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Background  The use of insecticides, through indoor residual spraying and long-lasting insecticide-treated nets (LLINs), is essential to control malaria vectors. However, the sustainability of these tools is challenged by the spread of insecticide resistance in  Anopheles  mosquitoes. This study was conducted to assess the susceptibility to insecticides and to determine the resistance mechanisms in malaria vectors in Dielmo, a rural area of western Senegal where LLINs were introduced a decade ago.    Methods  CDC bottle bioassays were used to determine the susceptibility of 2–5 day-old unfed  Anopheles gambiae  s.l. females to alphacypermethrin (12.5 µg/bottle), deltamethrin (12.5 µg/bottle), etofenprox (12.5 µg/bottle), lambdacyhalothrin (12.5 µg/bottle), permethrin (21.5 µg/bottle), DDT (100 µg/bottle), bendiocarb (12.5 µg/bottle), pirimiphos-methyl (20 µg/bottle) and fenitrothion (50 µg/bottle). The involvement of glutathione- S -transferases (GSTs) in insecticide resistance was assessed using a synergist, etacrynic acid (EA, 80 µg/bottle). Polymerase chain reaction (PCR) was used to investigate the presence of ‘knock-down resistance ( kdr )’ mutation and to identify sibling species within the  An. gambiae  complex.    Results  CDC bottle bioassays showed that mosquitoes were fully susceptible to lambdacyhalothrin, bendiocarb and fenitrothion. Overall, mortality rates of 97, 94.6, 93.5, 92.1, and 90.1% were, respectively, observed for permethrin, deltamethrin, pirimiphos-methyl, etofenprox and alphacypermethrin. Resistance to DDT was observed, with a mortality rate of 62%. The use of EA significantly improved the susceptibility of  An. gambiae  s.l. to DDT by inhibiting GSTs ( p  = 0.03). PCR revealed that  Anopheles arabiensis  was the predominant species (91.3%; IC 95 86.6–94%) within  An. gambiae  complex from Dielmo, followed by  Anopheles coluzzii  (5.4%; IC 95 2.7–8.1%) and  Anopheles gambiae  s.s. (3.3%; IC 95 0.6–5.9%). Both 1014F and 1014S alleles were found in  An. arabiensis  population with frequencies of 0.08 and 0.361, respectively, and 0.233 and 0.133, respectively in  An. coluzzii . In  An. gambiae  s.s. population, only  kdr  L1014F mutation was detected, with a frequency of 0.167. It was observed that some individual mosquitoes carried both alleles, with 19 specimens recorded for  An. arabiensis  and 2 for  An. coluzzii . The presence of L1014F and L1014S alleles were not associated with resistance to pyrethroids and DDT in  An. arabiensis .    Conclusions  The co-occurrence of 1014F and 1014S alleles and the probable involvement of GSTs enzymes in insecticide resistance in  An. gambiae  s.l. should prompt the local vector programme to implement non-pyrethroid/DDT insecticides alternatives.

malaria journal

Investigating insecticide resistance and knock-down resistance (kdr) mutation in Dielmo, Senegal, an area under long lasting insecticidal-treated nets universal coverage for 10 years