Dick Marron wrote:
>I've been thinking about this and it turns out you may be right too. This
>avirulence comes about because the isolated colonies, the many swarms, the
>small colonies (behaviors)--limit the mites to vertical transmission. 

It may also be due to inbreeding. Mites tend to inbreed anyway and to be
stuck in an isolated colony means they may never have the opportunity to
outcross with divergent populations. 

It may be that after a year or two of isolation, the mites have inbred
themselves down to a pretty weakened state. Meanwhile, the honey bees
continue to outcross and develop a vigorous colony. No beekeeper is coming
along to requeen with a susceptible line. 

In a typical apiary, the mite population may have much more opportunity to
cross breed with mites from other colonies and possibly from mites from
other states which have been moved about by beekeepers. 

But -- I don't know who but an acarologist could confirm or deny these
speculations.

pb

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