A novel setup for 3D chasing behavior analysis in free flying flies

• Varennes Léandre
• Krapp Holger
• Viollet Stéphane

• Aerial pursuit
• Free flight
• Blow fly
• Invertebrate pursuit
• Capture strategies
• Insect vision
• Neuroethology
• Fly body orientation

Background: Insects catching prey or mates on the wing perform one of the fastest behaviours observed in nature. Some dipteran flies are aerial acrobats specialized to detect, chase and capture their targets within the blink of an eye. Studies of aerial pursuits and its underlying sensorimotor control have been a long-standing subject of interest in neuroethology research. New method: We designed an actuated dummy target to trigger chasing flights in male blowflies. Our setup generates arbitrary 2D target trajectories in the horizontal plane combining translation up to 1 m/s and angular rotation up to 720°/s. Results: Using stereovision methods we reconstructed target and pursuer positions every 5 ms with a maximum 3D error of 5 mm. The pursuer's body pitch and yaw angles were resolved within an error range of 6deg. An embedded observation point provides a close-up view of the pursuer's final approach and enables us to measure its body roll angle. We observed banked turns and sideslip which have not been reported for chasing blowflies in the past. Comparison with existing method(s): Previous studies focused on pursuit along circular paths or interception of translating targets while our method allows us to generate more complex target trajectories. Measurements of body orientation in earlier accounts were limited to the heading direction while we extended the analysis to include the full body orientation during pursuit. Conclusions: Our setup offers an opportunity to investigate kinematics and governing visual parameters of chasing behaviour in species up to the size of blowflies under a large variety of experimental conditions.