Cotton production in Benin: a cause of the emergence of insecticide resistance in populations of Anopheles gambiae in Benin

Background: Agricultural pesticides may play a profound role in selection of resistance in field populations of mosquito vectors. The objective of this study is to investigate possible links between agricultural pesticides use and development of resistance to insecticides by the major malaria vector Anopheles gambiae from cotton field.Method: Susceptibility to 4% DDT, 0.05% deltamethrin, 0.75% permethrin, 0.1% bendiocarb was assessed using the WHO standard procedures for adult mosquitoes from cotton field. Tests were carried out with two to three days-old, non-engorged female mosquitoes. The An. gambiae Kisumu strain was used as a reference. Knockdown effect was recorded every 5 min and mortality scored 24 h after exposure. Mosquitoes were identified to species and molecular form by PCR-RFLP and genotypes at the knock down resistance (kdr) and, acetylcholinesterase mutations were determined in surviving specimens.Results: During this survey, full susceptibility to bendiocarb was recorded in all samples. WHO diagnostic tests showed high frequency of resistance in An. gambiae to permethrin (ranging from 3% to 4% mortality), deltamethrin (13% to 22%), DDT (1.01% to 2%) in the seven selected areas. The Kdr gene seemed the main target- site resistance mechanism detected at the rates ranging from ranging from 65 to 71%. The frequency of ace-1R gene was found but at very low frequency (< 0.1).Conclusion: This investigation of malaria vector susceptibility to insecticides revealed a strong resistance to pyrethroid insecticides (permethrin and deltamethrin). This Pyrethroid resistance may seriously jeopardize the efficacy of of IRS and LLINs on which, most African countries including Benin, rely to reduce malaria transmission. The current findings will help for decision making in the National Malaria control program particularly in the choice of insecticide to use during campaigns of Indoor residual spraying in this part of Benin.