Resistance Monitoring In 2019-2020 And Mixed Formulations Screening Of Insecticides Control On Rice Leaf Roller(Cnaphalocrocis Medinails)

Cnaphalocrocis medinalis is a lepidoptera pest,belonging to the family Cnaphalidae.It is an important pest on rice growing in China.Since 21 centrury,due to the changes in cultivation systems and suitable climate,it broke out occasionally and has caused serious damage.C.medinalis is a kind of migratory pest with strong adaptability,which brings great challenges on its control.Chemical control has always been the main measure to control this pest,but there are seldom reports on its resistance monitoring.Therefore,clarifying its resistant development and screening out high-efficiency insecticides can provide scientific guidance for the control of C.medinalis.In this study,rice-seedling dipping method was used to monitor the resistance levels of C.medinalis to 10 insecticides.The field populations were collected from 5 provinces（cities）.The sensitivity of different instars of C.medinalis to diamide insecticides was determined,so as to provide theoretical guidance for the suitable control period.The synergistic formulations of chlorantraniliprole and other insecticides with different mechanisms were screened for the purpose of delaying its resistant development.The target mutations in the ryanodine receptor of C.medinalis was preliminarily detected.1.Resistance monitoring of C.medinalisIn order to clarify the current status of the resistance of C.medinalis and guide the rational use of insecticides for practical control,the susceptibility of 12 field populations of C.medinalis to 10 insecticides was determined by the rice-seedling dipping method.Four field populations were all sensitive to chlorantraniliprole in 2019.Among eight field populations monitored in 2020,Wuwei and Yangzhou populations developed low-level resistance,with resistance ratios of 7.5 and 7.8 folds,respecively.For abamectin,the Chongqing,Shaoguan and Yizheng populations in 2019 reached low to moderate level of resistance（RR=9.8-22.2 fold）.Among 8 field populations monitored in 2020,five populations reached low to moderate level of resistance（RR=6.9-12.9 fold）.For spinetoram,all the field populations monitored in 2020 reached low to moderate levels of resistance（RR=5.4-17.3 fold）.For chlorpyrifos,Qianshan population monitored in 2019 and the Zhuji population monitored in 2020 reached low-level resistance,with resistance ratios of 6.8 and 6.1 folds,respecively.For emamectin benzoate,tetraniliprole,indoxacarb,cyfluprozone,methoxenozide and Bt,the field populations in 2019 and 2020 all kept sensitive.2.The sensitivity determination of different instars of C.medinalis to diamide insecticides.The sensitivity of the eggs and 1^st-4^thinstar larvae of C.medinalis to chlorantraniliprole and tetraniliprole were determined by egg dipping and rice-seedling dipping methods.Chlorantraniliprole and tetraniliprole have no obvious activity against the eggs of C.medinalis,but show high activity against larvae.The first-instar larvae are the most sensitive to chlorantraniliprole,and the second-instar larvae are the most sensitive to tetraniliprole.The sensitivity of the larvae to chlorantraniliprole is lower than that of tetraniliprole,and the difference in the sensitivity of 2^nd-instar larvae to chlorantraniliprole and tetraniliprole is the most significant.3.Screening of insecticide formulations for controlling C.medinalisTaking chlorantraniliprole as the main insecticide,the combined toxicity of chlorantraniliprole with other insecticides of different mechanisms were tested to obtain the synergistic insecticide formulations,so as to delay the resistant development of C.medinalis.Following synergistic insecticide formulations are obtained:chlorantraniliprole and chlorpyrifos are mixed at the ratio of 1:5,chlorantraniliprole and indoxacarb are mixed at the ratio of 1:1 and 1:4,chlorantraniliprole and emamectin benzoate are mixed at the ratio of 5:1 and 5:1.4.Comparison of the ryanodine receptor genes between strains with low-level resistance to chlorantraniliprole and sensitive strains.Chlorantraniliprole acts on the ryanodine receptor.Sequence alignment and analysis of the ryanodine receptor genes of the sensitive and low-resistant strains show that no target mutation sites have been found.Therefore,the low-level resistance of C.medinalis to chlorantraniliprole may not be related to the target mutation,but may be related to other factors such as mechanisms of detoxification metabolic.