Here are pictures of the sump, or base, of my hives. First picture is the base with the 1/2" hardware cloth acting as a mouse guard:
Here is a picture of the base upside down, showing how the 1/2" hardware cloth is stapled to the wood:
View of the inside, with the back door removed:
Backdoor in place:
The screen bottom board, essential part of IPM:
How the screen bottom board fits in the base. Hopefully I left enough gap for the particle wood to expand. Plywood would be a better choice. The hardware cloth should be 1/8th", but I could only find 1/4", so I used two 1/4TH inter-spaced.
View from the top. Notice the landing board is shorter, so as to not obstruct the mesh. I am now thinking the landing board should not extend inside, to avoid giving a chance to varroa mites to grab a passing bee.
Last view from the back, with the screen bottom board and the sticky board in place. The sticky board is just a piece of plywood to collect fallen varroa mites. It will be painted white, and a grid drawn on it to facillitate counting the varroas. Oil will be spread over it to make the mites stick and die. The sticky board is not staying in the sump, it is set a few days at a time, to monitor varroas. In normal operations, only the screen bottom board is in place.
This design still has a flaw: the combs in the lower box can extend inside the sump. To correct this flaw, my next sump will have a screen bottom board that mounts flush with the top of the base.