In case you weren’t aware, and I wasn’t for a long time, the foundation in common usage by beekeepers results in much larger bees than what you would find in a natural hive. I’ve measured sections of natural worker brood comb that are 4.6mm in diameter. This 4.6mm comb was drawn by a hive of commercial Carniolans and this 4.7mm comb was drawn on the first try by a package of commercial Carniolans. What most beekeepers use for worker brood is foundation that is 5.4mm in diameter. If you translate that into three dimensions, instead of one, that produces a bee that is about half again as large as is natural. By letting the bees build natural sized cells, I have virtually eliminated my Varroa and Tracheal mite problems.
Found an interesting article from Kottke.org. He lists other solutions, but I have to admit—it seems so simple that human greed has left left the bees vulnerable to disease and infestation. While the research from the Spanish scientists don’t jive with recent article in Scientific America, anything that can help crack this nut will be helpful.