Odor coding in the maxillary palp of the malaria vector mosquito Anopheles gambiae

Background: Many species of mosquitoes, including the major malaria vector Anopheles gambiae, utilize carbon dioxide (CO2) and 1-octen-3-ol as olfactory cues in host-seeking behaviors that underlie their vectorial capacity. However, the molecular and cellular basis of such olfactory responses remains largely unknown. Results: Here, we use molecular and physiological approaches coupled with systematic functional analyses to define the complete olfactory sensory map of the An. gambiae maxillary palp, an olfactory appendage that mediates the detection of these compounds. In doing so, we identify three olfactory receptor neurons (ORNs) that are organized in stereotyped triads within the maxillary-palp capitate-peg-sensillum population. One ORN is CO2-responsive and characterized by the coexpression of three receptors that confer CO2 responses, whereas the other ORNs express characteristic odorant receptors (AgORs) that are responsible for their in vivo olfactory responses. Conclusions: Our results describe a complete and highly concordant map of both the molecular and cellular olfactory components on the maxillary palp of the adult female An. gmnbiae mosquito. These results also facilitate the understanding of how An. gambiae mosquitoes sense olfactory cues that might be exploited to compromise their ability to transmit malaria.