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

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.

Genome-wide gene expression profiling reveals that cuticle alterations and P450 detoxification are associated with pyrethroid resistance in Anopheles arabiensis populations from Ethiopia

“…Higher expression of cuticular genes has previously been reported for pyrethroid resistant mosquito populations 32, 71–75 and in some cases was associated with a thicker cuticula. 73, 74 Further, some of these Anopheles cuticular genes were also shown to be expressed in the limbs, the most frequent site of contact with insecticides. 76 Apart from genes encoding cuticular proteins, cyp4g16 , which encodes a P450 that catalyzes epicuticular hydrocarbon biosynthesis, has also been reported to be frequently overexpressed in insecticide resistant Anopheles mosquitoes, including An.…”

Involvement of integument‐rich CYP4G19 in hydrocarbon biosynthesis and cuticular penetration resistance in Blattella germanica (L.)

“…Moreover, we can not exclude the possibility that in addition to the hexane‐soluble lipids, other cuticle components, such as structural proteins and chitin layers, might contribute to the cuticular resistance in B. germanica . Such a possibility is based on the validated contribution of cuticular proteins to peneration resistance and the thickening of the chitin layers in pyrethroid‐resistant mosquitoes. Whether these cuticular compounds are involved, and further, which genes are involved in peneration resistance in B. germanica are not well understood.…”

“…Insect cuticle is a complex of proteins in a matrix of chitin fibrils with an epicuticular lipid layer covering the outside body surface, and serves as the first line of defense against the penetration of xenobiotics . Cuticle thickening in resistant insects could be conferred by an increase in biosynthesis and/or the transport of cuticle building materials such as cuticular lipids, structural proteins, and chitin layers . In the bed bug, Cimax lectularius , the time‐to‐knockdown by insecticides was shown to be positively correlated with cuticle thickness, and in pyrethroid‐resistant Anopheles gambiae , thickening of the epicuticle was found to be accompanied by an enrichment of cuticular hydrocarbons (CHCs) …”

“…7 Cuticle thickening in resistant insects could be conferred by an increase in biosynthesis and/or the transport of cuticle building materials such as cuticular lipids, 9 structural proteins, [10][11][12] and chitin layers. 13,14 In the bed bug, Cimax lectularius, the time-to-knockdown by insecticides was shown to be positively correlated with cuticle thickness, 15 and in pyrethroid-resistant Anopheles gambiae, thickening of the epicuticle was found to be accompanied by an enrichment of cuticular hydrocarbons (CHCs). 9 As a major fraction of cuticular lipids, 9,16 CHCs covering the epicuticle are primarily responsible for water retention, 17 act as chemical communication cues, 18 and also constitute a barrier against pathogens and xenobiotics, including insecticides.…”

Prediction of malaria mosquito species and population age structure using mid-infrared spectroscopy and supervised machine learning

“…It is estimated that by using the ATR sampling technique in the mid-IR, the light penetrates the sample by 3-22 µm (see Supplementary Note 3). As the cuticle of a mosquito is approximately 2-5 µm thick, 21,52 the measured spectra encompass the outer shell and part of the interior of the insects. As the cuticle is mainly composed of chitin, proteins, and lipids, the spectra of these substances individually were compared with the whole-mosquito spectra (Figure 1).…”