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randy oliver <[log in to unmask]>
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Informed Discussion of Beekeeping Issues and Bee Biology <[log in to unmask]>
Wed, 16 May 2007 23:34:27 -0700
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Hi All,
I've been waiting to see if anyone could cite actual data re oxalic damage
to Malpighian tubules.  Still waiting...

Here are a few things I've learned since I wrote my article on OA in ABJ:

1.  The paper by Nozal (Apidolgie 34: 181-188) cited earlier clearly
demonstrated that OA is absorbed through the bees' cuticle, and makes its
way to various organs.  That study, when I read it some time ago, helped
answer a few vexing questions, but not all.  The data indicate that 6
microliters of 10% OA in water applied to a bee resulted in a brief spike in
OA in the hemolymph at 2 hrs, after which it returned to normal.  There was
nearly no change in the amount of OA in the rectum, malpighian tubles, or
digestive tract.

2.  To my knowledge, the mode of action of OA on the mite is still not
known, although studies by Ellis and Aliano demonstrate that it is quite
toxic to the mite when topically applied.  However, there are reports that
OA syrup fed to bees (when they could be induced to eat it) also killed
mites.  The fact that OA gets into bee hemolymph suggests that a mode of
action is likely by mites ingesting low pH hemolymph (since oxalic salts
don't kill mites).  However, in practice, OA dribble kills mites for about a
week.  Nozal's paper suggests that the OA in bee hemolymph spikes at 2
hours.  Go figure!

3.  The effect of the sugar in the OA solution is apparently as a humectant,
which allows the acid to be absorbed more effectively through the bees
chitinous "skin."  Glycerine will do the same.  Plain water when it's humid

4.  Several European studies found that spring buildup was slightly reduced
temporarily in colonies that received winter treatment with oxalic,
indicating that there was some sort of sublethal effect on the bees.

5.  Anecdotal reports to me demonstrate that overapplication (too much per
treatment) of OA can be frankly harmful to colonies.  DO NOT EXCEED THE
RECOMMENDED DOSAGES.  Gregorc (Apidologie 35:453-460) found that OA caused
increase cell death in bee larva gut epithelial cells.

6.  Dr. Ellis's experience, anecdotal reports, and my own experience
indicate that colonies can handle the recommended dosages well, even with
multiple summer treatments.  Anecdotal reports that they don't handle
multiple winter treatments well.   I have not seen any studies as to the
effect of nectar or pollen availability on sublethal effects of OA.  More
studies need to be performed re prolonged wintering of OA-treated bees.

7.  There are concerns about overuse of oxalic.  First, that residues may
build up in colonies (although I have seen data to the contrary).  Where OA
is used extensively and repeatedly in some European countries, some suspect
it of causing harm to colonies.

7.  The organic acids are rough chemicals!  They clearly have side effects.
However, the CCD team has not linked OA use to colony collapse, nor have I
in my own operation.  Oxalic is not a miracle drug--it is simply a
relatively safe "natural" chemical alternative to synthetics.  I recommend
that it be used only if needed, in a comprehensive IPM program.  Use it
carefully (where legal), and do not overuse it.

Randy Oliver

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