Suscepetibility of Rice Brown Planthopper Nilaparvata lugens Stal to Neonicotinoids

The susceptibility status of field populations of rice brown planthopper Nilaparvata lugens (Stal) (Hemiptera: Delphacidae) collected from three major rice growing tracts of Kerala (Alappuzha, Thrissur and Palakkad) was determined during 2023-24. Neonicotinoid insecticides viz., imidacloprid 17.8 SL, thiamethoxam 25 WG, clothianidin 50 WDG and dinotefuran 20 SG were in comparison to the laboratory susceptible population. All three field populations, viz., Alappuzha (ALP), Thrissur (TCR) and Palakkad (PKD) showed a shift in susceptibility to imidachloprid (LC₅₀ - 150.00 ppm, 129.217 ppm and 100.280 ppm, respectively) and thiamethoxam (LC₅₀ - 119.90 ppm, 109.035 ppm and 99.547 ppm, respectively) as compared to that of the laboratory susceptible (LS) population having respective LC₅₀ values of 3.38 ppm and 3.52 ppm. Similar trends, but only with slight shift, were observed for dinotefuran and clothianidin in ALP (7.145 ppm and 6.550 ppm), TCR (6.119 ppm and 4.400 ppm), and PKD (3.975 ppm and 2.786 ppm) as compared to that of the LS (2.62 ppm and 1.51 ppm). These findings advocate for the judicial application of neonicotinoid insecticides in managing rice brown planthopper.