Resmethrin

Resmethrin is a pyrethroid insecticide with many uses, including control of the adult mosquito population.

The resmethrin molecule has four stereoisomers determined by cis-trans orientation around a carbon triangle and chirality. Technical resmethrin is a mixture of (1R,trans)-, (1R,cis)-, (1S,trans)-, (1S,cis)- isomers, typically in a ratio of 4:1:4:1. The 1R isomers (both trans and cis) show strong insecticidal activity, while the 1S isomers do not. The (1R,trans)- isomer is also known as Bioresmethrin,(+)-trans-Resmethrin, or d-trans-Resmethrin; although bioresmethrin has been used alone as a pesticide active ingredient, it is not now registered as a separate Active Ingredient (AI) by the U.S. EPA. The (1R,cis)- isomer is known as Cismethrin, but this is also not registered in the U.S. for use alone as a pesticide AI.