Delhi study finds slight dip in mosquito susceptibility to common insecticide

Researchers at the University of Delhi reported that a laboratory strain of Aedes aegypti survived the diagnostic dose of α-cypermethrin at a rate just below the 98% threshold, hinting at early resistance.

A University of Delhi team evaluated the effectiveness of the pyrethroid α-cypermethrin against a lab-reared Aedes aegypti population using WHO bottle tests, finding a 97.91% mortality rate at the diagnostic dose of 10 µg per bottle. This figure falls short of the 98% benchmark used to declare full susceptibility, prompting concerns of emerging resistance, according to first author Rohit Lakhwani. The experiment measured five detoxifying enzymes, with β-esterase showing the greatest predicted binding and a 21.41-fold activity increase at the LC50, while CYP450 activity doubled and α-esterase rose over sevenfold.

Conversely, glutathione S-transferase activity declined and acetylcholinesterase displayed weak binding. Although the colony had not been exposed to insecticides previously, the biochemical response suggests a potential shift in defensive biology. The study underscores the need for insecticide rotation, enzyme inhibitors, biological controls, and source reduction to preserve dengue-vector management tools. Public-health officials are advised to monitor enzyme markers and field mortality to pre-empt resistance development.