Baseline Toxicity of Selected Insecticides against Third Instar Larvae of Spodoptera frugiperda (J.E. Smith)
Angothu Krishnaveni
Department of Entomology, College of Agriculture, Dharwad, University of Agricultural Sciences, Dharwad – 580005 (Karnataka), India.
G. S. Guruprasad *
Department of Entomology, College of Agriculture, Dharwad, University of Agricultural Sciences, Dharwad – 580005 (Karnataka), India.
S. S. Udikeri
Gulbarga University, Kalaburagi, Karnataka-585102, India.
Akbar S. MD.
Agricultural Research Station, Dharwad, Karnataka-580005, India.
*Author to whom correspondence should be addressed.
Abstract
The fall armyworm, Spodoptera frugiperda (J. E. Smith), is an invasive maize pest for which reliable baseline susceptibility data are required to support insecticide selection and resistance monitoring. This laboratory study compared the toxicity of five commonly used insecticides—emamectin benzoate 5 SG, chlorantraniliprole 18.5 SC, spinetoram 11.7 SC, spinosad 45 SC, and flubendiamide 480 SC—against third-instar larvae. Uniform larvae obtained from a laboratory culture were exposed to insecticide-treated maize leaf pieces using a leaf-dip bioassay. Each concentration comprised four replicates of 20 larvae, and mortality was assessed 48 hours after treatment. Corrected mortality data were subjected to probit analysis to estimate median lethal concentration (LC₅₀) values. The tested insecticides differed considerably in toxicity. Emamectin benzoate 5 SG was the most toxic, with the lowest LC₅₀ value of 0.13 ppm. It was followed by chlorantraniliprole 18.5 SC (2.61 ppm), spinetoram 11.7 SC (3.69 ppm), spinosad 45 SC (5.47 ppm), and flubendiamide 480 SC (56.37 ppm). The laboratory population was therefore most susceptible to emamectin benzoate and least susceptible to flubendiamide under the experimental conditions. These LC₅₀ estimates provide baseline information for subsequent susceptibility monitoring and may support the selection and rotation of insecticides with different modes of action within integrated insecticide-resistance-management programmes.
Keywords: Fall armyworm, Spodoptera frugiperda, baseline toxicity, emamectin benzoate, chlorantraniliprole, spinetoram, spinosad, flubendiamide, leaf-dip bioassay, insecticide re-sistance management