How sublethal concentrations of Bifenazate affect biological parameters of Tetranychus urticae (Acari: Tetranychidae) at laboratory conditions

In the present study, sublethal effects (LC10=21, LC20=52 and LC30=100 ppm) of Bifenazate (Floramite® 24% SC) on biological parameters of the most important phytophagous mite, Tetranychus urticae Koch, was evaluated under laboratory conditions. Data analysis was performed using Age-stage two sex life table theory. Our results revealed that immature development of treated deutonymphs of T. urticae was not significantly affected by sublethal treatments. Female longevity was affected by sublethal concentrations and the highest value for this period was recorded at control (23.36 day). Furthermore, total fecundity was also negatively affected in female mites developed from treated deutonymphs and the lowest value was obtained at LC30 (27.02 egg). We also present data supporting that the sublethal effects could carry over to the next generation. Accordingly, sublethal concentrations reduced the net reproductive rate (R0), and there were significant differences among the values of this parameter at all treatments tested when compared with control (control=57.93, LC10=49.17, LC20=41.50 and LC30=32.87 offspring/individual). The intrinsic (r) and finite (λ) rates of increase were also significantly lower in mites treated with sublethal concentrations. The highest estimated values for r and λ were recorded at control (0.208 and 1.232 day-1,respectively). Finally, with the reduce rate of development observed for individuals treated with sublethal concentrations, the mean generation time (T) was significantly higher in individuals exposed to any concentration tested (control=19.48, LC10=19.80, LC20=20.10and LC30=19.45 day). Our data underline the importance of considering the role of sublethal effects when attempting to evaluate the total impacts of specific pesticide on an insect pest population and its progeny.