Background: In order to know the level of malaria transmission in the city of Karimama in the north East of Benin, an entomological study was carried out in this city from January to December 2020. Method : Firstly, the study was based on sampling adults mosquitoes by Human Landing Catches (HLC) in two villages performed monthly over two consecutive nights (8:00 PM to 6:00 AM) in 4 randomly selected compounds. These populations of mosquitoes were completed by Indoor Pyrethrum Spray Catches (PSC) in 10 other selected compounds; the same compounds in each sampling method being consistently used throughout the study. The head-thoraces of these females from the human landing catches were tested for the presence of CircumSporozoite Protein (CSP). Finally, Knocked down mosquitoes falling on white bed sheets were preserved for identification of species and characterization of molecular forms within the An. gambiae complex were performed using Polymerase Chain Reaction (PCR). Results: i)-During the year of study, 9.019 female mosquitoes were caught by PSC against 21.474 by HLC among which, 26% were Anopheles species from HLC; ii)- In this city surveyed, the main malaria parasite Plasmodium falciparum was transmitted by Anopheles gambiae s.s where transmission was high from June to October during the rainy season and declined during the dry season (December-May); iii) - The Entomological Inoculation Rates (EIRs) were significantly higher (138 infection bites/person/night) during the rainy season than those obtained during the dry season (138 infection bites/person/night) (P<0.05). Conclusion: The present study showed that malaria transmission is unimodal in the city of Karimama and the main malaria parasite, Plasmodium falciparum was transmitted by Anopheles gambiae s.s. These findings will be very useful for National Malaria Control Program authorities in the choice of the method to fight against malaria in this city.

We investigated the impact of the kdr genotypes on the survival rate of mosquitoes exposed to insecticides in the main malaria vectors Anopheles coluzzii and An. gambiae s.s.. The genotype-phenotype interaction was investigated following two experimental designs; the first one consisted to determine the survival rate of well-characterized adult mosquito strains sharing different kdr genotypes but same genetic background to various insecticides, whereas the second one consisted to expose wild mosquitoes to the same insecticides. Two to five days old adult females were exposed to DDT (4%), deltamethrin (0.05%), and permethrin (0.75%) following WHO protocols. Alive and dead specimens were kept separately to screen the kdr mutations 1014F. The correlation between the kdr genotype and the survival rate to insecticides was investigated in An. coluzzii and An. gambiae s.s. using a logistic regression model. In the laboratory strains, after exposure to DDT and permethrin, the survival rate was significantly higher in F/F individuals comparing to L/F and L/L individuals (p<0.05). A perfect correlation was observed between the survival rate and the genotype in An. gambiae s.s.. The survival chance in this population was multiplied by 1.9 [1.2; 2.8] for L/F and 3.2 [2.1; 4.7] for F/F individuals after exposure to DDT; and 3.7 [1.8; 7.3] for L/F and 9 [4.8; 17.0] for F/F individuals after exposure to permethrin. In the wild population of An. coluzzii, the survival rate correlated with the genotype after exposure to permethrin and was significantly higher in F/F individuals comparing to L/F and L/L individuals (p<0.05). In L/F and F/F individuals, the survival chance was respectively multiplied by 2.7 [1.4; 5.8] and 3.2 [1.4; 6.9] after exposure to DDT; 2.1 [1.0; 4.1] and 4.1 [2.3; 8.7] after exposure to permethrin; and 2.5 [1.1; 5.3] and 3.9 [1.9; 8.0] after exposure to deltamethrin. Overall, the mosquito survival rates were significantly higher in wild population comparing to laboratory strains after exposure to pyrethroid insecticides. These results suggest that additional mechanisms such as metabolic resistance might contribute to a large extend to phenotypic resistance in malaria vectors.