Flashy Flies: Neural Adaptations of Aerial Predatory Insects

Last Friday on March 5, Dr. Paloma Gonzalez-Bellido of the University of Minnesota virtually visited Reed to share her life story and her research on the neural adaptations and behavioural strategies of aerial predatory insects. From dragonflies to killer flies, these aerial insects need to detect and catch small and fast moving prey mid-air in order to survive. Gonzalez-Bellido asks the questions: how do species detect and intercept targets? Do they share the same neural algorithm and flight strategy? How do their eye size and shape influence their predation techniques? Before she answered these questions, Gonzalez-Bellido first gave some insight into her background and how she even began to form said questions.

Dr. Paloma Gonzalez-Bellido. Photo Courtesy of University of Minnesota.

Dr. Paloma Gonzalez-Bellido. Photo Courtesy of University of Minnesota.

Gonzalez-Bellido was born and raised in Malaga, Spain by the beach, and her original dream was to become a marine biologist. She attended the University of Queensland in Australia as an undergraduate and took part in a fish sensory ecology project where she researched fish retinas, launching her passion for sensory neuroscience. After graduation, she wasn’t able to get a PhD studentship in Australia because she wasn’t Australian, and she couldn’t get accepted into a program in her home country of Spain because they only recognized five year undergraduate degrees at the time. So, she set off to pursue a PhD in England at the University of Sheffield. 

In England, she began her research on fruit fly retinas, but soon the cells she was studying began to get sick, and her research became stagnant. Part way through her program, she had to quickly switch her model organism and began her work on miniature predatory insects, comparing them to fruit flies. After the success of her PhD, she went to Virginia to study dragonfly vision at the Howard Hughes Medical Institute’s Janelia Research Campus for a year and a half. After that, she got the opportunity to study neural camouflage control in octopuses and squid at the Marine Biological Laboratory in Woods Hole, Massachusetts. There she was able to continue her own research on killer flies in the evening after she finished working with her squid. When looking for jobs, her husband, Trevor Wardill, also a neuroscience researcher, wanted to stay together; they sought out a permanent position for the two of them and the University of Minnesota offered them exactly what they wanted. Now, Wardill works as an assistant professor and Gonzalez-Bellido works as an associate professor in the University of Minnesota’s College of Biological Sciences. 

After recounting her experience, Gonzalez-Bellido launched into her current research. She wants to learn how insects detect, select, and approach their targets; how efficient the insects’ neural systems work; and where they expend their energy. To answer these questions, she observes their sensory cues, decision making, and movement strategies and analyzes the tradeoffs that species have had to undergo as they evolved; for example, while some flies take more time to accurately locate their prey, others use that time to launch less accurate, but faster attacks. The protagonist of much of Gonzalez-Bellido’s research, the killer fly, is small and has great mobility, but its attacks aren’t as accurate. As long as it can move fast, though, it can redirect its path and still catch its prey even if its first attack isn’t as accurate.

A close up of fly wing. Photo Courtesy of Dr. Gonzalez-Bellido’s Fly Systems Laboratory.

A close up of fly wing. Photo Courtesy of Dr. Gonzalez-Bellido’s Fly Systems Laboratory.

During her research with another fly species, the laphria, her team of researchers discovered the unique sensory cues that trigger the fly’s attack response. Gonzalez-Bellido and her team would adhere beetles — the laphria’s prey — to beads that they could pull along a fishing line in front of the laphria to observe its flight response and predation strategy. Quickly, they discovered that the laphria would ignore the dead beetle and instead attack the beads it was hanging from. The team did away with the beetles and instead began experimenting with different colored beads. They found that the laphria would ignore the black and white beads and would only attack the clear beads. They readjusted their perspective to observe the beads from the laphria’s point of view on the ground rather than continue to film the experiment from above. They soon discovered that the white and black beads looked the same when backlit by the sun, but when the translucent beads were pulled along the fishing line, little flashes of light would be emitted as the surface of the bead reflected different beams of light from the sun. Gonzalez-Bellido’s team began to wonder, could the laphria be sampling the wing beat frequency of their potential prey? 

The team hypothesized that because the clear beads were faceted — rather than being a smooth sphere, they had angled edges — they could reflect different beams of light from the sun at different angles, resulting in the flashes of light that the laphria observed. Flies and other insects have translucent wings, and as they beat they reflect flashes of light at different frequencies, just as the bead was doing.

To prove their hypothesis, Gonzalez-Bellido and the other researchers created a light board that would flash different lights in a line at different speeds. They found that the laphria don’t attack beat frequencies below 50 Hz or above 150 Hz, and the frequency of the light allowed the laphria to detect what insects could be considered prey and which ones they should attack. Although laphria’s prey come in all shapes in sizes, the beat of their wings is their key indicator. 

Gonzalez-Bellido also touched on the concept of motion parallax and how other insects use it to launch their attacks. Some insects identify how far away their prey is by swaying back and forth. If an object is closer to the fly, it will appear to move more as the insect sways back and forth, but if it’s further away, it will only appear to move a small amount. Using motion parallax, insects can identify how far they are from their prey and gauge whether or not they should attack. 

Although each aerial insect predator has the same goal — they identify, attack, and capture their prey mid-air — each species has a unique strategy, and the world of sensory neurology is vast and diverse. Scientists are forced to think outside of the box in order to tackle unique issues, and Gonzalez-Bellido has found herself in a few such situations.

For one species of fly, Gonzalez-Bellido’s team had expensive tiny glasses that they needed to glue to their fly specimens. The team had been working well into the night and Gonzalez-Bellido recounted a debate they had at two in the morning about how hairy their flies were and whether or not they should shave them before gluing on their glasses. In the end, they decided not to shave the hairs entirely, but to give the flies a little trim. The researchers stuck their specimens in the freezer to slow down their neurological responses and allow them to handle them. They then trimmed a little bit of the hair around the flies’ eyes and glued on their tiny glasses. By leaving a bit of hair, the glue was more adhesive and allowed the glasses to stick to the flies better than if they had shaved the hair entirely. On that note, Gonzalez-Bellido took a few more questions and concluded her presentation with a few emojis and amazed responses in the Zoom chat. 

Although Gonzalez-Bellido’s research centers on flies, the ability to detect and pursue a moving object is found in many species, including humans. The next time you toss a ball, you might also think about the laphria and the unique discoveries of Dr. Paloma Gonzalez-Bellido.

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