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>   ...............  It is alleged that the mites cannot develop an
>immunity to formic as they are doing to fluvalinate. Is this so and if so,
>why?  I think that formic is a simpler compound than fluvalinate.  If you
>don't know the answer, perhaps someone with a background in chemistry can
>give us the answer.
 
I certainly do not have a huge background in chemistry but I would like to
add some comments especially for us beginners or hobbyists.  At a recent OBA
meeting there was a researcher, Dr Nasr, discussing mite treatment with
Formic acid as well as a representative from the manufacturer of Apistan.
 Both made it clear that mites can build up a resistance (or tolerance) to
EITHER chemicals.  It was emphasized that ANY control (certainly any
chemical control) can lead to resistance if it is used exclusively and
continuously for long periods of time especially if during those periods the
chemical concentration diminishes below the effective level.
 
Thus it is desirable to have two (or more) alternate treatments used at
DIFFERENT times.  The idea is that any natural selection during the use of a
chemical is quite useless when the second is applied so we are controlling
those more resistant to the other chemical as well as the general
population.  Of course the mites might start a natural selection of
resistance to the second chemical but that is then defeated when we apply
the first chemical in the next cycle,
 
 Fortunately, the mechanism of these two, Formic acid and Apistan, are quite
different and thus the mechanism of resistance or tolerance has to be quite
different (i.e. the same change will not protect the mite from both).
Apistan works by contact.  As the bees walk over the strip, the chemical
adheres to their legs and is transferred to the mites.  It is effective in
controlling Varroa but not trachea (if for no other reason that the tracheal
mites are inside the bee and thus not contacted by the Apistan.
Formic acid, on the other hand, controls by its fumes being breathed.  Both
the bees and the mites breathe it but the mites are more susceptible thus
the concentration level is critical.  It was stated that Formic acid
controls both Tracheal and Varroa mites.  But, too low a concentration
encourages natural selection by allowing mites with a slight resistance from
breeding while destroying the general population.  If the concentration is
too high the mites are destroyed but the bees are damaged or destroyed.
 Since the concentration in the beehive is a factor of temperature,
ventilation, evaporation area etc. etc., one must be careful to follow
recommendations and watch temperatures etc.
 
The overall recommendation was to treat with formic acid in the spring
during colony build up but before honey super are put on a ten day
continuous treatment is recommended, this implies several visits for some
pads that only work for 3 or 4 days or one visit if using an 8X10 inch pad
of Homasote (tentest).  I have no experience with the Nassenheider pads but
intend to learn and try.  (I seem to have missed the details of these.)
In the fall, right after honey is taken off, it is recommended to treat with
Apistan for the recommended 45 days.
 
Thank you all for in depth discussions of the many areas.  It sure helps to
solidify understanding.
 
............. george fielder.