Synthetic Pyrethroids: A brief introduction.

Synthetic Pyrethroids

An insecticide is a substance which destroys insects by a chemical reaction.

Some insecticides affect the nervous systems, others oxygen metabolism, water balance, maturation process or other aspects of physiology. Pyrethroids affect the primary, nervous systems.

The earliest insecticides were of natural origin. Widespread use during  the 19th century of arsenic compounds proved the value of insecticides to agriculture. Since the 1940s chemists have invented hundreds of insecticides by synthesizing compounds such as chlorinated hydrocarbons and organic phosphates. The industry took a move towards increased development of natural insecticides in the 1990’s, which hit its balance with the Pyrethroid class of insecticide. Pyrethroids balance the effective toxicity of synthesised compounds with a base in naturally occurring insecticides, making the pyrethroid family of insecticides widely considered the safest of all man-made insecticides.

Pyrethrins are pesticides found naturally in chrysanthemum flowers, particularly the African Chrysanthemum. They are a mixture of six chemicals which are toxic to insects. The insecticidal properties of pyrethrins are derived from ketoalocholic esters of chrsanthemic and pyrethroic acids, these acids are strongly lipophilic and rapidly penetrate many insects to paralyze the nervous system.

Early pyrethroids were synthesized by chemists studying the structure of pyrethrins as a base model, with the addition of synergists their chemical effect while mimicked was substantially increased, making a more potent and longer lasting insecticide with increase stability in light and longer half-lives. Cypermethrin is one of a handful of light stable synthetic pyrethroids, with a long half-life even in direct sunlight. Of the synthetic Pyrethroids, permethrin resembles pyrethrins closest chemically, however it is chlorinated to increase its stability making it stable even when exposed to ultraviolet light.

How do Pyrethroids work?

Pyrethroids interfere with the ionic conductance of nerve membranes by prolonging the sodium current, this stimulates nerves to discharge repeatedly leading to hyper excitability. As such Pyrethroids are classed as a neuropoison/toxin acting on the axons in the peripheral and central nervous system through interaction with the sodium channels.