Anna Noreuil, an M.S. student in the Fritz Lab in the Department of Entomology at the University of Maryland, has been studying host-seeking behavior and differential chemosensory gene expression in above- and below-ground Culex pipiens for her master’s research. Cx. pipiens (Diptera: Culicidae) is a mosquito found in the northern regions of the U.S. and is also found in urban and suburban temperate areas around the world. Cx. pipiens is the primary vector of West Nile virus (WNV), a mosquito-borne disease that affects the nervous system, in the Northeastern US. Oddly, although there is only one species known as Cx. pipiens, two “bioforms” of the species exist which are morphologically indistinguishable but genetically, physiologically, and behaviorally different: “Cx. pipiens form pipiens” and “Cx. pipiens form molestus.” Cx. pipiens form pipiens differs from Cx. pipiens form molestus in three distinct ways: (1) it breeds in above-ground habitats, (2) it requires blood meals for egg production, and (3) it prefers avian hosts over humans (Figure 1). However, these two “bioforms” readily hybridize or crossbreed and as such they are both classified as the same species (Figure 2).
How Cx. pipiens detect and select hosts is also a point of interest for the species. Cx. pipiens uses a wide array of internal cues such as age, life stage, circadian clock, blood-feeding rhythms, and experience to guide its host detection and selection. External cues, such as carbon dioxide expelled during respiration, local increases in temperature and humidity, and odorants emitted from skin and breath also help mosquitoes find their host of choice.
With this background information about Cx. pipiens in mind, Noreuil set out to characterize the genetic ancestry of Cx. pipiens bioforms and quantify their host preferences. Ultimately, her goal was to figure out if their genetic ancestry dictates the differences in the mosquitoes’ host selection. Noreuil characterized the genetic ancestry of above- and below-ground populations of both Cx. pipiens bioforms using various DNA-focused molecular techniques and found that genetic ancestry varied significantly across above- and below-ground mosquito populations. Furthermore, Noreuil performed host-choice experiments – i.e. female mosquitoes were scored based on whether they chose the human or chicken host for a blood meal – to determine the host preference of each population. Noreuil’s results indicated that the genetic ancestry of the mosquito populations may not indicate the host preference of the mosquitoes, at least in the case of this assay.
- Fox AN, Pitts RJ, Robertson HM, Carlson JR, Zwiebel LJ (2001) Candidate odorant receptors from the malaria vector mosquito Anopheles gambiae and evidence of down-regulation in response to blood feeding. Proc Natl Acad Sci U S A 98(25): 14693‐14697. https://doi.org/10.1073/pnas.261432998
- Ishida Y, Cornel AJ, Leal WS (2002) Identification and Cloning of a Female Antenna-Specific Odorant-Binding Protein in the Mosquito Culex quinquefasciatus. J Chem Ecol 28: 867–871. https://doi.org/10.1023/A:1015253214273
- Matsuo T, Sugaya S, Yasukawa J, Aigaki T, Fuyama Y (2007) Odorant-Binding Proteins OBP57d and OBP57e Affect Taste Perception and Host-Plant Preference in Drosophila sechellia. PLOS Biology 5(5): e118. https://doi.org/10.1371/journal.pbio.0050118
- Rinker DC, Pitts RJ, Zhou X, Suh E, Rokas A, Zwiebel LJ (2013) Blood meal-induced changes to antennal transcriptome profiles reveal shifts in odor sensitivities in Anopheles gambiae. Proc Natl Acad Sci U S A 110(20): 8260‐8265. https://doi.org/10.1073/pnas.1302562110
About the Authors:
Mike Nan is a PhD student in the St. Leger lab studying how circadian rhythms affect Metarhizium infection of Drosophila.
Dylan Kutz is a MS student in the Lamp lab studying agricultural drainage ditches as sources of spider diversity for neighboring croplands.