Evaluation on the effect of 14 miticides on controlling Tetranychus urticae of different populations

Abstract:【Objective】In recent years, Tetranychus urticae has become one of the most harmful pests in apple production. It has a mixed diet and can damage thousands of crops, such as fruit trees, vegetables, flowers and so on. Tetranychus urticae will spoilt the plants by sucking the sap in the plants, which re- sults in the loss of water and necrosis of mesophyll cells, plant growth retardation, stagnation or even death. What’s worse, it will lead to premature ripening of fruit, and a marked decrease in quality and yield. At present, the field control of Tetranychus urticae is carried out by integrating agricultural control with chemical control, biological control and other methods. When the damage is serious or the population base is large, application of chemical acaricides is still the main method to control Tetranychus urticae in the field. Due to the long-term, large-amount, single-applied and unreasonable use of chemical acaricides, the problem of increasing resistance is very serious. At the same time, the resistance accumulation of Tetranychus urticae further accelerates because of its characteristic, such as short generation, strong fecundity and so on. In this study, we can realize the resistance of Tetranychus urticae in the field and screen out the suitable acaricides to control Tetranychus urticae in the future.【Methods】We se- lected 14 kinds of acaricides widely used in agricultural production in China, which were Spirodiclofen, Spirotetramat, Hexythiazox, Lice mite urea, Etoxazole, Avermectins, Fenbutatin oxide, Chlorfenapyr, Pyridaben, Diafenthiuron, Bifenazate, Propargite, Azocyclotin and Bromopropylate. The Tetranychus ur-ticae mites were collected from apple orchards in Lingbao city, Henan province, Shangqiu city, Henan province, and Aksu city, Xinjiang Uygur Autonomous Region. And we fed them with peanut leaves for several generations in the incubator. The incubator temperature was set at (28.0±1.0) ℃, the relative hu midity was 80.0%±5.0%, and the photoperiod was L∶D = 14∶10. According to the recommended dos-age of each acaricide for controlling Tetranychus urticae in the field, the original medicine of acaricide tested was dissolved by a small amount of organic solvent, and diluted with distilled water containing 1‰ Triton-X to the specified concentration. The same amount of the solvent was taken as the control. We selected the female adults with the same age and in the peak period of oviposition, and then trans- ferred them to peanut leaves with brush. Each leaf had 10 mites to serve as a repeat, and there were 4 re-peats. 1 mL diluted solution was used to spray evenly onto the mite and the leaf surface of the Potterspray tower. After spraying, it was put into the artificial climate box for observation. After 48 hours, the survival rate of Tetranychus mites was recorded. After the removal of female adults, we continued feed-ing them for about one week. Then, we counted the survival number and sex ratio of the second genera-tion of Tetranychus mites.【Results】The survival rate of Tetranychus erythematosus was observed after 9 kinds of acaricides were applied for 48 hours, including Avermectins, Fenbutatin oxide, Chlorfenapyr, Pyridaben, Diafenthiuron, Bifenazate, Propargite, Azocyclotin and Bromopropylate. Bifenazate showed good acaricidal effect on three populations, while Bromopropylate had no significant effect on Tetrany-chus mites in three populations. For Lingbao population, the other six acaricides showed 90% killing ef-fect, except Pyridaben and Propargite; The survival rate of Tetranychus erythematosus was observed af-ter 9 kinds of acaricides were applied for 48 hours, including Avermectins, Fenbutatin oxide, Chlorfena-pyr, Pyridaben, Diafenthiuron, Bifenazate, Propargite, Azocyclotin and Bromopropylate. Bifenazate showed good acaricidal effect on three populations, while Bromopropylate had no significant effect on killing Tetranychus mites in three populations. For Lingbao population, the other six acaricides showed 90% killing effect, except Pyridaben and Propargite. However, both the lethal effects of Fenbutatin ox-ide, Pyridaben, Propargite, Azocyclotin on Aksu population and Avermectins, Fenbutatin oxide, Pyrida-ben, Diafenthiuron and Propargite on Shangqiu population were all lower than 50%. Compared with the CK, the other 7 agents could reduce the number of females in the offspring of Tetranychus urticae ex-cept for Pyridaben and Bromopropylate. For the population of Tetranychus urticae in Shangqiu, only four kinds of acaricides, including Chlorfenapyr, Bifenazate, Propargite and Azocyclotin, had signifi-cant effects on reducing the number of female offspring. For sake of Aksu population, only Avermec-tins, Chlorfenapyr, Bifenazate and Propargite were effective. In this study, the effects of acaricides on fe-male offspring and male offspring were similar, and there was no significant gender difference. Only 5 kinds of acaricides, including Spirodiclofen, Spirotetramat, Hexythiazox, Lice mite urea and Etoxazole-had the activity of killing eggs or larvae. The results indicated that only Spirodiclofen showed nearly 100% control effect on the three populations of Tetranychus urticae, and the controlling effect of Lice mite urea on the offspring of Tetranychus urticae was not good. After the treatment with Spirotetramat, Hexythiazox and Etoxazole, the number of female mites in the progeny of Lingbao population was sig-nificantly lower than the previous generation, but the growth of progeny of Shangqiu and Aksu popula-tions were not inhibited.【Conclusion】The resistance accumulation of Tetranychus urticae was serious,and there were significant differences among different geographical populations. Most of the miticides had good controlling effect on the population of Tetranychus urticae of Lingbao, and they also had good controlling effect on the population number of its offspring. However, the resistance accumulation of Akesu and Shangqiu populations was serious, the lethal effect of most acaricides on the populations was weak, and the controlling effect on offspring was also poor.