Field Control Of Three Pesticide Microemulsions Against Spodoptera Frugiperda And Residue Behavior On Maize

Currently,the damage situation of invasive pests,Spodoptera frugiperda,is severe,which seriously affects the yield and quality of maize and other crops.Chemical pesticides are the most economical and effective methods to prevent Spodoptera frugiperda,especially microemulsions（ME）.The pesticide microemulsion has higher bioavailability,stronger biological activity,and is more friendly to the environment compared to traditional pesticide formulations.In this work,5.7%emamectin benzoate ME,2%indoxacarb ME,and 5%lufenuron ME were employed to evaluate the indoor virulence and field efficacy of Spodoptera frugiperda larvae.The dynamics and final residues of the tested microemulsion pesticides during maize planting were studied,and the results provided a scientific basis for formulating guidelines for the rational use of maize.The main results are as follows:1.The indoor virulence and field efficacy of three pesticide microemulsions on Spodoptera frugiperda larvaeThe results of the indoor virulence test by dipping method showed that the median lethal concentrations(LC₅₀)of 5.7%emamectin benzoate ME,2%indoxacarb ME,and 5%lufenuron ME to the third instar larvae of Spodoptera frugiperda at 72 h were 0.072 mg/L,174.847 mg/L and 7.755 mg/L,respectively,which exhibited a better indoor toxic effect compared to 5.7%emamectin benzoate water dispersible granule(LC₅₀=0.115 mg/L),30%indoxacarb water dispersible granule(LC₅₀=190.390 mg/L)and 50 g/L lufenuron emulsifiable concentrate(LC₅₀=23.680 mg/L).The results of field efficacy trials showed that the field efficacy of 5.7%emamectin benzoate ME at 15.00 g a.i./ha dosage,2%indoxacarb ME at 30.00 g a.i./ha dosage,and 5%lufenuron ME at 37.50 g a.i./ha dosage on Spodoptera frugiperda larvae was 62.50%,45.11%and 45.82%,respectively,on the 3rd day after application,and 95.83%,80.11%and67.90%,respectively,on the 14th day after application,which exhibited a better persistence compared with the control medicament.2.Confirmation of analytical methods for the residues of emamectin benzoate,indoxacarb and lufenuron in maizeThe QuEChERS analysis method combined with the UPLC-MS/MS was conducted to confirm the residual of emamectin benzoate,indoxacarb and lufenuron in maize plants,maize grains and fresh maize.The three pesticides had a good linear relationship in the concentration range of 0.002-0.500 mg/kg,and the correlation coefficient（r²）was 0.9982-0.9999.The limits of detections（LODs）and limits of quantifications（LOQs）of the method were 0.51-5.08μg/kg and 2.00-10.00μg/kg,respectively.The results of the addition and reclamation test showed that at the addition levels of 0.01,0.1 and 1.0 mg/kg,the average recoveries of emamectin benzoate in maize plants,maize grains and fresh maize were 75.94-117.20%,respectively,and the relative standard deviations（RSDs）were 1.20-7.28%,respectively.The average recoveries of indoxacarb were 67.56-98.13%,respectively,and the RSDs were 1.53-8.13%,respectively.Also,the average recoveries of lufenuron were 71.13-119.55%,respectively,and the RSDs were 2.07-9.46%,respectively.The sensitivity,accuracy and accuracy of the method meet the requirements of pesticide residue analysis.3.The dynamics of residual degradation of emamectin benzoate,indoxacarb and lufenuron on maize plantsThe results of the field degradation dynamic test showed that under the dosage of 30 g a.i./ha,the emamectin benzoate original deposition on maize plants was 0.06 mg/kg.The residues on maize plants after 5 d application were lower than LOQ（2.00μg/kg）.Under the dosage of 60 and 75 g a.i./ha,the original deposition amounts of indoxacarb and lufenuron on maize plants were 0.98 mg/kg and 8.18 mg/kg,respectively.And after 14 d application,the degradation rates of indoxacarb in maize plants were 98.88%.And after 28 d application,the degradation rates of lufenuron in maize plants were 98.98%.The degradation kinetics of indoxacarb and lufenuron on maize plants conformed to the first-order kinetic equation.The degradation half-life was 1.24 d and 2.48 d.4.Final residues of emamectin benzoate,indoxacarb and lufenuron on maize grains and maize strawThe final residues of emamectin benzoate（30 g a.i./ha）and lufenuron（75 g a.i./ha）in maize straw and maize grains were both lower than LOQ（0.002 mg/kg）and LOQ（0.01mg/kg）,respectively.At the application dose of 60 g a.i./ha,the final residues of indoxacarb in maize grains and maize straws were 0.01 mg/kg and 0.0098 mg/kg,respectively.After the application of 5.7%emamectin benzoate ME,2%indoxacarb ME,and 5%lufenuron ME,the final residues of the tested pesticides in maize straw and maize grains were lower than their MRL values on maize（0.05 mg/kg,0.01 mg/kg,0.01 mg/kg）.Above all,5.7%emamectin benzoate ME,2%indoxacarb ME,and 5%lufenuron ME were recommended for application at the maize bell mouth stage.The recommended dosages were 15 g a.i./ha of 5.7%emamectin benzoate ME,30 g a.i./ha of 2%indoxacarb ME,and37.5 g a.i./ha of 5%lufenuron ME,respectively,with a water spray.