Floral and honeydew foraging ecology of select mosquito species

Both male and female mosquitoes exploit a wide variety of plant sugar resources, including floral nectar and aphid honeydew, as important sources of carbohydrates. Mosquitoes are generally considered nectar thieves that do not pollinate the flowers they visit, and volatile semiochemicals are believed to be the primary driver of mosquito attraction to plant sugar sources. Using the northern house mosquito, Culex pipiens, and its nectar host the common tansy, Tanacetum vulgare, we showed mosquito-induced seed-set. We found that semiochemicals from T. vulgare flowers are attractive to Cx. pipiens and the yellow fever mosquito, Aedes aegypti, that visual and olfactory inflorescence cues in combination attract more mosquitoes than olfactory cues alone, and that plant CO2 enhances the attractiveness of a 20-component synthetic blend of tansy inflorescence odourants. This blend included 9 odourants found in human odour, which are also attractive. Electroretinograms revealed that Cx. pipiens eyes can sense ultra-violet (UV) wavelengths, with peak sensitivity at 335 nm. Experiments found that UV inflorescence cues of T. vulgare and the common hawkweed, Hieracium lachenalii, enhance the attractiveness of inflorescence odour to female Cx. pipiens through floral patterns of UV-absorption and UV-reflection. We then established the attraction of Ae. aegypti to honeydew odourants from the green peach aphid, Myzus persicae, and the pea aphid, Acyrthosiphon pisum, feeding on fava bean, Vicia faba. We collected and analyzed headspace odourants from honeydew of A. pisum feeding on V. faba. An 8-component synthetic blend of these odourants and synthetic odourant blends of crude and sterile honeydew we prepared from literature data all attracted female Ae. aegypti. The synthetic blend containing microbial odour constituents proved more effective than the blend without these constituents. Our data support the hypotheses that mosquitoes are pollinators, that the entire inflorescence Gestalt of olfactory, CO2 and UV cues is more attractive to mosquitoes than floral odourants alone, that olfactory cues attract mosquitoes to honeydew, and that microbe-emitted volatiles play a role in mosquito attraction to honeydew.