Monitoring insecticide resistance in cotton leafhopper in relation to enzymatic activity in major cotton growing areas of central India

Insecticide resistance complicates pest management by reducing chemical effectiveness and increasing environmental pollution from higher application rates. Monitoring resistance is essential before recommending chemicals in any agro-ecological region. The present study evaluated the extent and mechanisms of insecticide resistance in the cotton leafhopper, Amrasca biguttula biguttula (Ishida) (Hemiptera: Cicadellidae), across major cotton-growing regions of Maharashtra, India over five consecutive years, from 2015-16 to 2019-20 at ICAR-Central Institute for Cotton Research (CICR) in Nagpur. The bioassay studies using IRAC protocols revealed that populations collected from the Amravati district of Maharashtra exhibited higher LC₅₀ values for all tested insecticides, including Flonicamid 50WG, Thiamethoxam 25WG, Acetamiprid 20SP, Imidacloprid 17.8SL, Monocrotophos 36SL, Acephate 75SP, Clothianidin 50WDG, and Spiromesifen 22.9SC. The tentative discriminating doses were established based on a susceptible population of A. biguttula at 1, 0.2, 0.05, 0.01, 0.001, 0.0001, and a control of 0 ppm. Using standardized IRAC bioassay protocols, we assessed resistance levels for eight insecticides and noted significant increases in LC₅₀ values. Notably, the A. biguttula biguttula populations from Yavatmal, Chandrapur, and Amravati exhibited critical resistance to neonicotinoids and other classes of insecticides. Biochemical assays revealed elevated activities of detoxifying enzymes, including cytochrome P450 monooxygenases, carboxylesterases, and glutathione S-transferases (GST), indicating metabolic resistance as a key mechanism. Notably, Amravati populations displayed the highest enzyme activities (e.g., GST up to 555.56 pmol/min/mg protein), correlating with intense insecticide use. These findings emphasize the need for integrated pest management (IPM) strategies, including insecticide rotation, biological controls, and resistant cotton hybrids, to mitigate insecticide resistance and minimise environmental impact. Regular monitoring of resistance and enzyme activity is essential for sustainable pest control in cotton ecosystems.