Greetings

As has been often pointed out, I have no University degrees in any subject. I never took any chemistry courses, not even in high school. Chemistry and molecular biology is so complicated these days that people in the same fields often cannot understand what the other is doing. The general public realizes this, and for the most part makes no effort to look into these matters. They tend to rely on self-appointed experts like myself to present the details in understandable form, because the real experts have a hard time boiling stuff down into plain talk. However, if you take the trouble to read their work, you can understand the key points. For example:

> Nicotine is more toxic to mammals than to most insects, and systematic structural changes have not greatly improved its potency or safety. The breakthrough discovery of the highly insecticidal but photolabile nithiazine ... led ultimately to photostabilized compounds selective for insects relative to mammals, commercialized as imidacloprid. They act as agonists at multiple nAChR subtypes, with differential selectivity between insects and mammals conferred by only minor structural changes. 

Comment:
Nicotine was used as an insecticide for many years. Nicotine is the toxin produced by tobacco plants to keep bugs from eating the leaves. The nectar and pollen, however, is not toxic to pollinators. Neonics were developed in the effort to find chemicals that killed insects but were less toxic to mammals, making them safer to handle and less likely to harm consumers eating the foods that may contain traces of these products. 

> Almost all insecticides used in the 1940s to 1980s were neurotoxicants, but this had dropped to 79% of the total world market value by 1990. Between 1997 and 2010, there was a marked shift from OPs and MCs to neonicotinoids accompanied by a distinct trend toward a variety of non-neuroactive insecticides.Although insect growth regulators, including insect hormone analogs or agonists and inhibitors of chitin synthesis, can be highly potent, effective, and selective, they act slowly in stopping crop damage, thereby limiting their role in pest control.

Comment:
The history of insecticide research has always moved toward smarter, safer products. It is absolutely true that we cannot foresee the long term fate of new products, nor could we have foreseen the impact of the older technologies. This cannot be used as an argument for not proceeding with research and development of new products, and the introduction of such products; the stakes are far too high.

> WHY NEUROACTIVE INSECTICIDES?
> Insecticides are principal defenses against insect pests of crops, livestock, pets, and people. Most insecticides are nerve poisons and have been since dichlorodiphenyltrichloroethane (DDT) and various polychlorocycloalkanes (PCCAs) were introduced in the 1940s, followed by organophosphates (OPs) in the 1950s, methylcarbamates (MCs) in the 1960s, pyrethroids in the 1970s, and neonicotinoids in the 1990s. Neurotoxicants are the major synthetic insecticides for several reasons. They act rapidly to stop crop damage and disease transmission. There are many sensitive sites at which even a small disruption may ultimately prove to be lethal. 

Comment:
When people hear the term "nerve poisons" they immediately think of biological warfare. Pesticides have to kill insects by some pathway. Going for the nervous system or the reproductive system are sophisticated approaches. The older methods such as application sulfur, arsenic or oil, have major side effects. Modern techniques tend to be smarter, more highly targeted, with less collateral damage.

The human condition is we're "between a rock and a hard place". The old expression "do something, even if it's wrong" has all kinds of negative connotations, of course. But we must not fall prey to inaction, either. I suggest: keep learning, keep trying to find out, keep an open mind, don't let other people think for you -- certainly not me. 

SOURCE
John E. Casida and Kathleen A. Durkin  (2013). Selectivity Mechanisms of Neurotoxic Insecticides. Annual review of entomology, 58(1).
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