Pyrethroid cross resistance spectrum among populations of Anopheles gambiae s.s. from Cote d'Ivoire

Field samples of Anopheles gambiae s.s. from Cote d'Ivoire were tested with 5 pyrethroids (cyfluthrin, lambda-cyhalothrin, alpha-cypermethrin, deltame thrin, permethrin), 1 pseudo-pyrethroid (etofenprox), and an organochlorine (DDT). With the use of World Health Organization diagnostic tests, 5 out o f 6 samples were found cross-resistant to these insecticides. A strong decr ease in knockdown effect and mortality was also observed when testing delta methrin-impregnated nettings. With a polymerase chain reaction amplificatio n of spe cific alleles diagnostic test, resistance was found associated wit h the presence of a kdr mutation. The strong correlation between kd, alleli c frequency and resistance to DDT or etofenprox indicated that kdr was the main resistance factor for these 2 insecticides. On the contrary, a lower c orrelation was observed between kdr frequency and resistance to 4 of the 5 pyrethroids tested, suggesting that another mechanism was also involved, li kely a metabolic detoxification. These results point out the necessity to m onitor pyrethroid resistance and the presence of kdr before implementation of any impregnated bed-net programs for malaria control.