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United States Department of Agriculture

Agricultural Research Service


Location: Mosquito and Fly Research Unit

Title: Insights into host-finding by Culex mosquitoes: New tools for surveillance?

item Allan, Sandra
item Bernier, Ulrich

Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: September 28, 2010
Publication Date: N/A

Technical Abstract: Culex mosquitoes are important vectors of pathogens and parasites causing diseases such as West Nile virus, St. Louis encephalitis, Japanese encephalitis, Venezuelan equine encephalitis and bancroftian filariasis. Surveillance of these species is based on traps using conventional mosquito attractants that have been developed based on research on Aedes aegypti and Anopheles gambiae. Although birds play a critical role in maintenance and amplification of mosquito populations and as reservoirs of diseases that affect man and animals, little is known about the cues used by mosquitoes to locate birds. Most attractants for traps have been developed for anthropophilic species such as Aedes aegypti using cues emitted from human hosts. Additional attractants such as the bovine-breath component, 1-octen-3-ol, enhance collection of a broader range of species. Animal-baited traps provide volatile cues from hosts for attraction of mosquitoes (Service 1993) and often overcome inherent biases from conventional mosquito traps and attractants. For instance, baiting traps with birds results in collections of predominately ornithophilic Culex or Culiseta species (Emord and Morris 1982, Rutledge et al. 2003) that are not readily collected in conventional traps (Nayar et al. 2001). Because of the sensitivity of these traps, they are valuable in arbovirus surveys and for population monitoring (Reeves et al. 1961, Rutledge et al. 2003). However, relatively little is known about the volatiles emitted by avians other than the emanation of CO2 from breath. In Gambia, mosquitoes were attracted from a greater distance to avian hosts than to CO2 alone (Gillies and Wilkes 1974) indicating that volatiles other than CO2 play an important role in attraction. Recently Williams et al. (2003) collected and identified several volatile compounds by SPME analysis from chicken feathers, however, these compounds remain untested for behavioral response. Cooperband et al. (2008) reported several compounds f rom chicken feces that elicited EAG response in Culex response and Syed and Leal (2009) reported on the possible role of nonanal in Culex attraction. The lack of documentation on responses of Culex to attractants based upon avian odors is a roadblock for development of an avian-odor based lure for traps for use in mosquito population and arbovirus surveillance. Lactic acid, present on human skin in high quantities, is known associated with strong attraction of anthropophilic mosquito species such as An. gambiae and Ae. aegypti (Smith et al. 1970, Dekker et al. 2002). Lactic acid has been used to experimentally manipulate attraction with the addition of lactic acid to host odor resulting in increased attraction by An. gambiae (Dekker et al. 2002) and Ae. aegypti (Steib et al. 2001). In addition to its role as a host attractant, lactic acid also may contribute to host specificity for biting flies as seen with the reduced attraction and feeding of the zoophilic tsetse species after application of lactic acid onto hosts (Vale 1979). Other human-associated odors important in host location by Anopheles and Aedes spp. include acetone (Bernier et al. 2003, Taken et al. 1997), dimethyl disulfide and dichloromethane (Bernier et al. 2003), and ammonia (Geier et al. 1999, Braks et al. 2001). These compounds are most associated with humans but not unique to humans and may be present as emanations from a wide range of animals. Relatively little is known about the role of lactic acid and other human-associated compounds on attraction of Culex mosquitoes. This presentation summarizes our progress in several areas on examination of the role of chemical attractants on Culex. The first study examines the role of lactic acid on attraction of several Culex species that differ in their attraction to humans with comparison to Ae. aegypti which is readily attracted to humans. Lactic acid influenced attraction of Culex quinquefasciatus similarly to Ae. aegypti with strong attraction when synergized with CO2. Other Culex species which do not readily feed on humans, Culex nigripalpus and Culex tarsalis, were repelled by lactic acid even in the presence of CO2. When compounds were identified from blood and examined for attraction in an olfactometer, fewer individual compounds attracted Cx. quinquefasciatus than Ae. aegypti with significant attraction only to lactic acid, acetic acid, palmitic acid, stearic acid, dimethyl disulfide and methyl propyl disulfide. The avian feeding species, Cx. nigripalpus reported to fewer compounds. Several of these compounds have been evaluated in the field with traps. The identification of volatiles emitted from chickens provides the basis for discussion of the status of our current knowledge of attraction of Culex to host-derived cues. References Cited: Allan, SA, UR Bernier and DL Kline. 2006. Laboratory evaluation of avian odors for mosquito (Diptera: Culicidae) attraction. J Med Entomol 43: 225-231. Allan, SA, UR Bernier and DL Kline. 2006. Attraction of mosquitoes to volatiles associated with blood. J Vector Ecol 31: 71-78. Allan SA, UR Bernier and DK Kline. 2010. Laboratory evaluation of human-associated odors on attraction of Culex spp. (Diptera: Culicidae). J Vector Ecol 35: 1-7. Acree, F, RB Turner, HK Gouck, M Beroza and N Smith. 1968. L-lactic acid: a mosquito attractant isolated from humans. Science 161: 1346-1347. Bernier, UR, DL Kline, DR Barnard, KH Posey, MM Booth and RA Yost. 2001. Chemical composition that attracts arthropods. US Patent 6,267,953. 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