Degradation of malathion and pyrethroids by the mites Rhizoglyphus robini and Tetranychus urticae

Abstract

1. Degradation of malathion by diisopropyl fluorophosphate (DFP)-sensitive esterases is much faster in Tetranychus urticae as compared to Rhizoglyphus robini. The apparent values of K m and V max, kinetic parameters for T. urticae are 0.23 mM and 21.7 nmole min −1 mg −1 protein while for R. robini the values are 0.11 mM and 5.6 nmole min −1 mg −1 protein. 2. Based on the inhibitory effects of organophosphorus compounds such as DBF, DFP and profenofos, hydrolysis appears to be the major metabolic pathway for permethrin, cyfluthrin and fenpropathrin. The considerable inhibition of cyfluthrin by piperony butoxide indicates the involvement of microsomal oxidation in pyrethroid degradation. Levels of cytochrome P-450 and b 5 as well as the epoxidation rate of aldrin in the microsomal fraction of R. robini were determined. 3. Trans and cis isomers of permethrin are degraded much faster by T. urticae than by R. robini. Both isomers are extensively degraded as compared to cyfluthrin and fenpropathrin. Similar to other organisms, the two mite species degrade trans-permethrin much more rapidly (about 2-fold) as compared to the cis isomer. 4. The faster degradation rates of malathion and permethrin by T. urticae may reflect history of continuous pesticide use to control this spider mite.