Flies can discriminate the size and distance of virtual objects against a complex background, and trap directed airflow and smell to navigate to distant destinations. Photo credit: Photo courtesy of Shoot for Science: Deepak Kakara, Dinesh Yadav, Sukanya Olkar, and Parijat Sil.
Flying insects are notable for their ability to identify and locate food sources and partners as they navigate a complex 3D world. Little is known, however, about how they combine various sensory stimuli to find and reach the objects of their interest. Now researchers from Shannon Olsson’s laboratory at the National Center for Life Sciences in Bangalore have created a virtual reality (VR) arena in which they can observe the behavior of tethered flies.
If you’ve ever tried to hit a fly, you know how hard it is to follow its movements when it crouches and weaves around to escape. A scientist trying to observe and understand the behavior of insects in nature has stopped working. Rather than attempting the (almost) impossible task of following flies, scientists from Shannon Olsson’s lab took them inside into a world made just for them.
Researchers used VR (Virtual Reality) tools to simulate a complex, naturalistic 3D environment that insects can navigate. They showed that insects react to three-dimensional objects in a virtual world and can also use smell and wind keywords to make decisions. Olsson has long wondered how well small insects can find things – like a mosquito searches for a person or an apple fly finds an apple tree – that are several kilometers away. “With the VR we’ve built, we can start looking at this question, which is what drives it to make certain decisions,” says Olsson.
The use of VR to study insect behavior is not new. For several decades now, scientists have been presenting insects with simple sensory cues such as stripes that simulate a sense of movement. “Stripes are a very neat, simple structure for understanding the physiology or the mechanism of vision. But they don’t help us understand behavior,” explains Pavan Kumar Kaushik, PhD student and chief architect of her virtual fly world, in which a tethered fly presents itself with a natural panoramic view with sky, grass and trees. The fly responds by flapping its wings to move like it does in the real world. The screen moves in response to the flaps of its wings, giving the fly the illusion of actually navigating the world. It’s the flying version of a video game. Mosquitoes, apple flies and other insects were looking for objects of their interest in the VR world, just as they would in nature, the researchers report in their upcoming PNAS article.
The finishing touches to reality come in the form of a stream of air that mimics the wind and puffs of smell added to the mix. These were by far the hardest aspects to get to grips with, says Kaushik, who spent more than three years perfecting them. “If you have visual systems, you can just see if something is wrong,” he says. On the other clues, he had to use the insect’s behavior to fix mistakes and correct the system, mimicking reality as closely as possible.
“What’s really interesting? [this] The setup is to bridge the gap between traditional VR – simple shapes, simple environments – and the natural world of insects, “says Vivek Jayaraman, a cognitive neuroscientist from the Janelia Research Campus at the Howard Hughes Medical Institute in the United States.
Flies can discriminate the size and distance of virtual objects against a complex background, and trap directed airflow and smell to navigate to distant destinations. Photo credit: Photo courtesy of Shoot for Science: Deepak Kakara, Dinesh Yadav, Sukanya Olkar, and Parijat Sil.
The researchers chose the apple fly Rhagoletis pomonella for their behavioral studies. “It’s a specialist – it only likes apple trees – so we don’t have to worry about giving it the right impetus,” explains Olsson. In addition, a slew of studies done in apple orchards and other places for over 50 years have researched the shape of the trees they like, the types of fruits they like, and the types of smells they like, uncovered and given the truth to Kaushik and Olsson to form the foundation of VR.
“”[The VR arena] is pretty well controlled so it doesn’t lose the experimental advantages of VR. What they gain is the ability to gain insight into some of the more difficult aspects of insect navigation – remote location of a source of smell, visual algorithms that the insects use to decide whether or not to approach something and how olfactory the wind is, and visual cues are combined to get to a source of food, “says Jayaraman, who got a first-hand look at the facility during a visit to the lab.
First, the researchers measured the distance that the apple fly no longer flies to an apple tree. In one of their most fascinating experiments, the researchers show that flies can use a phenomenon called motion parallax to sense the depth of an object against a complex background. You present the fly with two trees that look the same size, but as the fly approaches, a tree grows much faster because it is actually twice as close. By choosing to maneuver on this tree instead of the more distant ones, the flies show that they can distinguish depth from movement and use this information to locate food sources.
Air flow cues are also important to help the flies orientate themselves, as the researchers find, in the absence of visual cues. This is similar to how we can rely on sound for orientation when we cannot see an object, such as trying to find a buzzing cellphone that is out of sight. If, on the other hand, they orientate themselves by smell, the flies must have a world they can “see” – without visual and windy cues they cannot localize the smells they discover. “There used to be no way to really isolate these cues. Our VR allows us to do that and show them how they use those cues in combination,” says Olsson.
Now that the researchers have shown that flies use perspective and parallax of motion in flight, and how they combine various sensory inputs to locate objects, they can now explore in their arena what key world features are required for these behaviors to occur. You can play with individual functions that cannot be manipulated in the real world – a world that may have been turned upside down? – to decipher the core aspects of insect navigation. The knowledge gained can be used by ecological models, robotics, search algorithms and a variety of other applications.
A nose for trouble: Fruit flies can detect predators by smell
More information:
Pavan Kumar Kaushik el al., “Characterization of Long Distance Search Behavior in Diptera Using Complex 3D Virtual Environments”, PNAS (2020). www.pnas.org/cgi/doi/10.1073/pnas.1912124117
Provided by the National Center for Life Sciences
Quote: The virtual reality of insects gives us the perspective of a fly on the world (2020, May 18), accessed on February 12, 2021 from https://phys.org/news/2020-05-insect-virtual-reality- perspective-world.html
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