Multimodal floral cues guide mosquitoes to tansy inflorescences

Abstract

Female mosquitoes exploit olfactory, CO 2 , visual, and thermal cues to locate vertebrate hosts. Male and female mosquitoes also consume floral nectar that provides essential energy for flight and survival. Heretofore, nectar-foraging mosquitoes were thought to be guided solely by floral odorants. Using common tansies, Tanacetum vulgare L., northern house mosquitoes, Culex pipiens L., and yellow fever mosquitoes, Aedes aegypti (L.), we tested the hypothesis that the entire inflorescence Gestalt of olfactory, CO 2 and visual cues is more attractive to mosquitoes than floral odorants alone. In laboratory experiments, we demonstrated that visual and olfactory inflorescence cues in combination attract more mosquitoes than olfactory cues alone. We established that tansies become net producers of CO 2 after sunset, and that CO 2 enhances the attractiveness of a floral blend comprising 20 synthetic odorants of tansy inflorescences. This blend included nine odorants found in human headspace. The “human-odorant-blend” attracted mosquitoes but was less effective than the entire 20-odorant floral blend. Our data support the hypothesis that the entire inflorescence Gestalt of olfactory, CO 2 and visual cues is more attractive to mosquitoes than floral odorants alone. Overlapping cues between plants and vertebrates support the previously postulated concept that haematophagy of mosquitoes may have arisen from phytophagy.

Is Anopheles gambiae attraction to floral and human skin-based odours and their combination modulated by previous blood meal experience?

“…From an applied perspective the results offer interesting angles. Although the study did not nd any augmentation of trap catches by combining oral and skin odours, the combination did catch both nulliparous and parous mosquitoes (which differs slightly from earlier reports [37][38][39][40]), and would therefore attract mosquitoes relatively independently of physiological status, these being either searching to replenish carbohydrate energy reserves for ight and maintenance ( oral odours) [19,66,67] or searching for hosts to support reproduction (skin lure, a human skin-mimicking blend of volatiles) [28,68,69]. Although there was signi cant attraction to either oral and skin odour blends, alone and in combination, to both parous and non-parous females, this study did not compare the attraction of the blends to a living human.…”

“…In this study, although mosquitoes were attracted to a combination of oral and human odour, the combination did not augment or synergize capture rates, in spite of each blend individually being attractive. This is largely in line with earlier reports [36][37][38][39]. In a recent eld studies in Kenya, a combination of plant-and human-derived odours was observed to elicit a masking effect in trapping Aedes aegypti [38].…”

“…Over the past 60 years, attraction of female mosquitoes to blood-host mimicking odours and plant-based attractants has rarely combined odours from different origin [46][47][48][49][50][51][52][53]. In those studies, where odours of presumed oral and vertebrate origin were combined, mixed results were obtained, by and large not indicating synergy [36][37][38][39]. In this study, although mosquitoes were attracted to a combination of oral and human odour, the combination did not augment or synergize capture rates, in spite of each blend individually being attractive.…”

Nectar-dwelling microbes of common tansy are attractive to its mosquito pollinator,Culex pipiensL

“…Floral nectar is the dominant source of plant sugar for most mosquitoes but other sugar sources such as extra-floral nectar, aphid honeydew, and fruit juices are also consumed [21,24]. Inflorescence semiochemicals [25] along with visual inflorescence displays [26] and CO2 [27] attract mosquitoes to various inflorescences [21,[27][28][29] that they discern [30,31] and may pollinate [32][33][34][35].…”

“…The volatile semiochemicals emitted by human skin microbes help attract host-seeking mosquitoes [37][38][39]. Carbon dioxide is another important vertebrate-and plant-host cue for mosquitoes [27,40], which originates not only from potential hosts but also from their symbiotic microbes [41]. Moreover, microbe-derived semiochemicals indicate suitable oviposition sites for many mosquito species and attract gravid females [42][43][44].…”