Combined over-expression of two cytochrome P450 genes exacerbates the fitness cost of pyrethroid resistance in the major African malaria vector Anopheles funestus

Abstract

Metabolic resistance driven by multiple P450 genes is worsening insecticide resistance in malaria vectors. However, it remains unclear whether such multiple over-expression imposes an additive fitness cost in the vectors. Here, we showed that two highly over-expressed P450 genes ( CYP6P9a and CYP6P9b ) combine to impose additive fitness costs in pyrethroid-resistant Anopheles funestus . Genotyping of the CYP6P9b resistance allele in hybrid mosquitoes from a pyrethroid-resistant FUMOZ-R and the susceptible FANG strains revealed that this gene imposes a fitness cost in resistant mosquitoes similar to CYP6P9a . Homozygote susceptible CYP6P9b_S (SS) significantly lay more eggs than the resistant (OR = 2.2, P = 0.04) and with greater hatching rate ( p < 0.04). Homozygote resistant larvae CYP6P9b_R (RR) developed significantly slower than homozygote susceptible from L1-L4 (χ 2 = 7.2; P = 0.007) with a late pupation observed for RR compared to both heterozygotes and homozygotes susceptible ( χ 2 = 11.17; P = 0.0008). No difference was observed between genotypes for adult longevity with no change in allele frequency and gene expression across the lifespan. Furthermore, we established that CYP6P9b combines with CYP6P9a to additively exacerbate the fitness cost of pyrethroid resistance with a greater reduction in fecundity/fertility and increased developmental time of double homozygote resistant mosquitoes. Moreover, an increased proportion of double homozygote susceptible individuals was noted over 10 generations in the insecticide-free environment (χ 2 = 6.3; P = 0.01) suggesting a reversal to susceptibility in the absence of selection. Such greater fitness cost imposed by multiple P450 genes shows that resistance management strategy based on rotation could help slow the spread of resistance.

Gene Conversion Explains Elevated Diversity in the Immunity Modulating APL1 Gene of the Malaria Vector Anopheles funestus

“…The fitness costs of metabolic resistance in An. funestus are well-established with respect to life-history traits [ 67 , 68 ]. Indeed, the opposite has been observed in the moth Trichoplusia ni , in which investment in immunity has its own negative effect on developmental fitness [ 69 ].…”

Reduced performance of community bednets against pyrethroid-resistant Anopheles funestus and Anopheles gambiae, major malaria vectors in Cameroon

“…These results provide evidence that continued exposure of mosquitoes to bednets will significantly contribute to the selection of resistant alleles and consequently increase malaria transmission. However, rotating insecticides with a different mode of action could help manage this resistance as in the absence of selection resistant mosquitoes are at a disadvantage compared to the susceptible mosquitoes, as previously shown for both markers [ 52 – 54 ]. In fact, P450 monooxygenases and GSTs are known to significantly alter the levels of reactive oxygen species in insects [ 55 ].…”

Susceptibility of Field-Collected Nyssorhynchus darlingi to Plasmodium spp. in Western Amazonian Brazil

“…In addition, P450 is linked to the catabolism and anabolism of xenobiotics such as drugs and pesticides in distinct groups of organisms such as plants, mammals, birds, and insects [29]. The cytochrome P450 genes are associated with insecticide resistance through increased metabolism of insecticides in Culex quinquefasciatus, Aedes aegypti, and Anopheles funestus [30][31][32][33]. In An.…”