Odor-mediated flight behavior ofAnopheles gambiae gilesSensu Stricto andAn. 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. gambiaedid not respond well to CO ₂,whereas An. stephansiwas positively affected by this compound. In contrast, An. gambiaeresponded significantly to CO ₂ + acetone (at a low concentration), but the behavior of An. stephensiwas completely suppressed by this combination of odor stimuli. CO ₂ + a high concentration of acetone or CO ₂ + 1-octen-3-ol did not cause significant effects in An. gambiaecompared to no odor, while these treatments elicited strong behavioral responses in An. stephensi.The latter species responded particularly well to CO ₂ + 1-octen-3-ol. The results suggest that the observed differences may be inherent to the known differences in host preferences, where An. gambiaeis highly anthropophilic and An. stephensimore zoophilic. This would explain why the latter species responds well to CO ₂ and even better to CO ₂ + 1-octen-3-ol, a compound readily emitted by bovine ruminants.