Simoneau André (DRMONTR) (L'Assomption) wrote:
>
> Bill Truesdell wrote:
>
> "We know that screened bottoms lead to increased brood production
> (Delaplane) in the beekeeping year as well as, when left open over
> winter, during spring buildup with more surviving bees and brood (Danish
> study), which yields more bees. (And more Varroa, which may explain the
> French-Canadian results, but just speculating.)

Then Simoneau André wrote

> as we can read in his study, the explanation of the increased Varroa
> population with an OPEN SBB would be that the lowering of temperature affect
> the larva maturation time, perhaps delaying 2 to 3 days the normal adult
> emerging time.The cell being closed 2 or 3 days more would allow MORE young
> Varroa female to become mature before the adult emerge.
> Hence, the increase of Varroa population during colder temperature with an
> OPEN SBB.
> Hope I have helped.

Actually it causes me a bit more trouble and would appreciate anyone
clearing this up for me.

In essence, their study indicates to me that the brood nest is not kept
at about 95F with open bottoms which causes a delay in normal adult
emerging time. Did they actually measure this or is this conjecture? All
the studies I have read show the brood nest is kept fairly constant and
there is no appreciable difference in the time for emergence of the
adult bee. Have there been studies that show a difference in emergence
time for larva/pupa on the edges of the brood nest?

The Danish study showed a later startup of brood production with open
bottoms (as well as more robust colonies compared to hives with mesh but
solid inserts), so that does not track either, since the closed bottom
would have more brood earlier, hence more Varroa. Unless there is more
brood/bees in the open mesh hive when the F-C measurements were made.
Which makes more sense than delayed emergence and tracks with other
findings.

The Deleplane study shows an increase in brood production and says
nothing about changes in emergence, but they probably were not looking.
However, there was no increase in Varroa, but a decrease. Another
difference in results.

There are so many anomalies in the data about open bottoms that it is
obvious that the variables involved have quite an effect on data. One of
the most apparent is the site of the hive and if it is sheltered or open
to the prevailing winds. That would have a pronounced difference in the
conditions inside the hive body. Or if there is also an upper entrance.
The Danish study indicated that there should be none for overwintering,
but do have them in warmer weather. But upper entrances are standard in
most northern hives.

None of this really matters since the key in each of these studies is
that open bottoms are good. The reasons differ, but not much.

Bill Truesdell
Bath, Maine