The emergence and spread of insecticide resistance among the main malaria vectors is threatening the effectiveness of vector control interventions in Senegal. The main drivers of this resistance in the Anopheles gambiae complex (e.g., An. gambiae and Anopheles coluzzii) remains poorly characterized in Senegal. Here we characterized the main target site and metabolic resistances mechanisms among the An. gambiae and An. coluzzii populations from their sympatric and allopatric or predominance area in Senegal. Larvae and pupae of An. gambiae s.l. were collected, reared to adulthood, and then used for insecticides susceptibility and synergist assays using the WHO (World Health Organisation) test kits for adult mosquitoes. The TaqMan method was used for the molecular characterization of the main target site insecticide resistance mechanisms (Vgsc-1014F, Vgsc-1014S, N1575Y and G119S). A RT-qPCR (Reverse Transcriptase-quantitative Polymerase Chaine Reaction) was performed to estimate the level of genes expression belonging to the CYP450 (Cytochrome P450) family. Plasmodium infection rate was investigated using TaqMan method. High levels of resistance to pyrethroids and DDT and full susceptibility to organophosphates and carbamates where observed in all three sites, excepted a probable resistance to bendiocarb in Kedougou. The L1014F, L1014S, and N1575Y mutations were found in both species. Pre-exposure to the PBO (Piperonyl butoxide) synergist induced a partial recovery of susceptibility to permethrin and full recovery to deltamethrin. Subsequent analysis of the level of genes expression, revealed that the CYP6Z1 and CYP6Z2 genes were over-expressed in wild-resistant mosquitoes compared to the reference susceptible strain (Kisumu), suggesting that both the metabolic resistance and target site mutation involving kdr mutations are likely implicated in this pyrethroid resistance. The presence of both target-site and metabolic resistance mechanisms in highly pyrethroid-resistant populations of An. gambiae s.l. from Senegal threatens the effectiveness and the sustainability of the pyrethroid-based tools and interventions currently deployed in the country. The Kdr-west mutation is widely widespread in An. coluzzii sympatric population. PBO or Duo nets and IRS (Indoor Residual Spraying) with organophosphates could be used as an alternative measure to sustain malaria control in the study area.

Background: Anopheles funestus is one of the major malaria vectors in sub-Saharan Africa. In Senegal, it is found across nearly all biogeographical areas, often replacing An. gambiae s.l. and sustaining malaria transmission during the dry season. Despite its recognized role as a major vector, the specific contribution of An. funestus to malaria transmission in many malaria-endemic areas remains underexplored. This study aims to assess the contribution of An. funestus in malaria transmission in two health districts in Central Senegal. Methods: Adult mosquitoes were collected from July 2018 to November 2019 in the health districts of Nioro (Ndramé Ndimb) and Ndoffane (Tawa Mboudaye) using Human Landing Catches (HLCs) and Pyrethrum Spray Catches (PSCs). Anopheline specimens were identified morphologically using standard dichotomous keys, with species confirmation performed by polymerase chain reaction (PCR). Plasmodium falciparum infection and blood meals sources were determined using Enzyme-Linked Immunosorbent Assay (ELISA) techniques. Results: A total of 6,932 Anopheles mosquitoes were collected. Of these, 73.7% (5,108/6,932) were identified as An. funestus , which was the predominant species at both study sites, with 1,364 specimens collected in Nioro and 3,744 in Ndoffane. Molecular analysis confirmed that An. funestus sensu stricto (s.s) was the only member of the An. funestus group recorded. In Ndramé Ndimb, the mean human biting rate and indoor resting density were 2.8 bites per person per night (b/p/n) and 9.0 females per room (f/r), respectively, compared to 12.4 b/p/n and 19.1 f/r in Tawa Mboudaye. The P. falciparum circumsporozoite rate was 0.3% in both villages, resulting in estimated entomological inoculation rates (EIRs) of 0.008 and 0.038 infected bites per person per night in Ndramé Ndimb and Tawa Mboudaye, respectively. The human blood index was relatively low, with only 22.3% (324/1,452) of An. funestus specimens found to have fed on humans. Conclusions: This study highlights the predominance of An. funestus and its important role in sustaining residual malaria transmission in central Senegal, even where overall transmission intensity remains low.

