Resistance mechanisms of a field population of diamond back moth, Plutella xylostella (Lepidoptera: Plutellidae) to current organophosphate pesticides

The toxicological and biochemical properties of four organophosphate (OP) insecticides, chlorpyrifos, diazinon, phosalone and dichlorvos, were examined in terms of the diamond back moth, Plutella xylostella (L.) susceptible (Gu-S) and resistant (Kar-R) to OPs. The Kar-R population had significantly high resistance to chlorpyriphos (69.3 fold), medium resistance to diazinon (14.49-fold) and phosalone (10.3-fold), and had less resistance to dichlorvos (5.17-fold) compared to Gu-S population. DEM and TPP reduced Chlopyrifos resistance of Kar-R population as an inhibitor of glutathione S-transferase (GST) and esterases (EST), respectively. Biochemical studies clarified that GST and EST kinetic parameters in the Kar-R population were significantly higher than parameters of Gu-S population. Moreover, this study examined the Kinetics of hydrolysis of acetylthiocholine iodide, butyrylthiocholine iodide as artificial substrates by AChE of resistant and susceptible population. IC50 of monocrotophos, neostigmine bromide and eserine were also determined on AChE of resistant and susceptible populations. Kinetic analysis and inhibition tests indicated that an alteration in AChE of Kar-R population has an effect on both kinetic and inhibition results. The results distinctly showed that multiple mechanisms such as GST, esterases and altered AChE created chlorpyrifos resistance in the Kar-R and insensitivity of AChE is a significant factor for resistance to conventional OP compounds.