a mn beekeeper who ran pollen traps on several thousand of his migratory hives all season told me 
that some important factors to consider are not restricting air flow (use screened bottom boards) and 
allow ample entrance openings under the trap (large side rails on bottom board) so the bees can 
come and go without jamming up at the entrance.

 his advice made sense to me and I seem to get the same honey production as compared to adjacent 
hives without pollen traps.  

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