Background: The biting and resting behaviours of Anopheles species, which are human malaria vectors, are specifically linked to ecological and climatic requirements that characterize certain geographical settings, such as forests and humid savannah areas where favourable conditions for malaria mosquitoes are found. In southern Senegal, the outdoor resting behaviour of Anopheles gambiae s.l. populations is suspected to be a major problem in malaria control, given that indoor-based control tools are currently deployed across the country. A longitudinal study was conducted to investigate the population dynamics, trophic preferences and resting behaviours of Anopheles gambiae s.l. in mainland and island areas in south-western Senegal. Methods: Indoor and outdoor resting mosquitoes were collected from September 2020 to November 2021 using Pyrethrum Spray Catches and Prokopack aspirators, respectively. Field-collected mosquitoes were morphologically identified using conventional dichotomous keys, and in the laboratory, the mosquito blood meal source and molecular species identification were determined using enzyme-linked immunosorbent assays and polymerase chain reaction, respectively. Results: Out of 765 Anopheles collected, 181 were from the mainland, and 584 were from the island. Anopheles gambiae s.l. was the predominant species (91.1%), with seasonal variation. The indoor resting densities did not significantly differ ( P = 0.082) between the mainland (0.41 females per room) and island (4.09 females per room) areas. In mainland areas, the human blood index (HBI) was significantly greater ( P = 0.035) in indoor resting females (76.2%) than in outdoor resting females (47.6%), whereas in island areas, the HBI was generally lower, with no significant difference ( P = 0.51) between indoor (25.1%) and outdoor (31.1%) resting populations. Endophilic populations had greater HBIs in mainland areas than in island areas ( P = 2.63 × 10 ⁻⁵ ), whereas no significant difference was observed for exophilic populations ( P = 0.13). Conclusions: These findings provide a preliminary basic understanding of the feeding and resting behaviours of Anopheles gambiae s.l. populations in mainland and island areas for evidence-based malaria control programmes. Graphical

Malaria is a public health problem in Senegal, with heterogeneous transmission and little known about transmission drivers at the Senegalese border. This study aimed to determine bionomics of major vectors and malaria transmission in the Senegambian border. The study was conducted from July 2023 to March 2024 in Nemataba and Ndrame Ndimb (near the border), and in Medina Dianguette and Paoskoto (farther). Adult mosquitoes were collected using human landing catches and pyrethrum spray catches. Laboratory analyses were performed by Enzyme-Linked Immunosorbent Assay and Polymerase Chain Reaction techniques. Anopheles gambiae s.l. human biting rates (HBRs) were 1.05 bites/person/night (b/p/n) in Nemataba and 6.55 b/p/n in Ndrame Ndimb, while they were 14.73 b/p/n in Medina Dianguette and 1.47 b/p/n in Paoskoto. Anopheles funestus HBR was 2.88 b/p/n in Paoskoto and 0.37 b/p/n in Ndrame Ndimb. Human blood index for An. gambiae s.l. were 77.08% in Medina Dianguette, 66.67% in Nemataba, 2.42% in Ndrame Ndimb and 0 in Paoskoto, while for An. funestus they were 5.93% in Ndrame Ndimb and 3.65% in Paoskoto. Malaria transmission was detected in Medina Dianguette and Paoskoto, with 0.078 and 0.209 ib/p/n, respectively. This study highlights the diverse bionomic characteristics of major malaria vectors along the Senegambian border.

Anopheles arabiensis is a major malaria vector in Senegal, particularly in the Dakar region. The lack of a reference colony limits research on its biology and vector control. This study aimed to establish a stable An. arabiensis colony from urban populations in Keur Massar and Rufisque. Larvae were collected from 11 breeding sites and reared under controlled insectary conditions up to the F2 generation. Emergence rate, sex ratio, blood-feeding rate, and reproductive success were monitored. Species identification was performed morphologically and confirmed by PCR. Data were analyzed using R software, and differences between generations were assessed using Pearson’s chi-square test. Emergence rates in Keur Massar were 98.76%, 84.56%, and 85.15% for F0, F1, and F2, respectively, compared with 98.46%, 77.79%, and 86.22% in Rufisque. Females were most prevalent than the males, in both Keur Massar and Rufisque. In F2, blood-feeding rates reached 63.31% in Keur Massar and 90.91% in Rufisque. Eppendorf tubes inhibited oviposition, making group oviposition necessary for colony stabilization. PCR confirmed An. arabiensis. The study demonstrates the feasibility of establishing a stable An. arabiensis colony from Senegalese urban populations, providing a useful resource for future vector research and control strategies.