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Acharya N G Ranga Agricultural University
The Research work entitled “Studies on insecticide resistance monitoring in fall armyworm, Spodoptera frugiperda (J.E. Smith) and persistence of insecticide residues in sweet corn” was conducted at Department of Entomology, S. V. Agricultural College, Tirupati and Pesticide Residue Testing Laboratory, Institute of Frontier Technology (IFT), Regional Agricultural Research Station (RARS), Tirupati. During survey conducted in five different districts of Andhra Pradesh during rabi, 2021-2022, the highest incidence of S. frugiperda was noticed in Kurnool district (64.32%) followed by Chittoor (58.94 %), Vizianagaram (46.65%). The low incidence was noticed in Krishna (22.34 %) and Guntur districts (26.47%). The low incidence in Krishna and Guntur districts is may be due to high insecticidal sprays used by the maize farmers for the fall armyworm control compared to Kurnool, Chittoor and Vizianagaram districts of Andhra Pradesh. Among different surveyed mandals, maximum incidence of fall armyworm (86.05%) was recorded in Timmapuram village of Mahanandi, Kurnool district while the minimum FAW incidence (15%) was recorded in Keesara village of Kanchikacherla mandal, Krishna district. As per the Davis Scale (1-9), highest FAW leaf damage score of 5-9 was recorded in Kurnool district followed by Chittoor (4-8) > Vizianagaram (3-7) > Guntur (2-4) and Krishna (2-3) respectively. During the survey, mycosed larvae attacked by Green Muscardian fungus, Metarhizium rileyi were observed to a tune of 50 – 60 per cent and resulted in natural mortality due to epizootics at Lam mandal of Guntur district. Bioassay studies were conducted on third instar FAW larvae from F1 population of field collections from five different districts of Andhra Pradesh using diet incorporation assay (IRAC test method). The studies on the resistance levels in S. frugiperda to ten insecticides viz., emamectin benzoate, thiodicarb, profenofos, chlorpyriphos, lambda-cyhalothrin, chlorantraniliprole, cynatraniliprole, spinetoram, indoxacarb and lufenuron revealed the high level of resistance to four insecticides viz., chlorpyrifos, thiodicarb, lambda cyhalothrin, lufenuron and low level of resistance to new chemicals like chlorantraniliprole, cyantraniliprole, spinetoram, emamectin benzoate and indoxacarb. Among different FAW populations of Andhra Pradesh, Krishna district population showed significantly higher resistance to all the test insecticides (1.8-161.7 folds) followed by Guntur (1.5-132.5 folds), Kurnool (1.2-120.7 folds), Chittoor populations (1.2-114.8 folds) and lower levels of resistance was observed in Vizianagaram population (1.1-110.2 folds). A simple, robust and efficient QuEChERS extraction method combined with Ultra High Performance Liquid Chromatography (UHPLC) was developed to analyze the pesticide residues of chlorantraniliprole, emamectin benzoate and spinetoram in baby corn, sweet corn, corn leaf (straw) and corn seeds. To the best of our knowledge, dissipation kinetics and residues of these new chemicals in sweet corn and baby corn under field conditions was not studied in India. The studies on persistence of three insecticides viz., emamectin benzoate, chlorantraniliprole and spinetoram on sweet corn during rabi, 2021-2022 revealed that, the chlorantraniliprole reached Below Detectable Level at 15 days after application of insecticides in leaf, baby corn and sweet corn for both the recommended and double the recommended doses. The half-life were 3 to 4 days in baby corn and sweet corn and for leaf the half-life was 4 days in single dose and 5 days for double dose. The dissipation of emamectin benzoate followed first order of kinetics with initial residues deposit (0 day) of 1.647 and 3.217 mg kg-1 in leaf for both the doses. In baby corn the initial deposits were 2.107 and 2.568 and for sweet corn it was 1.895 and 4.553 for both single and double doses respectively. The residues were dissipated to BDL at 7th and 15th day after application of insecticides, in leaf for single dose and dose and in baby corn it was 10th and 15th day. The residues were dissipated to BDL at 7thand 5thdayafter application of insecticides, in sweet corn for single dose and double dose for with half-life was 6 days for leaf, 6 to 7 days for baby corn and 3 to 4 days in sweet corn. The spinetoram residues dissipated to BDL at 20th day after application of insecticide in leaf and the half-life were calculated as 3 days. The spinetoram in baby corn detected with initial residue of 3.270 and 4.225 mg kg-1 in both doses and the residues reached BDL at 10th and 15th days after application of insecticide. The half-life of 2.81and 3.50 and waiting period of 23 and 30 days was observed. All the three insecticides tested followed the dissipation of first order of kinetics in their persistence studies in sweet corn/ Baby corn. There were no residues recorded from maize straw and maize seed at the time of harvest i.e., 25 days after last spray. The MRL’s for emamectin benzoate, Chlorantraniliprole and spinetoram in sweet corn/baby corn were not established in FSSAI. As per the dissipation studies, the half-life values of 3.31- 4.39 days for emamectin benzoate, 3.52 - 4.28 days in spinetoram and 3.76 - 4.23 days for chlorantraniliprole were recorded respectively in sweet corn.