Reduction in olfactory receptor neuron responsiveness is correlated with reduction in host-finding behavior in fungus-infected mosquitoes

Development of resistance to insecticides is a major impediment in controlling the malaria mosquitoes worldwide. Even though bed nets and various trapping methods are used to combat mosquitoes, a natural and a better control strategy is still lacking to effectively kill the mosquitoes in a shorter time frame and preventing them from spreading the malaria pathogens. Laboratory studies have isolated different strains of entomopathogenic fungus that are effective in killing mosquito larvae and adults. Using fungi as a control strategy is highly promising for controlling the malarial vectors, because there are fewer chances for developing resistance compared to insecticides. Very little is known how fungal infection might affect the olfactory behavior in mosquitoes and whether the mosquitoes would be able to respond to host odors and feed on the hosts. This study shows how the fungal infection affects the olfactory processes in a species of malaria mosquito, Anopheles stephensi Liston, using electro antennogram (EAG) and electro palpogram (EPG) techniques. Also, neuronal action potentials (spikes) from palps were recorded using tungsten electrodes to perform single-cell analyses of olfactory neuron exctitation. The number of spikes produced in fungal-infected versus untreated mosquitoes were recorded in response to 1-octen-3-ol and CO2. Our results show that Beauveria bassiana infection significantly reduces the propensity of mosquitoes to feed The single cell recordings show that fungal infection significantly impairs the degree of peripheral neuronal excitation received by the brain and these mosquitoes cannot effectively respond to host-related cues by flying upwind to them.