Age-related pyrethroid resistance is not a function of P450 gene expression in the major African malaria vector, Anopheles funestus (Diptera: Culicidae)

Anopheles funestus is a major vector of malaria in most of the African region. Resistance to pyrethroid and carbamate insecticides has been recorded in populations of this species in South Africa and Mozambique. The P450 gene, CYP6P9, has been shown to be highly transcribed in a permethrin (pyrethroid)-resistant laboratory strain, FUMOZ-R, originating from southern Mozambique. We examined the relationship between pyrethroid resistance and gene transcription levels of two closely related genes, CYP6P9 and CYP6P13, in FUMOZ-R. Levels of resistance to 0.75% permethrin were determined based on standard WHO insecticide susceptibility assays using females and males of different ages, ranging from 3 to 30 days old. The transcription levels of the two genes were quantified using qPCR for each age cohort. In the WHO insecticide susceptibility assays, survival of both males and females significantly decreased as age increased. Quantitative analysis of the two genes CYP6P9 and CYP6P13 showed the highest levels of expression at 10 days of age. There was no correlation between expression of these two genes and pyrethroid survival by age. We conclude that the resistance of this mosquito strain to permethrin is not directly related to age-mediated differences in CYP6P9 and CYP6P13 expression.