> I keep, observe and treat 20+ colonies now and as a researcher...
> ...treating with oxalic acid in broodless time windows...is in my
> opinion enough to get the mite population down. I fail to see the
> need of more compex compounds in beehives. Why does one need
> compounds like coumaphos?

Well, coumaphos is not the best example.  Many of us have never used it
and would never use it in beehives, but still see reasons to use Amitraz
and fluvalinate -- carefully and when needed.

Keeping 20 hives as a researcher is not anything like running the 
thousands of colonies that are required to meet the demand for 
pollination or to make a viable honey operation, so maybe that 
experience does not transfer.  For one thing, researchers have a 
different view of time and don't need to make  a living off the hives.

Additionally, 20 hives is getting near the upper bound of where 
intensive colony-by-colony management is practical.  I know as I was 
doing fine while I was under that number, but as I got up near 100 
colonies, the intensive mite management became impossible.

Moreover, when running bees for pollination or honey production, the 
timing and management for mite control can interfere with the primary 
tasks.  Mite management is not a profit centre, but rather an expense.

In migratory operations, the colonies may be in many differing climates 
and  as result the logistics and timing of complex tasks can quickly 
become unmanageable.

> ...you can devise a managment style that includes broodless periods
> in the tropics.

You can, but can you also run an efficient, profitable operation on any 
large scale while running such a scheme?

> What ARE the advantages of the complex compounds, apart from easyness
> of application?

Reliability, predictability, simplicity.  Moreover, they can be applied 
  at any time of day, in any location, and any weather by unskilled 
labour -- without intensive work inside the hives.

Granted, such chemicals are not the ideal solution and I am sure most 
commercial beekeepers are looking for better solutions and trying 
resistant stocks, etc. with a view to minimizing chemical use, but such 
chemicals are the fallback.

In my case, when I did not have adequate control after five oxalic 
applications, I fell back on Apivar and my bees are looking great in 
spite of the worst winter and spring I can recall in decades.

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