Tarsitano, M. *; Dickinson, M.: Visual-Olfactory Fusion in the Flight Behavior of Drosophila

Food is often associated with odor, so olfaction is an important sense which animals use to guide them to food. Course control in insects, however, is strongly influenced by visual cues. We are testing Drosophila to see how the visual algorithms they use to control flight change to enable them to search for food in the presence of attractive odors. We examined the 3-D flight paths of flies within a 100 x 60 cm chamber under three conditions: with the wall of the chamber covered with a background of randomly distributed white and black squares, with the wall covered with a background but also with an odor source embedded in its floor, and with an odor but no visual background. The flies tended towards the middle of the arena when tested with the random background (condition #1). In addition, flies flew at a height between 200 and 300 mm. When tested with a background and an odor (condition #2), flies flew around the location of the odor and at a height between 0 to 100 mm. When flies were tested with an odor but no background (condition #3), they could not locate the odor in the horizontal plane. However, the flies flew at a height between 0 – 100 mm, the same altitude as per condition #2. Our tests suggest that optic flow is required for the localization of an odor source. The process whereby one sensory modality (olfaction) modulates another sensory mediated behavior (vision) is termed ‘sensory fusion’. It is not clear if the mechanism that enables a fly to localize the altitude of an odor source also requires visual input. In the case of vertical localization, flies might use the top and bottom edges of the arena as visual cues.