Peter wrote:

> Three years ago I began doing experiments with screened bottoms. At
> that time, I was optimistic, like everyone else. If we could knock
> the mites down with some kind of smoke made from a natural substance
> like mint oil, and trap them under the hive, we could really make
> progress. Soon it became apparent that the method did not perform
> reliably, and the screens did not seem to be curtailing mite
> development.

There may be some true believers that have placed all their money on
screened bottoms, but my guess is most of us who use them do so in
conjunction with normal mite treatments, such as Apistan or Cumophose.

As you also noted, all the studies I have seen show that the buildup of
Varroa is slowed but by no mean stopped, so when Varroa hits its usual
end game, open bottoms do no better than closed as you also noted.

Also, what I have learned, which may be incorrect, is that screened
bottoms started as a summer ventilation tool for migratory beekeepers in
Europe (I believe it was Denmark). They use to put the closed bottoms
back on but one beekeeper forgot and found his bees did as well or
better than closed bottoms, so generally most shifted to year round
screened bottoms. This was 20 or more years ago. So best reason to use
screened bottoms is ventilation.

Since then several techniques of possible varroa control have latched on
to screened bottoms, including FGMO, wintergreen patties and smoke as
something to be used in conjunction to increase their techniques
efficacy. Only the wintergreen patty treatment meets my criteria of a
good test, but I am not an expert, only skeptical. And that, like most
other supposed natural techniques, require a lot more labor than the
strips.

I also wondered why mites dropping from high in the hive would make it
to the bottom and not get stuck somewhere on the way down. Can only
guess, but if the mite was trying to escape from the irritant, it may
keep dropping to get away from it, so you could make it from the top of
the hive to the bottom. And a variety of treatments cause mite drop.

So screened bottoms is not a Varroa control. But they do give other
benefits, so I will continue to use them, especially since they do more
good than harm.

Bill Truesdell
Bath, ME