Abstract
Many studies have shown the role of agriculture in the selection and spread of resistance of Anopheles gambiae s.l. to insecticides. However, no study has directly demonstrated the presence of insecticides in breeding sources as a source of selection for this resistance. It is in this context that we investigated the presence of pesticide residues in breeding habitats and their formal involvement in vector resistance to insecticides in areas of West Africa with intensive farming. This study was carried out from June to November 2013 in Dano, southwest Burkina Faso in areas of conventional (CC) and biological cotton (BC) growing. Water and sediment samples collected from breeding sites located near BC and CC fields were submitted for chromatographic analysis to research and titrate the residual insecticide content found there. Larvae were also collected in these breeding sites and used in toxicity tests to compare their mortality to those of the susceptible strain, Anopheles gambiae Kisumu. All tested mosquitoes (living and dead) were analyzed by PCR for species identification and characterization of resistance genes. The toxicity analysis of water from breeding sites showed significantly lower mortality rates in breeding site water from biological cotton (WBC) growing sites compared to that from conventional cotton (WCC) sites respective to both An. gambiae Kisumu (WBC: 80.75% vs WCC: 92.75%) and a wild-type strain (49.75% vs 66.5%). The allele frequencies L1014F, L1014S kdr, and G116S ace -1R mutations conferring resistance, respectively, to pyrethroids and carbamates / organophosphates were 0.95, 0.4 and 0.12. Deltamethrin and lambda-cyhalothrin were identified in the water samples taken in October/November from mosquitoes breeding in the CC growing area. The concentrations obtained were respectively 0.0147ug/L and 1.49 ug/L to deltamethrin and lambdacyhalothrin. Our results provided evidence by direct analysis (biological and chromatographic tests) of the role of agriculture as a source of selection pressure on vectors to insecticides used in growing areas.
Highlights
The current control strategy of malaria is mainly based on limiting human-vector contact by the use of insecticide-treated nets (ITNs), this last decade, indoor residual spraying (IRS) of insecticides has scaled up many African countries [1]
Mortality rates obtained with spring water were below 5% whatever the strain used, which confirms its non-contamination by insecticide residues or other pollutants
Comparing the susceptible strain mortality in water collected at breeding sites from Soumousso and Dobao, we found a highly significant difference (n = 400, P-Kisumu (Dobao vs Soumousso) < 0.0001, χ = 30.83, df = 1) (Fig 2)
Summary
The current control strategy of malaria is mainly based on limiting human-vector contact by the use of insecticide-treated nets (ITNs), this last decade, indoor residual spraying (IRS) of insecticides has scaled up many African countries [1]. The emergence and distribution of the resistance to insecticides of Anopheles gambiae s.l. perfectly overlaps the cotton areas where there is an increase of allelic frequencies of kdr mutations L1014F and ace-1R [20, 21] within the past five years and a very extensive geographic spread of resistance towards new cotton areas previously free of resistance [22]. These examples of agricultural-related resistance threaten the efficacy of insecticide-based vector control (LLIN) tools, in West Africa [5, 22, 23]
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