hmmm
To keep mice out of hives in winter, I use a strip of #4 (quarter
inch mesh) hardware cloth stapled to the front of the bottom board.
It's a strip 14-1/2 inch long by 2 wide strip with one side bent up
enough so that it clears the bottom of the box above.
It gives the bees, queen, drones, a quarter-inch by quarter-inch
hole to pass through to get in and out.
I gather those hornets Can't pass through a quarter inch hole.
It should keep them out, if they ever get established out here, but
I wonder if that's enough.
A few years ago I saw a european bottom board that had baffle
entrances for honey bees, and false entrances for wasps.
The wasps would get lost in the screen box below the bottom board
screen, and starve or dry out.
The big plus was that it would catch queens in the fall.
j