Odor-mediated flight behavior of Anopheles gambiae Giles Sensu Stricto and A-stephensi Liston in response to CO2, acetone, and 1-octen-3-ol (Diptera: Culicidae)

The flight behavior of Anopheles gambiae s.s. Giles and An. stephensi Patton exposed to different odor cues was studied in a wind tunnel. Odors consisted of CO2, CO2 + acetone (at two concentrations), and CO2 + 1-octen-3-ol. Mosquitoes were released singly and their behavior was recorded on video. Parameters studied included flight velocity, percentage of time spent flying, percentage of time spent in plume, and number of turns toward the plume. Large differences in behavior toward the odors tested were observed An. gambiae did not respond well to CO2, whereas An. stephansi was positively affected by this compound. In contrast, An. gambiae responded significantly to CO2 + acetone (at a low concentration), but the behavior of An. stephensi was completely suppressed by this combination of odor stimuli. CO2 + a high concentration of acetone or CO2 + 1-octen-3-ol did not cause significant effects in An. gambiae compared to no odor, while these treatments elicited strong behavioral responses in An. stephensi. The latter species responded particularly well to CO2 + 1-octen-3-ol. The results suggest that the observed differences may be inherent to the known differences in host preferences, where An. gambiae is highly anthropophilic and An. stephensi more zoophilic. This would explain why the fatter species responds well to CO2 and even better to CO2 + 1-octen-3-ol, a compound readily emitted by bovine ruminants.