The male silkmoth was chosen as the “driver” of the robot due to its characteristic “mating dance” when reacting to the sex pheromone of the female. Once the male is stimulated by the pheromone it exhibits a distinctive walking pattern: straight-line and zigzagged walking consisting of several turns followed by a loop of more than 360 degrees.
Lead author of the research, Noriyasu Ando, says, “The simple and robust odor tracking behavior of the silkmoth allows us to analyze its neural mechanisms from the level of a single neuron to the moth’s overall behavior. By creating an ‘artificial brain’ based on the knowledge of the silkmoth’s individual neurons and tracking behavior, we hope to implement it into a mobile robot that will be equal to the insect-controlled robot developed in this study.”
The researchers, from the Univ. of Tokyo, attached the silkmoth to a free-moving polystyrene ball at the front of the robot which was used for overall control, much like the ball in a computer mouse.
Two 40 millimeter fans were attached at the front to divert the pheromone-containing air to the on-board moth – the researchers believe the fans are comparable to the wings of the silkmoth that flap to generate air flow across its antennae.
A 1,800 millimeter wind tunnel was used in the experiments; the pheromone and robot were placed at opposite ends. Fourteen silkmoths were used in the study and all of them were able to successfully guide the robot towards the source.
The researchers also introduced a turning bias to the experiments, changing the power of one of the robot’s two motors so it veered towards one side when moving. This put the silkmoth into an extraordinary situation and required it to adapt and change its behavior.
“The best way to elicit adaptive behaviors of insects is to put them into extraordinary situations. The turning bias in our study is analogous to a situation in which we try to ride unbalanced bicycles. We need training to ride such bicycles smoothly but the silkmoth overcomes the situation with only simple and fast sensory-motor feedbacks,” says Ando.
It is important that the chemical sensors attached to a potential robot have a short response and processing time when tracking down odors continuously, which is why the researchers also investigated the effect of a time delay between the movement of the silkmoth and the response of the motor.
“Most chemical sensors, such as semiconductor sensors, have a slow recovery time and are not able to detect the temporal dynamics of odors as insects do. Our results will be an important indication for the selection of sensors and models when we apply the insect sensory-motor system to artificial systems,” continues Ando.