Bob asked the question -
"Apistan worked excellent  in most areas of the U.S. for around ten years as told Apistan would by
the makers. If in say the ninth year of control the beekeeper had switched to an essential oil/
organic acid treatment with a very high efficacy and then  rotate back to Apistan every other year
would Apistan still work even if other beekeepers in his/her area are having the same fluvalinate
resistance problem problem? Many Canada beekeepers are asking.

and directed it towards Max. Watkins.

I pen my thoughts in response for two reasons:
1. They are how I perceive the situation.
2. If they are incorrect - People will see where I am coming from and then hopefully I will be
corrected !

Apistan is effective on average for ten years in specific areas and regions.
It may be more or less than this period.
During the "effective" time span - a high % of mites are killed - but each treatment period leaves
mites in place.
The mites that remain do so for several reasons.
The particular one grieving beekeepers is where mites are not being killed due to being able to
resist the presence of the active material.

These resistant mites are a low % of the original population - but not being affected by the
treatments applied - they  have the potential to multiply.
Being originally low in numbers - resistance is not evident for a reasonable period of time - but
eventually manifests itself as the mite population grows.

Acquired resistance may be simple - i.e. once the active material is changed - efficiency in
treatment increases.
or,
It maybe (and appears usually to be the case) to be more complex - i.e. if the active material is
changed but with a related chemical type, then efficiency in treatment increases, but not to the
expected level, or for the expected period of time.

Changing to a different chemical type or mode of attack (re. Formic acid, thymol etc.) will result
in efficient treatment being achieved again.
In this situation, the resistant mites are killed BUT not all!
Here is a crucial question - WHY?
Several responses are possible.
1. The molecule may not be as efficient as the required 99% wished for (100% if one wishes).
2. The mode of application used may cause problems and result in a diminution in treatment
efficiency.
3. The mites may have again a low % in the population that are resistant!!!!

If these resistant mites are ones that are not also resistant to the original molecule - then
treatment may continue until the resistant population reaches levels where the original molecule may
be reverted to.
But, again as appears to be the usual case,
The remaining mites are resistant to both treatments - at least to a degree.

Therefore, a third molecule is required, and the cycle goes on!

If, as the original molecule approaches the end of its "natural", a replacement substance is used,
which is then again replaced by the original molecule after several years - there are mites present
in the colony that are possibly carrying double "simple resistance".
Then they are no longer being attacked by the second treatment (it having been halted and replaced
by the original molecule), against which a resistant population was gradually building up, and they
are still exhibiting resistance to the original molecule.
End result: The mite population carries on building.

Also, it there are colonies in the area that have only been treated with the original molecule - the
colonies maybe a great potential source for resistant mites - and if these colonies are collapsing,
drifting bees will infest the hives which were treated by the original and second molecule.
This would overwhelm and finish off the colonies which underwent the two different treatments.

Hoping that this makes sense!
Regards,
Peter

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