Sublethal effects of cyetpyrafen and cyenopyrafen on Tetranychus viennensis

Abstract:【Objective】Tetranychus viennensis is an important pest on deciduous fruit trees like apples in northern China, damaging mainly leaf blades, leaf tips and calyx. When the mite seriously damages, it causes fruit yield reduction. Today, acaricides are still of utmost importance in the control of T. viennensis and this is unlikely to change in the near future. Excessive chemical use also leads to accumulation of pesticide residues in the produce, destruction of beneficial insects, pest resurgence and environmental pollution. The experiment was conducted to clarify the effect of the sublethal concentration of cyetpyrafen and cyenopyrafen on T. viennensis. At present, the promotion and application of the new acaricides cyetpyrafen and cyenopyrafen have been tried in the field, and this study can provide a theoretical basis for the rational rotation of the two acaricides and the management of pest resistance to mites.【Methods】The sponge pad was trimmed to be flat and square, and placed in the Petri dish after fully absorbing water. Filter paper was placed on the sponge, and the apple leaves were trimmed to round leaf discs with a diameter of 25 mm. The apple leaves were placed downward on the filter paper to make leaf discs. The distilled water was added into the Petri dish, and the water surface kept lower than the filter paper. T. viennensis were raised in leaf dishes that were placed in an artificial climatechamber [(28±1) ℃, 16 h∶8 h (L∶D) and (70%±10%) RH]. The indoor toxicity of two acaricides to female adult mites and eggs of T. viennensis was determined by leaf dish spray method. Cyetpyrafen and cyenopyrafen were diluted at 5-7 concentration gradients with distilled water. Potter spray tower was used to atomize and evenly spray the solution onto the surfaces of mites and leaves, and then they were placed in an artificial climate chamber for observation. LC15 and LC30 were selected to treat female adult mites and eggs, and the parameters related to the life table were recorded.The parameters of the population life table were calculated according to the following formula: Finite rate of increase (λ): λ= erm, Intrinsic rate of increase (rm):∑e- r(x + 1) lxmx=1, Net reproductive rate (R0): R0=∑lxmx, Population doubling time (DT) DT=ln(2)· rm -1 , Mean generation time (T): T=lnR0 ·rm -1 ; The enzyme activity was measured by UV-Vis spectrophotometer.【Results】The eggs treated with cyetpyrafen LC15 significantly increased the fecundity of female adults of F0 generation to 41.263 6, and net reproductive rate increased (R0) to 33.647 8. The eggs treated with cyetpyrafen LC30 increased the fecundity of female adults of F0 generation to 37.435 1, but not significantly, and mean generation time (T) was significantly extended to 15.649 3 d. Mean generation time (T) of female adults of F0 generation of eggs treated with cyenopyrafen LC15 was shortened to 13.021 8 d; Female adult mites treated with cyetpyrafen LC30 significantly decreased the adult longevity (7.817 4 d), eggs per female (13.579 4), F1 hatchability (72.42%) and net reproductive rate (R0, 10.581 3). Female adult mites treated with cyenopyrafen LC30 significantly decreased the adult longevity (5.429 3 d), egg numbers per female (12.952 5), F1 hatchability (74.37% ) and net reproductive rate (R0, 11.043 3). The mean generation time of the cyetpyrafen LC15 and cyenopyrafen LC30 was significantly shortened to 13.296 3 d and 11.0706 d, respectively. Cyetpyrafen LC30 significantly reduced the sex ratio of offspring (3.274 8) and prolonged the population doubling time (4.028 0 d). Compared with the adult mite treatment group, the egg laying peak in the egg treatment group was higher and lasted longer. The activities of glutathione S-transferase (GST) and carboxylesterase (CarE) were measured. The results showed that glutathione S- transferase (GST) activity in each treatment was lower than that in the control, but in terms of the activity of adult mites treated with sublethal doses of cyetpyrafen LC15, no significant difference was achieved. The activity of adult mites treated with sublethal doses of cyenopyrafen LC15 and LC30 was the lowest, only 3.87 U·g-1 . The activity of carboxylesterase (CarE) in each treatment was higher than that in the control, and the highest activity was 247.20 U·g-1 in the egg group treated with cyetpyrafen LC30.【Conclusion】The treatment of female adults of T. viennensis with Tcyetpyrafen and cyenopyrafen inhibited the development of the population. The treatment of T. viennensis eggs with cyetpyrafen promoted the reproduction of the population, but the treatment of T. viennensis eggs with cyenopyrafen had no effect on the population.