Urban adaptation and pyrethroid resistance driven by molecular resistance mechanisms in Anopheles coluzzii populations from a peri‑urban setting in southwestern Nigeria.

BACKGROUND

Urbanisation and increasing insecticide resistance threaten malaria vector control in Nigeria. This study assessed mosquito species composition, insecticide susceptibility and molecular resistance mechanisms in Anopheles gambiae s.l. populations in Ado-Odo Ota, Ogun State, Nigeria.

METHODS

Mosquitoes were collected from January to June 2024 using CDC light traps and larval sampling. Specimens were identified morphologically and confirmed by PCR. Insecticide susceptibility of 150 adult female mosquitoes was evaluated using WHO protocols for permethrin (0.75%) and deltamethrin (0.05%). Knockdown resistance (kdr) mutations (L1014F and L1014S) were detected using allele-specific PCR.

RESULTS

A total of 579 mosquitoes were collected, of which 197 were identified as Anopheles gambiae s.l. Molecular analysis identified Anopheles coluzzii as the predominant species within the analysed subset. Vector abundance increased during the rainy season. Resistance to permethrin was observed, with mortality of 22% (95% CI: 14.6 - 30.9%), while susceptibility to deltamethrin remained high at 98% (95% CI: 93.0 - 99.8%). Knockdown time was prolonged for permethrin (KDT50: 107 mins, 95% CI: 71.1 - 142.0; KDT95: 156 mins, 95% CI: 91.1 - 221.0) compared to deltamethrin (KDT50: 39.9 mins, 95% CI: 38.2 - 41.5 min; KDT95: 60.8 mins, 95% CI: 57.6 - 64.0 min). kdr mutations were identified in fifteen analysed specimens (n = 15), indicating the presence of resistance-associated alleles.

CONCLUSION

These findings highlight the need for continued resistance surveillance and integrated vector management strategies.