The evolution of the genetic structure of populations of two species of the Anopheles gambiae s.l. complex using the Kdr gene before and after indoor residual spraying in some agroecological zones of Benin (West Africa)

Abstract

Abstract In Benin, the resistance of An. gambiae s.l. mosquitoes to pyrethroids remains a major concern. The development and use of alternative insecticides seems to be the solution. Organophosphates (Actelic@300 CS) are currently the best candidates to meet this challenge. The present study aims to compare the genetic structure of vector populations of two species of the An. gambiae complex through the L1014F resistance allele of the Kdr gene during two periods marked by characteristic environments to better understand its impact on the dynamics and biology of these organisms. Eight localities divided into three agro-ecological zones, one of which is a control, were studied. Larval surveys were carried out during the rainy seasons from May to July 2016 for the pre-PID period and from May to November 2018 for the subsequent period. Larvae were reared at the insectarium of the Centre de Recherche Entomologique de Cotonou. The adult females obtained were identified morphologically and by molecular approaches. The genetic structure of the populations at various hierarchical levels could be determined using the L1014F and L1014L alleles of Kdr. Molecular analysis revealed three vector species of the An. gambiae complex both before and after IRS, two of which were in the majority. These were 171 An. coluzzii, 297 An. gambiae s.s., 11 An. arabiensis and 211 An. coluzzii, 256 An. gambiae s.s., 8 An. arabiensis respectively out of 479 sampled before treatment and 475 sampled after IRS. In both An. gambiae s.s. and An. coluzzii, the gene frequency of L1014F was found to increase significantly following treatment, approaching the limit of fixation in some populations. A deficit of heterozygosity is widespread with values of the indices, FST, FSC and FCT, expressing little or no differentiation within and between the defined populations. IRS didn’t adversely affect the selection and spread of the L1014F resistant allele of the Kdr gene. The apparent adaptation of An. coluzzii to polluted areas would be a factor in its proliferation to the detriment of its twin sister An. gambiae in IRS areas. The genetic structuring of the populations, whatever the species, remains almost the same despite the treatment.