> Unless you rotate varroa chemical strip treatments then resistance is 
> bound to come... It used to be you could place a strip in a beehive and be 
> sure you would not lose a hive to varroa. Not today! Now you need to check 
> varroa load and treat if necessary and *more important *check after 
> treatment to see if the treatment worked. Now in most areas both apistan & 
> checkmite are almost worthless as varroa control so I would not recommend 
> trying a single strip. If one does you need to check to see if works.

That about sums it up.  Perfectly.

If we all worked in isolation, then  the mechanisms would be different, too, 
but US beekeepers, and Alberta pollinators each find themselves in one huge, 
migrating, constantly mixing beeyard where the activities of others, 
sometimes clandestine, affect what shows up in each separate outfit.

While it may be possible to predict the trajectory of resistance in an 
isolated situation, in an environment where any one player can affect the 
nature of the pests in all adjacent outfits, misuse or premature use of a 
chemical can result in widespread resistance appearing more quickly than 
expected.

As an example, the active ingredient in Apivar has not been legal for 
miticide use in beehives until Apivar was permitted recently here in 
Alberta.  However, if any beekeepers here have been using it on the sly, or 
we import bees with mites acclimated to it from elsewhere, we may not get 
the three or four years of strong efficacy we expect to see.  We are 
watching carefully to make certain it is working as expected across the 
province.

So far, AFAIK, it is. 

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