Hello Peter & All,

I will venture a guess but I can only guess.

Peter said:
By fall they were full of mites. Of course, we treated. But I wonder
which is more likely: 1) they had many mites upon arrival, or 2) they
picked them up after they got here?

The hives with high mite loads in fall  and started from packages in a
remote yard most likely brought a high mite load with them. Moderators will
not let me publish the names of those package senders on BEE-L  from which
high varroa load packages were sent..

Peter said:
Other 2002 packages that were put in yards with over-wintered
colonies had many times more mites than those in the isolated yard,
and some crashed before they could be treated in September.

I suspect these brought a high varroa load with them and then picked up
additional varroa from robbing other colonies and drifting drones.

Peter told us earlier that he had problems with varroa last year from
controls which failed. Colonies overwintering with a high varroa load became
sources of varroa for new colonies started from packages.

 Without the packages in the isolated yard with high fall varroa counts the
whole scenario could be blamed on robbing and drifting drones. Because of
the isolation I suspect those packages carried a high varroa load when
arriving.

Bob

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