Laboratory and pot culture experiments were conducted to assess the acute and persistent toxicity of new molecular insecticides against the notorious invasive pest of maize, Spodoptera frugiperda during 2020- 2021 at Department of Agricultural Entomology, Tamil Nadu Agricultural University, Coimbatore. Results revealed that, the LC50 value of emamectin benzoate, chlorantraniliprole, spinetoram, flubendiamide and novaluron were 0.05, 4.08, 0.1, 85.89 and 0.91 ppm, respectively for second instar larvae and 0.03, 5.63, 0.02, 162.99 and 0.99 ppm for third instar larvae of fall armyworm. Among insecticides tested emamectin benzoate and spinetoram showed high toxicity to S. frugiperda than other insecticides by registering a minimum LC50 value. But in the persistent toxicity studies, the same insecticides showed less persistence on maize crop. Hence, insecticides like flubendiamide and chlorantraniliprole need to be recommended in the early stage of the crop period (within 20 days after sowing) and less persistent insecticides viz., emamectin benzoate and spinetoram should be recommended in the middle stage (25 to 40 days) of the maize crop for the management of S. frugiperda so that the residues may not accumulate in the harvested produce both in the stalk and grain.

Maize fall armyworm, Spodoptera frugiperda (J.E. Martin (Noctuidae: Lepidoptera), first recorded in the Americas spread to Africa during 2016 and later spread to more than 40 countries including India during July, 2018. Infestation by maize fall armyworm results in extensive defoliation besides damage to tassels and cobs at later stages of the crop. The infestation levels are measured through various injury rating scales of which the 1-9 whorl leaf injury rating scale (Davis et al., 1992; Ni et al., 2011) is the mostly used one. It was felt that, the Davis 1-9 scale proposed by Davis et al. (1992) was prone to observer bias in field experiments conducted at Tamil Nadu Agricultural University by a team of researchers and students. Thus, a new TNAU 1-5 scale was evaluated which was more feasible, precise, easy and less time consuming compared to modified Davis et al., (1992) 1-9 scale proposed by Ni et al.