Mosquitoes that transmit dengue, chikungunya and Zika have developed resistance to the pyrethroid insecticide permethrin in several parts of Pune, raising concerns over the effectiveness of conventional mosquito-control measures. Researchers found that genetic mutations may be helping the mosquitoes survive insecticide exposure that would normally kill them.
Study Tested Mosquitoes From Nine Pune Wards
The findings emerged from a study conducted by researchers associated with the ICMR-National Institute of Virology (ICMR-NIV) and ICMR-National Institute of Translational Virology and AIDS Research (ICMR-NITVAR).
Researchers collected Aedes aegypti mosquitoes from nine wards across Pune Municipal Corporation areas Pashan, Susgaon, Khadki, Yerawada, Warje, Hadapsar, Kondhwa, Kothrud and Dhankawdi between February and May 2024.
The adult mosquitoes were exposed to the standard 0.75% permethrin dose used in World Health Organisation (WHO) susceptibility testing to determine their survival rates.
Resistance Found in Six Wards
The study found clear resistance to permethrin among mosquitoes from Khadki, Pashan, Susgaon, Warje, Hadapsar and Kondhwa. A significant proportion of mosquitoes from these areas survived exposure to the insecticide.
Yerawada showed an intermediate level of resistance, while mosquitoes from Kothrud and Dhankawdi remained susceptible, with most dying after exposure.
Researchers suggested that areas reporting higher dengue cases may have experienced more frequent insecticide spraying, potentially contributing to resistance. However, the study did not directly measure insecticide use in individual areas and therefore could not establish a direct link between spraying and resistance.
Genetic Mutations Linked to Resistance
The researchers also examined genetic changes known as knockdown resistance (kdr) mutations, which occur in a gene targeted by pyrethroid insecticides.
Four mutations were identified in different combinations across the study areas. The F1534C mutation was the most widespread and was detected in mosquitoes from Khadki, Susgaon, Warje, Yerawada and Hadapsar.
The S989P and V1016G mutations were found together in Pashan and Kondhwa, while the T1520I mutation was detected only in Hadapsar.
Resistance Could Have Implications for Other Pyrethroids
Although permethrin is not routinely used in India’s current vector-control programme, it belongs to the synthetic pyrethroid family, which includes other insecticides used for mosquito control.
Because these insecticides act through similar mechanisms, the researchers indicated that the resistance observed in Pune could have implications for the effectiveness of other pyrethroids as well.
The study has therefore highlighted the need for regular, local-level monitoring of insecticide resistance and appropriate adaptation of mosquito-control strategies.
Experts Call for Regular Monitoring and Insecticide Rotation
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 continued use of the same insecticide could gradually reduce its effectiveness and called for regular monitoring and rotation of insecticides.
Former ICMR-National Institute for Vector Control Research scientist Dr T Mariappan also noted that insecticide resistance has remained a persistent challenge in mosquito control. He said resistance can emerge against successive classes of insecticides, including pyrethroids such as permethrin and deltamethrin, particularly when they are used indiscriminately.
PMC Steps Up Mosquito-Control Measures
Meanwhile, the Pune Municipal Corporation (PMC) said it has intensified mosquito-control measures across the city amid conditions favourable for mosquito breeding.
The civic body said it had reviewed dengue, chikungunya and malaria cases over the past three years and conducted a map-based analysis across all 41 wards.
Departments have been directed to identify and eliminate breeding sites, including stagnant water at construction sites, roads, drains, parks and other public spaces.
The PMC also said it is using Gambusia fish, which feed on mosquito larvae, in fountains and other municipal parks and public spaces. The civic body’s focus, it said, is on preventing mosquito breeding at the source through coordinated action across departments.