This has been discussed before, but maybe someone has data or new insights to
sort this out.  

  

Tracheal mites became widespread all through the US after their arrival in the
early 80s- as in present in most colonies, in many with high percentages of
workers infested, and definitely killing colonies particularly in areas with
long winters.  

  

It became pretty clear in the 90s that some bee stocks were more resistant to
the mites than others. This difference was evident in field samples of
colonies through the seasons as well as in standardized tests where recently
emerged bees from different sources were simultaneously exposed to infestation
in a common environment of infested bees.  

  

However, as with varroa mites, these resistant lineages were not the
predominant types out there in the commercial world, at least not in the early
to mid 2000s. The mysterious part of a change started occurring around that
time. It became harder and harder to find highly infested colonies, even in
environments where they were particularly problematic in the 80s and 90s. I
kept lines susceptible and resistant to the mites as part of a research
program in Baton Rouge Louisiana, using II. Even in susceptible colonies,
tracheal mites were not that common. As a reality check, whenever I could find
highly infested colonies in which to run exposures of young workers for
standardized tests, the divergent lines would differ appreciably in
infestation. The divergent lines were retired sometime in the early 2010s as
the threat and interest in tracheal mites waned. So we do not know at this
point how they would behave when exposed, or where other lineages would fall
in the range between those two different lines.  

  

Lilia de Guzman at the bee lab in Baton Rouge reported in the late 2010s
continued low levels of tracheal mites, mostly in colonies in Louisiana, but I
believe a few other places. Anyone looking? Anyone has any recent data? Anyone
have any insights on how to explain the rather dramatic change that came about
in the mid 2000s? I have some skepticism regarding the most common explanation
given: resistance became widespread. Why would resistance to tracheal mites
spread rapidly and comprehensively while resistance to varroa has not given
similar time frames?  


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