The effect of blood feeding on insecticide resistance intensity and adult longevity in the major malaria vector Anopheles funestus (Diptera: Culicidae)

Shüné V Oliver,Basil D Brooke,Candice L Lyons

doi:10.1038/s41598-022-07798-w

Abstract

Insecticide-based vector control is key to the reduction and elimination of malaria. Although insecticide resistance is common in malaria vector populations, the operational implications are often unclear. High intensity pyrethroid resistance in the major malaria vector Anopheles funestus has been linked to control failure in Southern Africa. The aim of this study was to assess linkages between mosquito age, blood feeding and the intensity of pyrethroid resistance in two An. funestus laboratory strains that originate from southern Mozambique, namely the moderately pyrethroid resistant FUMOZ and the highly resistant FUMOZ-R. Resistance tended to decline with age. This effect was significantly mitigated by blood feeding and was most apparent in cohorts that received multiple blood meals. In the absence of insecticide exposure, blood feeding tended to increase longevity of An. funestus females and, following insecticide exposure, enhanced their levels of deltamethrin resistance, even in older age groups. These effects were more marked in FUMOZ-R compared to FUMOZ. In terms of programmatic decision-making, these data suggest that it would be useful to assess the level and intensity of resistance in older female cohorts wherever possible, notwithstanding the standard protocols for resistance testing using age-standardised samples.

Highlights

Vector control is key to the reduction and elimination of malaria
The effect of blood feeding on subsequent susceptibility to insecticide exposure
Multiple blood meals resulted in longer survival times for both strains, and there was no significant difference in survival between FUMOZ-R and FUMOZ

Summary

Introduction

Vector control is key to the reduction and elimination of malaria. A limited number of Anopheles species transmit malaria, and their control is primarily insecticide-based, relying on the deployment of insecticides via indoor residual spraying (IRS), insecticide treated nets (ITNs) and larviciding as a component of larval source management[1–3]. This is because surveillance for insecticide resistance in vector populations is typically assessed first by measuring phenotypes using standardised response-to-exposure a ssays[16] These assays are based on the use of diagnostic insecticide concentrations that in no way resemble those used on ITNs and to spray walls during IRS operations. Resistance is diagnosed if mortality < 98% 24 h after the one hour exposure, and intensity can subsequently be measured in the same manner using dosages at 5X and 10X the diagnostic c oncentration[16] These data can be used to make assessments about the potential operational impact of resistance, especially where IRS is used for c ontrol[17, 18]. A documented example is pyrethroid resistance in southern African populations of the major African malaria vector species Anopheles funestus This resistant phenotype is primarily mediated by monooxygenase detoxification (cytochrome P450s CYP6P9 and CYP6P13)[25–27] that is facilitated by increased expression of glutathione-S-Transferases (GSTs) and thickened cuticles[28, 29]. Available evidence further suggests that this phenotype does not incur fitness costs in affected An. funestus populations[32]

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