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Date: | Wed, 13 Jan 2021 16:39:40 -0700 |
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Tracheal mites were common in the U.S. and normally took off in most
untreated colonies until about the middle of the 2000 decade. They
became harder to find after that, but once in a while pockets of
colonies with high prevalences popped up, particularly in colonies kept
through long winters. Curiously, using standard bioassays exposing
young workers from test colonies at the same time as those from
resistant and susceptible standard colonies, showed that susceptibility
was still pretty common in U.S. colonies of various lineages, even at
the time that colonies in the field showed low infestations. There has
been speculation that widespread use of Amitraz has had an effect,
perhaps in combination with some selection for resistance. It is still
possible that we are missing a more arcane explanation. I have found
tracheal mites in our hobby colonies in Colorado but not at dangerous
levels. And we do not treat at all for varroa since levels stay below
threshold. In this case the explanation is probably pretty clear: very
short seasons and running queens of VSH lineages.
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