A major breakthrough in understanding how insect flight evolved was achieved with the help of robots built by engineers at the University of California San Diego. The study, described in the Oct. 4, 2023 issue of the journal Nature, is the result of a six-year collaboration between roboticists at UC San Diego and biophysicists at the Georgia Institute of Technology.
Evolution of Insect Flight
The study focuses on the evolution of two different modes of flight in insects. Most insects use their brains to activate their flight muscles for each wingstroke, similar to how we activate our leg muscles when we walk. This is known as synchronous flight. However, some insects, like mosquitoes, can flap their wings without their nervous system commanding each wingstroke. Their wing muscles automatically activate when stretched, which is called asynchronous flight. Asynchronous flight allows certain insects to flap their wings at high speeds, like mosquitoes that can flap their wings more than 800 times a second.
Scientists previously believed that the four major groups of insects (bees, flies, beetles, and true bugs) evolved asynchronous flight separately. However, a new analysis by the Georgia Tech team suggests that asynchronous flight actually evolved in a common ancestor. Some groups of insects later reverted back to synchronous flight, while others retained asynchronous flight.
Moths: Ideal Specimens for Study
Hawkmoths were chosen as the ideal specimens to study the evolution of synchronous and asynchronous flight. Moths currently use synchronous flight, but their evolutionary record indicates that they have ancestors with asynchronous flight.
Researchers at Georgia Tech first examined the Hawkmoth muscle to determine if it still had signatures of asynchrony. They discovered that Hawkmoths retained the physical characteristics of asynchronous flight muscles, even if they were no longer used.
Using Robots to Understand Flight Evolution
In order to understand how insects can have both synchronous and asynchronous properties and still fly, researchers realized that robots could be used to perform experiments that would be impossible with actual insects. By building a flapping wing robot, they were able to emulate combinations of asynchronous and synchronous muscles and test the transitions that may have occurred during millions of years of flight evolution.
According to Nick Gravish, a professor of mechanical and aerospace engineering at UC San Diego, the work highlights the potential of robophysics, which is the use of robots to study the physics of living systems. The flapping wing robot helped provide answers to evolutionary questions in biology.
The research also revealed that these transitions between synchronous and asynchronous flight occur in both directions, and that there is only one independent origin of asynchronous flight. Multiple revisions back to synchrony have happened from this single origin.
Building Robo-Physical Models
The research team studied moths, measured their muscle activity during flight, and built a mathematical model of their wing flapping movements. The mathematical model was then translated into commands and control algorithms that were sent to a robot mimicking a moth wing. Two robots were built: a large flapper robot for underwater testing and a smaller flapper robot for testing in air.
Findings and Next Steps
The robot and modeling experiments demonstrated that insects can transition from synchronous to asynchronous flight under the right circumstances. This provides a possible pathway for this evolution and transition. The researchers encountered challenges, such as modeling fluid flow around the robots and the feedback property of stretched insect muscle, but were able to overcome them.
Future steps from a robotics perspective include working with material scientists to equip the robots with muscle-like materials. These findings not only contribute to the understanding of insect flight evolution and biophysics, but also have implications for robotics. Asynchronous motors in robots can adapt and respond quickly to the environment, making them more efficient. This research could lead to the development of responsive and adaptive flapping wing systems in robotics.