Screened bottom boards are a small part of the mite solution. A big part if no pesticides are used to control mites.
Somewhere, I read that about 20% of the mites on the bees could fall out...I'd use them even if it was 10%.
During the course of the year I think I go to my hives 4 times at most with powder sugar.
In between flows, twice, ten days apart, then once in September, and again once in October/December after the queen has stopped laying.
I believe that the last application is the most powerful, at that time all the mites are on the bees, not in the brood.
As far as stressing them out, I think that Formic Acid in the concentration needed to make it effective might be a tad more stressful to the girls...also, it is not temperature sensitive, if it's 75 degrees out, the bees will out live the sugar, not the acid. Apistan is becoming less and less effective, producing better mites, not better bees.
Here in CT(shoreline), we have a really long, humid cold and miserable winter, all but one made it with open screened bottoms, the one that didn't...condensation, level hive and inner cover with hole dead center, I think that it dripped right on the cluster...
In any case, 6 out of 7 survived,Opened to the weather, not board or plastic, just opened.... then Beek error, that darn stone on the cover that I didn't put back on, the cover blew off and by the time I got there it must have been too late...good honey though. I lost that one in March.
Feral bees might seal their trees or nests real tight, the bees still do what they have done for millions of years and have not read some of the research on mites since 1984. Bee school is for beeks, not bees.
Maybe solid boards are cheaper, tighter, easier to maintain, I just think that it helps the girls be healthier.
I agree with Tyro, they do better with than without.
So If you are just starting out, do the experiment 1 with, one without...see what happens. It might work, it might not. At least try to keep a detailed journal throughout the season so that you can read what worked last year or the year before. The journal might be the most valuable part of your equipment. The journal, BTW should be kept even if you don't experiment.
Pretty certain that every time something new comes around there will be opposition to change. Why, just look at congress! Hahaha!
If you haven't done the experiment then why voice an opinion, that's just spreading gossip.
sorry for going on and on...I like the SBB, don't think I'd do solids ever again.
For sale:7 solid bottom board.