Hello Tom,
Most researchers will not touch this post . I will give you my opinions and
thoughts but am only a informed beekeeper.

Tom wrote:
> I read recently that three states in the USA now report resistance to
> Coumaphos. In one case if memory serves me correctly, the efficiency of
> Coumaphos was down to 19%.
Actually it was the opinion of the inspectors aaat the Apiary inspectors
meeting in Georgia that the bees  in this instance came from a illigal use
of coumaphos aand not from the use of Checkmite as the beekeeper claims. I
agree with the opinion of the  USDA apiary inspectors. In my opinion a
illegal use of coumaphos was involved creating the resistance.
Trying to save money cost the commercial beekeeper most of his hives and
caused the rest of us early problems with coumaphos resistant mites. At this
time I only express my opinion and so far to my knowledge the USDA can not
prove a illigal use was done.

Where now stands Apistan in the USA generally - I
There are areas  which are still using Apistan and reporting control. There
are however areas of the U.S. in which you can put in as many Apistan strips
as you want. Four to a hive body have been told to me and varroa numbers
rise in testing instead of go down.

Tom wrote:
> presume that in the three states concerned that resistance to Apistan
forced
> them into using Coumaphos.

Some beekeepers simply ask what other beekeepers are using. Buy the strips
and use.
Some other beekeepers  monitor mites loads, use IPm methods and check for
resistance and if methods are working.
bad advice on treatments is around. I suspect the beekeeper with the
coumaphos resistant mites was given bad advice and now has to pay for
listening to a fellow beekeeper instead of his state bee inspector.

What do we do when Coumaphos resistance occurs
> since we are using our most powerful weapon?

There are other methods of controlling varroa but none as easy for the large
beekeeper to use as Apistan or Checkmite.

Do we go back to Apistan, or is
> Apistan still useless, or is IPM the only answer?

Beekeepers need to know the varroa load in their hives and then do whatever
works to reduce varroa load. The days of stopping by the bee supply house
and picking up whatever the owner recommends is over. The bee supply houses
will provide all the chemicals which are legal. All have got problems and
might not work    or they might work. Most be supply houses should not today
guarantee any method will absolutely control varroa and should recommend
testing before ,during  and after a method is used.

And what becomes of
> beekeepers who cannot find/afford the labour/skill to implement IPM?

They will in my opinion join the ranks of those beekeepers which have
already been put out of beekeeping by varroa.
All those reading this post using the illegal coumaphos which is only 1%
instead of the 10% of Checkmite you are heading for trouble  aand making
problems for the rest of beekeepers. You have recieved bad information.  1%
coumaphos is like a light slap in the face to varroa.  Your friends which
are telling you you can use Checkmite later if the 1% does not work are
sadly misinformed.