Pyrethroid resistance in Culex quinquefasciatus from West Africa

Pyrethroid resistance was investigated in thirty-three samples of #Culex quinquefasciatus$ Say from twenty-five cities in Côte d'Ivoire and Burkina Faso. Permethrin resistance ratios at LC50 ranged from 9.5- to 82-fold in Côte d'Ivoire and from 17- to 49-fold in Burkina Faso. For deltamethrin, resistance ratios were lower and ranged from nine to thirty-eight in both countries. A strain was selected with permethrin to investigate resistance mechanisms. After forty-two generations of selection, permethrin resistance level reached 3750-fold, but deltamethrin resistance involved in permethrin resistance. Synergist assays and biochemical tests indicated that resistance was partly due to P450-dependent oxidases. A target site insensitivity (kdr) was also involved, associated with DDT cross resistance and a dramatic loss of permethrin knockdown effect on adults. This resistance should be taken into consideration when planning the use of pyrethroid-impregnated materials in urban area, as #Culex$ is by far the main source of nuisance. Any failure in nuisance control due to resistance is likely to demotivate people in using impregnated materials. (Résumé d'auteur