Nathan Lawrence said:

> On the other hand, if the screened bottom board was placed on top of
> a closed bottom board, (to achieve that 37% decrease in fall mite
> counts as claimed above), wouldn't the mites simply climb their way
> back up into the hive?  Or do they simply keep still and wait for a
> passing bee to grab onto?  > (I've heard this claim before, but only
> from one source)

I was led to understand that the rationale behind the screened bottom
board was that varroa mites cannot (or will not) climb back into the hive
once they have fallen below the screen.  I was led to understand that it
was a simple matter of distance, and a sticky-board was not required.
(The critical distance is less than the height of a screened bottom above
a traditional solid bottom.)

One can test this with ease, by putting a sheet of paper or cardboard
under the screen, and seeing of the mite drop is about the same as
the equivalent prior period with a sticky board.  With some care, one
can remove the non-sticky board without the mites sliding off.

When I do this, I see live mites on the non-sticky paper.
If they could climb back up, I would not see many live mites.
Heck, the mites I see don't even make much effort to crawl
around on the paper, and upon close examination, many appear
to be undamaged, and capable of crawling around.

> I know there are sticky-boards that can be used to
> prevent this-- are these sticky-boards necessary?

I certainly don't think so, but it is a risky thing to say much of anything
about varroa.  The more they are studied, the more is found that was
unknown before.

I am not sure what to think about the study at issue, but I have traditional
solid bottom boards under my screened bottom boards simply to act as
a tray for the slide-in sheets of paper.  Clearly, one could close off
the original bottom board entrance with a wooden plug, but I have never
done this.  I did staple some 8-mesh over them to keep bees and other
creatures out of the space, stapling at the top only to create a "door" of sorts.

The question in my mind in regard to the study at issue is about the reaction
of the bees to any "excessive ventilation" caused by an open screened bottom:

a)  Let's assume for a moment that the statement as made is strictly
     true, that a screened bottom board actually increases the overall
     varroa population.

b)  We know that the bees do their best to tightly regulate the
     temperature and humidity of the brood area.  They at least
     do well enough at this to avoid dead brood.

c)  If a screened bottom lowers the humidity and/or temperature,
    one would presume that more bees would participate in "climate
    control" activities to maintain acceptable parameters for brood
    development.

d)  If one accepts (a) through (c), the study would imply that bees
     cannot maintain "tight" control over the brood chamber environment,
     but can only maintain a "range".  It also implies that varroa can
     "better thrive" at the "cooler, dryer" end of the "acceptable" range
     for brood.

e)  It follows from the above that a hotter, more moist environment
     (still within the acceptable range for brood) would inhibit varroa
     reproduction, but this would be at the "price" of reducing honey
     production, according to the many studies on ventilation that
     have stated the obvious (more ventilation making it easier to
     evaporate moisture from nectar).

If all of the above is taken as "true", then the study would suggest
to me that one would want to limit airflow through the brood area,
while maximizing airflow through the supers.

One might attempt this by decreasing the bottom entrance opening,
plug the opening between the traditional bottom board and the screened
bottom board, and provide WIDE upper entrances above the brood chamber
in the location where one might place a queen excluder (a sort of "Mega-Imirie-Shim").
To avoid a convection flow between the brood area and the honey storage area,
one might want to consider making this "Mega-Imire-Shim" out of an inner cover, to
restrict airflow between brood and honey areas.  (Another approach would be to
offset alternating supers forward and backward slightly to create bee-sized openings
between each super.)

Stuffy brood boxes, and (still) breezy supers.  It can be done, but would
it help?  I dunno.  I'd bet that more bees would fan at the brood chamber
entrance more often to overcome the "stuffy" effect, as they can clearly
be seen doing this even with a screened bottom that has nothing below it.
(At least it can be seen in summer in Virginia, your mileage may vary.)

        jim