My basic feelings about the availability of resistant stock at the present time, is: "buyer beware". While some queen breeders (like Glenn Apiaries of California) have direct access to programs like the Russian bees from the USDA, not all queen breeders advertising supposedly "resistant stock" have such direct lines of offspring. And by the time you order fourth and fifth generation removed queens, I think their mite resistance is pretty "watered down". By that time, it's pretty much 'luck of the draw' as to the true amount of mite resistance any given queen has. But as Bjorn has pointed out, if you're willing to pay the $50 per queen for queens more directly descendant from such programs as the SMR or Russian project, the higher the likelihood of becoming chemical free.
I have ordered Russians from Jester Bees in Arkansas (who get their "breeder" queens from Glenn Apiaries). They, in turn, are open mated and so the resistance begins to get diluted; but the price has also dropped to $10 or $12 per queen. {NOT an endorsement of either operation} The real secret is to get away from AI (time consuming, labor intensive and $$costly$$) to where mating areas have plenty of Russian drones (using Russians, as an example). Once Russian drones are widespread within a queen breeder's mating areas, then the cost of the queens will come down and the genetic dilution (for non-mite resistance) will be minimized. Just now, are we starting to get to that point among most commercial queen breeders - this was always envisioned as a four or five year process by the USDA. This was as the USDA planned - they could have made the introduction of mite resistant genetics more widespread and much more quickly. But they were also walking a fine line so as not to destroy (financially) many commercial queen breeders. Thus the reasoning and control for the initial $500 queen releases to a very small group of selected queen breeders. [Too bad, the USDA just didn't get into the queen breeding effort wholesale and make the queens available to anyone and everyone who wanted one - drone populations sure would have become more widespread across the country much more quickly]. But again, the reality of economic and political pressures insure that the plan progresses according to what's acceptable to the USDA. To some extent, this also accounts for the wide variability of "good vs. bad" assessments of the Russian bees - no doubt in my mind that some beekeepers have had excellent results from the Russians and some beekeepers would swear never to buy them again! The only people who have experienced "first hand" what the Russians are really like, are the USDA personnel controlling their importation and the few selected queen breeders who paid the $500 price tag - everyone else is getting a mutt (some are lucky to get good mutts and some are not). My point here is, that once the cross breeding starts to happen, you loose control over identifying whether a certain characteristic is intrinsic to the Russian genetics or to the Italian (or whatever was the cross-breeder race) or if it's unique to the hybridized Russian queen only.
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But just so the government folks don't EVER think they have absolute control over our borders and mother nature (and thus the introduction of such pests as AHBs, Varroa, fire ants, Japanese carp, small hive beetle, well the list goes on and on...), as I understand, some people have found ways to get fresh infusions of potentially mite resistant genetics across our borders, so the hope for "good" also exists. Sooner or later (assuming Darwin was right), mite resistance will become widespread - but until then, "buyer beware".