Impact of elevated CO2 background levels on the host-seeking behaviour of Aedes aegypti

Abstract

Mosquitoes rely on carbon dioxide (CO 2 ) to detect and orient towards their blood hosts. However, the variable and rapid fluctuations of atmospheric CO 2 concentrations may have an impact on the hostseeking behaviour of mosquitoes. In this study, we analysed the effect of transient elevated background levels of CO 2 on the hostseeking behaviour and the physiological characteristics of the CO 2 -sensitive olfactory receptor neurones (ORNs) in female yellow fever mosquitoes, Aedes aegypti. We show that the take-off and source contact behaviour of A. aegypti is impeded at elevated background levels of CO 2 as a result of masking of the stimulus signal. The mechanism underlying this masking during take-off behaviour is one of sensory constraint. We show that the net response of the CO 2 -ORNs regulates this CO 2 -related behaviour. Since these neurones themselves are not habituated or fatigued by the transient elevation of background CO 2 , we propose that habituation of second-order neurones in response to the elevated CO 2 -ORN activity could be one mechanism by which the net response is transduced by the olfactory system. The findings from this study may help to predict future shifts in mosquito-host interactions and consequently to predict vectorial capacity in the light of climate change.

Detection and perception of generic host volatiles by mosquitoes: responses to CO2constrains host-seeking behaviour

“…Here, we support the previous finding that detection and perception of CO 2 by the olfactory system play a vital role in the activation of host-seeking behaviour [8–16]. The response characteristics of the CO 2 -detecting ORNs differ, however, among mosquito species, correlating with differential behavioural outputs.…”

“…In all species, the ORN with the largest amplitude is, by convention, referred to as the A cell, and has previously been shown to be an absolute detector of CO 2 below 1200 ppm [15,16,19,20]. Electrophysiological recordings from this neuron were made and analysed as previously described [16]. …”

“…), as previously described [16], with minor modifications (figure 3 b ). Briefly, the tube assay was illuminated from above with white light at 280 lux for the diurnal Ae.…”

“…A pulsed flow of pure CO 2 (Strandmöllen AB), regulated by a stimulus controller (SEC-2/b, Syntech, Germany), was introduced into a pulse generator. Homogenized CO 2 pulses were delivered, using the same pulsation protocol as for the physiological experiments above, at the desired concentration (600, 1200, 2400 or 4800 ppm) through mixing pure CO 2 with pressurized air at 4.5 l min −1 in the pulse generator, as previously described [16]. The concentration of CO 2 in the flight tube was measured using a CO 2 analyser (LI-820, LICOR Biosciences, Lincoln, NE, USA).…”

“…Emitted by all vertebrates, CO 2 also gates the attraction to host odours over a range of distances in host-seeking mosquitoes [11,12]. Observed interspecific variation in the behavioural response to CO 2 may be attributed to differences in the dynamic range of the CO 2 -chemosensory system for each mosquito species [9,13,14], and the underlying mechanism regulating the CO 2 dynamic range is one of sensory constraint [15,16]. …”