I'm not sure that you're getting my point here Pete.  There are certainly
apiary-to-apiary disease issues.  But perhaps even more relevant to
beekeepers in general is within-apiary pathogen transmission via drift.  If
one nips a potential epidemic in the bud, one may be able to save an entire
apiary.

Re the 4 per square mile colony density, that figure is relative to the
type of habitat.  In areas in which the only cavities available are along
stream beds (typical in some arid areas), the natural colony density may be
very dense within a patch of old trees, yet sparse if one considers the
foraging area overall.  This may be analogous to placing a crowded apiary
in the middle of the prairie.

>In commercially exploited areas such as the eucalyptus forests, the
concentration can go to 100 per square mile

In almonds, the typical density is about 1300 colonies per square mile.
And in areas of Southern California, apiaries of over 500 hives in one spot
can make honey during an intense flow.

-- 
Randy Oliver
Grass Valley, CA
www.ScientificBeekeeping.com

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