Laboratory bioassays were conducted to evaluate the effects of spiromesifen on gross fecundity, gross fertility, net fertility and population growth of two-spotted spider mite (Tetranychus urticae Koch) after treatments with four acaricide concentrations: 180 mg/l, i.e. maximum recommended concentration for use in glasshouses against spider mites, 18, 1.8, and 0.18 mg/l, i.e. concentration discriminative for eggs and immatures in preliminary studies which produced 100% mortality of these stages. Quiescent female deutonymphs were treated in the first assay, and young pre-ovipositing females in the second and third, in which exposure lasted 6 h and 20 h, respectively. In the first assay, the 180, 18, and 1.8 mg/l concentrations significantly reduced gross fecundity (61-85%), gross fertility (64-87%) and net fertility (85-94%) of the surviving females. In the second one, only the highest concentration achieved a significant statistical reduction in gross fecundity (52%), gross fertility (67%) and net fertility (84%). In the third assay, fecundity and fertility reduction under the two highest concentrations was 98-99% and 93-98%, whereas it was 50-74% under the 1.8 mg/l concentration, and statistically different from control values. In all three trials, treatments with 180, 18, and 1.8 mg/l concentrations significantly reduced the instantaneous rate of increase. In the third assay, treatments with the two highest concentrations caused population decline. Sublethal activity of the 0.18 mg/l concentration was not found in any assay to be statistically significant. Sublethal effects of spiromesifen and its impact on T. urticae management are discussed.
Acute toxicity of spirotetramat to immatures and its sublethal effects on adult females of two-spotted spider mite, Tetranychus urticae Koch, were investigated in laboratory bioassays, at 27 ± 2°C, 50–80% RH and 16/8 L/D photoperiod.Acute toxicity was tested by successive treatments of eggs, larvae, protonymphs and deutonymphs on bean leaf discs, and mortality was evaluated based on the number of mites reaching the adult stage. Concentration-mortality data were subjected to probit analysis and the following LC50 data were computed: 0.10 mg/l (larvae), 0.17 mg/L (protonymphs) and 0.15 mg/L (deutonymphs). The acaricidal effect after the treatment of eggs was not the result of spirotetramat toxicity to this developmental stage, but rather of its residual activity on hatched larvae (LC50=0.62 mg/L). Sublethal effects were evaluated after the treatment of pre-ovipositing adult females on leaf discs using the concentrations of 2 mg/L, 20 mg/L and 200 mg/L.After 18–20 hours of exposure on treated discs, females showing no visible symptoms of poisoning were transferred to untreated leaf discs and re-transferred to new discs at 48 h intervals over ten days. Based on the number of eggs laid and survival rate of females, gross fecundity and net fecundity were calculated. At the end of the tenth day, the survival rate was 0.72 in untreated and 0.40, 0.27 and 0.05 in females treated at the concentrations mentioned above. Compared with the control mites, gross fecundity was reduced by 9% (2 mg/L), 29% (20 mg/L) and 93% (200 mg/L), while net fecundity decreased by 40%(2 mg/L), 67%(20 mg/L) and 98%(200 mg/L). The results indicate that spirotetramat exerts similar effects on spider mites as do the acaricides spirodiclofen and spiromesifen.
