High Resistance to Deltamethrin and DDT in Major Malaria Vector Anopheles gambiae s.l. from South-Western Nigeria is Driven by Metabolic Resistance Mechanisms

Insecticide resistance in Anopheles gambiae s.l. poses a significant challenge to malaria vector control efforts in Nigeria. Both target-site insensitivity and metabolic resistance have been implicated in the resistance process, with the latter often receiving less attention. To address this, we assessed metabolic enzyme activities in Anopheles gambiae s.l populations resistant to Deltamethrin and Diethyldichlorotriethylethane (DDT) in South-West Nigeria. A total of 600 Anopheles larvae were collected from all sites (Ibadan, Oyo, Badagry and Lagos) and resistance was classified according to WHO guidelines. Insecticide-exposed and unexposed cohorts were examined for metabolic enzyme activities. Results were compared between exposed and unexposed samples: ANOVA (P<0.05). Mosquitoes were identified as An. gambiae (89%, Ibadan; 0%, Badagry) and An. coluzzii (11%, Ibadan; 100%, Badagry). The population exhibited varied resistance levels: Deltamethrin mortality was 26% in Ibadan and 71% in Badagry while DDT mortality rates were 2% and 44% respectively. Biochemical analysis revealed significantly elevated levels (P<0.05) of cytochrome P450 and glutathione-S-transferases in resistant vs susceptible samples. This finding underscores the need for integrated vector management strategies that specifically address metabolic resistance mechanisms in the country.