John,
The reasoning behind my questions:
If one has a hypothetical colony of 1000 bees and no brood in January - 
a count of mites would produce 100% infestation rate (1 to 1 bees to mites)

Still in hypothetical situation:

By April, still 1000 adult bees + brood being now present - 50% of the 
mites may be situated on the enclosed brood, therefore a count would 
indicate only 1 mite to 2 bees.

The raw count indicates an apparent fall in mite numbers.
Add to this situation an increase in adult bee #'s and that would lower 
the apparent count of mites present again.

Applying the same logic to the population dynamics that you may observe 
in your colonies - Does this suggest an explanation to your mite level 
observations?

Excuse my trying to keep things on a simple level - the mail would be 
tediously long if written as a full blow population dynamics scenario.

Regards,

Peter

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