Mosquitoes that transmit dengue, chikungunya and Zika are showing resistance to permethrin in several parts of Pune, potentially reducing the effectiveness of insecticide-based mosquito control. A study by researchers associated with the Indian Council of Medical Research (ICMR) has identified genetic mutations that help Aedes aegypti mosquitoes survive exposure to permethrin, a synthetic pyrethroid insecticide that affects the mosquito nervous system. The findings highlight the need for regular surveillance of insecticide resistance and more targeted mosquito-control strategies.
Study Tests Mosquitoes Across Nine Pune Wards
Researchers from the ICMR-National Institute of Virology (ICMR-NIV), with affiliations to the ICMR-National Institute of Translational Virology and AIDS Research (ICMR-NITVAR), examined Aedes aegypti mosquitoes collected from nine areas of the Pune Municipal Corporation (PMC). The researchers exposed adult mosquitoes to 0.75% permethrin, the standard concentration used in World Health Organization (WHO) susceptibility testing. They then monitored mosquito survival to determine the level of insecticide resistance in each location.
Resistance Levels Vary Across Pune
The study found significant differences in permethrin resistance between wards. Mosquito populations from Khadki, Pashan, Susgaon, Warje, Hadapsar and Kondhwa showed clear resistance. A substantial proportion of mosquitoes survived the insecticide exposure, even though the standard test dose would normally kill susceptible mosquitoes. Yerawada recorded an intermediate level of resistance. In contrast, mosquito populations from Kothrud and Dhankawdi remained susceptible, with most mosquitoes dying following exposure to permethrin. These variations suggest that insecticide resistance is not uniform across the city and reinforce the importance of localised resistance monitoring.
Genetic Mutations Help Mosquitoes Survive
To understand the biological basis of resistance, the researchers also analysed the mosquitoes for genetic changes known as knockdown resistance (kdr) mutations. These mutations occur in genes targeted by pyrethroid insecticides and can alter the insecticide’s ability to affect the mosquito’s nervous system. The researchers identified four kdr mutations in different combinations across the study areas. The F1534C mutation was the most widely distributed and was detected in mosquitoes from Khadki, Susgaon, Warje, Yerawada and Hadapsar. Other mutations showed more localised distribution. S989P and V1016G occurred together in Pashan and Kondhwa, while T1520I was identified only in Hadapsar. The presence of these mutations provides important evidence of a genetic component behind the observed insecticide resistance.
Frequent Insecticide Use May Contribute to Resistance
The researchers suggested that areas reporting higher numbers of dengue cases may have experienced more frequent insecticide spraying. Repeated exposure can create selection pressure that favours mosquitoes carrying resistance-associated mutations. However, the study did not directly measure insecticide use in the individual wards. Therefore, it could not establish a direct cause-and-effect relationship between spraying frequency and the development of resistance. Nevertheless, the geographic differences in resistance underline the importance of monitoring how mosquito-control programmes affect local mosquito populations.
Why Pyrethroid Resistance Matters
Permethrin is not routinely used in India’s current vector-control programme. However, it belongs to the synthetic pyrethroid class, which includes other insecticides used for mosquito control. Because pyrethroids share similar modes of action, resistance detected against permethrin could have implications for the effectiveness of other pyrethroid insecticides. As a result, researchers have called for continued local surveillance of insecticide resistance so that mosquito-control programmes can adapt to changing resistance patterns.
Experts Call for Insecticide Rotation
The findings have prompted experts to emphasise the importance of monitoring and adapting vector-control strategies. Senior entomologist Dr Rahul Marathe, who was not involved in the study, said the findings should serve as a warning for Pune. He stressed that relying on the same insecticide across locations could gradually reduce its effectiveness as resistant mosquito populations increase. He also highlighted the importance of regular resistance testing and insecticide rotation as part of an effective mosquito-control strategy. Similarly, Dr T Mariappan, former scientist at the ICMR-National Institute for Vector Control Research, noted that insecticide resistance has remained a persistent challenge in mosquito control. According to him, mosquito vectors have developed resistance to successive classes of insecticides over time. Even newer compounds, including pyrethroids such as permethrin and deltamethrin, can face resistance, particularly when used indiscriminately. Therefore, continuous surveillance and flexible vector-control strategies are essential.
Source Reduction Remains Critical
The PMC’s approach focuses on preventing mosquito breeding at its source rather than relying solely on insecticides. This strategy is particularly important as mosquitoes develop resistance to chemical control measures. Eliminating stagnant water, improving drainage and maintaining public spaces can reduce mosquito breeding opportunities and complement insecticide-based interventions.
Monitoring Will Shape Future Mosquito Control
The emergence of permethrin resistance in Aedes aegypti populations across several Pune wards highlights a growing challenge for dengue and other mosquito-borne disease control. Genetic mutations such as F1534C, S989P, V1016G and T1520I provide evidence that mosquito populations are adapting to insecticide exposure. Going forward, combining insecticide-resistance surveillance, strategic insecticide rotation, source reduction and targeted vector-control measures could help maintain the effectiveness of mosquito-control programmes. As reported by thetimesofindia.com, the Pune findings also demonstrate why resistance patterns need to be assessed locally rather than assuming that a single insecticide strategy will work equally well across an entire city.