
things nature can throw at them (apart from fire and flood).

Where a local strain is established and a different strain of the same race
is introduced there should be full compatability and perhaps some improvement
in brood pattern if there has been some spottiness due to inbreeding.  On the
other hand if a different race is introduced then the heterosis or "hybrid
vigour" effect can be expected.  This may manifest itself for the first
season in a larger brood nest, more honey gathering and better health but
there is a probability also of better defensiveness ie. bad temper.  Some
crosses are worse than others in this respect.

So the advice is: if you have a local strain of bees that is doing ok don't
rock the boat and to mangle metaphors don't open Pandora's box just because
the grass is greener.

Chris