Insecticide resistance in malaria vectors: seasonal susceptibility, mechanisms and relationships to agricultural practices, in Magu and Sengerema agro-ecosystem zone

Malaria is a major public health challenge, globally and in Tanzania. The main method to reduce malaria transmission is through vector control using insecticides, mainly the Pyrethroids. Pyrethroids are also widely used in agriculture, thus exerting more selection pressure among malaria vectors breeding in agricultural areas. The aim of the present study therefore, was to investigate the role of agro-chemical use, on the selection for resistance to insecticides among malaria vectors. Mosquito larvae were collected from the rice, cotton and tomato farms and reared to obtain adults for susceptibility testing. The susceptibility status of An. gambiae s.l. was assessed using WHO bioassay tests to the 5 Pyrethroids [Permethrin (0.75%), Deltamethrin (0.05%), Lambdacyhalothrin (0.05%), Etofenprox (0.5%), Cyfluthrin (0.15%)] and DDT (4%). The survivors were screened for knockdown resistance (kdr) both western (L1014F) and eastern (L1014S) variants. Questionnaires and field observations were used to assess the Knowledge, Attitude and Practices (KAP) of Farmers regarding pesticide usage and management. Pesticide residues levels in soil and sediments from the mosquitoes’ breeding habitats were determined by Gas Chromatography Mass Spectrophotometer (GS-MS. Anopheles arabiensis constitute over 90% of the natural population of An. gambiae s.l. in the studied area. Anopheles gambiae s.l. was resistant to all the insecticides tested. The East African kdr (L1014S) allele was found in 13 out of 535 specimens, (435 that survived insecticide exposures and 100 that following exposures) , the allele frequency ranged from 0.9% to 50%. Pyrethroids constitute 50% of all pesticides used against crop and livestock pests. The majority of farmers (80%) applied pesticides in mixed form and up to 15 times per cropping season. Furthermore, DDT and its metabolites (DDE & DDD) residues were found in the soil and sediment samples, the concentration ranged from undetectable amounts – 9.90 ng/g (dry weight). Vector control interventions