>
> >This Mite immigration collapse theory, why does everyone stick with it
> when basic math says it nonsense??
>
Anyone who experienced a fall overload of immigrating mites from collapsing
feral colonies in the early days of Apistan wouldn't use the word
"nonsense." Nor anyone sitting next to a commercial operation that isn't
controlling their mites (a number of commercial guys have told me that
they'll move their bees away if they have reason to think that another guy
is about to suffer a varroa collapse).
Perhaps we should clarify what we're talking about. Mite immigration is
well documented by several studies, and can be in high numbers (well over
1000 mites). But as you point out, Charlie, this could only occur if the
proportion of collapsing colonies was high relative to the proportion of
receiver colonies.
This is unlikely to occur any more from any feral population, unless such
population was established by a beekeeper's colonies all swarming the
previous season and surviving the winter.
On the other hand, a hobbyist in suburbia, surrounded by treatment-free
beekeepers who lose 50% of their colonies to mites in the fall, would stand
a good chance of picking up a lot of those mites.
The point that I suspect that you're trying to make is that immigration
within an operation, or in a stable population, is not likely to cause a
serious spike in mite levels across the board in the survivors. You and I
have discussed the math off List, and I'm in complete agreement. Since
mite transfer is a zero sum situation, any colony that gains mites means
that another lost the same number of mites. So the mean mite level in the
entire operation would remain the same--*provided that no colonies collapse*.
Once colonies start to collapse, a domino effect can occur, as collapsing
hives provide additional virus-carrying mites to nearby colonies.
I occasionally observe sudden immigration occurring in the field. We
monitor mite levels closely in fall. And sometimes we see alcohol wash
counts suddenly explode, which cannot occur mathematically unless there is
a sudden curtailment of broodrearing (which isn't occurring in our hives at
that time of season). So I'm left blaming immigration.
The other thing that I've found in mathematical modeling of bee and mite
populations is that we're talking about very few mites in a hive at the end
of the season. Since you asked, let's do the math. An 8-frame cluster of
bees in the fall contains roughly 14,400 adult bees. At the 2% "safe" mite
threshold that I use, that colony could safely carry 288 mites (the 5%
threshold, which is more commonly used, would result in a mite population
of only 720 mites).
If I were to take an alcohol was of an 8-frame colony without brood, but
with those 288 mites, I'd get a mite wash (from 300 bees) of 6 mites.
But that colony would only need to pick up an additional 144 mites from a
colony collapsing a mile away to put the infestation rate half again as
high (3%, or 9 mites in the alcohol wash). And if that colony picked up
432 mites (again a realistic number), it's infestation rate would reach the
deadly 5% level. My point is that it doesn't take many mites to strongly
affect the mite count at the end of the season.
And if your colonies were weaker, they'd be even more strongly affected by
the same number of mites.
Summary: in a closed population of hives, immigration is a zero sum game,
and the mean mite infestation rate would not be affected, so long as no
hives collapse.
But keep in mind that if one does, and contains, say 3000 mites, that that
number of mites could seriously affect the infestation rate in 10 other
colonies.
This large multiplier effect can be deadly.in an environment in which many
beekeepers are not adequately managing mites, resulting in a fair
percentage of fall collapses. In such a situation, mite immigration can be
a serious problem.
--
Randy Oliver
Grass Valley, CA
www.ScientificBeekeeping.com
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