Resistance mechanisms of the two-spotted spider mite, Tetranychus urticae (Acari: Tetranychidae) populations to fenpyroximate

The two-spotted spider mite, Tetranychus urticae (Acari: Tetranychidae) is one of the most important pests of field crops, orchard trees and ornamentals around the world. The short life cycle, high reproductive potential, accompanied by frequent acaricide applications have caused resistance development to wide range of acaricides. In this study the susceptibility of two populations, collected from Karaj and Mahllat, was investigated against fenpyroximate. The bioassay test was carried out by using the leaf-dip method. The results showed that the LC50 values for Karaj and Mahallat population were 2.1 and 92 (mg/ml), respectively. The resistance ratio was 43.8. The enzyme assay results revealed that the activity ratios of esterase in Mahallat to Karaj populations were 2.5 and 1.2 when α-NA and β-NA were used as a substrate, respectively. The activity of cytochrome P450 in Mahallat population was 1.37 times higher than the Karaj population. There was no significant difference in glutathion S-transferase activity between the two populations. The gene expression (qRT-PCR) results showed that the expression level of CYP392A11 in Mahallat population was 3.52 times higher than Karaj population. These results suggested that esterase and cytochrome P450 monoxygenase are probably involved in resistance of T. urticae to fenpyroximate.