BIOCHEMICAL MECHANISMS OF INSECTICIDE RESISTANCE AND ASSOCIATED LIFE-HISTORY CHANGES IN FIELD COLLECTED NILAPARVATA LUGENS FROM BARGARH, INDIA

Abstract

The brown planthopper (Nilaparvata lugens  Stål) is a major insect pest of rice, and the development of insecticide resistance poses a serious challenge to its effective management. The present study was undertaken to assess the insecticide resistance status, detoxification enzyme activity, and biological characteristics of a field population of N. lugens collected from Bargarh, an insecticide-intensive rice-growing region. The field population was evaluated against nine insecticides representing different insecticide groups using a rice plant spray bioassay. Mortality was recorded at 24, 48 and 72 h after treatment, and LC₅₀ and LC₉₀ values were estimated by probit analysis. Resistance ratios were calculated relative to a long term susceptible glasshouse population maintained at ICAR-Indian Institute of Rice Research, Hyderabad. The Bargarh population exhibited low resistance to acephate, dinotefuran, fipronil and pymetrozine, while comparatively higher resistance was observed against chlorpyriphos. Very high resistance was detected against the neonicotinoids imidacloprid and thiamethoxam, the ethiprole + imidacloprid combination, and the insect growth regulator buprofezin, with the highest resistance recorded against BPH. Biochemical assays revealed elevated activities of esterases, glutathione S-transferase (GST), and cytochrome P450 monooxygenases in the Bargarh population compared with the susceptible glasshouse population, with increases of 1.5-, 1.1- and 2.2-fold, respectively. The greater elevation of P450 monooxygenase activity suggested an important role for oxidative detoxification, particularly in resistance to neonicotinoid insecticides. Biological studies further indicated fitness costs associated with the resistant field population, including prolonged pre-oviposition and nymphal development, lower egg hatchability and nymphal survival, reduced fecundity, and a longer overall life cycle compared with the susceptible population. The findings demonstrate substantial variation in insecticide susceptibility among chemical groups and indicate the involvement of metabolic detoxification in resistance development in the Bargarh BPH population. These results provide useful baseline information for resistance surveillance and support the implementation of insecticide rotation, judicious insecticide use, and integrated pest management strategies for sustainable management of N. lugens in rice ecosystems