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Subject:
From:
"W. Allen Dick" <[log in to unmask]>
Reply To:
Informed Discussion of Beekeeping Issues and Bee Biology <[log in to unmask]>
Date:
Tue, 23 Nov 1999 02:21:38 -0500
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>> Rod reports significant varroa mite drop in Missouri USA after using
>> Apistan treatment.  It really sounds to me like he is seeing mites in his
>> colonies that are resistant to fluvalinate the active ingredient in
>> Apistan.

>...but this statement doesn't make much sense to me.
>Surely, a lack of mite fall on using Apistan would be more
>indicative of mite resistance to Apistan? A 'significant
>varroa fall'would indicate that the Apistan is working.

I've just gone through this whole exchange in the logs and as far as I can
tell, here is the story:  The original post said that the hives were
treated with four Apistan(r) strips *in the summer*, and I quote:

>This hive was requeened in June and treated with four apistan
>strips (two per hive body) from July 17 through August 29.

I assume that that is a dearth time or the hive was weak, and that the
supers were removed at that point, and also that the strips were correctly
applied in the brood area of the hive.  The post then mentioned putting a
sticky board under the hive recently and finding dead mites in considerable
numbers.  Again, I quote:

>We have been having unseasonably warm temps here in SW Missouri,
>so yesterday I decided to uncover the back and install a sticky
>board to check for mite drop.  After five hours I counted nine
>mites, most still alive, and today, after 22 hours, counted 20
>mites.  The 20 included the original nine and almost all of the
>mites appear dead.

This seems to indicate that the hive currently is not under Apistan
treatment and that this is *natural* mite drop.

There are a number of logical conclusions that can be drawn from the facts
given.  We do not have sufficient information to choose among them.

1. The hive was successfully treated and subseqently re-infested from an
other nearby hive collapsing.

2. The treatment was not completely sucessful and a sufficient number of
mites survived it to build into the current infestation.

That second option, in turn, could indicate that the summer treatment was a
failure due to incorrect application, defective product (bad manufacture,
left in the sun, etc.) or resistant mites among the original population.

In any case, that leaves the problem of analysing the situation and
deciding on a course of action.  The important questions are 1. What does
this observed mite drop indicate in terms of risk to the hive? and 2. What
control agent can be used to control these mites when and if such a measure
is indicated?

Again assuming that nothing was done recently other than opening the back
access and slipping in a sticky board of the normal sort, 20 mites dropping
means that there are quite a few mites in the hive.  Since we know little
about the amount of brood or even queen-right state of the hive other than
the statement that

>It seems to have a good population is is just
>finishing it's second gallon of 2:1 syrup with fumidil,

we must again assume that it is normal and may have a frame or two of
brood.

If no brood, then the dynamics will be different, since *all* the mites
will be without an opportunity to reproduce and will be wintering and
aging, exposed, on the adult bees.  In this latter case they would be much
more vulnerable and also their expansion would be temporarily checked, but
they would still be sucking haemolymph and weakening adults.  In this case
we would expect natural mite drops that are relatively large in number
compared to the actual total mite population as the mites age and/or are
damaged without protection or replacement.  In this case, there is likely
no rush to treat until the beginning of brood rearing.  However all the
mites are now exposed and very vulnerable to any treatment that occurs.

If they have brood, then there is a hidden and protected mite population,
and, moreover, younger mites are replacing the older individuals that
drop.  The natural drop count will thus represent a smaller proportion of
the total mite population numbers, and the same number dropping will
indicate a significantly more serious infestation than in the previous case.

I really do not know how many mites a hive can tolerate, since it so much
depends on the geographical location, the bees, the time of year, and
probably a number of other factors.  I have heard of bees tolerating fairly
high loads.  Nonetheless, a drop such as described does indicate that a
treatment of some sort will likely be necessary soon.  Since we really do
not know -- or care to find out -- the point at which the bees will
collapse, most beekeepers will be thinking of treating sooner, rather than
later.

Then the question is whether Apistan is working, and how well.  There are a
number of ways, and the simplest is likely to just get some Apistan(r) and
insert it for a day or two and track the mite drop numbers.  Then remove it
and try an alternate method.  Personally, I use formic acid, as would most
of those in the free world, but in this particular case I believe that
formic may not be prudent.  CheckMite, is available and effective and not
closely related to Apistan, so it would be a logical choice.  Insert it
according to instructions, and track the mite drop for a day or two.

Comparing the mite drops over time under the two treatments will give you
and idea if the Apistan is working.  If Apistan is working you should knock
down most of the phoretic mites in the first day or two, assuming the bees
are sufficiently active to contact the strips, and the number dropping
should then diminish fairly quickly.  If you get an initial rise in the
drop immediately on inserting the second treatment, then fluvalinate has
been losing effectiveness on your mites, and now only gets some -- but not
all -- of the mites, or takes longer than it should.

This is my understanding of the whole thing, but I am certainly not an
expert.  I hope that others will help me out if I have made any errors or
missed anything.

allen

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