Biochemical Mechanisms and Cross Resistance Patterns of Chlorpyrifos Resistance in a Laboratory-Selected Strain of Diamondback Moth, Plutella xylostella (Lepidoptera: Plutellidae)

Diamondback moth (Plutella xylostella) is a serious pest of cruciferous vegetables worldwide. In Iran, it is commonly controlled by using chlorpyrifos. Due to a range of biochemical and behavioral features, this pest can rapidly develop resistance to many insecticides from different groups. To achieve a better resistance management plan, a chlorpyrifos resistant strain of P. xylostella was selected under laboratory conditions and its cross resistance to five other insecticides and resistance characteristics were investigated. After 15 generations of selection, the selected strain (CLRS) developed 39.61-fold higher resistance to chlorpyrifos in comparison with susceptible strain (AL). CLRS exhibited 19.62-, 17.84-, 3.43- and 3.33-fold cross resistance to hexaflumuron, indoxacarb, thiodicarb and flubendiamide, respectively, but showed no cross resistance to abamectin. Synergism and biochemical studies suggested potential involvement of Esterase (EST) in CLRS. However, no difference was seen for Glutahion-S-Transferase (GSTs) and Mixed Function Oxidase (MFO) in CLRS and AL strains. To determine the role of AcetylCholinEsterase (AChE) insensitivity in resistance mechanism, Kinetic parameters (Km and Vmax) and inhibitory effect of chlorpyrifos-oxon on this enzyme were evaluated. Affinities and hydrolyzing efficiencies of AChE in CLRS were higher than AL. This enzyme in CLRS was also less sensitive to inhibition by chlorpyrifos-oxon. Results indicated that chlorpyrifos resistance exhibited cross resistance to other insecticides from different classes and enhanced EST activity and AChE insensitivity were probably the main factors in chlorpyrifos resistance. These results can help the users of insecticides and can delay the resistance development of P. xylostella.