Low Knockdown Resistance Frequency In Anopheles Gambiae Complex Resistant To Some Who-Approved Insecticides In Selected Areas Of Lagos State, South-West, Nigeria

Background: Decline in malaria prevalence is usually attributed to the efficient vector control strategies implemented in such endemic areas. The spread of insecticide resistance in Anopheles mosquitoes is a major drawback to the gains in malaria vector control. Here we assessed the susceptibility status of Anopheles gambiae s.l. to some selected WHO-approved insecticides and frequency of knockdown resistance gene in two Local Government Areas of Lagos State, Nigeria. Methods: Three to five days old adult female mosquitoes were exposed to deltamethrin, permethrin and bendocarb. Knockdown time was recorded every ten minutes and % mortality taken at 24hr post exposure. KDT50 and KDT95 were determined using probit regression analysis. The resistant mosquitoes were used for species identification by Polymerase Chain Reaction (PCR) assays and characterized for the knockdown resistance (kdr) mutation by allele-specific PCR (AS-PCR). Results: The results of twenty-four hour post exposure mortality rate showed that mosquitoes sampled at differ-ent locations were resistant to permethrin (39% mortality for Lagos Mainland L.G.A.; 45% for Kosofe L.G.A.), del-tamethrin (51% for Lagos Mainland L.G.A; 68% for Kosofe L.G.A), but susceptible to bendiocarb (100% for Lagos Mainland L.G.A.; 99% for Kosofe L.G.A.). The KDT50 varied from 34 minutes in bendiocarb for both LGAs to 190 minutes in deltamethrin for Kosofe and 119 minutes in permethrin for Lagos Mainland. In all insecticides tested for both LGAs, KDT95 was greater than 60 minutes. Only the 1014F kdr mutation was detected. The overall kdr frequen-cy was low (1.79%). There was no significant association between the presence of the 1014F kdr allele and ability of Anopheles mosquitoes to survive exposure to the tested insecticides (P > 0.05). Conclusion: This level of resistance to WHO approved insecticides is a threat to control programs and can have significant operational impact, if action is not taken.