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Date: | Wed, 15 Jul 2015 06:50:13 -0500 |
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Always been somewhat skeptical of the role this may play in mite
growth. Certainly there are experiences and experiments where there
is no other explanation. Have not played with the numbers much, but
it seems like the cumulative mite load from immigration (drifters or
robbers?) is small compared to that produced by exponential growth
through reproduction of resident mites.
This may be one place in which highly resistant colonies (those with
net negative mite population growth) have an advantage over chemical
controls. A control application drops mite levels to very low, and
then the numbers start growing again, with immigration adding to the
growth.
Active defensive mechanisms against mites in theory are there all the
time, so immigrant mites are immediately at risk. One of the
simplified methods of gauging Varroa Sensivite Hygiene (VSH) in
colonies is to introduce a comb with recently sealed brood that is
moderately to highly infested (measured right before introduction of
the frame). Then after a period that allows bees to attack infested
brood at the time when they seem to be able to detect infestation, the
resulting infestation of the comb is evaluated and compared with the
infestation when it was introduced. Very good colonies routinely
decrease the infestation by 70 - 90 %.
If this happens in every round of reproduction, simple math explains
how these colonies can drop resident mite levels to negligible, and
can even deal with small, and possibly large numbers of immigrating
mites.
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