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<p>Abstract</p> <p>Background</p> <p>Chemical insecticides against mosquitoes are a major component of malaria control worldwide. Fungal entomopathogens formulated as biopesticides and applied as insecticide residual sprays could augment current control strategies and mitigate the evolution of resistance to chemical-based insecticides.</p> <p>Methods</p> <p><it>Anopheles stephensi </it>mosquitoes were exposed to <it>Beauveria bassiana </it>or <it>Metarhizium acridum </it>fungal spores and sub-lethal effects of exposure to fungal infection were studied, especially the potential for reductions in feeding and host location behaviours related to olfaction. Electrophysiological techniques, such as electroantennogram, electropalpogram and single sensillum recording techniques were then employed to investigate how fungal exposure affected the olfactory responses in mosquitoes.</p> <p>Results</p> <p>Exposure to <it>B. bassiana </it>caused significant mortality and reduced the propensity of mosquitoes to respond and fly to a feeding stimulus. Exposure to <it>M. acridum </it>spores induced a similar decline in feeding propensity, albeit more slowly than <it>B. bassiana </it>exposure. Reduced host-seeking responses following fungal exposure corresponded to reduced olfactory neuron responsiveness in both antennal electroantennogram and maxillary palp electropalpogram recordings. Single cell recordings from neurons on the palps confirmed that fungal-exposed behavioural non-responders exhibited significantly impaired responsiveness of neurons tuned specifically to 1-octen-3-ol and to a lesser degree, to CO₂.</p> <p>Conclusions</p> <p>Fungal infection reduces the responsiveness of mosquitoes to host odour cues, both behaviourally and neuronally. These pre-lethal effects are likely to synergize with fungal-induced mortality to further reduce the capacity of mosquito populations exposed to fungal biopesticides to transmit malaria.</p>