I'd like to respond to Peter's comments of some days ago, now that it is Friday night and I can pay attention to them:
I said:
> If insect response to neonicotinoids is similar to the nicotinoid response by vertebrates (and why not),
Peter says:
Why not is because they are insects, not mammals. There is absolutely no reason to suppose that it would be the same
Well Peter, you are wrong. Neonics are in the same class of compounds as nicotine, and the response by insects and humans to each is similar in nature although not in dosage. I thought most people on this list would know this...I just didn't have a reference on insects "to hand". Guess I spend too much time with other physiologists!!!
Imidocloprid (and other neonics) acts as an agonist on the postsynaptic nicotinic acetylcholine receptors of motor neurons in insects . This interaction results in convulsions, paralysis, and eventually death of the poisoned insect.
--Yamamoto, I.; Casida, J.E. (1999). Nicotinoid Insecticides and the Nicotinic Acetylcholine Receptor. Springer. ISBN 443170213X.
Bayer gives the following symptoms of human imidocloprid poisoning (ConfidorŪGuard Soil Insecticide) in its online MSDS information: Systemic:Symptomatic (nicotine-like effects). Check blood pressure and pulse rate frequently, as bradycardia and hypotonia are possible. Provide supportive measures for respiratory function and cardiac action. Give artificial respiration if signs of paralysis appear.
Nicotine acts as a nicotinic acetylcholine receptor agonist in humans (for reference, check any pharmacology handbook). That's exactly the same effect as found in the insect. Human nicotinic ACh receptors are found on all peripheral motoneurons, and they are also on autonomic presynaptic neurons as well as neurons of the central nervous system. Fundamentally, we aren't all that different from insects, Pete. Slight molecular (shape) differences make bees more susceptible to neonics than people are...they kill us too but at a much larger dose. Nicotine, on the other hand, is more toxic to humans and it kills insects in the same manner. My grandfather used tobacco smoke to treat his cactus plants back in the '30s.
I said:
> the toxic threshold would continue to be reached in spite of any increased threshold (adaptation).
Peter said:
I think the use of the word adaptation is unhelpful here. I believe you are referring to the development of tolerance.
In physiology, we call changes in cellular responses to ligands "adaptation".
I said:
> However, if bees adapt as verts do, they will become "addicts" and tolerate much higher doses
Pete said:
This is erroneous. Organisms develop tolerance to plenty of substances. Addiction is a completely separate phenomenon (which may also include tolerance).
I put "addicts" in quotes, for that reason.
I said:
> At that point of high tolerance, taking the drug AWAY is more "harmful" in the short term than continuing to feed the addiction.
Pete said:
This is a non-sequitir. We don't know if insects become addicted to pesticides.
I didn't claim that insects become addicted. I am suggesting that it could happen, that is my next statement (below);
> I just don't know if insects react the same way.
Peter responds:
Very small changes on the molecule make enormous differences. Neonicotinoids are not the same as nicotine. Take the example of ethanol and methanol. Very similar molecules; very different properties. The neonics were developed precisely to exploit the fact that they do NOT produce the same effects in mammals as insects.
In summary: This is baloney. They do have exactly the same effect, but at a much lower dose because the affinity they have for the nicotinoid receptors in insects is greater than the affinity they have for the nicotinoid receptors in humans. This is what your next statement says:
> Neonicotinoid insecticides display excellent selectivity profiles that are largely attributable to specificity for insect versus mammalian nAChRs (Nicotinic acetylcholine receptors).
Christina
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