Evidence that agricultural use of pesticides selects pyrethroid resistance within Anopheles gambiae s.l. populations from cotton growing areas in Burkina Faso, West Africa

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Résumé

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.

Mots-clés

pesticides, selection of resistants populations , cotton systems, Anopehles