Resistance Monitoring In Panonychus Citri Mcgregor And Tetranychus Urticae Koch And Risk Assessment Of Tetranychus Urticae Koch To Spiromesifen

Panonychus citri Mc Gregor,which belong to tetranychidae,panonychus,is one of the most important pests caused a decline in citrus production.Tetrangchus urticae Koch is a worldwide pest which belongs to acarina,tetranychus.It mainly influences the growth of crop products such as fruit trees,flowers,and vegetables.Chemical pesticides is still an important tool to control these two mites.However,due to the long-term or abuse of chemical insecticides,these two mites have developed different level of resistance to most of the insecticides.Therefore,it is very necessary to monitor the dynamic changes of the resistance of P.citri and T.urticae to acaricides in different regions.Therefore,the relative sensitivity baselines of the two mites to commonly-used acaricides were established,and the resistance of 6-8 kinds of acaricides against these two mites was also monitored by leaf-disc dipping method in this study.Spiromesifen is the second-generation spirocyclic quaternary acid insecticide and acaricide developed by Bayer Crop Science.It is mainly used to control mites and whiteflies on vegetables,ornamental plants and cotton,spiromesifen has not been registered in China yet.Therefore,to assess the resistance risk of spiromesifen will be helpful before it is commercially used.The results will provide guidance for preventive resistance management strategy.The main results are as follows:1.Resistance monitoring of P.citri to 6 common acaricidesThe resistance of 12 field populations of P.citri collected from Guangxi,Sichuan,Jiangxi,Zhejiang and Hunan were monitored during 2019 to 2020 by leaf-disc dipping method.The results showed that the resistance level of P.citri to abamectin was the highest.About 91.7%of the field populations developed high level of resistance to abamectin（112.1-560.5 fold）,and the resistance increased in 2020 than that in 2019.The resistance to bifenazate also reached high level（140.4 to 686.1 fold）except Xiangshan 2019（51.6 fold）and Yudu 2019（84.7 fold）showed moderate resistance to bifenazate,50%of the populations developed high-level resistance（123.0-202.7 fold）to pyridaben,and the left populations showed moderate resistance（25.6-80.3 fold）,and the resistance increased in the past two years.In 2019,five of the monitored populations developed highly resistant（147.4-223.7fold）to YZ-4748 and five of the monitored populations were moderately resistant（86.1 fold）,but all the populations reached high resistance（108.9-409.1 fold）to YZ-4748 in 2020.The high resistance of spirodiclofen was monitored in most populations（109.8-288.1 fold）.To etoxazole,high resistance（104.9-291.5 fold）was also monitored except for Yongfu 2019（59.1 fold）,Nanning 2019（33.2 fold）and Meishan 2019（61.6 fold）populations.2.Resistance monitoring against T.urticae to spiromesifenThe resistance of 5 field populations of T.urticae collected from Yunnan,Shandong and Jiangsu province were monitored during 2019 to 2020 by leaf-disc dipping method.The results showed that T.urticae from Nanjing,Jiangsu province developed moderate resistance to all the monitored acaricides（17.8-79.3 fold）,the resistance level to YZ-4748was the highest（79.3 fold）.To Shouguang population collected in 2019,the resistance to bifenazate and cyflumetofen was at moderate level.Most populations developed high resistance to abamectin,bifenazate,cyflumetofen,cyenopyrafen,YZ-4748,spirodiclofen,etoxazole and spiromesifen（106.0-413.0 fold）during the two years.T.urticae collected from rose in Kunming developed high level resistance to all the 8 acaricides（150.6-1359.8 fold）.Among them,the resistance to cyflumetofen was the highest and the resistance to bifenazate was the lowest.3.Risk assessment of resistance of T.urticae to spiromesifenIn order to evaluate the resistance risk of T.urticae to spiromesifen,the screening of T.urticae with spiromesifen for continus 18 generations was carried out by leaf-disc dipping method in laboratory.The LC₅₀ of the susceptible strain increased from 0.166 mg/L to 1.519mg/L after spiromesifen screened continuously,and the resistance increased by 9.6 fold and reached low resistance level.The threshold trait analysis was adopted to evaluate the resistance risk of T.urticae to spiromesifen.The realistic heritability（h²）was 0.185 and 0.109when the T.urticae selected with spiromesifen for 10 and 18 generations respectiviely.When the slope was 1.351 and the realistic heritability（h²）was 0.185,it would take 18.3 to 8.3generations for T.urticae to increase 100-fold resistance under the selection pressure between50%and 90%.When the slope was 1.346 and h² was 0.109,31.3～14.1 generations will be needed for the 100-fold resistance increasing when the selection pressure was on 50%to 90%.In summary,it is necessary to pay more attention on the resistant development of P.citri and T.urticae.Abamectin,bifenazate,cyflumetofen,cyenopyrafen,cyetpyrafen,spirodiclofen,etoxazole and spiromesifen should be applied alternatively so as to prevent the resistance of the two mites developed rapidly.