Contributions of cuticle permeability and enzyme detoxification to pyrethroid resistance in the major malaria vector Anopheles gambiae

Gildas A Yahouédo,Vasileia Balabanidou,Natacha Garcia Albeniz Mendez,Marie Rossignol,Olivier Pigeon,Carole Ginibre,John Vontas,Sylvie Cornelie,Fabrice Chandre

doi:10.1038/s41598-017-11357-z

Abstract

To tackle the problem of insecticide resistance, all resistance mechanisms need to be studied. This study investigated the involvement of the cuticle in pyrethroid resistance in a strain of Anopheles gambiae, MRS, free of kdr mutations. Bioassays revealed MRS to be resistant to pyrethroids and DDT, indicated by increasing knockdown times and resistance ratios. Moreover, biochemical analysis indicated that metabolic resistance based on enhanced CYP450 activity may also play a role. Insecticide penetration assays showed that there were significantly lower amounts of insecticide in the MRS strain than in the susceptible control. Analysis of the levels of the selected transcripts by qPCR showed that CYP6M2, a major pyrethroid metaboliser, CYP4G16, a gene implicated in resistance via its contribution to the biosynthesis of elevated epicuticular hydrocarbons that delay insecticide uptake, and the cuticle genes CPAP3-E and CPLCX1 were upregulated after insecticide exposure. Other metabolic (CYP6P3, GSTe2) and cuticle (CPLCG3, CPRs) genes were also constitutively upregulated. Microscopic analysis showed that the cuticle layers of the MRS strain were significantly thicker than those of the susceptible strain. This study allowed us to assess the contribution made by the cuticle and metabolic mechanisms to pyrethroid resistance in Anopheles gambiae without target-site mutations.

Highlights

To tackle the problem of insecticide resistance, all resistance mechanisms need to be studied
Increase in detoxification processes as a result of high levels of multi-function oxidases (MFO), non-specific esterases (NSE) and glutathione S transferases (GST)[9, 10], and reduced sensitivity of the target proteins on which the insecticide acts in the voltage-gated sodium channel due to point mutation of the genes encoding these target proteins, i.e., the knockdown resistance mutation[11]
According to WHO criteria based on 24 h mortality[31], MRS was resistant to deltamethrin (60.8%), etofenprox (47.0%) and DDT (73.8%), suspected resistant to permethrin (91.9%), and susceptible to fenitrothion (100%) and bendiocarb (100%)