STABILITY AND BIOLOGICAL-ACTIVITY OF CYFLUTHRIN ISOMERS

A GO-MS method capable of completely separating the four pairs of dias tereoisomers of cyfluthrin is presented and the method used to show th at isomerisation of the cyfluthrin enantiomers occurs in methanol. Thi s methanol-induced isomerisation could also be demonstrated by bioassa ys using water fleas. The biological activities of the various cyfluth rin isomers contained in the commercial products cyfluthrin and beta-c yfluthrin were assayed using several strains of lepidopteran larvae in cluding Plutella xylostella, Heliothis virescens and Spodoptera frugip erda. With the susceptible strains, the efficiencies of the isomers mi xtures of cyfluthrin and beta-cyfluthrin were shown to obey the rules of additivity. However, in tests with a resistant strain of P. xyloste lla originating from Thailand, the 'inactive' isomer III acted synergi stically with the active isomer IV. Resistance factors in strains of H . virescens and P. xylostella were found to be higher with cis than wi th trans isomers. This probably contributes to the superior action of cyfluthrin and beta-cyfluthrin against various pests of agricultural i mportance since the commercial products contain a high content of tran s isomers ('high trans pyrethroids').