Olfactory Responses and Odor Coding of Culex quinquefasciatus to Human Odorants
Type of DegreeMaster's Thesis
Entomology and Plant Pathology
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The southern house mosquito, Culex quinquefasciatus (Diptera: Culicidae), transmits a number of potentially fatal diseases, including West Nile virus (WNV). From 1999 to 2013, WNV caused 39,557 cases of human infection and 1,668 deaths in the United States alone, and the lack of a vaccine for WNV makes mosquito control central to reducing the spread of this and other serious diseases. Mosquitoes recognize their hosts by detecting chemical cues via the olfactory receptor neurons (ORN) in their sensilla, most of which are located on the insects’ antennae. Cx. quinquefasciatus’ antennal sensilla are functionally separated based on morphological distinctions and are highly sensitive to plant-derived repellents. However, a comprehensive study of the response of Cx. quinquefasciatus to human odorants is still lacking. In this research, single sensillum recording was conducted to investigate Cx. quinquefasciatus’ neuronal responses to more than one hundred human odorants selected from eleven chemical categories. Five morphological types of antennal sensilla were identified, namely short sharp-tipped (SST), long sharp-tipped (LST), short blunt-tipped type I (SBTI), short blunt-tipped type II (SBTII) and grooved peg (GP). The results of the single sensillum recordings revealed that Cx. quinquefasciatus only responded to a very limited number of the human odorants selected. Different types of sensilla presented distinctive response profiles to the human odorants tested and the responses were dose-dependent. In particular, SST, SBTI and SBTII responded to more than one category of human odorants, while GP and LST were narrowly tuned to amines and methyl nonanoate, respectively. Temporal dynamics analysis demonstrated that the temporal structure is based on the chemical structure. A behavioral study was also carried out that utilized a hand-in-cage bioassay to characterize the odorant modulating behaviors of Cx. quinquefasciatus, confirming that heptanal indeed modulates opposite mosquito behaviors and that this behavior is concentration-dependent. The antennal lobe is the first center that processes olfactory information among insects. Olfactory receptor neurons aggregate in the antennal lobe and construct spherical units called glomeruli and the spatial separation of these glomeruli forms the basis of insect odor-coding. Anterograde fluorescent staining and confocal microscopy were also performed to examine the structure of Cx. quinquefasciatus’ antennal lobe and the spatial relationship between glomeruli in more detail. Taken together, our study sheds new light on the olfactory physiology and response of Cx. quinquefasciatus to human odorants and provides meaningful information to support the development of new reagents for mosquito control.