Malaria vector control using Beauveria bassiana fungus

Malaria kills more than 650,000 people each year, primarily in developing nations. Contemporary control efforts focus on suppressing mosquito vector populations with chemical insecticides applied either as indoor residual sprays or as insecticide impregnated nets. Unfortunately, insecticide resistance threatens to undermine these strategies. Fungal biopesticides, which kill mosquitoes by different mechanisms to conventional chemicals, offer a promising alternative. Both fungal kill rate and the malarial incubation period depend strongly on temperature, but to date, no comprehensive effort has been undertaken to examine fungal virulence in mosquitoes across the thermal range relevant for malaria transmission. To address this knowledge gap, we evaluated the virulence of Beauveria bassiana fungus against Anopheles stephensi mosquitoes at constant temperatures from 10-34°C. We found that, regardless of temperature, fungal exposure resulted in greater than 95% mosquito mortality prior to the end of the predicted Plasmodium falciparum malaria incubation period. We then utilized a theoretical model to examine what this might mean for malaria control. The model predicted significant decreases in infectious mosquito density even when nightly fungal infection probability was low. When we accounted for diurnal temperature variation in the model, predicted densities of infectious mosquitoes decreased further. These results suggest that fungal biopesticides may be a potent tool for malaria control in a broad spectrum of thermal environments.