Paul,
I use plywood inner covers and they tend to get ants. To control the ants,
I seal all the joints in the inner cover with propolis (just like the bees
would if they could get to the joints), and I also turn over the inner cover
every so often so the bees can get to the ants.
Saw a lot of other good ideas posted.
Good luck!
Bill Miller
Gaithersburg, MD