I've never seen or used the 'traditional' design of this device, but have
used a variant.  I'm familiar with their design and principle.
 
They were, from memory, espoused primarily by Eugene and Carl Killion, and
were particularly popular in the 8 frame hives used for comb honey.  The
bkprs wanted to 'compress' the bees, crowding them so they would
effectively work section comb boxes well, but at the same time needed to
reduce the consequent swarming impulse.
 
These racks are made to fit inside a specially made (deep) floor.  That is,
the risers (who knows a GOOD word for that part of the floorboard???) are
about 50mm (2 in) deep.  If you just put the deep floor on, the bees would
build all sorts of propolis and wax mountains up to and down from the
frames.  But if you put this slatted rack in, the hive gets the advantage
of the space in the deep floor and won't build wax/propolis on the bottom
bars.
 
The theory is that the slatted rack reduces a lot of the air movement in
and out of the entrance.  The bees are then supposed to be willing to use
ALL of the bottom box, down to the corners of the frames, rather than
keeping the brood 'circle' away from the (draughty) entrance.
 
Here in NZ the variation used is to use a normal floor, but nail a piece of
galvanised iron about 100-150mm (4 to 6 inches) wide across the width of
the floor, so that the bees come in the entrace and crawl through this
'tunnel' before going *up* into the hive.  Is that word description clear?
 
Here we do it more as a wasp damage reducer.  Wasps (Vespula germanica and
Vespula vulgaris) tend to go into a hive at the edges of the entrance, then
up into the outside combs that aren't defended as well.  By making them
crawl through a tunnel type entrance, they are more likely to have to come
up into the hive through part of the bee cluster.  The idea, then, is that
the bees, especially when the weather is a bit cooler, are better able to
defend the hive.
 
But again, and this from experience, the bees WILL put brood right down to
the front corners of the frames, giving better utilisation and reducing
that 'dead' greyish brown comb that results from bees avoiding/chewing out
the corners of the comb.
 
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          Nick Wallingford
      Bay of Plenty Polytechnic
 (East coast, N Island, New Zealand)
     Internet [log in to unmask]
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