Several people have debated the merits of follower boards in brood boxes,
queen excluders, etc.  For almost two decades, we have been measuring
brood areas, food stores, etc. in brood boxes of both nucleus and
full-sized commercial hives.
 
Every commercial beekeeper had a slightly different approach.  Each had
"fine-tuned" for his or her area.
 
So, what did we find.  Well, drop on a queen excluder and all sorts of
things happen downstairs.
 
1) A high percentage of queen are lost, superseded, etc.  Some of this
seems to be in response to use of chemicals to drive bees down into the
lower boxes; some seems to be a response to the "constrained" brood nest
area.
 
2) The queen loss produces a brood break - an obvious, but unplanned, result.
 
3) Nectar plugging produces additional reductions of brood area.  Under
heavy flows, the bees dump nectar in brood cells.  In colonies without
excluders, the queens often move higher and maintain more brood.
Colonies dropped to thre first story often get plugged out.
 
4) Some colonies even abort brood.  With the constraints put on the brood
nest area, there is less room for pollen storage, brood rearing, etc.
Looks like we get an imbalance, and the bees make adjustments.
 
Now, if your goal is to reduce brood rearing, numbers of bees to
overwinter, number of mouths to feed, etc. then go right ahead and use
excluders, follower boards, etc.  But remember, the reduction that you
get is likely to be a lot larger than you expected.
 
Quite frankly, most beekeepers do what they think works best - most have
no hard comparative data to show whether it does or doesn't.
 
A commercial beekeepers running thousands of hives may have to use
excluders just to keep the time in the field to a minimum and to reduce
the chance of pulling the queen and brood with the honey supers.
 
That is clearly an advantage, one that can save dollars in labor.
 
In areas where nectar flows come in distinct cycles, reducing the number
of bees between flows may reduce the amount of honey consumed and induce
the queen to produce more new bees for the next flow.  Our models suggest
this might increase production.
 
However, in most cases and in most years in Montana, constraining the
brood area and slowing bee movement to the honey supers reduces honey
production and overwintering success.  I have 20+ years of hard data to
support these conclusions for this climate.
 
On the other hand, the Seattle beekeepers that we worked with have a
vastly different climate.  Their bees sit around for a "long, cool"
winter, and apparently eat lots of stores over the winter.  Because the
temperatures are mild, the bees stay more active, and seem to eat more.
So, smaller cluster sizes for winter seem to be a reasonable goal - but I
don't have the data to truly access this outcome.
 
In these times where tracheal and varroa mites impact colonies, we may
want to revist the minimalist approach to overwintering.  Maybe we ought
to aim for stronger colonies going in to the winter, to help offset the
mite impacts.  This assumes you use some form of treatment to control
mites, or have some mite resistance in your colonies.  Otherwise, strong
colonies may just end up with more mites and even bigger piles of dead bees.
 
Food for thought.
 
Jerry Bromenshenk
The University of Montana-Missoula
[log in to unmask]
 
http://grizzly.umt.edu/biology/bees