Finding a path: Local search behavior of Drosophila larvae

Orientation and navigation are essential features of animals living in changing environments. Typically, animals integrate a variety of allothetic and idiothetic cues to achieve their navigational goals. Allothetic cues, such as visual or chemical landmarks from the environment, provide an external frame of reference. In contrast, idiothetic cues are based on internal proprioceptive feedback and internal copies of motor commands. When Drosophila larvae are exposed briefly to a Teflon container holding a food stimulus, they show a characteristic behavior as soon as the container is removed: They briefly crawl away from the detected resource, remain in its vicinity and then return to the area where they experienced the earlier stimulus. We quantified this behavior with respect to the chemosensory nature of the stimulus, starvation time of the larvae, and agarose concentration of the test plate substrate. We conclude that this behavior represents a centered local search. Furthermore, we exclude various external stimuli (vision and taste), which suggests that possibly idiothetic as opposed to allothetic cues have a stronger influence on the larval local search behavior. In the long term, this behavioral description will enable us to gain insights into the comparability of larval foraging strategies. We also want to investigate whether, despite the simpler organization of the larval brain and the alleged lack of a central complex, a brain region that is important for orientation and navigation in adult Drosophila and other insects, there are common solutions for the brain circuits underlying search behavior.