Seen a different problem with it. Was contacted this spring by a beekeeper who was caring for around 45 hives at a site, plus had (from memory) maybe a dozen hives of their own at the same site plus maybe a dozen at another site. The 45 other hives were at this point not treated yet, and the other hives had Apitraz. The hives with Apitraz had had it for around 2 weeks.
All the hives with Apitraz the bees were listless and just sitting there like they were cold or something, and the hives were going backwards in number, at a time when they should have been building up. The beekeeper wanting to make splits but it was looking like the hives may fade away and die completely. None of the hives with no treatment had the problem.
The only difference I could see was that some hives had Apitraz and some did not. So we pulled the Apitraz and replaced with Apivar. In a couple of weeks those bees were looking normal and hives beginning to recover.
Of course this is not a scientific double blind study, it's just anecdotal.
Some time ago I heard talk from some commercials about Apitraz not working for them, end of treatment bees still had mites. For whatever reason and I am not sure what the reasoning was, they thought the strips were releasing the amitraz very quickly and giving a very strong dose for 3 weeks, then not enough. Allowing some mites to survive. If that was the case, then a very strong early release of amitraz might explain the problem with the hives I looked at this spring.
Of course we don't know what goes on in a boardroom and behind closed doors. But if an early release of too much amitraz had been detected from the strips, something may have been done to counter that, and had the opposite effect and hence you still got mite problems. Of course that too, is pure conjecture on my part, I got no idea what the manufacturers do and such unscientific opinion should be no reflection on the product. But as you asked, I'm just sharing my thoughts and observations.
