Species and structural variations affecting pyrethroid neurotoxicity.

Pyrethroids provide fascinating patterns and examples of species selectivity resulting from variations in nerve sensitivity and detoxification rates. Three classification systems are useful in considering pyrethroids: origin, structure, stability and use relative to the natural pyrethrin I; lethal and sublethal or knockdown agents; Types I and II symptoms and nerve action. Pyrethroid-detoxifying esterases and oxidases contribute importantly to the species and strain specificity and provide an opportunity to use inhibitors as synergists for improved effectiveness. Pyrethroids are potent and selective neuropharmacological agents inducing repetitive discharges or conduction block in a variety of sensory and motor nerves and in the CNS. Small structural modifications in the pyrethroid often change the type of action as well as the potency and species specificity. Pyrethroid resistance in selected strains of insect pests may involve a modified and pyrethroid-insensitive target site.