Study in Benin: Anopheles coluzzii mosquitoes resist deltamethrin and alpha-cypermethrin, with stronger resistance in farming areas with heavy pesticide use

A study published in Tropical Medicine and Health on 20 September 2026 (featured by MalariaWorld on 8 October 2026) assessed pyrethroid resistance in Anopheles coluzzii collected in southern Benin, from two agricultural areas (Sèmè-Kpodji, Abomey-Calavi) and one non-agricultural urban area (Yenawa).

Main points

• Methods: WHO tube bioassays with deltamethrin 0.05% and alpha-cypermethrin 0.05%; species identification by PCR-SINE200; kdr-West (L1014F) genotyping by PCR; P450, esterase and GST enzyme activity, and expression of CYP6Z1, CYP9K1 and GSTE2 by RT-qPCR.
• Results: all populations were resistant to both insecticides, with mortality of 78–82% for deltamethrin and 36–89% for alpha-cypermethrin. Alpha-cypermethrin resistance was stronger in farming areas: Sèmè-Kpodji 36% and Abomey-Calavi 52%, against 89% in Yenawa.
• All specimens were Anopheles coluzzii. The resistant kdr-West allele occurred at 73.3–93.3%, with no susceptible homozygotes. P450, GST and esterase activity was clearly raised, especially in Sèmè-Kpodji and Yenawa; however, CYP6Z1, CYP9K1 and GSTE2 were not overexpressed relative to the susceptible N’Gousso strain.
• The authors conclude that resistance is multifactorial; agricultural pesticide use strengthens it, while high kdr markers in the city point to extra selection from public health and household insecticides. They call for integrated resistance management combining regulation of farm pesticides, continuous resistance surveillance and next-generation tools.

VPMA’s note

The results show that both farm and household insecticides can drive pyrethroid resistance in mosquitoes. Members should rotate insecticide classes as guided, check results after treatment and report to health authorities when efficacy drops.

Source: MalariaWorld – Agricultural practices drive multifactorial pyrethroid resistance in Anopheles coluzzii populations from southern Benin (Trop Med Health 2026;54:203) (summarised in English by VPMA). Read the Vietnamese page.

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