Hi James and Everyone,
In those areas where you have been using pyrethroids for about 10 years you will start to find resistance.  That is our experience here and everywhere in the world where they have been used against varroa.  Don't blame misuse.  Resistance is the result of use, any use of pyrethoids to claim that it is only misuse that causes resistance it a flat out lie.  Sorry for the frank language but any use of a treatment selects for resistance to that treatment whether the label is followed or not.  Your resistance will spread more quickly than you may think and the best way to manage it is to provide and use treatments that have different mechanisms of action.  For example if thymol products are available and have been shown to be reasonably effective ( note: I am assuming approved treatments with proper labels are available ) the best management course is to switch for one or two treatments to such products.  In theory this should remove many of the mites that are showing increasing resistance to pyrethroids thereby delaying the development of full blown resistance.  You would than get on a rotation program so you are not using the same treatment over and over and over.  Here now Apistan ( our only approved pyrethroid treatment ) is pretty much useless for varroa control.  The first documented case of Apistan resistance here in Minnesota USA was in an outfit that I am completely convinced was pretty much following the label completely but they had been treating a little longer than many other beekeepers because of picking up the mites a little before some and finding them when levels were low.  Many beekeepers who are carefully following the label will find resistance when their colonies collapse due to high mite levels if you continue to hide your head in the sand and tell them that misuse is the cause.  Again hard words but it happened here and caused a lot of damage to many good and careful beekeepers.
Rotate to other approved treatments to try to extend the usefulness of the pyrethroid treatments you have or you will loose them more quickly than you think.  Do all you can to avoid the situation we have where many many beekeepers have been forced to switch to a more toxic treatment to keep their bees alive and healthy.  As you point out the residue issues from these treatments are much worse than the pyrethroid treatments.
The best test for resistance is to monitor varroa populations before and after treatment so you know that the treatment actually worked.  The trick is you cannot rely on mite drop on a sticky board from treatment since you need to know how many mites the treatment didn't and won't kill.  Ether roll, sugar shake, and sticky board counts of natural mite fall will all work and give enough information to know if the treatment didn't work.

Good luck and I really hope you can manage this resistance better than we have.

blane



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Blane White
MN Dept of Agriculture
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