Inhibition of AChE from Phenthoate-Selected Diamondback Moth, Plutella xylostella (Lepidoptera: Yponomeutidae)

The Inhibition of AChE activity was compared between susceptible and phenthoate resistant diamondback moth (DBM) using in vitro enzyme assay and native Polyacrylamide gel electrophoresis (PAGE). Dichlorvos and carbofuran were very effective to inhibit the AChE activity from S strains with I50 values of 0.38 and 0.21 μM, respectively. However, the AChE from R strain was much less inhibited to dichlorvos, i.e. insensitive to dichlorvos with R/S ratio of 11.4, than phosphamidon, BPMC, and carbofuran with the R/S ratio of 2.8, 4.2, and 2.5, respectively. Direct-staining of native gel revealed that the majority of AChE from S strain was quickly deactivated by 50 μM of dichlorvos that was the lowest concentration of the inhibitor in the experiment. However, the AChE activity from R strain was not fully inhibited by 500 μM of dichlorvos. This result was confirmed in the repetitive experiment with head extracts of both strains separately prepared with three replications. In the incubation of AChE with 100 μM of dichlorvos on native gel, the AChE from R strain was apparently insensitive to the inhibitor in contrast to the fully inhibited AChE from S strain.