Thanks for posting the preprint Jim!

When the final paper is published, perhaps they will clarify whether they
indeed used "dehydrated oxalic acid" or oxalic acid dihydrate (the more
common form, and likely what they meant).

A brief take-home on their findings:

Spraying was effective, but tough on the bees, invasive, and time
consuming, so I will discuss it no further.

Dribbling and sublimation were fairly comparable, with some notable
differences.

At the 2.25 g dose (medium strength dribble, or typical sublimation dose),
the efficacy at mite kill (in colonies completely lacking brood) was
exactly the same.  However, sublimation appeared to be somewhat more
"gentle" to the colony, as evidenced by less bee mortality, and more brood
in spring.  Indeed, colonies appeared to tolerate a 4.5 g dose by
sublimation
remarkably well.

Of particular note is that following January treatment, in early May
sublimated colonies tended to have more brood (4.9 frames, compared to 3.9)
than dribbled colonies.  This suggests that sublimation has less of a
lasting negative effect upon the colony than does dribbling (likely of
greater impact in cold-winter areas with an extended period of dormancy).

Unfortunately, they did not compare a higher-dose dribble to the high dose
vaporization.  Nor did they take nosema samples, in order to determine the
comparative effect upon nosema by treatment method.

Two other practical aspects are operator safety and the amount of time
involved in application.  The researchers wore vaporizers, but found that
if they loaded the hot vaporizer with OA immediately before shoving it into
the hive entrance, and then sealed the entrance with foam, that they were
exposed to little escaping vapor.  Unfortunately, this entails dropping
oxalic crystals onto the hot vaporizer at each hive (a safety
consideration).

As far as the amount of time involved in application, it took them 3
minutes per hive for sublimation, 2.5 minutes for dribbling.  I do not know
why it took so long for them to dribble since it takes me only 10 seconds
to dribble a 10-frame colony (I apply at the calibrated rate of 1 second
per seam of bees).

My take on their  excellent studies is that dribbling or sublimation are
both practical methods, each with advantages and disadvantages:

*Dribble is safer to the applicator (and quicker), but a bit harder on the
bees.  It may be the preferred method in climates with late fall and a
short winter, due to its safety to the operator, quickness, and the
colonies being able to rapidly recover.

*Sublimation may be the preferred method where winters are colder and
longer, and the cluster is broodless for a longer period.

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

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