Abstract
BackgroundUnderstanding the mechanisms used by Anopheles mosquitoes to survive insecticide exposure is key to manage existing insecticide resistance and develop more suitable insecticide-based malaria vector control interventions as well as other alternative integrated tools. To this regard, the molecular basis of permethrin, DDT and dieldrin resistance in Anopheles funestus (sensu stricto) at Akaka-Remo was investigated.MethodsBioassays were conducted on 3–5-day-old adult An. funestus (s.s.) mosquitoes for permethrin, DDT and dieldrin susceptibility test. The molecular mechanisms of mosquito resistance to these insecticides were investigated using microarray and reverse transcriptase PCR techniques. The voltage-gated sodium channel region of mosquitoes was also screened for the presence of knockdown resistance mutations (kdr west and east) by sequencing method.ResultsAnopheles funestus (s.s.) population was resistant to permethrin (mortality rate of 68%), DDT (mortality rate of 10%) and dieldrin (mortality rate of 8%) insecticides. Microarray and RT-PCR analyses revealed the overexpression of glutathione S-transferase genes, cytochrome P450s, esterase, trypsin and cuticle proteins in resistant mosquitoes compared to control. The GSTe2 was the most upregulated detoxification gene in permethrin-resistant (FC = 44.89), DDT-resistant (FC = 57.39) and dieldrin-resistant (FC = 41.10) mosquitoes compared to control population (FC = 22.34). The cytochrome P450 gene, CYP6P9b was also upregulated in both permethrin- and DDT-resistant mosquitoes. The digestive enzyme, trypsin (hydrolytic processes) and the cuticle proteins (inducing cuticle thickening leading to reduced insecticides penetration) also showed high involvement in insecticide resistance, through their overexpression in resistant mosquitoes compared to control. The kdr east and west were absent in all mosquitoes analysed, suggesting their non-involvement in the observed mosquito resistance.ConclusionsThe upregulation of metabolic genes, especially the GSTe2 and trypsin, as well as the cuticle proteins is driving insecticide resistance of An. funestus (s.s.) population. However, additional molecular analyses, including functional metabolic assays of these genes as well as screening for a possible higher cuticular hydrocarbon and lipid contents, and increased procuticle thickness in resistant mosquitoes are needed to further describe their distinct roles in mosquito resistance.
Highlights
Understanding the mechanisms used by Anopheles mosquitoes to survive insecticide exposure is key to manage existing insecticide resistance and develop more suitable insecticide-based malaria vector control interventions as well as other alternative integrated tools
The pre-exposure of mosquitoes to diethyl maleate (DEM) and DEF, and to DDT resulted in mortalities of 71% and 82%, respectively, which suggests the role of glutathione S-transferase (GST) and esterase in DDT resistance
This study, which is, to our knowledge, the first to depict the molecular basis of An. funestus (s.s.) in Nigeria, highlights the vital role of GSTe2 in permethrin, DDT and dieldrin resistance
Summary
Understanding the mechanisms used by Anopheles mosquitoes to survive insecticide exposure is key to manage existing insecticide resistance and develop more suitable insecticide-based malaria vector control interventions as well as other alternative integrated tools. To this regard, the molecular basis of permethrin, DDT and dieldrin resistance in Anopheles funestus (sensu stricto) at Akaka-Remo was investigated. A population of Anopheles funestus (sensu stricto) in Nigeria was recently shown to be resistant to different classes of public health insecticides commonly used for malaria vector control [1]. Populations within the same region may share similar resistance mechanisms, which might be a consequence of gene flow across these regions [6]
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