I would love to use oxalic strips but first I want to know why many very experienced beekeepers who used them lost around 50% of their hives in one winter.Any veterinary treatment that had even a 10th of that death rate would never make it on the market.
Not an easy question to answer!
There are quite a few potential variables in the system and for any particular beekeeper it could have been caused by one or a combination of several. Some possible contributors are:
1) Placement of strips. For experienced beekeepers this shouldn't really be something that comes into it but based on photos and comments on the previous forum I think it is. My experience is that the staples need to be in amongst the brood (much like with another sort of strip). This is especially important for late season treatment when broodnests are contracting. I think there are some beekeepers who tried putting strips more towards the edge of the broodnest in spring and it worked fine (as the hives expanded into those areas anyway), then expected it to work the same in autumn and it didn't...
2) Treatments being put in too late/ too much varroa in hives prior to treatment. Early on with varroa you could usually rescue a mite-riddled hive late in the season with bayvarol or apistan. That is much less the case now and (again in my experience) oxalic staples will not rescue a hive with severe mite infestation/damage. It is critical to never let mites get too much of a foothold. Again, in spring it is relatively easy to rescue a badly infested hive by treating and adding healthy bees and/or brood from another hive but this is more difficult in autumn.
3) Insufficient treatment amounts/time. This is a little more vague and I think needs the beekeeper to spend some time with oxalic staples as a treatment option. I've explained how I use mine elsewhere so won't go through that again. I don't view staples as a put in and forget about treatment option though. It is best to check the hives around 3 weeks after treating to make sure they are still in the right place and haven't been excessively chewed out. They can easily be renewed/replaced if necessary.
4) Staples made up incorrectly. While I think they're relatively easy to make up, they are not an off the shelf ready to use product. This means there is room for mistakes, misinterpretation etc.
If I had to guess my money would mostly be on the second point. It is easy to look at a hive in late summer that is full of bees and think it's fine when actually it is about to collapse. Most of us have seen this happen to hives at some point. I think the margins for error here are less forgiving now than they were in the early days of varroa.
My advice to any commercial beekeeper thinking of trying them is to pick an apiary close to home and take the plunge. Be prepared to visit more regularly so you can make some observations, do some monitoring etc. I think a treatment regime of putting fresh staples in early spring, early summer and early autumn should work in nearly all situations...