Pyrethroid insecticides, mechanism classed

Pyrethroids have low oral toxicity to mammals, and in general their insect (topical) to mammal (oral) toxicity ratio is much higher than that of the other major classes of insecticides [25]. As the reason, at least the following mechanisms are conceivable (1) negative temperature dependence - differences in body temperature between insects and mammals makes the insect nerves much more sensitive, (2) metabolic rate - insects metabolize the insecticide more slowly than mammals, and the metabolizing enzyme systems are different, and (3) differences in body size - insects will have less chance to metabolize the insecticides before reaching the target site [26]. 

The fact that nature has chosen to use a cyclopropane skeleton to design a defense mechanism for certain pyrethrum flowers against insect attack has been known since 1924, when Staudinger and Ruzicka isolated and characterised (-t-)-Jrans-chrysanthemic acid 1 from the petals of these plants [1]. The active insecticidal ingredients in these plants are in fact esters of 1, which can be easily modified and which have been commercially exploited to give birth to one of the most successful classes of biomimetic insecticides, the pyrethroids. In 1997, the market value of this class of insecticides amounted to a staggering 1.5 billion US [2],... 

Abundant use of one of the most commonly used insecticides in crop protection, pyrethroids, has led to the development of resistance in many insect species.One of the most important mechanisms is that of knockdown resistance (kdr), caused by several mutations in the gene (L1014F and M918T), which confers crossresistance to the entire class of pyrethroids. Another problem is that most insecticides cause toxicity in organisms other than insects because of the general conservation of the voltage-gated Na" " channel structure... 

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