A novel behavioral strategy, continuous biased running, during chemotaxis in Drosophila larvae.

Animals collect and integrate information from their environment, and select an appropriate strategy to elicit a behavioral response. Here, we investigate the behavioral strategy employed by Drosophila larvae during chemotaxis toward a food source functioning as an attractive odor source. In larvae, sharp turns have been identified as the main strategy during locomotion to odorant sources, but the existence of runs orienting toward the direction of higher odor concentrations has not been described. In this study, we show the existence of such a successive orientation toward an odor source, which we term as biased running. Our behavioral analysis, which examines the relationship between larval rotational velocities and larval positions relative to an attractive odor source, brings out this newly found behavioral strategy. Additionally, theoretically estimated concentration gradients of chemoattractants between left and right olfactory organs were statistically correlated with rotational velocities during biased running. Finally, computer simulations demonstrated that biased running enhances navigation accuracy. Taken together, biased running is an effective behavioral strategy during chemotaxis, and this notion may provide a new insight on how animals can efficiently approach the odor source.