Mechanism of metabolic resistance in Anopheles coluzzii to insecticides in two urban areas of southern Benin

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Abstract
Malaria is a disease transmitted by the Anopheles gambiae complex, represented mainly in Benin by the sister species An. coluzzii and An. gambiae sensu stricto. Intensive vector control interventions have selected physiological, behavioural and biochemical adaptation mechanisms in these populations of An. vectors. This study aimed to investigate the mechanism of the metabolic resistance of An. coluzzii to insecticides in two urban areas in southern Benin. Larvae and pupae of An. gambiae s.l. and were collected in the municipalities of Cotonou and Porto-Novo between May and August 2021. The World Health Organization (WHO) sensitivity tests were performed on adult An. gambiae s.l. derived from larvae and pupae. Diagnostic doses of 0.05% deltamethrin, 0.75% permethrin, and 0.1% bendiocarb were used. Species belonging to the An. gambiae complex were identified by PCR, and detoxification enzymes (oxidase, glutathione-S-transferase and esterase) were investigated in An. coluzzii. The results showed that An. gambiae s.l. developed resistance to deltamethrin, permethrin and suspected resistance to bendiocarb in the municipalities of Porto-Novo and Cotonou. In addition, the PCR results revealed that An. coluzzii was the predominant species in the municipalities of Cotonou (p < 0.0001) and Porto-Novo (p = 0.002) compared with An. gambiae. Biochemical analysis revealed significantly greater oxidase activity in An. coluzzii in the municipality of Cotonou (p < 0.0001) and low activity in Porto-Novo (p = 0.0958) compared with the susceptible An. coluzzii N’gousso reference strain. Compared with the susceptible An. coluzzii N’gousso reference strain, very high GST activity was detected in the populations of An. coluzzii of Cotonou (p < 0.0001) and Porto-Novo (p = 0.0015). Finally, significantly greater esterase activity (α- and β-esterase) was detected in Porto-Novo than in the susceptible reference strain An. coluzzii N’gousso. Low but not significant esterase activity was also observed in An. coluzzii in Cotonou (p = 0.2120). This study reveals metabolic resistance mechanisms to pyrethroids and carbamates in An. coluzzii populations in the Porto-Novo and Cotonou municipalities. This study confirms the involvement of detoxification enzymes in increased tolerance to these insecticides.

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