Mosquitoes need sugar for flight and other metabolic activities [1–3]. Male mosquitoes, and females of some species, depend entirely on plant nectars [1, 2, 4, 5]. Both autogenous and anautogenous mosquitoes require carbohydrates for survival [6, 7], and evidence shows that sugar ingestion plays a critical role in longevity, fecundity, flight capacity, and host-seeking behaviour [8–11]. Mosquitoes forage for sugars mainly from floral nectaries [12, 13], but also from extra-floral nectaries, honeydew, plant phloem, and damaged and rotting fruits [2, 14]. As such, the availability of sugar sources in the local environment is a major determinant regulating survival, the dynamics of mosquito populations and their vector potential [15, 16].
Although previous studies have found scant evidence of sugar feeding in field collected An. gambiae, suggesting that this feeding habit rarely, if ever, occurs , recent studies have shown that these afrotropical malaria vectors feed intermittently on plant sugars when present in the plant habitats [10, 11, 17–19], and in a discriminating manner. The cues responsible for this discriminative feeding behaviour remain largely unclear. Previous studies have implicated potential fitness-related benefits (i.e. survival and fecundity) as the basis of host plant selection among malaria vectors . In semi-field experiments with some An. gambiae-associated plants commonly found growing around homesteads in western Kenya, non-blood fed females were found to survive relatively longer and laid more eggs when presented with certain plants including Manihot esculenta Crantz (Euphorbiaceae), Tecoma stans L. (Bignoniaceae), Ricinus communis L. (Euphorbiaceae), and Senna didymobotrya Fresen (Caesalpiniaceae) [10, 18, 20], than when presented with other associated plants. Interestingly, these four plant species also ranked among the highly preferred host plants for the vector. On the other hand, Lantana camara L. (Verbenaceae), Bidens pilosa L. (Asteraceae), Datura stramonium L. (Solanaceae) and Flaveria trinervia Mohr (Asteraceae) performed poorly in supporting these vital life parameters and were also the least preferred host plants [10, 11, 18, 20]. While these findings lend support to the hypothesis of benefit-based host plant selection, it was noted that Parthenium hysterophorus L. (Asteraceae) another highly preferred host plant, did not improve survival and fecundity . Manda et al.  attributed this phenomenon to a possible self-medication benefit to the malaria vectors. However, the mechanism by which these malaria vectors discriminate between beneficial and non-beneficial host plants is still not clear.
Previous studies have shown that floral scents play a critical role in the location of sugar sources by mosquitoes of both sexes [2, 21–24]. It would seem, therefore, that plant odours contribute to the discriminative host plant selection by females of the malaria vector An. gambiae. From a management perspective, if these chemicals could be identified, and particularly those from plants which are highly attractive to mosquitoes, they can be used as lures in mosquito surveillance and control programs. Despite this potential, little is known about the composition of the volatiles released from these host plants attractive to mosquitoes . Their capacity to attract mosquitoes of both sexes and of varying physiological states and ages [2, 3, 25] makes plant-based attractants more appealing as a surveillance and control tool. In this study, we define the chemical basis by which An. gambiae females discriminate between different host plants. We used electrophysiological, behavioural and chemical analysis to demonstrate that olfactory cues mediate the discrimination of three differentially preferred host plant species for sugar feeding by females of this species. Our study also demonstrated that altering blend ratios of electrophysiologically-active components can increase their attractiveness to female mosquitoes, to the point of being more attractive than intact plants, thereby providing a practical direction for developing plant-based lures for this disease vector.