Multimodal floral cues guide mosquitoes to tansy inflorescences

Female mosquitoes exploit olfactory, CO₂, 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 aegpyti (L.), we tested the hypothesis that the entire inflorescence Gestalt of olfactory, CO₂ 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 CO₂ after sunset, and that CO₂ 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, CO₂ 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.