Synergism of Insecticidal Action by Inhibition of Microsomal Oxidation with Phosphorothionates

Abstract

IN some resistant strains of housefly (Musca domestica) the activation rate in vitro of the phosphorothionates parathion and diazinon to the corresponding oxygen analogues as well as the detoxication of these analogues has been found to be larger than in susceptible strains¹. The activation reaction was measured by estimation of the amount of oxygen analogue formed. Their simultaneous degradation might lead to an underestimation of the activation, and we tried to measure this in mixtures with the thionate analogues. Surprisingly, degradation of the oxygen compounds was blocked by the thionates. This prompted a further study of inhibition of microsomal oxidations by these compounds and their possible synergistic activity. To avoid confusion it should be pointed out that the activity of the thionates on oxidative detoxication is distinct from the well known effect of S-alkyl phosphorothionates² which block hydrolytic detoxication enzymes³.