Impact assessment of CDC bottles treated with a combination of insecticide and synergist on insecticide-resistant Anopheles gambiae populations in Benin

Abstract

Despite the proven efficacy of LLINs and IRS in reducing malaria transmission, vector resistance to insecticides seriously threatens to undermine vector control efforts. The present study aims to assess the impact of CDC bottles treated with a combination of insecticide and DEF or PBO synergists on insecticide-resistant An. gambiae populations in Benin. The study was conducted in 13 localities in Benin, following the south_north transect from September 2019 to June 2020. Thus, adult females of An. gambiae s.l. reared from field-collected larvae were used to assess the susceptibility of the vectors to permethrin and bendiocarb. Molecular species identification, as well as L1014F Kdr and Ace-1R mutations, was performed using PCR. Also, the expression level of biochemical enzymes was assessed. Mortality rates obtained with permethrin ranged from 34% to 71% in the 13 localities in our study. When mosquitoes from these same populations were pre-exposed to PBO, mortality rates increased significantly and ranged from 52% to 97%. With bendiocarb alone, mortality rates ranged from 93% to 100% while pre-exposure of vectors to the synergist DEF resulted in 100% mortality for all localities. The present study showed that the addition of the synergist PBO or DEF to pyrethroids or carbamates significantly increased their effectiveness. Thus, dual-active LLINs such as PBO-based LLINs or IRS using a combination of bendiocarb and the synergist DEF should be evaluated in the Benin context for possible use as an alternative or rotation of vector control tools in Benin.