Randy Oliver has written several good, practical articles on this issue that can be found at his web site:

http://scientificbeekeeping.com/

Many Others have written on this subject.

Mites per 300/200 bees is just % infestation (mites counted divided by 3 or 2 depending on size of sample) of the colony.  It does mater where you take your sample from.  Most agreement is on any frame of brood from the upper super.  2 mites in a 300 bee sample is a 0.7% infestation for the colony.  Most beeks, agencies, groups accept a 2-3% infestation (6 or 9 mites for 300 sample) to keep a colony healthy.  Colonies with a higher % are likely to be impacted by other stressors (weather, infections, decease) and could die if not treated.  I only monitor % not total number of mite as this works for me in my IPM.

As for monitoring method, there is much out there on this topic including Randy's papers.  I selected the alcohol wash because I can run them very quickly and the rough field data I get tells me how a colony/yard is doing overall and when i need to treat to avoid losses.  I've personally seen the result of not monitoring or treating and in my area that means rampant DWV and colony die off.

Scott Ball
East Bay Area, No. CA
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