> Grant Gillard wrote: wouldn't a dusting hasten and increase the mite drop,
that if done repeatedly, over the course of the summer, reduce the mite levels?

I'll chime in because I've done some experimentation with this method, but
have not published anything.  The key question is whether your sugar dusting
practice is eliminating enough mites fast enough.  In my opinion, one has to
make measurements and not just assume the dusting is getting enough mites. 
Conditions vary based on location, your bee genetics, and your other
management practices.  Mr. Dowda has claimed that weekly sugar dusting is
sufficient and he is probably correct for many but not all situations.

Here is a way to verify the performance of a mite control method, like sugar
dusting or Sucrocide, that take out some portion of phoretic mites.  Since
this method is labor intensive, I use it to check out a treatment method but
not routinely thereafter.

Measure daily mite drops for the one or a few colonies to be studied.  Do
this for enough days to get a reasonable looking pattern established (in my
case the natural mite drops were fairly consistently increasing from day to
day, so 5 days of history was enough).  Then apply your sugar dusting
treatment.  Keep tabulating the daily mite drops and do another dusting in 7
and then maybe 14 days.  At this point you have enough data to do some
analysis and see whether your efforts have a prayer of working.

To do the analysis, here are some varroa population parameters that seem
reasonable to me in the summer in the Northeast.  Roughly one-third of the
mite population is phoretic and vulnerable to the powder.  Typical natural
mite fall is about 3% of total mite population, with most of this mite fall
associated with bee hatchout (immature mites and mites that die when in with
the bee pupae) which for workers is about 12-13 days after varroa
infestation of the cell.

If your sugar dusting is perfectly effective, meaning it eliminates 100% of
phoretic mites, (and there is no drone brood in the colony) then your
natural mite drop counts will show a sharp decline around day 12-13 after
the first dusting.  Mite drops will then drift back up only to plunge again
12-13 days after your second dusting.  If you do not see a significant
plunge in natural mite drop counts at those points, then your sugar dusting
is not effective.  If it is not demonstrably effective, then you need to
change something, either switch to some other method or dust differently. 
Not all brands of powdered sugar are equal and humidity can affect how the
dust disperses.  Parts of your state are famous for high humidity, unlike
parts of California.  You could also have a neighbor who is dusting
regularly and letting the dust and mites fall to the ground where they are
harvested by your bees.  Bees quickly learn to forage for powdered sugar and
other goodies under screened bottom boards.

If you get modest declines in natural mite fall at the 12-13 day marks, you
can estimate the frequency of dusting needed to get a steady decline in mite
population over time in your circumstances.  When you dust, you will notice
it is quite disruptive to the colony (not quite as disruptive as Sucrocide)
and so there are probably some negative side effects to dusting very frequently.

****************************************************
* General Information About BEE-L is available at: *
* http://www.honeybeeworld.com/bee-l/default.htm   *
****************************************************