>The criticism that the neurons should be treated with “field-level
concentrations” is specious and shows a complete lack of understanding of
this type of experiment. The question was: What happens to the neurons
when these chemicals get into the synapses? That’s what they tested and
they did a good job of it.
Perhaps I misunderstood your previous post, Christina. It suggested that
you were going to attempt to stop being so deprecating and insulting to
other posters. Yet here again you use words like "specious" and "shows a
complete lack of understanding"--hardly evidence that you are trying to
engage in friendly discussion. I pity your students!
So in this post, I am not responding to you, since I am not interested in
whatever you are trying to prove by denigrating others. I am responding to
those such as Bill, who wish to engage in informed discussion.
The experiment in question confirmed that neonics caused depolarization of
neurons in the honey bee brain--I applaud the researchers for clarifying
this specific biological effect. Where I have a problem is when the
researchers then claim that: "These effects are observed at concentrations
that are encountered by foraging honeybees." According to Christina, the
researchers themselves showed a complete lack of understanding of their own
experiment, or they would never have made such a statement!
Let's go back 500 years to Paracelsus, who noted that toxicity is a
function of dose. Let's go the extreme to illustrate. There are many
receptors at each synapse. I ask Mark or someone else to correct me if I
have it wrong, but as I understand it, a single molecule of imidacloprid
binding at a single receptor at a single dendrite would not be enough to
initiate an action potential (a nerve signal to be sent down an axon) from
the neuron to the next neurons. If a single molecule were enough, then we
would all die from minuscule doses of neurotoxins (as by smoking a single
cigarette).
So it would seem that the dosage is critical. At some level of dosage, the
enough sodium gates will be opened to depolarize the Kenyon cells. So the
question is, would they depolarize at field-relevant doses of the
pesticides?
And that dose would depend upon how much of the compound actually made it
to the brain (only a small percentage of ingested dose ever makes it out of
the gut), and also upon the equilibrium of exposure vs. degradation of the
compound (rapid for imidacloprid in bees). At low doses, bees metabolize
imidacloprid into harmless CO2 within hours--eliminating it from their
systems. Dr. John Casida personally confirmed to me that the effect is
reversible, not irreversible, as is often stated.
So at a low enough dose, there would be zero to minimal effect upon bees.
So it would seem to be absolutely critical to test the compounds at field
and physiologically-relevant doses to make any sort of statement as to
behavioral effects upon bees (again, anyone who wishes to politely correct
me if this statement is in error, please do so).
My criticism of the study is that the authors applied far too high a dose
directly to the brain tissue, and then claimed that their results could
applied to real world situations.
I suggest that we all use some common sense here--if doses of 2.5 ppb
indeed prevented bees from recognizing flowers, how in the world would bees
on canola, with that sort of dose in both the nectar and pollen, manage to
put on 300-lb honey crops in a few weeks?
--
Randy Oliver
Grass Valley, CA
www.ScientificBeekeeping.com
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