pyrethroid

Pyrethroids are a class of synthetic insecticides designed to mimic the natural pyrethrins produced by chrysanthemum flowers. They are more stable in light and generally more potent than their natural counterparts, and they are widely used in agriculture, public health, and consumer and veterinary products.

Most pyrethroids act on the nervous system by prolonging the opening of voltage-gated sodium channels in nerve cells, causing repeated firing, paralysis, and death of insects. They are typically categorized as Type I (lacking an alpha-cyano group) or Type II (containing an alpha-cyano substituent).

Common examples include permethrin, deltamethrin, cypermethrin, lambda-cyhalothrin, fenvalerate, and bifenthrin. They are formulated as emulsifiable concentrates, wettable powders, dusts, granules, and microencapsulated products for use on crops, in stored-product protection, and in residential and veterinary pest control, including ectoparasite management in animals.

Toxicity in mammals is relatively low compared with many older insecticides, because mammals detoxify pyrethroids efficiently. However, high-level exposure can cause neurologic symptoms. Pyrethroids are more toxic to aquatic organisms and to bees and other non-target insects, especially when residues enter water or flowers. Resistance can arise via mutations in sodium channels or enhanced metabolic detoxification.

Environmental fate varies by compound and formulation; many pyrethroids degrade rapidly in soil and water but can persist in sediments. They are subject to regulation and stewardship to minimize non-target effects, and usage often includes considerations of formulation choice, crop type, and pollinator protection.