Pollinators, annoying pests, thirsty bloodsuckers, pathogens, nutrient recyclers – insects play a diverse role! While they make up about 80% of all multicellular organisms known to us, they are also the fastest disappearing life forms. From an ecological point of view, we seem to have some idea of the critical role these flying animals play in our survival. However, we have hardly understood how they can easily navigate their surroundings and what functions wind direction and smell play in their guidance. A new study is now using three-dimensional virtual reality to gain some insight into how insects fly.
In the study, which was published in the Proceedings of the National Academy of Sciences (PNAS), researchers from the National Center for Biosciences (NCBS) in Bengaluru and Bielefeld University examined the search behavior of flying insects. They have shown that insects can distinguish size and distance in a complex environment, and can also use clues from the blowing wind and smell to navigate. The study was funded by the Science and Engineering Research Board (SERB), Microsoft Research, and the Department of Atomic Energy.
“Insects are one of the few groups of organisms that have mastered the sky. This contributes significantly to their immense diversity, ”says Dr. Shannon B. Olsson, Associate Professor at NCBS who led the study.
However, studying their ability to fly is associated with many challenges, which is why there are very few studies on it.
“Because of their small size and speed, it is difficult to follow insects in nature. It is also difficult to judge what an insect sees, smells or feels at any one time,” she cited.
The researchers solved this problem by using virtual reality and simulating a real-world environment with three-dimensional objects to understand how flying insects navigate.
“With our setup, we can measure which sights, smells and air currents cause them to change direction,” says Dr. Olsson.
They glued a few insects to tiny poles and let them fly in a room with monitors that provided images of an open meadow with grass, sky, and trees. They also simulated the wind flow direction and smell around the insect with tiny glass capillaries that had valves to release bursts of air and odor. These capillaries also revolved around the insects as they moved.
The study is the first to use three-dimensional simulations in virtual reality to understand flying insects.
“It is essentially a video game that is controlled by the fly using its wings as a joystick,” says Pavan Kumar Kaushik.
He is a PhD student at NCBS and a co-author of the current study.
A tethered apple fly approaches a tree-like virtual object. Computer monitors offer a visual panorama and glass capillaries offer 360 ° wind and odor signals. [Image credits: Pavan Kumar Kaushik]
Complex calculations in a pinhead-sized brain
The researchers conducted various experiments on many insects to test whether they could navigate to virtual objects. They started with a leashed apple fly (Rhagoletis pomonella), a North American pest. When he was shown a world of grass and sky, he didn’t seem to care where he wanted to fly. But when a tree was added to the area, it approached the tree and tried to land on it. The researchers then repeated this experiment with other flying insects, including a mosquito (Aedes aegypti), a crane fly species (Pselliophora laeta), and a hover fly (Eristalis tenax). They found that all of these insects can distinguish, navigate, and react to virtual three-dimensional objects from the surrounding background.
It is known that insects have compound eyes with many light-sensitive units that make it easier for them to see. Could this pixelated view help them navigate?
“Compound eyes can recognize movements particularly well. They see the world ten times faster than we do,” says Kaushik. “Combined with sophisticated neural circuits, they compute complex image processing tasks much better than our best computer vision algorithms, with the brain being smaller than the head of a pin!”
Opo Terser / CC BY (https://creativecommons.org/licenses/by/2.0)
In the next set of experiments, the researchers introduced more trees at different distances and sizes into the virtual environment to allow apple flies to navigate. They found that these flies preferred to approach the nearest tree, even though it was smaller. The researchers then blocked the visual cues by having a static background with no objects, just wind flow and smell. They found that the flies used the wind direction and smell to get closer to the desired object.
It is a commendable achievement for insects with primitive neural structure to perform such stunts.
“It is known that insects use their antennae in conjunction with visual cues to measure airflow. We show that they can do this without visual cues,” says Kaushik of her results.
Probably so soaring and nocturnal insects that cannot see well could measure wind speed and the direction in which they are supposed to migrate hundreds of kilometers, he says.
It is fascinating and has many implications to decipher the exact mechanism by which insects fly, which, unlike our 80 billion, only have a few hundred thousand neurons in their brains.
“When we understand how flying insects navigate, we know how to find flowers to pollinate, plants to eat, or arms to bite (in mosquitoes). It can also help us live more in harmony with them,” says Dr. Olsson.
It can also benefit computer vision and robotics.
“Nothing that humans have created has the ability to navigate the world like a little fly. But if we learn how to do it, we can develop better technologies that use less computing power,” she says.
This article has been paced by the researchers whose work is being covered to ensure accuracy.