More rain in Virginia... chilly too.  In the 40s.
60s and 70s predicted for the weekend, so today
I type, and mess with wrenches and bicycles with
hopes of doing this again soon:

......... __o
......... \<
..... (_)/(_)....................



> do open bottom boards really help in reducing the varrola problem?

I assume that you mean "screened bottom boards", since an truly
"open bottom" would create a very large "entrance" to defend.

In regard to screened bottoms, USDA studies say "yes".
The original name for them was "Beltsville Screens", since
the Beltsville Bee Lab developed the early prototype.

But even if one does not feel that the "natural mite fall" makes
a significant difference in the total mite population, a screened
bottom allows one to monitor the natural mite fall, and track
the (estimated) mite population, week by week.

As I often intone to companies that ask me why they need
servers to simply watch all their other servers:

   One cannot control that which one does not measure.

Some people worry about the impact of screened bottoms on early
spring brood rearing and comb drawing.  Here's a trick - assuming
that you have a screen board sitting on a backwards-facing solid
bottom (which is how you slide in the sticky paper to be able to
count mites), you put a groove that is slightly wider than 1/4-inch
on the inner vertical surfaces of the solid bottom's sides (the part
that the brood chamber sits upon) you can then slide in a 1/4 plywood
sheet, and plug the very small opening that remains with a stick about
the size of an entrance reducer.

This blocks the "extra" airflow that so many fear may chill the
bottom brood chamber, and prevent the queen from laying early.
One can still place sticky paper on the plywood.

Since we have problems with "damp" in Virginia, I cut some vent
holes in the plywood sheets towards the back of the hive, to
allow ventilation airflow to help remove the damp air from
the hive, but keep the airflow at the rear of the hive.

If you look at where your earliest eggs get laid, you may find
what I found, which is that the queen starts laying close to the
front wall of the brood chamber.  Why?  The front of your hive
likely faces southward, and the sun heats up the front surface
of the hive, even in winter.  The small amount of "thermal mass"
of the front of the hive body appears to make a difference.

So if you wanted to enhance this effect, you might want to both
slide in the plywood sheet and insert an entrance reducer with
the smallest opening "open" just to keep cold air away from
the front area of the hive.

The modification looks like this (in rear view):

+-----+
|     | <=== One "side" of a solid bottom board
|     |
|  +--+
|  |    <=== New groove, wider than 1/4-inch
|  +--+      and perhaps 1/8" to 1/4" from top
|     |
|     |
|     |
|     |
|     |
|  +--+
|  |
|  |            <=== Groove for solid bottom
|  |
|  +--+
|     |
|     |
|     |
+-----+


A kludge for existing in-place hives would be a
slide-in "platform" of sorts, like this:

+-----+
|     |
|     |+---------------  <=== 1/4" plywood
|     |+---------------       Nailed or screwed
|     |  |  |                 to spacer legs
|     |  |  |
|     |  |  |   <==== Vertical spacer "legs"
|     |  |  |         cut from scrap
|     |  |  |
|     |  |  |
|     |  |  |
|  +--+  +--+
|  |+---------------------------
|  ||           Solid Bottom
|  |+--------------------------
|  +--+
|     |
|     |         <=== One "side" of a bottom board
|     |
+-----+

                        jim  (byte for byte, ASCII art is your best
                              entertainmnet value)

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