The effects of impregnated bednets treated with
deltamethrin at a dosage of 25 mg a.i./m2 were evaluated at two testing stations in Côte d'Ivoire. The first one was located in Yaokoffikro, where Anopheles gambiae s.s. are resistant to
pyrethroids (including
deltamethrin), and the second in M'be, close to a large rice-growing area where An. gambiae s.s. are susceptible
pyrethroids. In both situations, treating bednets with
deltamethrin was very effective in limiting contact between man and vector. 72% fewer female An. gambiae entered the huts in the susceptible area, whereas a decrease of 43% was recorded in the resistant area, indicating that
deltamethrin still has a certain repellent effect on resistant populations of An. gambiae s.s. Overall mortality induced by bednets treated with
insecticide was significantly higher in the resistant area (56.4% as versus 44.3%). An explanation for this apparent paradox is that the mosquitoes being less repelled by the
insecticide remain on the treated material for longer periods of time and most of them eventually die. The results of this study indicate that bednets treated with
deltamethrin are an effective prophylactic measure even in areas where An. gambiae s.s. are resistant to
pyrethroids and should still be considered as a practical means of personal protection against
malaria even in
pyrethroid resistance areas with high frequency of kdr resistance genes.