STRUCTURE-ACTIVITY-RELATIONSHIPS OF PYRETHROIDS BASED ON DIRECT ACTION ON NERVE

The structure-activity relationships of 30 synthetic pyrethroids have been studied by measurements of their direct action on isolated crayfish nerve cord. The concentrations of pyrethroids used to increase the frequency of spontaneous discharges to 200% of the control (NS200), those to decrease the frequency back to the control level, and those to further decrease the frequency to 10% of the control were measured as indexes of the nerve action. These values did not necessarily run parallel with those for the lethal dose 50 or the knock-down 50. Large differences in NS200 were found among optical isomers of tetramethrin and phenothrin, and there was a synergism with respect to the nerve stimulating action between (+) and (-) forms of tetramethrin. (+)-trans-Permethrin was unique in that it exhibited a potent insecticidal action with a very weak nerve action. It is necessary to compare the direct action on the target site for the purpose of establishing the true structure-activity relationships of synthetic pyrethroids. © 1978.