Re: Slatted rack
As far as I know, the worst case is that is is an unnecessary expense. No harm can come from using them. On the other hand, there may be increased use of the lower comb for brood rearing and bees in the hive can do a better job of controlling airflow than the ones furiously fanning on the landing board. I am going to use my first solid bottom board this spring. That hive will get a slatted rack that I aquired a few years ago and is still taking up space in the bee room. I doubt any of the screened bottom board hives would see a benefit.
Thankfully, the bees are smarter than I am. They are doing well, in spite of my efforts to help them.