PYRETHROID RESISTANCE IN CULEX-QUINQUEFASCIATUS FROM WEST-AFRICA

Pyrethroid resistance was investigated in thirty-three samples of Cule x quinquefasciatus Say from twenty-five cities in Cote d'Ivoire and Bu rkina Faso. Permethrin resistance ratios at LC50 ranged from 9.5- to 8 2-fold in Cote d'Ivoire and from 17- to 49-fold in Burkina Faso. For d eltamethrin, resistance ratios were lower and ranged from nine to thir ty-eight in both countries. A strain was selected with permethrin to i nvestigate resistance mechanisms. After forty-two generations of selec tion, permethrin resistance level reached 3750-fold, but deltamethrin resistance remained unexpectedly unchanged. This indicated that a spec ific mechanism was involved in permethrin resistance. Synergist assays and biochemical tests indicated that resistance was partly due to P45 0-dependent oxidases. A target site insensitivity (kdr) was also invol ved, associated with DDT cross resistance and a dramatic loss of perme thrin knockdown effect on adults. This resistance should be taken into consideration when planning the use of pyrethroid-impregnated materia ls in urban areas, 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.