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.
For a very long time, mosquitoes have been known or suspected to consume plant liquids. Recently eclosed mosquitoes cannot survive long without consuming sugary plant liquids that provide fuel for flight and enable blood‐feeding and mating. Populations of even highly synanthropic mosquitoes may not be able to persist without phytophagy, even when vertebrate blood is readily available. Phytophagy is a key element of mosquito ecology, and understanding it is critical to combat mosquito‐borne diseases. In this review, we summarize the current knowledge about mosquito phytophagy and outline future research needs. Specifically, we review the many plant‐derived food sources mosquitoes exploit, study the pollination function of mosquitoes, highlight the predation risks of plant‐foraging mosquitoes, investigate the role of microbes in the sugar‐foraging ecology of mosquitoes, and shed light on the evolution of haematophagy.
The Asian bush mosquito, Aedes japonicus japonicus, and the coastal rock pool mosquito, Aedes togoi, are potential disease vectors present in both East Asia and North America. While their ranges are fairly well‐documented in Asia, this is not the case for North America. We used maximum entropy modeling to estimate the potential distributions of Ae. togoi and Ae. j. japonicus in the United States, Canada, and northern Latin America under contemporary and future climatic conditions. Our results suggest suitable habitat that is not known to be occupied for Ae. j. japonicus in Atlantic and western Canada, Alaska, the western, midwestern, southern, and northeastern United States, and Latin America, and for Ae. togoi along the Pacific coast of North America and the Hawaiian Islands. Such areas are at risk of future invasion or may already contain undetected populations of these species. Our findings further predict that the limits of suitable habitat for each species will expand northward under future climatic conditions.
Inflorescence patterns of ultraviolet (UV) absorption and UV-reflection are attractive to many insect pollinators. To understand whether UV inflorescence cues affect the attraction of nectar-foraging mosquitoes, we worked with the common house mosquito, Culex pipiens and with two plant species exhibiting floral UV cues: the tansy, Tanacetum vulgare , and the common hawkweed Hieraciumm lachenalii . Electroretinograms revealed that Cx . pipiens eyes can sense UV wavelengths, with peak sensitivity at 335 nm. Behavioural bioassays divulged that UV inflorescence cues enhance the attractiveness of inflorescence odour. In the presence of natural floral odour, female Cx . pipiens were attracted to floral patterns of UV-absorption and UV-reflection but preferred uniformly UV-dark inflorescences. Moreover, Cx . pipiens females preferred UV-dark and black inflorescence models to UV-dark and yellow inflorescence models. With feathers and pelts of many avian and mammalian hosts also being UV-dark and dark-coloured, foraging Cx . pipiens females may respond to analogous visual cues when they seek nectar and vertebrate blood resources.
Plant sugar is an essential dietary constituent for mosquitoes, and hemipteran honeydew is one of the many forms of plant sugar that is important to mosquitoes. Many insects rely on volatile honeydew semiochemicals to locate aphids or honeydew itself. Mosquitoes exploit volatile semiochemicals to locate sources of plant sugar but their attraction to honeydew has not previously been investigated. Here, we report the attraction of female yellow fever mosquitoes, Aedes aegypti, to honeydew odorants from the green peach aphid, Myzus persicae, and the pea aphid, Acyrthosiphon pisum, feeding on fava bean, Vicia faba. We used solid phase micro-extraction and gas chromatography-mass spectrometry to collect and analyze headspace odorants from the honeydew of A. pisum feeding on V. faba. An eight-component synthetic blend of these odorants and synthetic odorant blends of crude and sterile honeydew that we prepared according to literature data all attracted female A. aegypti. The synthetic blend containing microbial odor constituents proved more effective than the blend without these constituents. Our study provides the first evidence for anemotactic attraction of mosquitoes to honeydew and demonstrates a role for microbe-derived odorants in the attraction of mosquitoes to essential plant sugar resources.
We identified and field-tested the sex pheromones of Dasineura oxycoccana (Johnson) (Diptera: Cecidomyiidae) midges collected from cranberry, Vaccinium macrocarpon Aiton, and from highbush blueberry, Vaccinium corymbosum L., commonly named cranberry tipworm (CTW) and blueberry gall midge (BGM), respectively. Coupled gas chromatographic-electroantennographic detection (GC-EAD) analyses of pheromone gland extract from the ovipositor of calling CTW females revealed one component (<10 pg per ovipositor/pheromone gland) that elicited antennal responses from CTW males. Stepwise identification was based on its mass spectrum in a concentrated sample with 300 pheromone gland equivalents, retention indices (RI) on three GC columns (DB-5, DB-23, and DB 210), RI inter-column differentials, and RIs and double bond positions of other midge pheromones. These analyses indicated that (8Z)-2,14-diacetoxy-8-heptadecene (2,14-8Z-17) was the candidate pheromone of the CTW. GC-EAD analysis of pheromone gland extract from calling BGM females revealed two components that elicited antennal responses from BGM males. Retention times on the three GC columns were consistent with 2,14-8Z-17 and 2,14-17, indicating that these were candidate pheromone components of the BGM. The four stereoisomers of 2,14-8Z-17 were stereoselectively synthesized and field-tested in cranberry. Delta-type traps baited with SS-2,14-8Z-17 captured significantly more CTW males than did traps baited with any other single stereoisomer or with all four stereoisomers combined. In blueberry, delta-type traps baited with RR-2,14-8Z-17 captured significantly more BGM males than did traps baited with any other single stereoisomer or with all four stereoisomers combined. Subsequent field experiments demonstrated that RR-2,14-17 is the major pheromone component of BGM, and that RR-2,14-8Z-17 is a pheromone component that does not enhance attractiveness of RR-2,14-17. The BGM pheromone RR-2,14-17 has no antagonistic effect on the CTW pheromone SS-2,14-8Z-17 and vice versa. Our results substantiate the conclusion that populations of D. oxycoccana on cranberry and blueberry represent two cryptic species.
Plant essential oils (EOs) have been considered as spatial repellents to help disrupt the pathogen transmission cycle of mosquitoes. Our objective was to assess spatial repellency effects of EOs on the tropical yellow fever mosquito, Aedes aegypti (L.) (Diptera: Culicidae) and on local mosquito populations in coastal British Columbia (Canada). In laboratory experiments using protocols of the World Health Organization, three of the solitary EOs tested proved repellent to Ae. aegypti: cinnamon bark, lemongrass, and rosemary. Binary combinations of select EOs enhanced the repellent effect of single EOs through synergistic interactions. The EO blend of geranium and peppermint lowered the RD50 (the dose required to obtain 50% repellency) of each solitary EO by >1,000-fold. Compared with binary EO blends, ternary EO blends were typically less repellent to mosquitoes, possibly due to a dilution effect of the most effective EO constituent(s) in the blend. In field experiments, the EO blend of lemongrass and cinnamon bark expressed spatial repellency towards the cool weather mosquito, Culiseta incidens (Thomson) (Diptera: Culicidae), even when this blend was disseminated from devices as much as 1 m away from a sentinel trap releasing attractive vertebrate host odorants and CO2. Deployment of EOs as spatial repellents in small outdoor gatherings could help protect humans from mosquito-borne diseases, particularly when this tactic is coupled with other tools of mosquito management.
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