In spite of widespread insecticide resistance in vector mosquitoes throughout Africa, there is limited evidence that long lasting insecticidal bed nets (LLINs) are failing to protect against malaria. Here, we showed that LLIN contact in the course of host-seeking resulted in higher mortality of resistant Anopheles spp. mosquitoes than predicted from standard laboratory exposures with the same net. We also found that sub-lethal contact with an LLIN caused a reduction in blood feeding and subsequent host-seeking success in multiple lines of resistant mosquitoes from the lab and the field. Using a transmission model, we showed that when these LLIN-related lethal and sub-lethal effects were accrued over mosquito lifetimes, they greatly reduced the impact of resistance on malaria transmission potential under conditions of high net coverage. If coverage falls, the epidemiological impact is far more pronounced. Similarly, if the intensity of resistance intensifies, the loss of malaria control increases non-linearly. Our findings help explain why insecticide resistance has not yet led to wide scale failure of LLINs, but reinforce the call for alternative control tools and informed resistance management strategies.

Anopheles funestus, Malaria, Anopheles gambiae, Anopheles arabiensis, Insecticide resistance, Disease, Biology