Effect of sublethal concentrations of avermectin on population parameters of Tetranychus urticae (Acari : Tetranychidae) on strawbery

摘要

Experiments were carried out under laboratory conditions to determine the effect of sublethal concentrations of avermectin on population parameters of the two-spotted spider mite Tetranychus urticae Koch. Initially, a series of bioassays were developed to determine the lethal concentration of avermectin. Bioassays were performed using the immersion technique exposing mites to seven different concentrations of the product. Once the mortality-concentration curve was obtained, concentrations of 0.04 and 0.18 ppm. were selected corresponding to the LC10 and LC35, respectively. With these concentrations, the second stage of the experiment which consisted of analyzing populations of mites exposed to these concentrations and comparing them to a control population, was performed. To achieve Us, mites were exposed to strawberry leaves treated with avermectin. The results indicated that concentrations of 0.04 and 0.18 ppm. avermectin had a significant effect on population parameters of T urticae compared with the control. With the concentration of 0.04 ppm, the intrinsic rate of increase (r(m)) was 0.3001, the net reproductive rate (Ro) 31.6430, the generation time (T-G) 11.510 days and the duplication time (t(2)) 2.3095 days, while the control population showed values of 0.2816, 30.150, 12.094 and 2.4611, respectively, for these same parameters. The above results indicate that more vigorous populations emerged after avermectin treatment at 0.04 ppm. compared to those derived from non treated individuals. At the higher concentration (0.18 ppm), avermectin caused a considerable decrease in all of the population parameters with 0.1581 for r(m) 7.20 for Ro, 12.4880 for T-G and 4.3847 for t(2).