Insecticide treatments for crops protection in cotton fields have often been cited as the main factor in the selection of insecticide resistance in Anopheles gambiae populations. To explore this hypothesis further, the present study was designed to identify potential practices that may contribute to the emergence of insecticide resistance in Anopheles gambiae in cotton crop protection strategies such as the “Calendar Control Program (CCP)” and “Targeted Intermittent Control Program (TICP)” officially recommended already operate in Benin. Firstly, Knowledge Attitude-Practice (KAP) surveys were organized in the study sites to generate adequate information on the use of insecticide on cotton fields. In each site, leaders of farmer’s organizations were interviewed using semi-structured questionnaires that focused on the treatment strategies, and the use of insecticides in the farms. Further, bioassays were performed on adult mosquitoes collected from various of each program to assess the susceptibility of malaria vectors to insecticide-impregnated papers (permethrin 0.75%, delthamethrin 0.05%, DDT 4%, and bendiocarb 0.1%) following WHOPES guidelines. Results of this study showed that various pesticides particularly pyrethroids were used for pests control in CCP and TICP sites; ii)-Susceptibility tests showed that An. gambiae populations have developped resistance to DDT (4% as mean mortality despite the strategies), permethrin (30% in CCP and TICP), deltamethrin (38% and 46% as mean mortality in CCP and TICP respectivetly), but fully susceptible to bendiocarb . These findings confirmed the role of insecticide treatments in mosquitoes resistance. Measure must be taken for better management of the use of insectides for pest control.

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.

For better management of the use of insecticide in public health against Culex quinquefasciatus, an arboviral and filarial vector, a study was conducted at Natitingou, a town located in northern Benin, from October 2015 to March 2016, to evaluate the susceptible of this mosquito to insecticides and the mechanisms of resistance developed. The protocol was based on mosquito collection during both dry and rainy seasons across the four areas selected in northern Benin. Bioassays were performed on adult mosquitoes collected from the field to assess the susceptibility of filarial vectors to insecticide-impregnated papers (permethrin 0.75%, delthamethrin 0.05%, DDT 4%, and bendiocarb 0.1%) following WHOPES guidelines. Moreover, mosquitoes from the susceptible tests were used to search for the presence of the knock down resistance (Kdr) and the Acethylcholinesterase (Ace-1R) mutations. Finally, F1 generation of the wild population of Cx. quinquefasciatus were used for biochemical analysis to target Mixed Function Oxidase (MFO), non-speci?c esterase (NSE) and glutathione-S-transferases (GST) enzymes. This research showed: 1)-A wide spread of resistance to permethrin, delthamethrin and DDT was found in samples of Cx. quinquefasciatus despite the collection areas with 4%; 7% ; 19% and 60% as average of mortality respectively with DDT, permethrin, deltamethrin and bendiocarb; 2)- The kdr mutation was detected in all areas at various frequencies (0.8 to 0.88) whereas the Ace-1 mutation was found at a very low frequency (? 5%); 3) - Enzymes activities (oxidase, esterase and glutathion-S-transferases) were detected in all mosquito populations despite the areas of collection. This work has highlighted the high resistance of Cx. quinquefascitus to the 3 classes of insecticides used in public health. Moreover, the high frequency of kdr and the presence of enzyme activity in Cx. quinquefasciatus will augment the existing data on the insecticide resistance of filariasis vectors and will be useful for making decision to control this mosquito.