Was surprised to find there were still 40+ mites on the board. Does this mean the treatment isn't working?
No.
Or does it mean the treatment is working because the mites are dying?
That's not really the full answer either.
We are told to keep checking mites after putting treatment in but it's hard to find any clear information on what is a normal mite count during this time.
It depends on several factors, the main one being what the mite level was at the start of treatment.
However. Amitraz which is the active ingredient in both apivar and apitraz, kills mites slowly. Because it does not actually kill them direct, but causes them to become paralyzed so they eventually stop feeding and reproducing. This is unlike the fast acting pyrethroid based product that just quickly knocks the mites down.
So because the brood cycle is 3 weeks, it takes three weeks from the time treatment was placed until you should expect a reduction in the numbers of mites emerging with hatching brood. After that they are mostly being killed but some get to survive long enough to get back into a brood cell and reproduce. So they are reduced in number with each brood cycle but it takes several brood cycles to get mite numbers down to extremely low levels, which is why the strips should be left in a couple of months.
Like you I sometimes see alarming mite levels in hives after apivar has been in several weeks and it's easy to question if it's really working. But usually by the end of the full treatment period and for me i go the full 10 weeks, mite levels are near zero.
A few other things to consider. - The strips have to be placed correctly, ie, center of where the brood is, not the edge of the brood or the box, or you get poor results.
After that, amitraz is believed by some to not be working as well as it used to, although it is still the most reliable treatment we have.
Some beekeepers have reported problems with apitraz and now only use apivar if they decide to use an amitraz based product.