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ABSTRACT
In this study the esterases involved in abamectin resistance have been characterized from the two-spotted spider mite, Tetranychus urticae Koch. The resistant strain of T. urticae showed ≥ 3000-fold resistance to abamectin compared with the susceptible strain. Enzyme assays revealed that esterase activity in the resistant strain was 2.14-fold and 1.33-fold higher than that of the susceptible strain when α-naphthyl acetate (α-NA) or α-naphthyl propionate (α-NP) was used as substrate, respectively. In contrast, there was no significant difference in the enzyme activity among the resistant and susceptible strains when β-naphthyl acetate (β-NA) or α-naphthyl butyrate (α-NB) were used as substrate. Km and Vmax values of the resistant strain to α-NA were 1.43 and 1.68 times lower and higher than that of susceptible strain, respectively. The results showed a significant difference in the esterase patterns and abamectin and rosemary essential oil showed a potent inhibitory effect on esterase in resistant and susceptible strains. The optimum temperature (30°C) and optimum pH (pH 6.5) for relative activity of esterase for both strains is the same. The effects of different concentrations of several reagents on the relative activity were also investigated.
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ACKNOWLEDGEMENTS
The authors express their gratitude to the research council of the University of Guilan and Ministry of Science, Researches, and Technology for financial support during the course of this project.