Symptomatic and neurophysiological activities of new synthetic non-ester pyrethroids, ethofenprox, MTI-800, and related compounds

Abstract

Ethofenprox (MTI-500), MTI-800, and related compounds, which have a m-phenoxybenzyl moiety but lack ester bonding, were compared with DDT-type compounds and pyrethroid insecticides for their lethal and convulsive activities toward American cockroaches. The most potent among them ranked between phenothrin and cyphenothrin. Neurophysiological effects were also examined by extra- and intracellular recording and voltage clamp techniques. Some derivatives induced repetitive discharges in the excised central nerve cord of the American cockroach. The after-potential recorded intracellularly from the crayfish giant axon was markedly increased by some compounds. Voltage clamp experiments with the crayfish giant axon showed that ethofenprox decreased the peak sodium current and induced a large residual current during a step depolarization. It also induced a large and prolonged tail current after a step repolarization of the membrane. The effects of the test compounds on the action potential and the sodium current were similar to those of DDT-type compounds and the pyrethroids such as allethrin and phenothrin. A shift of sodium channel population from normal to modified was thought to result in modifications of the sodium current which, in turn, cause the increase in after-potential and the induction of repetitive discharges.