pyrethroids

Pyrethroids are a class of synthetic insecticides modeled after the natural pyrethrins produced by chrysanthemums. Chemically, they are ester derivatives of chrysanthemic acid or pyrethric acid combined with various alcohol moieties. They are commonly divided into Type I, which lack the alpha-cyano group, and Type II, which carry an alpha-cyano substituent.

Mechanism of action: Insects' nervous systems are targeted by prolonging opening of voltage-gated sodium channels, causing extended nerve impulses, paralysis, and death. Type II pyrethroids often produce additional motor symptoms such as choreoathetosis and salivation.

Toxicology and safety: Pyrethroids are generally more toxic to insects than to mammals due to faster detoxification by mammalian enzymes (carboxylesterases and cytochrome P450s). Acute human toxicity is typically low, but high exposure can cause nervous system symptoms (tremors, dizziness, seizures in severe cases). They are also toxic to aquatic organisms and can affect bees, depending on the compound and exposure conditions.

Environmental fate and regulation: Pyrethroids degrade relatively quickly in sunlight through photolysis and hydrolysis, though some persist in soil or sediment. Their use is subject to regulatory controls in many countries, including residue limits and safety labeling by agencies such as the US Environmental Protection Agency.

Uses and examples: They are widely used in agriculture, public health, veterinary medicine, and household pest control. Notable examples include permethrin, deltamethrin, lambda-cyhalothrin, cypermethrin, and cyfluthrin; etofenprox is sometimes classified separately as a non-ester pyrethroid.