SUMMARYLaboratory bioassays were conducted to evaluate the effects of spiromesifen on the fecundity, fertility and population growth of two-spotted spider mite (Tetranychus urticae Koch) after treatment of pre-ovipositing females with five acaricide concentrations: 180 mg/l (maximum recommended concentration for use in glasshouses against spider mites), 18 mg/l, 1.8 mg/l and 0.18 mg/l (the last one was discriminative for eggs and immatures in preliminary studies, i.e. produced 100% mortality of those stages) and 0.018 mg/l. After 24h exposure, the percentages of females surviving treatment without visible symptoms of poisoning were 50% (180 mg/l), 45% (18 mg/l), 51% (1.8 mg/l), 74% (0.18 mg/l), 96% (0.018 mg/l) and 98% (0 mg/l). Over the first four days after treatment, the females that survived 180 mg/l and 18 mg/l laid no eggs. The total number of eggs laid after treatment with these two concentrations was reduced to less than 2% against the control by the end of the trial. The females that survived 1.8 mg/l laid 50% less eggs, compared to the control, while the number of eggs laid by the females treated with 0.18 mg/l and 0.018 mg/l were 19% and 4% lower, respectively. Over the initial four days, egg hatch rates in treatments were 73-87%, and 92-93% in the control. Significant statistical differences between gross fecundity (FCg) and gross fertility (FTg) values in the control and treatments were detected for females surviving 180 mg/l, 18 mg/l and 1.8 mg/l. On the other hand, only the net fertility (FTn) value of females treated with 0.018 mg/l showed no statistically significant difference from the control value. Treatments with 180 mg/l and 18 mg/l significantly reduced the instantaneous rate of increase (r i ) 6, 8 and 10 days after treatment, compared to the control. The negative r i values in those treatments indicated a declining population. Sublethal effects of spiromesifen and its impact on T. urticae management are discussed.
Spirodiclofen, an acaricide with a novel mode of action (inhibition of lipid synthesis), has recently been commercialized and recommended as a compound that effectively controls mite populations resistant to other acaricides. The efficacy of the spirodiclofen against European red mite [Panonychus ulmi (Koch)] on apple, and two-spotted spider mite (Tetranychus urticae Koch) on greenhouse cucumber was tested in Serbia from 2004 to 2008. Spirodiclofen efficacy was compared to the effectiveness of several other acaricides (bifenthrin, clofentezine, fenazaquin, fenpyroximate) that had been in use for some time. The acaricides were applied at their recommended application rates. Control efficacy against P. ulmi was tested in a commercial apple orchard at Morovic (45°00.711’N; 19°15.146’ E). Applied at the BBCH 09 growth stage (green leaf tips about 5 mm above bud scales) against overwintering eggs, spirodiclofen achieved 89.1 and 86.0% efficacy in evaluations 12 and 25 DAT (days after treatment), respectively. Similar effectiveness was demonstrated for fenazaquin (91.3 and 84.4%), while clofentezine achieved a considerably lower efficacy (67.4 and 27.8%, respectively). In three trials involving the summer population of P. ulmi in three vegetation seasons, spirodiclofen achieved high and steady efficacy: 91% (15 DAT), 97.2% (30 DAT) and 98% (45 DAT) in the first season; 95.2% (14 DAT), 96.3% (29 DAT) and 95.7% (47 DAT) in the second season; and 97.4% (14 DAT), 95.6% (21 DAT) and 97% (38 DAT) in the third season. The highest clofentezine efficacy in the first season was 90.9% (30 DAT), 77.4% (29 DAT) in the second and 68.1% (21 DAT) in the third season. Bifenthrin achieved the highest efficacy in the first season, 78.2% (15 DAT), while it declined to 65.9% (14 DAT) in the second and was practically negligible in the third season. Such unsatisfactory efficacies of bifenthrin and clofentezine were probably the result of resistance development under selection pressure of these compounds at Morovic. The efficacy of fenpyroximate, tested in the second season, was high (97.4%) in evaluations 14 and 29 DAT, but it was only 50.3% in evaluation 47 DAT. Efficacy in controlling T. urticae was tested in a commercial greenhouse in Padinska Skela (44°57.012’ N; 20°25.741’ E). In evaluations 6 and 10 DAT, spirodiclofen achieved 98.4 and 96.8% efficacy, while clofentezine effectiveness was 95.4 and 93.4%, and bifenthrin efficacy 96.5 and 98.8%, respectively. The results showed that spirodiclofen is effective in controlling European red mite on apple and twospotted spider mite on cucumber, and a good alternative to older acaricides.
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