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Sat, 4 Aug 2007 10:01:42 -0700 |
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When colonies are widely separated as in the Arnot forest
>the mites have nowhere else to go so it is in their interest not to
exterminate
>the host.
The key point that I glean from the Arnot and Gottland studies is the
influence of a long, cold winter.
Horizontal transmission is greatly decreased since colonies that die from
mite stress during the winter are not immediately robbed, and the mites
within are killed by the cold. Therefore, there is a strong selective
pressure for mites NOT to kill the colony.
In warmer climes, this selective pressure would not apply, since collapsing
colonies would be robbed while their mites were still alive, and the mites
would actually benefit by killing the colony, as long as there were other
colonies around to be infested. Without human intervention, colony density
in warm climes would likely decrease to the point that mite avirulence would
become a benefit to the mite. But that is unlikely to happen, as beekeepers
will keep restocking the bee population.
Randy Oliver
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