Active sensation during orientation behavior in the Drosophila larva: more sense than luck

The fruit fly Drosophila larva demonstrates a sophisticated repertoire of behavior under the control of a numerically simple neural system. Historically, the stereotyped responses of larvae to light and odors captivated the attention of biologists. More recently, the sensory receptors responsible for chemosensation, thermosensation, and vision have been identified. While our understanding of the molecular logic of perception has clearly progressed, little is known about the neural and computational mechanisms guiding movement in sensory gradients. Here we review evidence that larvae orient based on active sensation - a feature distinct from the strategies used by simpler model organisms. Reorientation maneuvers are controlled by the spatiotemporal integration of changes in stimulus intensity detected during runs and lateral head movements.

► Larval behavior can be reduced to a tractable number of motor programs. ► In the fruit fly larva, sensory orientation is based on a direct orientation mechanism relying on active sensing. ► Temporal changes in stimulus intensity measured during side-to-side head casts direct individual turns toward/away from the local gradient. ► Larval chemotaxis represents an intermediate strategy between the biased random walk of bacteria and the stereo-olfaction of vertebrates.