Study On Monitoring And Mechanism Of Insecticide Resistance Plutella Xylostella (L).

Plutella xylostella(L).is a worldwide distributed polyphagous pest on various cultivated crops, including vegetables, cotton, fruittrees, ornamentals, and so on. In past two decades. Exigua has emerged as a serious pest in many countries. Resistance to 9 insecticides in six field populations of Plutella xylostella (L), was evaluated in laboratory. Resistance to fenvalerate is the most.Biochemical mechanism of resistance in Plutella xylostella (L) to fenvalerate has been investigated by enzyme synergists (PBO, SVI, DEF and DEM) and enzyme activities assays of esterase , glutathione S-transferase and microsomal O-demethylase. The synergism ratios of PBO, SV,, DEF and DEM to cyhalothrin were 3.2, 1.8, 2.8 and 1.9folds in susceptible strain, respectively; 50.5, 20.5, 8.8and4.6-fold in resistant strain, respectively. Ratios between resistant and susceptible strain were 15.8, 11.3, 3.1 and 2.4 folds, respectively. The result shows that synergism to fenvalerate by PBO was the most distinct. This implied that mixed-function oxidase was involved in the resistance to fenvalerate. Synergism to fenvalerate by DEF and DEM was not much significant. The ratios of enzymatic activity of esterase, glutathione S-transferase and microsomal O-demethylase in susceptible and resistant strains were 1.08, 1.02, 1.13-fold, respectively, no significant difference. All these indicated that detoxification enzymes such as esterase, glutathione S-transferase and microsomal O-demethylase contributed little to the resistance of beet armyworm to fenvalerate.