ABSTRACT
These two groups of insecticides have a number of features in common, and there are advantages in describing them both in a single chapter. As has already been explained, both of them are derived from natural products that have insecticidal activity (Chapter 3). Pyrethroids are related to naturally occurring pyrethrins that are found in Chrysanthemum species. At one time pyrethrum, a preparation made from the flowering heads of these plants and containing natural pyrethrins, was used quite extensively as an insecticide. It came to be replaced by the analogous synthetic pyrethroid insecticides, which are more stable, both chemically and biochemically, than the natural product. Nicotine, another naturally occurring compound, was also once used as an insecticide. Commercially produced nicotine insecticide was extracted from tobacco plants (Nicotiana tabacum), which are rich in the chemical. Subsequently, the neonicotinoid insecticides were developed, which bear a structural resemblance to nicotine and express toxicity through the same mechanism. Like the synthetic pyrethroids, these are more effective insecticides than the natural products to which they are related.
