Functional Roles of Five Cytochrome P450 Transcripts in the Susceptibility of the Yellow Fever Mosquito to Pyrethroids Revealed by RNAi Coupled With Insecticide Bioassay

Abstract

We evaluated the possible roles of five cytochrome P450 transcripts in the susceptibility of both adults and larvae of Aedes aegypti to three pyrethroids using RNA interference (RNAi) coupled with insecticide bioassays. RNAi by feeding larvae with chitosan/dsRNA nanoparticles led to reductions of CYP6AA5, CYP6AL1, CYP9J32, CYP4J16A, and CYP4J16B transcripts by 38.7%, 46.0%, 46.52%, 44.0%, and 41.0%, respectively, and increased larval mortality by 46.0% to permethrin when CYP9J32 was silenced and by 41.2% to cypermethrin when CYP6AA5 was silenced. RNAi by injecting dsRNA in adults led to reductions of CYP6AA5, CYP6AL1, and CY4J16A transcripts by 77.9%, 80.0%, and 87.1% (p < 0.05), respectively, at 96 h and reduction of CYP9J32 transcript by 46.5% at 24 h after injection. In contrast, CYP4J16B was repressed by 78.2% at 72 h after injection. Exposure of the adults injected with CYP6AA5 dsRNA resulted in 1.5- to 2.0-fold increased susceptibility to cypermethrin as compared with the control. Homology modeling of CYP6AA5 followed by ligand docking showed that distances between the heme iron and the putative aromatic hydroxylation site were 9.2, 7.2, and 9.1 Å for permethrin, cypermethrin, and deltamethrin, respectively. For the aliphatic hydroxylation site, these distances were 5.3, 4.9, and 3.1 Å. These results supported that CYP6AA5 may be able to metabolize cypermethrin preferentially by aliphatic hydroxylation as indicated by the close interaction with the heme iron. Our study also suggests that the detoxification roles of cytochrome P450 genes in A. aegypti may vary according to the mosquito developmental stages, cytochrome P450 genes, and insecticides.