Impacts of Indoor Residual Spraying with Bendiocarb and Pirimiphos-methyl on Allelic Frequencies of kdr and ACE-1 Mutations in Central Senegal

Abstract

The use of long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) has been the primary vector control strategy in Senegal since 2007, significantly reducing the burden of malaria. However, the emergence of vector resistance to insecticides poses a serious threat to the effectiveness of these strategies. This study aimed to assess susceptibility, spatio-temporal variations and, the impact of IRS using bendiocarb and pirimiphos-methyl on allele frequencies and resistant genotype of kdr and Ace-1 in An. gambae s.l. in IRS and control zones in central Senegal between 2013 and 2014. Larvae of An. gambiae s.l. were collected from four IRS and two control districts in central Senegal. Adult females obtained from these collections were exposed to paper impregnated with pyrethroids, DDT, dieldrin, bendiocarb and pirimiphos-methyl over a two-year period. Specific identification of An. gambiae complex and the research into insecticide resistance markers were conducted using PCR. The species identified were characterized by investigating kdr mutations (Vsgc-1014F and Vsgc-1014S) and Ace-1 mutations. Susceptibility tests showed resistance to permethrin and deltamethrin in at least three of the four IRS districts, while control districts exhibited resistance or suspected resistance to these insecticides. Resistance to DDT and dieldrin was detected in all districts. However, susceptibility to bendiocarb and pirimiphos-methyl was observed in all An. gambiae s.l. populations in IRS districts. Identification of the An. gambiae complex revealed the presence of three species (An. arabiensis, An. gambiae s.s., and An. coluzzii) and hybrids. An. arabiensis populations collected from IRS areas exhibited significantly lower allele 1014F frequencies but significantly higher allele frequencies compared to those from control areas. The effects of IRS use with bendiocarb and pirimiphos methyl on allele frequencies were evident over the two-year period. This study suggests that IRS using bendiocarb and pirimiphos methyl may result in shifts in vector populations less likely to carry kdr mutations, potentially reducing the frequency of alleles 1014F and 1014S.