Autonomous robots capable of finding an odor source can be important for the safety and security of society. They can be used for the detection of disaster victims, of drugs or explosive materials at an airport, and of hazardous material spills or leaks in the environment. At present, we rely entirely on well-trained animals (e.g., dogs) for these tasks, and robotic odor source localization has been strongly expected to relieve the workload of these animals. Finding an odor source is a challenging task for robots because odorants are distributed intermittently in an atmosphere¹; therefore, continuous sampling of the odor concentration gradient is not always possible. Thus, a search strategy using intermittent odor cues is necessary for the achievement of robotic odor source localization^2-4.

Odor source localization is essential for organism survival and includes tasks such as finding food, mating partners, and sites for oviposition. To overcome the difficulty in tracking patchy distributed odorants, organisms have evolved various behavioral strategies consisting of two fundamental behaviors: moving upstream during odor reception and cross-stream during cessation of odor reception^5,6. These reactive strategies have been well-documented in insects and further combined with other modalities, such as wind direction and vision^5-8. The insect behavioral models have also been useful examples for robotics^3,9-11, in which behavioral algorithms or neural circuit models are implemented into mobile robots for the evaluation of odor source localization abilities^10,12-15. From biomimetic perspectives, this “bottom-up” approach is certainly a fundamental way to develop biomimetic robots. However, the bottom-up approach is not a shortcut to obtaining a useful search strategy, because biological analyses are still ongoing, and the modeling of the sensory-motor systems behind insect behaviors has not been completed. Therefore, it is still unknown how such a biological system actually works as a controller of a robotic platform.

In this article, we demonstrate the protocol of a straightforward “top-down” approach to develop an odor-tracking mobile robot controlled by a biological system^16,17. The robot is controlled by a real insect and can be regarded as a prototype of future insect-mimetic robots. In the robot’s cockpit, a tethered adult male silkmoth (Bombyx mori) walked on an air-supported ball in response to the female sex pheromone, which was delivered to each antenna through air suction tubes. The ball rotations caused by the walking of the onboard moth were measured by an optical sensor and were translated into the movement of the two-wheeled robot. The advantage of this “hybrid” approach is that experimenters can investigate how the insect sensory-motor system works on the robotic platform where a pilot insect is in a closed loop between the robot and a real odor circumstance. The manipulation of the robotic hardware alters the closed loop; therefore, the insect-controlled robot is a useful platform for both engineers and biologists. For engineering, the robot represents the first steps of applying a biological model to meet the requirements for robotic tasks. For biology, the robot is an experimental platform for studying sensory-motor control under a closed loop.