Abstract
Natural selection has favoured specialization in anthropophilic mosquito host choice, yet in the absence of human hosts, females feed on a selected range of vertebrates. For host recognition, we hypothesize that mosquitoes primarily rely on generic host volatiles. Detection and perception of such compounds would provide the mosquito with a flexible, yet constrained, odour coding system that could delineate host preference. In this study, we show that the quintessential generic volatile for host-seeking, carbon dioxide, activates and attracts the malaria mosquito, Anopheles coluzzii, and the arbovirus vectors, Aedes aegypti and Culex quinquefasciatus, within boundaries set by the dynamic range and coding capacity of the CO2-sensitive olfactory receptor neurons. These boundaries are sufficiently broad to elicit behavioural responses to various hosts within their preferred host range. This study highlights the significance of the sensitivity of the carbon dioxide detection system and its regulation of host seeking and recognition.
Highlights
Mosquitoes that transmit infectious diseases often express a marked, inherent host preference [1,2,3,4,5,6]
At concentrations of 150 and 300 ppm CO2, the olfactory receptor neurons (ORNs) activity was significantly higher in An. coluzzii than in Ae. aegypti and Cx. quinquefasciatus (t = 3.12, d.f. = 8, p < 0.05; t = 4.80, d.f. = 8, p < 0.001 and t = 3.09, d.f. = 8, p < 0.05; t = 2.92, d.f. = 8, p < 0.05, respectively)
The A cell of Cx. quinquefasciatus, while detecting pulse onset rapidly, adapted to each CO2 pulse and with subsequent pulses affecting its ability to disadapt, limiting its capacity to track the stimuli at the higher concentrations
Summary
Mosquitoes that transmit infectious diseases often express a marked, inherent host preference [1,2,3,4,5,6]. There remains sufficient plasticity in host preference to provide a mechanism by which mosquitoes can adapt to different environmental conditions [1,3,5], which is an important. Variable regulating disease transmission by predominantly anthropophilic mosquitoes [6]. This indicates 2 that there is both a cost and benefit to maintaining plasticity [1] and/or that these species are physiologically limited in the capacity to be plastic
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