Study of the immune system of mosquitoes against insecticides: enzymatic activities and genetic mutation in anopheles gambiae populations at natitingou, north-east of Benin

In order to study the immune system of mosquitoes against the use of insecticides in their ecological environment, a study has been carried out on the enzymatic activities and genetic mutation in Anopheles gambiae populations in the district of Natitingou, northern Benin from January to May 2016. Bioassay tests to assess the susceptibility of malaria vectors were done where females of An. gambiae aged to 2-5 were subjected to insecticide-impregnated papers (permethrin 0.75%, delthamethrin 0.05%, DDT 4%, and bendiocarb 0.1%) following WHO testing protocol. The presence of knock down resistance (kdr) and acetylcholinesterase (ace-1R) mutations were determined by Polymerase Chain Reaction (PCR). Finally, biochemical analysis was done in order to detect Mixed Function Oxidase (MFO), non-specific esterase (NSE) and glutathione-S-transferases (GST) activity in individual 2–5 days old adult An. gambiae that had been not previously exposed to insecticides. This research showed that the improper manner of the use of insecticides by farmers contributed to the emergence of insecticide resistance in malaria vectors with a wide spread of resistance to DDT (3% as a means of mortality), permethrin (23%) and delthamethrin (30%) but fully susceptible bendiocarb. The knockdown resistance (kdr) mutation was the main resistance mechanism identified in these An. gambiae populations with 0.85 as frequency. The Ace-1 mutation was found at a very low frequency (≤ 5%). The presence of enzymatic activity (Esterase, Glutathione-s-transferase (GST) and P450 monooxygenase) in the wild population of An. gambiae was significantly higher than the control strain (P < 0,05). This study provides clear evidence that the use of insecticides by local farmers for crop protection is one factor that impacts negatively the immune system of mosquito which has led to the emergence of insecticide resistance in malaria vectors. Therefore, the need to develop Integrated Pest and Vector Management (IPVM) strategies and management of insecticide resistance in malaria vectors seem to be very important for vector control.