Screened Bottom Boards
There is a difference of opinion by beekeepers as to use or not to use screened bottom boards. I think that they help in the controlling of the Varroa Mite. One reason is that if you use powdered sugar as a dusting agent, the dust gets on the feet of the mite and it loses its suction and falls off the bee down through the screen and onto the ground. (Or into a trap so you can actually count the mites that drop.) The mites cannot walk very well and can only jump about 3/4 of an inch. When they are on the ground, they cannot get back on a bee and are at the mercy of the ants and spiders.
The sugar will not harm the brood as you are dusting from the top bars and what little gets into the cells is not enough to dry out the bee larva. The bees get coated with the powdered sugar and that forces them to groom themselves and others. While grooming, they will help dislodge the mites also and most of the adult mites will drop making the bees more stronger and vigorous. The more vigorous the bees the more they will want to work.
You must have the hive above the ground at least 8-12″. It makes it impossible for the mites to get back in and the height helps your back by not having to bend over so far.
Powdered sugar will not work as well with a solid bottom board unless you insert a sticky board to secure them. The reason is that the mites will fall to the bottom board and all they have to do is wait until a bee walks close to them and then they will just jump on and continue their blood sucking.
What you need to do is ask an experienced beekeeper to explain how he combats the mites. Some will say use a miticide. Some will say use a fogger. Some will say use powdered sugar. And some will say, “I don’t have mites.” Remember, ask a group of bee keepers and you will get that many different answers. There is nothing wrong with any of them. You have to try all these things to find the one that works for you and that you are comfortable with and use that one until it doesn’t work anymore then do something different.
Remember that anything you do will cost some money. Take that into consideration when you start experimenting. Sometimes the cheap cost works just as good as the expensive, but sometimes you need to consider the more costly way because it is better. The choice is yours.