Susceptibility of Anopheles gambiae s.l. to pyrethroid insecticides in vegetable farms in the city of Yaoundé, Cameroon

Agricultural practices play a major role in the selection of insecticide resistance in field populations of Anopheles mosquitoes. Here, we investigated the possible links between agricultural practice and the resistance to pyrethroid insecticides in the major malaria vector Anopheles gambiae s.l in the city of Yaounde in Cameroon. Entomological surveys were conducted in the peri-urban and urban areas of Yaounde. KAP surveys on agricultural practice and the use of pesticides in vegetable farms were conducted in all farms and the susceptibility status of female Fo An. gambiae s.l progeny to permethrin (type I pyrethroid) and deltamethrin (type II pyrethroid) was assessed using the WHO tubes bioassay protocol. The resistance mechanisms were assessed using synergist and kdr-genotyping assays. Our findings revealed that the application of pesticide active molecules is a common practice in vegetable farms across Yaounde. This phenomenon has increased the development of resistance to pyrethroid insecticides in An. gambiae sl. The observed phenotypic resistance was higher in peri-urban sites (7% and 17% mortalities for deltamethrin and permethrin, respectively) than in urban sites (63 % and 17% mortalities for deltamethrin and permethrin, respectively). Synergist assays with PBO revealed the high implication of monooxygenase P450 enzymes in the observed phenotypic resistance pattern. The L1014F kdr-resistant allele is almost fixed in the exposed mosquito populations. These data suggest that the metabolic resistance with monooxygenase P450-enzymes might play a crucial role in the resistance of wild An. gambiae s.l. populations to type I and type II pyrethroid insecticides in vegetable farms across Yaounde.