"Just routinely slapping on pyrethroids is what leads to resistant mites."
A specific problem leading to increased numbers of resistant mites - according to both my local SBI and my tutor - is the misguided attitude of "getting moneys-worth" out of the strips by leaving them in the hive for longer than the instructions specify.
The strips become weaker as time passes and the chemical release slows before it runs out.
When it becomes too weak to kill, it is actually selectively breeding more of the more-resistant mites.
Their advice to me was unqualified - don't use routinely, use only rarely when faced with a really serious infestation, and make absolutely certain to remove the strips promptly when time's up.
They felt that the business of some users
leaving the strips in the hive for too long was a major factor in building resistance in the mite population.
And that the less they are used generally, the more effective they can be when they are required.
They also quoted "4 years" as being about the time for resistance to be effectively lost.
It seems that statements like "Bayvarol and Apistan will never work again, once resistance becomes established in an area"
http://www.cheshire-bka.co.uk/News/VarroaResearch.php are not quite true.
The hope appears to be to keep the level of resistant mites down to a tolerable level, like Varroa itself, rather than expecting to eliminate the problem entirely.
Just routinely slapping on pyrethroids is what leads to resistant mites. I think they can have a role where resistance is not too great, but only as part of a mixed approach.
