Hydroxyl functionalized multi-walled carbon nanotubes (MWCNTs) were blended with Polyacrylonitrile (PAN) to prepare ultrafiltration membranes by a phase inversion process. Three different concentrations of MWCNTs were used in PAN, i.e. 0.5, 1 and 2 wt%. The water flux of the membranes increased by 63% at 0.5 wt% loading of MWCNTs compared to neat PAN membranes. The water flux decreased upon further increase in the concentration of MWCNTs, but at 2 wt% loading it was still higher compared to pure PAN membranes. The surface hydrophilicity of the membranes was enhanced upon the addition of MWCNTs, as observed by contact angle measurements. The increased hydrophilicity might have an impact on the improved water flux. All the membranes showed a molecular weight cut off (MWCO) of approximately 50 Kg/mol. Surface pore size analysis by scanning electron microscopy (SEM) showed no significant difference in the mean pore size of the nanocomposite membranes compared to the neat membranes. The cross section morphology was influenced by the introduction of MWCNTs where less but enlarged macrovoids were observed, particularly prominent at a loading of 2 wt% MWCNTs. The membranes containing 2wt% MWCNTs showed 36% improvement in resistance against compaction compared to neat membranes. Furthermore, the tensile strength of the membranes at 2wt% MWCNTs loading increased over 97% compared to neat ones.

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Olfactory information drives several behaviours critical for the survival and persistence of insect pests and vectors. Insect behaviour is variable, linked to their biological needs, and regulated by physiological dynamics. For mosquitoes, CO2 is an important cue that signifies the presence of a host, and which elicits activation and attraction. To investigate the genetic basis of olfactory modulation in mosquitoes, we assayed changes in CO2 detection from receptor gene expression through physiological function to behaviour, associated with the onset of host seeking in the malaria vector, Anopheles gambiae. The gene encoding a subunit of the CO2 receptor, AgGr22, was found to be significantly up-regulated in host-seeking females, consistent with a significant increase in sensitivity of CO2-responsive neurons (cpA) housed in capitate peg sensilla of the maxillary palp. In addition, the odorant receptor AgOr28, which is expressed in cpC neurons, was significantly up-regulated. In contrast, AgOr8, which is expressed in cpB neurons, was not affected by this change in physiological state, in agreement with results for the obligate co-receptor Orco. Moreover, the sensitivity of the cpB neuron to (R)-1-octen-3-ol, a well-known mammalian kairomone, did not change in response to the onset of host seeking. The concentration of CO2 flux influenced both the propensity of A. gambiae to take off into the wind and the speed with which this activation occurred. Female A. gambiae mosquitoes responded to CO2 whether mature for host seeking or not, but onset of host seeking enhanced sensitivity and speed of activation at relevant doses of CO2.

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Natural selection favours a restricted host breadth in disease vector mosquitoes, indicating that there is an adaptive value associated with maintaining plasticity in host preference. One mechanism to maintain such plasticity is via the detection of generic cues by conserved peripheral olfactory pathways, which when perceived in different host odour contexts enable the identification of and discrimination among potential host species. Here, we show that the context of an odour cue shapes host perception in mosquitoes, by altering the release rate of the generic host-related volatile (R)-1-octen-3-ol, within its natural range, and in the background odour of known hosts and non-hosts. This result highlights that host recognition is contextual and dependent on quantitative and qualitative differences in odour blends and the olfactory codes evoked. From the perspective of vector management, understanding the perception of odour blends and their context is essential to the process of developing synthetic blends for the optimal attraction of mosquitoes in efforts to control and monitor populations.

1-Octen-3-ol is a kairomone for many haematophagous insects including mosquitoes. Numerous studies have examined the effects of racemic 1-octen-3-ol; however, few studies have investigated the role of individual enantiomers in relation to mosquito attraction. In the present study, we investigated the behavioural and electrophysiological responses of two mosquito species, Aedes aegypti and Culex quinquefasciatus, to individual enantiomers and mixtures of 1-octen-3-ol, employing a laboratory Y-tube olfactometer and single sensillum recordings. The olfactory receptor neurons of both Ae. aegypti and Cx. quinquefasciatus had a significantly higher response to the (R)-1-octen-3-ol enantiomer compared to the (S )-1-octen-3-ol enantiomer at 10 À9 g μl À1 to 10 À6 g μl À1 . Behaviourally, Ae. aegypti was more responsive to the (R)-1-octen-3-ol enantiomer, showing an increase in flight activity and relative attraction compared to Cx. quinquefasciatus. The (R)-1-octen-3-ol enantiomer caused an increase in activation for Cx. quinquefasciatus. However, the most notable effect was from an (R:S)-1-octen-3-ol mixture (84:16) that caused significantly more mosquitoes to sustain their flight and reach the capture chambers (demonstrated by a reduced non-sustained flight activity), suggesting that it may have a behaviourally excitatory effect. For Cx. quinquefasciatus, a reduced relative attraction response was also observed for all treatments containing the (R)-1-octen-3-ol enantiomer, either on its own or as part of a mixture, but not with the (S)-1-octen-3-ol enantiomer. This is the first time enantiomeric selectivity has been shown for Ae. aegypti using electrophysiology in vivo. The implications of these results for exploitation in mosquito traps are discussed.

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.

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