Have we lost the plot a bit?
My understanding is that the damage to colonies is not caused by directly by
varroa, but by the fact that they act as vectors for viruses. Of these, the
most significant are Deformed Wing Virus (DWV) and Acute Paralysis Virus
(APV). So a large infestation of varroa may not be a problem if DFW and APV
are absent, whereas a small infestation can cause severe problems where
these viruses are present.
Should we, therefore, be monitoring the presence of the viruses (how do we
do that?) rather than getting obsessed about the actual number of varroa
present?
Peter Edwards