Displacement experiments provide evidence for path integration in Drosophila.

Like many other animals, insects are capable of returning to previously visited locations using path integration, which is a memory of travelled direction and distance. Recent studies suggest that Drosophila can also use path integration to return to a food reward. However, the existing experimental evidence for path integration in Drosophila has a potential confound: pheromones deposited at the site of reward might enable flies to find previously rewarding locations even without memory. Here, we show that pheromones can indeed cause naïve flies to accumulate where previous flies had been rewarded in a navigation task. Therefore, we designed an experiment to determine if flies can use path integration memory despite potential pheromonal cues by displacing the flies shortly after an optogenetic reward. We found that rewarded flies returned to the location predicted by a memory-based model. Several analyses are consistent with path integration as the mechanism by which flies returned to the reward. We conclude that although pheromones are often important in fly navigation and must be carefully controlled for in future experiments, Drosophila may indeed be capable of performing path integration.

A Cyborg Insect Reveals a Function of a Muscle in Free Flight.

While engineers put lots of effort, resources, and time in building insect scale micro aerial vehicles (MAVs) that fly like insects, insects themselves are the real masters of flight. What if we would use living insect as platform for MAV instead? Here, we reported a flight control via electrical stimulation of a flight muscle of an insect-computer hybrid robot, which is the interface of a mountable wireless backpack controller and a living beetle. The beetle uses indirect flight muscles to drive wing flapping and three major direct flight muscles (basalar, subalar, and third axilliary (3Ax) muscles) to control the kinematics of the wings for flight maneuver. While turning control was already achieved by stimulating basalar and 3Ax muscles, electrical stimulation of subalar muscles resulted in braking and elevation control in flight. We also demonstrated around 20 degrees of contralateral yaw and roll by stimulating individual subalar muscle. Stimulating both subalar muscles lead to an increase of 20 degrees in pitch and decelerate the flight by 1.5 m/s2 as well as an induce in elevation of 2 m/s2.

A robotic leg inspired from an insect leg.

While most insect-inspired robots come with a simple tarsus, such as a hemispherical foot tip, insect legs have complex tarsal structures and claws, which enable them to walk on complex terrain. Their sharp claws can smoothly attach and detach on plant surfaces by actuating a single muscle. Thus, installing an insect-inspired tarsus on legged robots would improve their locomotion on complex terrain. This paper shows that the tendon-driven ball-socket structure provides the tarsus with both flexibility and rigidity, which is necessary for the beetle to walk on a complex substrate such as a mesh surface. Disabling the tarsus' rigidity by removing the socket and elastic membrane of a tarsal joint, means that the claws could not attach to the mesh securely. Meanwhile, the beetle struggled to draw the claws out of the substrate when we turned the tarsus rigid by tubing. We then developed a cable-driven bio-inspired tarsus structure to validate the function of the tarsus as well as to show its potential application in the legged robot. With the tarsus, the robotic leg was able to attach and retract smoothly from the mesh substrate when performing a walking cycle.

Neurotransmitter-Loaded Nanocapsule Triggers On-Demand Muscle Relaxation in Living Organism.

This paper reports the on-demand artificial muscle relaxation using a thermosensitive liposome encapsulating γ-aminobutyric acid (GABA) inhibitory neurotransmitter. Muscle relaxation is not feasible in principle, although muscle contraction can be easily induced by electrical stimulation. Herein, thermosensitive liposomes (phase transition temperature = 40 °C) were synthesized to encapsulate GABA and were injected into a leg of a living beetle. The leg was wrapped around by a Ni-Cr wire heater integrated with a thermocouple to enable the feedback control and to manipulate the leg temperature. The injected leg was temporarily immobilized by heating it up to 45 °C. The leg did not swing even by electrically stimulating the leg muscle. Subsequently, the leg recovered to swing. The result indicates that GABA was released from liposomes and fed to the leg muscle, enabling temporal muscle relaxation.

Insect-machine Hybrid System: Remote Radio Control of a Freely Flying Beetle (Mercynorrhina torquata).

The rise of radio-enabled digital electronic devices has prompted the use of small wireless neuromuscular recorders and stimulators for studying in-flight insect behavior. This technology enables the development of an insect-machine hybrid system using a living insect platform described in this protocol. Moreover, this protocol presents the system configuration and free flight experimental procedures for evaluating the function of the flight muscles in an untethered insect. For demonstration, we targeted the third axillary sclerite (3Ax) muscle to control and achieve left or right turning of a flying beetle. A thin silver wire electrode was implanted on the 3Ax muscle on each side of the beetle. These were connected to the outputs of a wireless backpack (i.e., a neuromuscular electrical stimulator) mounted on the pronotum of the beetle. The muscle was stimulated in free flight by alternating the stimulation side (left or right) or varying the stimulation frequency. The beetle turned to the ipsilateral side when the muscle was stimulated and exhibited a graded response to an increasing frequency. The implantation process and volume calibration of the 3 dimensional motion capture camera system need to be carried out with care to avoid damaging the muscle and losing track of the marker, respectively. This method is highly beneficial to study insect flight, as it helps to reveal the functions of the flight muscle of interest in free flight.