2011 Ontario Treatment Recommendations for Honey Bee Disease and Mite Control

Monitoring Method -- Number of Varroa Mites in August
Ether Roll -- 2 mites/100 bees
Alcohol Wash -- 3 mites/100 bees

This translates to 6 or more per ether roll, 9 or more with the alcohol wash. 
These levels are not very high, and I would be surprised to see untreated colonies without these levels.
Formic acid is less effective the later it is applied, but even a 60% knockdown could bring the levels down below these numbers. 

PLB

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