Studies on Selection and Resistance Mechanism by Some Acaricides in (Two Spotted Spider Mite, Tetranychus urticae)

The progress of resistance was evaluated in susceptible strains of Tetranychus urticae to several chemicals, including Fenpyroximate, Cyhalothrin, Abamectin, and Ethion, and to measure the specific activity of Acetylcholine esterase (AChE) and Glutathione-S-transferase (GST) enzymes under laboratory conditions to understand the resistance mechanisms. The resistance levels to Fenpyroximate showed significant variability over two generations, with the ninth and tenth generations exhibiting high resistance levels of 65.63 fold and 76.73 fold, respectively. Resistance to Cyhalothrin increased over ten generations, achieving a 36.63-fold resistance. Abamectin resistance gradually rose, reaching 138.44-fold by the tenth generation. For Ethion, the ninth and tenth generations demonstrated resistance levels of 70.27-fold and 91.99-fold, respectively. The results indicated that the AChE enzyme's specific activities were significantly lower in the susceptible strain, with notable differences among the compounds. The Cyhalothrin-resistant strain of T. urticae exhibited the highest specific AChE activity at 2.23, compared to 0.83 in the susceptible strain. Conversely, the Abamectin-resistant strain showed the lowest specific AChE activity at 1.18. Ethion and Fenpyroximate significantly reduced AChE activity to 1.82 and 1.83, respectively. Additionally, higher GST activity in all resistant strains of T. urticae compared to the susceptible strain.