Abstract: Introduction: Dengue, a major re-emerging mosquito-borne viral disease, continues to pose a serious public health threat in India, including Delhi. With no effective vaccine or antiviral treatment available, vector control particularly the use of insecticides like Temephos remains the primary prevention strategy. However, repeated use of the same insecticides has led to growing concerns about resistance in Aedes aegypti mosquitoes.
Method: A door-to-door entomological survey conducted in South Zone, Delhi during July 2025 to assess the susceptibility of Aedes aegypti larvae against Temephos using WHO protocols. Larvae collected from various household containers were exposed to four concentrations of Temephos, with mortality recorded after 24 hours. Probit analysis revealed reduced susceptibility in field populations, highlighting the need for regular monitoring and alternative control strategies.
Results: The bioassay results show that Aedes aegypti larvae from South Zone, Delhi exhibited varying levels of resistance against Temephos. At lower concentrations (0.002-0.004 mg/L), mortality remained below the WHO threshold, confirming resistance, while higher doses (0.008 mg/L) showed possible resistance. Complete susceptibility was observed only at 0.012 mg/L, with LC50 and LC90 values calculated as 0.0022 mg/L and 0.0058 mg/L, respectively.
Conclusion: This study from eight selected localities of South Zone, Delhi reveals reduced susceptibility of Aedes aegypti larvae against Temephos, with resistance detected at lower concentrations and susceptibility restored only at higher doses. Continuous use of Temephos under the Urban Malaria Scheme (UMS) for over two decades appears to be driving this trend. The findings emphasize the need for routine resistance monitoring, rotational use of alternative larvicides, and stronger Integrated Vector Management (IVM) practices. Regular surveillance and timely policy adjustments are essential to sustain the effectiveness of dengue control programs and protect public health.
