Hello Frank and All,,
The Coumaphos story is in the archives and one need not search farther than the last two years. A half hours reading should bring a Bee-L person up to speed. Coumaphos is a sensitive subject as was Apistan when first introduced. 
Coumaphos was registered to save an industry but was never intended as the final answer. I  am surprised by those beekeepers which talk about alternating coumaphos and fluvalinate for the next century as the answer. Coumaphos  resistant mites have now been documented. 
Not a big concern for most hobby beekeepers but I assure you the commercial beekeeper will pick up the list of  around 100 chemicals shown to be effective in controlling varroa and choose a new  chemical.  None left on the list carry the control of fluvalinate, amatraz or  coumaphos so the saga continues.   Many on the list are in fact more dangerous then coumaphos. 
All the chemicals which have been tested against varroa are listed on the last page of "The Varroa Handbook".
I am giving a  talk about Varroa on February 17th.  In Kansas City. All facets of the varroa problem will be discussed. The talk is free and the Midwestern beekeepers assn. Would welcome beekeepers from the  surrounding states. Email me for information on time, place and directions.   Every time I have posted a location I was going to be at  least one beekeeper I have never met has stepped up and introduced himself and said he reads  Bee-L. and my posts. 
Sincerely,
Bob Harrison
Odessa, Missouri