Lethal Effects of Abamectin and Propargite on Moghan Population of Two Spotted Spider Mite, Tetranychus urticae Koch (Acari, Tetranychidae), and Efficacy of Their Residual Effects on the Bean Plants

For assessing the lethal effects of abamectin and propargite on Moghan Population of Tetranychus urticae and persistence of their lethal effects on the bean plants, adult mites were treated in separated experiments. Leaf disks of bean plant were prepared and leaf dipping method was used for bioassays. Five concentrations of each acaricide were provided and 20 adult mites were used for each concentration in each replication and the experiment was replicated three times for each acaricide component. Unit of replication was a Petri dish including a bean leaf piece (2 cm ×2 cm) treated with acaricide concentration with ventilated lid which lined with water soaked cotton and 20 mites were placed on the leaf piece. Mite mortality was recorded 48 h post treatment. For evaluating the persistence of lethal effects of the acaricides on bean plants against T. urticae, bean plants were sprayed with concentration of twentieth of recommended field dose of each acaricide component, separately. Leaf disks were prepared from treated plants in different time intervals including 1, 3, 7, 10 and 21 days after treatments. 20 adult mites were transferred on each of the leaf disks and their mortality was recorded 48 h post transfer. The experiment was repeated three times and distilled water was used as control. Probit analysis of lethal experiment data revealed that LC20, LC50 and LC90 values were 0.108, 0.417 and 3.26 ppm for abamectin and 0.657, 2.26 and 14.90 ppm of commercial material for propargite, respectively. Evaluating the persistence of lethal effects of the acaricides on the bean plants revealed that mite mortality was 100% at 1 day after plant spraying for abamectin which decreased to 55.62% in 21 days after spraying. While, mite mortality was 81% in 1 day after plant spraying for propargite which decrease to 0% in 21 days after spraying.