Acaricidal and sublethal effects of the biopesticide RequiemEC (containing an essential oil extract of Chenopodium ambrosioides near ambrosioides) on the two-spotted spider mite, Tetranychus urticae Koch, were evaluated in laboratory bioassays. The biopesticide was applied to bean leaves or leaf discs using a Potter spray tower. Acaricidal activity against eggs and immatures was evaluated in successive acute toxicity bioassays. Concentration-mortality data were subjected to probit analysis and the following LC values (ml/l) were calculated: 2.47 (eggs), 0.71 (larvae), 1.13 (protonymphs), 2.23 (female deutonymphs), and 6.02 (female teleiochrysalises). In adult bioassay, in which pre-ovipositional females were treated with a series of concentrations (0.31-10 ml/l), a run-off effect ranging 4-80% (after 24 h) and 8-93% (after 72 h) was observed. In two-choice bioassay, T. urticae females preferred the untreated halves of leaves over the halves treated with 1.25-10 ml/l biopesticide and they laid significantly more eggs on the untreated halves in the first 24 h and summed over 72 h. The indices of repellency and oviposition deterence ranged 11.2-77.3 and 14.8-87.9%, respectively. In age-stage two-sex life table bioassay, the females that hatched from eggs treated with 2.5 ml/l biopesticide and reached adulthood on treated leaf surface showed a significantly reduced the intrinsic rate of increase (r = 0.222), compared to the control (r = 0.317). The reduction of population growth was mainly due to a reduced preadult survival rate (0.42 ± 0.04) and extended juvenile developmental time (9.27 ± 0.11 days), compared to the control (0.93 ± 0.03 and 7.70 ± 0.06 days, respectively).

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Spirodiclofen is characterized by a relatively slow acaricidal action against adult females of the two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), with reduction of their fecundity (eggs laid/female) and fertility (eggs hatched/female). Exposure of pre-ovipositing T. urticae females to the acaricide may affect population growth, considering that a high reproduction of young females is crucial in the population biology of this colonizing species. Effects of spirodiclofen on life-history traits and population parameters of T. urticae were evaluated in demographic bioassay using the age-stage two-sex life table, constructed in fecundity-based and fertility-based variants. The acaricide was applied against pre-ovipositing females in a series of nine concentrations, starting from the recommended field rate (96 mg/l). The treatments with concentrations ranging from 12 - 96 mg/l significantly reduced fecundity and longevity, while 27 - 40% of females didn’t lay eggs. Exposure was lethal to 2 - 21% of the females, of whom a large majority didn’t lay eggs. A considerable part of surviving females also failed to lay eggs within the first four post-treatment days (when around 50% of all eggs in the control were laid) i.e., they were sterilized by the acaricide. At the same time, the percentage of dead females rose to 17 - 55%, mainly due to the mortality of sterilized females. The three highest concentrations (24 – 96 mg/l) significantly reduced the net reproductive rate (R₀), intrinsic rate of increase (r) and finite rate of increase (λ), by 49-72%, 20-34%, and 4-6%, respectively, compared to the control. This reduction was mainly the result of sterilization and high mortality of treated females, in combination with reduced fecundity and longevity of reproductive ones. Application of the fertility-based life table showed significant decrease of r and λ (by 23-40%, and 4-7%, respectively, compared to the control), in the treatments with the three highest concentrations. The short-lived transovarial toxic effect observed in the fertility-based life table was not sufficient to cause a significant reduction in population parameters, compared to those acquired by the fecundity-based life table.