Thank you for the reply Christina. The question at hand was whether IMI
binds irreversibly, which apparently actually means that it cannot be
displaced by another chemical that also binds very strongly to the sodium
gate.
This putative property of irreversible binding was briefly mentioned in a
very old paper by Abbink. It has since been the foundation of speculation
by Tennekes and Sanchez-Bayo, as well as others, and it concerned me
greatly!
So I sought the opinion of a world expert on neonics, Dr. John Casida of
Berkeley, who emphatically told me that the binding was not irreversible.
This opinion has been experimentally supported by Cresswell, and by anyone
who has watched an insect recover from IMI intoxication.
So when I found that we had a neurophysiologist on the List, I sought your
opinion as well, and asked you to review some meticulous research by
Suchail, who tracked the presence of radiolabeled IMI and its degradates.
>I then followed up with a request to you to demonstrate that IMI does
degrade in 72 hours to CO2
I apologize for the distraction as to whether the IMI in Suchail's study
degraded to CO2--this is irrelevant to our question. In her study, she
clearly showed that the backbone of the chemical rapidly disappears from
the bees' bodies. It makes no difference whether it degrades to CO2 or
into something else. Somehow the bee quickly eliminates the vast majority
of the chemical from its body. Suchail states: "In thorax and abdomen,
total radioactivity was at a maximum 20 min after the beginning of exposure
and then rapidly decreased with time" and that "Elimination
of total radioactivity from the whole honeybee followed first-order
kinetics (ñ2 = 0.8483) and the elimination half-life of radioactivity,
which represents the sum of radioactivity of all detected compounds in all
honeybee compartments, was about 25 h." Christina, please refer to
Suchail's plate 1. It clearly shows how the radioactivity in the thorax
(the main binding site) rapidly disappears.
So, Christina, I ask you once again (and I'm not trying to prove a point,
I'm just trying to understand), does not Suchail's study and subsequent
research suggest to you that even if IMI "irreversibly" binds, that its
biological/neurological effect must rapidly diminish as the compound and
its metabolites disappear from the bee's body?
>Most of these studies deal with acute exposures.
Not Suchail's, nor Cresswell's, nor Pettis', nor many others.
>
> >After that, I would ask you...How do bees benefit when they are
> *chronically* exposed to the neonics?
Why would you try to put such words into my mouth? I have never said that
bees "benefit" from exposure to neonics. However, some research suggests
that they perform increased foraging and broodrearing at low doses, similar
to humans amped up on coffee. Please be clear, I understand that the
neonics are insecticides, and by definition, are intended to kill insects.
i'm as concerned about them as anyone. That is why I am begging you to
help me understand their effects.
> > If IMI degrades withijn 72 hours (or any other degradation scenario) how
> does it matter if the bees are continually re-exposed? A continual renewal
> of a chemical that binds irreversibly to ACh receptors (within
> stoichiometric parameters) will continue to depolarize the neurons. What
> do you see that is different in this scenario?
>
As I've discussed with Tennekes and Sanchez-Bayo, your scenario is similar
to that of a human tobacco smoker. Every single day, a smoker is exposed
to a lethal dose of nicotine, yet can smoke for a lifetime and not die from
nicotine poisoning (they die from the unrelated tar). A smoker depolarizes
his neurons continuously, and feels withdrawal pangs when he stops doing
so. As I type these words, I am feeling the effects coming on from the
caffeine in my first cup of coffee. These effects are in part due to the
caffeine antagonizing the neurotransmitter adenosine, thus allowing higher
levels of ACh to depolarize the sodium gates in my neuronal synapses (as
you likely understand this far better than I). Yet I have no fear of dying
from caffeine toxicity when I have additional cups of coffee today. This
is because the effects are REVERSIBLE.
>
> >This is the way the neonics work in systemically treated crops...isn't it?
No. That's not correct at all! The product must be present at a high
enough concentration to cause toxicity--it is not a cumulative thing.
Aphids are quickly killed when they suck the juice of a young canola
plant, but do not die if the plant is past about a month old, since the
concentration in the plant is then below the lethal dose. If the effects
were indeed cumulative, the aphids would continue to die--it would just
take longer.
In the case of bees on that canola. Of the 52 weeks of the year, canola
only produces nectar and pollen for a few. Once the colony has consumed
those products, there would be no more exposure to the residues. In
general, the turnover of nectar and pollen is pretty quick in a hive,
although I readily allow that some may be stored for later use.
But all evidence that I've seen to date suggests that if the nectar and
pollen aren't toxic enough to kill the foragers, nurses, and mid aged bees
outright (all are involved in the processing of the raw products), that any
sublethal effects would be minor. Just look at the first results from Lu's
"Harvard" study. His colonies thrived when fed field-relevant doses of IMI
for four weeks--nearly the entire adult lifespan of a bee.
So Christina, I implore you to answer my question. Does the scientific
evidence support that Abbink's claim of "irreversible" binding appears to
have biological/neurological relevance to the extent that we would expect
to see (despite research and other observation to the contrary) cumulative
toxicity due to exposure to sublethal doses of IMI?
--
Randy Oliver
Grass Valley, CA
www.ScientificBeekeeping.com
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