>
> >The reason I am looking at the persistence of OA crystals is because the
> mites are not always on the bees.


Bill, I haven't seen evidence to support the above claim.  It appears to be
rare for a mite outside of the cell to not be on a bee at all times.  Thus
your hypothesis that phoretic mites are crawling over the OA-exposed comb
surfaces is questionable.


> >But the emerged bee mites on the bees will be there for 5 or more days


The amount of time that a mite spends in the phoretic phase appears to be a
function of the ratio between the adult bee population and the number of
8-day larvae in the hive (refer to Boot's studies).  A mite can be phoretic
for less than a day, or for hundreds of days.  Based upon my modeling (and
hard data collected in the field) the phoretic phase typically AVERAGES
around 5 days during much of the summer.

At 5 days of phoresy, the mite repro cycle would be 17 days, of which 12
take place under the capping.  Thus, 5/17 of the mites would be phoretic at
any time.  In actuality the percentage would be higher, due to the
additional daughters emerging.  My modeling (and hard data) indicate that
roughly 50% of the mites are typically phoretic at any time in late summer,
prior to serious reduction in broodrearing (as low as 20% may be phoretic
at swarming time in spring).

Thus, an oxalic vaporization in late summer, with 90% efficacy, would be
expected to kill only around 45% of the mites in the hive.  And if repeated
at 7 days (assuming the OA being active for 3 days), for 4 days a
proportion of the emerging mites could reenter cells without being hit by
the acid.

Nancy's data supports this (Nancy, I'd love for you to send me your data).
We see the same with sugar dusting--it's effective only if repeated at
intervals of only a few days.

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

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