Pyrethrins and Pyrethroid Insecticides
Pyrethrum is one of the oldest and most widely used botanical insecticides and its insecticidal properties have been known for more than 150 years. The commercial limitations of pyrethrum extracts, which are collectively known as pyrethrins, have long been recognized because of their high rate of photodegradation and a short “knockdown”(rapid paralysis) effect. After the discovery of the constituents of pyrethrins, researchers searched for derivatives of pyrethrins that had a higher resistance to photodegradation. This search directly led to the synthesis of pyrethroids. The advantages of pyrethrins and pyrethroids in pest management are that they are highly lipophilic, have a short half-life in the environment, have a low terrestrial vertebrate toxicity, and do not biomagnify like older chemical classes such as organochlorines. This chapter reviews the chemistry, mode of action, metabolism, environmental fate, and human-health and environment risks for pyrethrins and pyrethroids.