Toxic Effects And Corn Seed Treatment Efficiency Of Cyantraniliprole Against Athetis Dissimilis

Athetis dissimilis?Hampson?,an emerging lepidopteran agricultural pest in Huang-Huai-Hai summer corn area in China since 2012.A.dissimilis occurred with Athetis lepigone?Müschler?together under field conditions,the two pests are very similar in habits,morphology and damage characteristics.This pest can damage the tender leaves,stem and root of corn,wheat,peanuts and soybeans at the seeding stage,even damage rows of crops seriously.However,compared with A.lepigone,A.dissimilis had greater consumption,longer damage cycle and higher fecundity,showed a high risk of pest outbreak in field.Until now,studies about A.dissimilis mainly focus on distribution,classification and biological characteristics,chemical control has not been reported.Considering the potential threat of A.dissimilis to corn and other crops,it is urgent to search for the effective,low-toxic and safe insecticides for emergency pest control.In this paper,we determined the toxicities of 18kinds of common insecticides to 3-6 instar larvae of A.dissimilis under laboratory conditions,and studied the sublethal effect of cyantraniliprole on A.dissimilis,the control efficacy and persistent period of cyantraniliprole seed treatment against A.dissimilis were evaluated through plant pot experiments and field experiment.Additionally,the residual dynamic of cyantraniliprole and its metabolite in corn plant and soil after seed treatment was also evaluated.The results were summarized as follow:1.The toxicities of 18 insecticides?eight classes?to A.dissimilis larvae were determined using leaf dipping method.The results showed that cyantraniliprole,chlorantraniliprole,deltamethrin,lambda-cyhalothrin,bifenthrin and emamectin benzoate were high toxic to 3-6instar larvae of A.dissimilis with LC₅₀ values ranging from 0.14 mg/L to 27.40 mg/L.Chlorfenapyr,indoxacarb,beta-cypermethrin,chlorfluazuron and chlorpyrifos were high toxic to 3-4 instar larvae of A.dissimilis(LC₅₀<22.63 mg/L),whereas all those insecticides were low toxic to the 5th and 6th instar larvae(LC₅₀>38.13 mg/L).However,neonicotinoids,pirimiphos-methyl and chlorbenzuron were low toxic to different instar larvae of A.dissimilis(LC₅₀>40.83 mg/L).2.The sublethal effects of cyantraniliprole to the growth,development,fecundity,as well as nutrient utilization and the content of major energy substances of A.dissimilis were determined by using the method of artificial diet mixed with insecticides.The result of bioassay showed that cyantraniliprole exhibited high toxicity on the fourth instar larvae of A.dissimilis with LC₅₀0 value of 0.66?g/g incorporated artificial diet.The feeding amount and the nutrient contents,including lipids,protein and carbohydrates,were declined significantly in LC₅,LC₂₅ and LC₅₀ cyantraniliprole treatments compared with the control group.These changes were adverse in the normal growth,development and fecundity of A.dissimilis,such as prolonging the larval and pupal duration period,decreasing the percentage of larval that pupated and adults that emerged,reducing the pupae weight and fecundity of female adults.Low-lethal dosages of cyantraniliprole decreased growth speed and reduced population reproduction of A.dissimilis population.3.Plant pot experiments showed that at 9 days after emergence?DAE?,A.dissimilis larval mortality was greater than 90%and that the percentage of corn seedlings damaged by A.dissimilis was about 10%when corn seeds were treated with cyantraniliprole at 2 and 4 g a.i./kg seed.Therefore,2 g a.i./kg seed regard as the recommended dose of field experiment.Cyantraniliprole applied at 2 g a.i./kg seed was safe for the growth of summer corn in 2018field trial.The experiment of insect inoculation was conducted at 5 DAE.Results showed that the percentage of corn seedlings with A.dissimilis damage in the cyantraniliprole-treated plots?10.52%?was significantly lower than the percentage of damaged seedlings in the control treatment plots?35.76%?at 15 DAE,As well as,the control efficacy of the cyantraniliprole seed treatment against A.dissimilis was 70.59%,and were obviously higher than the control efficacy of the chlorantraniliprole seed treatments?60.00%?.4.Corn seeds were sown after treated with cyantraniliprole at a dosage of 2 g a.i./kg seed,at different days after seedling emergence,the whole plant,stem and leaf of corn were collected and fed on the 3-5 instar larvae.The results showed the mortality of the 5th-instar larvae of A.dissimilis was significantly lower compared to the mortality of the 3rd or4th-instar larvae.For summer corn,the mortality of 3-5 instar larvae of A.dissimilis was46.67%-76.67%?whole plant?,46.67%-83.33%?stem?and 33.33%-60.00%?leaf?at 7 DAE.Similarly,mortality in A.dissimilis fell with decreasing concentrations of cyantraniliprole in different tissues of corn plants.In brief,cyantraniliprole applied at 2 g a.i./kg seed,the efficient pest control period to the 3rd and 4th-instar larvae was 7-10 DAE,but to the fifth and above instar larvae was not good.5.A method for the determination of cyantraniliprole and its metabolites residues in corn plant and soil were established using ultra-performance liquid chromatography tandem mass spectrometry.The results showed that the mean recoveries of cyantraniliprole and its metabolites at three spiked levels?0.01,0.1 and 1 mg/kg?were 81%-103%,with RSDs both less than 10.1%.The results demonstrate the concentrations of cyantraniliprole and its metabolites have a good linear relationship with the corresponding peak area in the range of0.1-50?g/L,with determination coefficient?R²>0.999?,and limits of quantitation were 0.01mg/kg.All the above observations indicate that the established analytical method is sensitive,fast,highly efficient,and suitable for monitoring the residues of cyantraniliprole and its metabolites J9Z38 in corn plant and soil.6.The fate of cyantraniliprole and its metabolites in corn plant and soil after seed treatment was evaluated.Results for residual dynamic test showed that the degradation trends of cyantraniliprole and J9Z38 were both in line with the first order kinetic equation.Equation of residues and dissipation dynamics of cyantraniliprole applied at 4 g a.i./kg seed were C_t=2.005e^-0.083t?r²=0.9847?and C_t=4.089e^-0.085t?r²=0.9769?in spring corn plant and soil,and C_t=2.216e^-0.178t?r²=0.9627?and C_t=0.431e^-0.153t?r²=0.9195?in summer corn plant and soil.The half-lives of cyantraniliprole in corn plant and soil were 8.3 and 8.2 d?in spring?,and 3.9and 4.5 d?in summer?,respectively.