Stage-specific insecticide susceptibility of Culex quinquefasciatus in an urban area of Gujarat, India

Abstract

Background: Culex quinquefasciatus is an important urban mosquito vector in India, and chemical insecticides remain the primary tool for controlling it. The prolonged use of larvicides and adulticides in urban environments has raised concerns regarding the development of insecticide resistance, which can compromise vector control.Methods: Larval and adult Cx. quinquefasciatus were collected from urban areas of Rajkot City, Gujarat during 2006-2007. Larval susceptibility to Abate (temephos 50% EC) and Baytex (fenthion 82.5% EC) was evaluated using standard larval bioassays, with mortality recorded at different exposure durations. Adult susceptibility to deltamethrin (0.05%) and malathion (5%) was assessed using WHO bioassay procedures. In addition, the fumigant effects of the commercially available insecticides cyfluthrin (0.025%) and transfluthrin (0.04%) were evaluated at room temperature.Results: Larval bioassays revealed variable susceptibility to organophosphate larvicides, with Baytex (fenthion 82.5% EC) showing higher effectiveness than Abate (temephos 50% EC), particularly during longer exposure periods. Adult bioassays indicated tolerance to deltamethrin (0.05%) and resistance to malathion (5%). The commercial insecticide formulation produced moderate to high adult mortality, with increased effects observed after prolonged exposure to the formulation.Conclusion: These findings indicate stage-specific resistance patterns in urban Culex quinquefasciatus populations from Rajkot and highlighted the limitations of relying solely on chemical insecticides for mosquito control. Regular monitoring of susceptibility status and resistance management strategies is essential for improving the effectiveness of urban vector control programs.