Ultra-prolonged activation of CO(2)-sensing neurons disorients mosquitoes

CO(2) present in exhaled air is the most important sensory cue for female blood-feeding mosquitoes, causing activation of long-distance host-seeking flight, navigation towards the vertebrate host(1), and, in the case of Aedes aegypti, increased sensitivity to skin odours(2). The CO(2) detection machinery is therefore an ideal target to disrupt host seeking. We use electrophysiological assays to identify a volatile odourant that causes an unusual, ultra-prolonged activation of CO(2)-detecting neurons in three major disease-transmitting mosquitoes: Anopheles gambiae, Culex quinquefasciatus and A. aegypti. Importantly ultra-prolonged activation of this neuron severely compromises its ability to subsequently detect CO(2) for several minutes. We also identify odours that strongly inhibit the CO(2)-sensitive neuron as candidates for use in disruption of host-seeking behaviour, as well as an odour that evokes CO(2)-like activity and thus has potential use as a lure in trapping devices. Analysis of responses to panels of structurally related odours across the three mosquitoes and Drosophila, which have related CO(2)-receptor proteins, reveals a pattern of inhibition that is often conserved. We use video tracking in wind-tunnel experiments to demonstrate that the novel ultra-prolonged activators can completely disrupt CO(2)-mediated activation as well as source-finding behaviour in Aedes mosquitoes, even after the odour is no longer present. Finally, semi-field studies demonstrate that use of ultra-prolonged activators disrupts CO(2)-mediated hut entry behaviour of Culex mosquitoes. The three classes of CO(2) response modifying odours offer powerful instruments for developing new generations of insect repellents and lures, which even in small quantities can interfere with the ability of mosquitoes to seek humans.