I am posting this from another list, that has been discussing the
transalation of the french/canadian study.  Possibly the increase in the
Canadian study was only some sites - either site location of local climate
played a role in the increase over winter or the increased clustering in
cold weather.  The first is an initial translation of the summary (computer
trans, with comments from translator), the second comments from another
beekeeper who reads French and translated it also.

Karen

****** From the PDF file, via Altavista *****

Summary

A plate [floor] antivarroas equipped with a latticed bottom was put at the
large-scale test during apicoles seasons 2000 and 2001 in the area of Estrie
in Quebec. Used `.fond closed [with the ventilation closed], the plate made
it possible to slow down of 37% on average the population of varroas of the
colonies during the season 2001. The overall performance obtained is however
not statistically significant except for certain sub-groups for the sample
where the conditions of eperimentation were more homogeneous [less
variability]. These results reinforce those obtained from two other recent
studies (1,2) carried out in the United States, but which was also
nonsignificant. The output of the plate was variable according to ruchers
[hive] and it is possible that certain environmental factors modulate its
effectiveness. Research would be necessary to better include/understand this
aspect. One should not absolutely use the plate antivarroas with its open
bottom [Don't use it with the ventilation open] because the fall in the
temperature of the nest with couvain [? Isabelle isn't around right now!]
which results from this creates optimal conditions for the development of
the varroa. As we A could check it in 2000 this condition cancelled not only
the beneficial effect of the plate but resulted in rates of infestation
definitely raised (29,2% more varroas, nonsignificant) compared to the
reference group. The output of this plate was also very variable from one
colony to another. It was observed that the spring force [strength in
spring] of the colony and especially the line of its queen were factors
which had a great influence on the progression of the infestation. The plate
antivarroas also appears to increase the effectiveness of the acaricide
treatments and could slow down the development of resistance to the
pesticides in the bee. The plate antivarroas lends itself easily to the
insertion of a drawer of sampling under its bottom. The plates used during
our tests were thus designed. This characteristic simplifies tracking
largely and even makes it possible to use the natural fall of the varroas
over periods prolonged like indicator of the level of infestation of the
colonies. This is an advantage Net in period of miellie. [miel means Honey -
'honey season'?] The use of the plate antivarroas is a means easy, economic,
durable and clean to fight the varroa. It constitutes in our opinion an
essential tool in a strategy of fight integrated not only because it
contributes to slow down the infestation but also because it allows
constantly to easily know the level of infestation of the colonies. It
becomes thus a tool significant for the decision-making as for the choices
of measurements of control to be adopted and as for the moments when to
apply them. It can be used in conjunction with other means of fight like the
use of resistant queens and the specific application of essential oils or
formic acid. It will thus make it possible to reduce if not eliminate the
dependence with the chemical treatments. Such a panoply could probably
constitute a strategy of adequate integrated fight. The plate antivarroas
emphasizes the behavior of natural delousing of the bee. This behavior could
be developed thus besides more by selection. The plate antivarroas presents
also prospects interesting for the development for methods of control which
would quite simply consist in causing the fall of the varroas which are on
the adult bees.

***********

-----Original Message-----
From: Ettamarie Peterson

I had my friend Serge look at that French Canadian site as he is French
and very interested in this subject. This was his reply:

> Subject: Canadian test of screen bottoms
> Date: Sun, 21 Apr 2002 08:49:45 -0700
> From: "Serge J Labesque"
> To: "Ettamarie Peterson"
>
> Dear Ettamarie:
>
> Thank you for the link to this report. It is a text of twenty pages and it
> took me a little while to go through it. I have to say that the
> observations made by the researchers corroborate the ones I have made, and
> we are reaching the same conclusions as far as the utilization of the
screen
> bottoms. Where we differ is in some of our explanations of the reasons why
> leaving the screen open can be negative, but that is academic.
>
> The report in a nutshell:
> The use of screened bottoms in beehives is strongly recommended as a means
> of controlling the varroa population, particularly at the time of
treatment
> with chemicals such as Apistan¨. The report shows that, in some climatic
> conditions or in some apiaries, leaving the screen open can have adverse
> effects. An open screen mesh allows temperature inside the beehive to
> fluctuate too much. The researchers simply say that "cooler temperatures
> favors the multiplication of the mites".
> Incidentally, they also say that adequate distance should be maintained
> between the trays and the screens as the mites can climb back up (as you
> know from our previous correspondence, I concur with them on this).
>
> My observations, the recording of minimum/maximum temperatures and the
> monitoring of daily mite fall show that there is a direct correlation
> between the atmospheric temperature and number of varroas that is
collected
> on the trays. My explanation is that the bees cluster for longer periods
of
> time and more tightly when they are exposed to lower temperatures. A large
> difference between a daily minimum and maximum can be rather stressful on
a
> colony, and this is a typical feature of our local "Mediterranean"
climate.
> When it is cold, the bees cluster tightly around the brood area and the
> mites can pass very easily from one bee to another, from a cell to a bee
or
> from a bee into a cell. In warm weather the bees move about in the hive
> leaving relatively large spaces between them. Not only the increased
> activity dislodges more varroas, but there is less of a "safety net", and
> more mites fall through the screen.
>
> In conclusion, use screened floors in your beehives but keep them closed
> with the trays. Open mesh bottom probably work in Ireland and similar
> climates.
>
> Serge
>
>