Is there any problem with a top and bottom entrance at the same time? I was thinking about putting my old solid bottom boards on top as a top entrance. I have screened bottom boards on, but these have built in entrances. Are the benefits of the top entrance defeated by having a bottom entrance too? The only point that lept to mind was creating two places to defend, but I am sure I am missing something else.
No no problem at all. I have up to 3 upper entrances on my stack O boxes during the flow including the exposed notch notch on the inner cover. The more ventilation the better, and some field bees use these entrances.
I've had two of my hives with top and bottom entrances this year and haven't seen anything out of the ordinary by doing it that way, other than like you said, more guard bees. I used M. Bush's plan http://www.bushfarms.com/beestopentrance.htm of plywood cut to the dimenision of the hive body with two shims on each side. When I first put them on the foragers were using both entrances but now they are only using the bottom. I have no idea why. I had thought about switching all my hives to this type of top and closing the bottoms off so there would be less equipment to make or buy, but not sure exactly how I would reduce the opening in the winter other than just ripping a piece of wood the lenght of the opening minus 1/2 " or so.
I use solid bottom boards for top entrances. If defence is a concern us the medium entrance on the entrance block, I just tack mine in place to the bottom board with the entrance of choice in place. Works great.
[When I first put them on the foragers were using both entrances but now they are only using the bottom.]
It depends on what is being brought in and where it is needed.
Pollen maybe brought in on the lower and nectar might be brought in on the top.
I have seen a change sometimes between entrance choice as the foraging population 'turns over'.
I also see it depends on the colony.
I have some that rather use a hole in the super over either entrance.
I agree on improving ventilation.
I don't like competing with foragers waiting to get into a hive when I am working a hive.
So I don't exactly promote upper entrances as an exclusive entrance.
I also think its a bit cruel to make the hive carry debris to the cover to clean itself.
Screen bottom boards help, but things can grossly pile up in cold spells.
Naturally, I think openings are utilized at all heights (you use what you can get).
I just feel that lower openings allow for better sanitation with the least effort.
I also feel it keeps forager traffic at a location that miminally impacts my inspections.
My experience with upper entrances also concludes that notched inner covers and telescoping covers do not provide as much ventilation as the bees could use. Its probably better than what they get in a tree, but I think that's a low expectation.
-Jeff