Hi Blane, You are right, of course that in the States, the widespread use of Apistan has probably been the strongest selection pressure, as Klartan/other agro formulations aren't used as frequently in beekeeping as in some other countries (so I believe). This pyrethroid resistance was bound to arise sooner or later, as there was only really one control agent being used with a specific mode of action. It doesn't matter what the formulation was, the resistance to the active ingredient was inevitable in the circumstances. If there had been other types of treatment available, the selection for resistant strains would have been at least slower, giving the industry longer use of what tools it had. It could be that resistance, caused directly by use of Apistan, has appeared in Europe. It's possible. But in most European countries, besides Apistan and Klartan there are commonly other types of treatment used which could have some retarding effect on the emergence of resistant strains. The account that I gave earlier, however, describes what happened in Italy and it looks very much like the resistant populations emanated from one central source. The uncontrolled dosage at that source must have had an accelerating effect on resistance emergence. It may also be true that the dose-response curves for pyrethroid-resistant mites in the USA are similar to those in Europe - I don't know, as I've not seen any of the US data but it would be interesting to compare. Do the US mite population(s?)have the same characteristics as the Western European mites? I agree that similar traits should probably be selected for and the curves indeed should look something like those we have generated here. I just wonder if you'll see the resistance factor of 400+ ? Maybe. I'm not trying to set myself up as an expert and of course, I may be entirely wrong. I do make mistakes - let's see now, I remember I made one back in 1978.... Max Dr Max Watkins Vita (Europe) Limited Brook House, Alencon Link Basingstoke, Hants RG21 7RD UK Tel. +44 (0) 1256 473177 Fax +44 (0) 1256 473179 http://www.vita.demon.co.uk