>What worries me is that Randy writes in 'Trying to make

> sens of the science - part 2': "The point is, that nicotine and neonics
> appear to be so rapidly metabolized, that there is no buildup (as there is
> in the case of DDT), the binding to the nerve receptors is reversible and
> insects recover fully, and there is generally no increased mortality due to
> low-level chronic exposure."
>
> Ghislain, I reviewed the paper again this morning.  The study was
performed with homogenized fly head tissue, frozen and then thawed, and the
binding affinity was determined to see whether imidacloprid or nicotine
preexposure would prevent the chemical's displacement by a second dose of
radiolabeled bungaroo toxin (which binds irreversibly).  Abbink found that
nicotine had a 10x higher binding affinity than imidacloprid.

At this point, I'd like Christina, due to her better familiarity with this
subject, to step in to help interpret the experimental methods, results,
and conclusions.

This study was performed with dead, frozen tissue, not living bee tissue.
 Christina, wouldn't this make one hell of a difference on whether the
binding was reversible or not?

I don't see the amount of time for which the study tested for
"irreversibility," plus the authors noted that the acetylcholinesterase
present would have destroyed any acetylcholine that could have displaced
the imidacloprid, and thus reversed the binding.  Christina?

The authors also appeared not to understand the mode of action of
imidacloprid--implying that its action was due to blocking the receptors,
rather than by opening the sodium gate.  Christina?

The binding also appeared to be highly dependent upon concentration--as the
concentration of imidacloprid increased, the binding affinity rapidly
dropped off, suggesting to me that imidacloprid binds to only a small
proportion of the available receptors.  Christina?

Christina, I'd like to hear your interpretation of the findings of this
paper, and whether you feel that they are applicable to living bees,
especially in light of Cresswell's recent findings of the apparent
reversibility in living bees.

Again, if the binding were truly irreversible, wouldn't we expect to see
every forager on seed-treated canola to drop dead after a day or so?
 Christina?

I'm not suggesting that only Christina can answer--anyone who has read the
paper can feel free to jump in!

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

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