Insecticides susceptibility of An. melas and its morphological discrimination with its sympatric siblings using the biometric palps technique

In the central western Senegal, great progress has been made against malaria following the successful implementation of effective malaria control interventions, including Indoor Residual Spraying (IRS) and Seasonal Malaria Chemoprevention (SMC). However, residual transmissions are still occurring in several hotspots involving some secondary vector species, such as An. melas. This study was undertaken in central and western costal area of Senegal, to provide the first data on the insecticide susceptibility of local An. melas population using WHO test kits, the allelic frequencies of the Kdr and Ace-1ᴿ mutations using qPCR and also re-evaluate the palp biometry technique as a proxy to discriminate An. melas from other freshwater species within the Gambiae complex. Insecticide susceptibility test revealed a susceptibility of An. melas to Pirimiphos-methyl, and Bendiocarb, the two main non-pyrethroid insecticides recommended by the WHOPES for use in public health. The molecular characterization of the Kdr and Ace-1 target site mutations revealed the absence of both mutations. The biometric palps technique has been a valid method for species diagnose between An. melas and its freshwater sibling. Indeed, while the former species collected exclusively from salty breeding sites (with a level of salinity above 21 g/l), consistently displayed a palpal index ≥0.81; the latter, sampled for breeding site of low salinity level (up to 3.6 g/l) and subsequently mainly identified as An. arabiensis and in a lesser extend as An. gambiae, presented a palpal index less than 0.81. This study has re-evaluated and validated the palps biometric technique as a morphological tool for the identification of An. melas, which population still susceptible to main insecticide used in public health and revealed the absence of KDR and Ace-1 mutations. The data provided here can help the Senegalese NMCP to better target and efficiently control An. melas populations in malaria hotspot, where they contribute to maintain residual transmission hampering the malaria elimination goal.