Assessment of insecticide resistance and enzymatic mechanisms in Helopeltis theivora from tea plantations of Assam

Aim: To investigate the extent of insecticide resistance in H. theivora within Assam's tea-growing areas and to understand the defence mechanism that contribute to its development. Methodology: Adult population of H. theivora from an organic tea plantation were collected for susceptible laboratory culture and other seven adult populations were collected from major tea-growing parts of Assam following conventional practices and reared under controlled laboratory conditions. The leaf dip method was used to conduct concentration mortality bioassays with thiamethoxam, deltamethrin and quinalphos. Biochemical assays were carried out to assess the activity of major detoxifying enzymes in the insects, including general esterases involved in hydrolysis, oxidative enzymes of cytochrome P450 family, and transferases that conjugate glutathione to xenobiotics. Furthermore, synergistic assays with piperonyl butoxide and diethyl maleate were carried out to evaluate their influence on the efficacy of insecticides. Results: Resistance to thiamethoxam and deltamethrin was quite significant, with resistance coefficients ranging 2.04-22.14 and 1.56-23.90 times, respectively. All tested populations remained susceptible to quinalphos (RC<1). Increased enzyme activities exhibited a strong positive correlation with LC50 values, while the use of synergists significantly improved the insecticide efficacy. Interpretation: The findings highlight the field-evolved resistance in H. theivora and its association with elevated detoxifying enzymes. This study recommends the strategic use of insecticides, rotation, and synergists for better resistance management, contributing to more sustainable pest control in tea plantations. Key words: Esterase, H. theivora, Insecticides, Tea mosquito bug