Evolution of vector susceptibility to insecticides and usage of pesticides by farmers in the city of Yaoundé Cameroon

Introduction:
The combined use of insecticides in agriculture and disease prevention constitute a potential inducers for resistance in malaria vectors. Prevention strategies combining larval control could improve insecticide resistance management. The present study aimed to assess the evolution of An. gambiae populations susceptibility to insecticides in the city of Yaoundé Cameroon.
Methods: WHO susceptibility tests, synergist PBO and CDC bottle bioassays were conducted on adults Anopheles gambiae s.l. mosquitoes aged 3 to 5 days emerging from larvae collected from the field. Seven insecticides (deltamethrin, permethrin, DDT, bendiocarb, propoxur, fenitrothion and malathion) were evaluated. Additionally, the target site mutations conferring insecticide resistance (kdr) were investigated using Taqman assay and mosquito species were identified using SINE-PCR. Surveys with retailers and farmers were conducted to assess the type of pesticide sold on the market and used by farmers.
Results: The study revealed high insecticide resistance patterns in An. coluzzii and An. gambiae s.s. populations to different types of insecticides. A high frequency of the L1014F resistance allele was detected. Metabolic resistance was present. High insecticide resistance intensity to pyrethroids was observed. Many synthetic fertilizers and insecticides families including pyrethroids, organochlorines, carbamates, organophosphates, neonicotinoids and nicotinoids were commonly used as pesticides by farmers in Yaoundé. Retailers did not had great knowledge of insecticide sold. Safety measures were not effectively implemented. The study also indicated excessive and improper use of pesticide by farmers.
Conclusion: The present study showed rapid evolution of insecticide resistance in vector populations in Yaoundé and the possible influence of pesticide use by farmers in the development of insecticide resistance.
Keywords: Vector control; Anopheles gambiae; insecticide resistance; pesticide management; Yaoundé; Cameroon