F. Ruttner wrote in his book "Biogeography and Taxonomy of Honeybees" on page
150 "Hetterospecific instrumental insemination of A. mellifera and A. cerana
(with semen of the reciprocal species) is feasible: spermatzoa enter the
spermateca  ...  No hybrid lava or imago developed in these experiments (Ruttner
and Maul 1983 Experimental analysis of reproductive interspecific isolation of
Apis mellifera L. and Apis cerana Fabr.  Apidologie 14: 309-327)
 
Personaly I think A. mellifera has to go its one way to find a coexistence with
the varroa mite. Only about 3/5 of the A. mellifera genome is similar the DNA of
A. cerana. So A. mellifera may have to develope its one defence mechanism and
cannot copy these of A. cerana.
 
Andreas Hdhnle