Susceptibility status of Culex pipiens larvae (Diptera: Culicidae) to the main insecticides used in larval control in the regions of Rabat and Casablanca in Morocco

Abstract

In Morocco Culex pipiens mosquitoes cause serious nuisance in most urban areas. Control programs mainly rely on chemical insecticides, but numerous failures have been reported in the area, suggesting the development of resistant populations. In this study, we determined the resistance levels of the larval populations to two organophosphates; temephos and chlorpyriphos, commonly used in four prefectures from the regions of Rabat and Casablanca. We conducted bioassays following WHO standard procedures to calculate lethal concentrations LC₅₀ and LC₉₀ then resistance ratios by dividing values for the tested strains by those of the susceptible strain. We show that larval populations of Cx. pipiens developed resistance to temephos and chlorpyriphos in all four sites with different levels. We argue this is due to heterogeneous selection pressure triggered by local treatment practices. The high levels of resistance developed to these insecticides in the four studied areas may compromise their use in mosquito control. It hence becomes urgent to find alternatives to control larval populations of Cx. pipiens in these regions.

Keywords:

• Culex pipiens
• Insecticide resistance
• susceptibility
• organophosphates
• insecticides
• Morocco

Acknowledgements

Authors are thankful for the support from the University Hassan II of Casablanca and the Moroccan Ministry of National Education, Professional Training, Higher Education and Scientific Research and the Institut National d’Hygiène of Rabat from the Moroccan Ministry of Health. Authors are also grateful to Mr. Laqrâa Houssein and Mr. El Kohli Mohammed from Institut National d’Hygiène of Rabat and Mr. Youssef Ben Omar from the Municipal Hygiene office of Mohammedia for their help and all their guidelines for the collection of biological material.

Disclosure statement

No potential conflict of interest was reported by the authors.