author(s)
E Priyadharshini, N Muthukrishnan, N Sathiah and K Prabakar

abstract
Rice brown planthopper (BPH), Nilaparvata lugens (Stål) (Hemiptera: Delphacidae), is a serious pest and inflicts a severe threat to rice cultivation throughout East and Southeast Asia. Susceptibility of BPH against sulfoxaflor 21.8 SC insecticide was investigated with four different populations of Tamil Nadu viz., Coimbatore, Bhavani, Nagapattinam and TNAU susceptible strains. The bioassay method followed was the seedling dip method (IRAC method No. 5) under three replications. Results revealed that the Nagapattinam population registered the highest LC 50 value of 5.40 ppm followed by Bhavani (4.17 ppm), Coimbatore (3.06 ppm) and susceptible population (1.61 ppm) for the insecticide sulfoxaflor 21.8 SC. The resistance ratio values were 3.35 fold for the Nagapattinam population, 2.59 fold for the Bhavani population, and 1.90 fold resistance for the Coimbatore population. The order of toxicity of sulfoxaflor 21.8 SC to all four populations based on LC50 was Nagapattinam> Bhavani > Coimbatore > TNAU susceptible.