Yes to all, Charlie.  The window for invasion in drone brood is longer than
that for worker brood.

>I think there is a fair amount of disagreement as to whether varroa end up
in drone cells by attraction or by chance.

Pete, I haven't seen any disagreement in the literature.  Varroa are of
course "attracted" by the esters and some organic acids.  But that
attraction applies only at very close range.  Any beekeeper can confirm by
looking at a comb of brood in a colony with a moderate mite infestation.
He won't see varroa mites walking across the combs due to being "attracted"
by drone or worker brood.  If you have an observation hive, you can easily
see that the mites ride on the undersides of the nurse bees--just waiting
for the right olfactory cue.

That attractive cue occurs when the nurse bee brings the mite into very
close proximity to the ripe propupa.  This has been confirmed
experimentally by filling the base of brood cells with beeswax in order to
bring the propupa closer to the top of the cell--which resulted in a
greater rate of mite invasion.

BTW, this is a great thread.  The more that we understand our number one
enemy, the better our chance at managing it!

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

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