Fruit flies are ‘extreme ultramarathon kites’, according to research

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Although they are best known for buzzing in circles in search of bananas, scientists reveal that fruit flies have a very impressive range.

The species, Drosophila melanogaster, can fly up to nine miles (15 km) in one trip, the researchers at California Institute of Technology (Caltech) reveal.

Impressively, this is about 6 million times their average body height, which is just 2.5 millimeters or one-tenth of an inch.

This would be the same as the average human who travels just over 10,000 kilometers in a single trip – roughly the distance from the North Pole to the equator.

Caltech experts conducted experiments in a dry soil in California’s Mojave Desert by releasing thousands of flies and enticing them into traps with fermenting sap to determine their speed.

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Drosophila melanogaster is a small common fly found near unripe and rotten fruit.  It has been used to study genetics and behavior for over a century

Drosophila melanogaster is a small common fly found near unripe and rotten fruit. It has been used to study genetics and behavior for over a century

“The dispersal power of these tiny fruit flies has been hugely underestimated,” said study author Michael Dickinson, a biologist at Caltech.

‘They can travel as far or further than most migratory birds in one flight.

“These flies are the standard laboratory model organism, but they are almost never studied outside the laboratory, so we had little idea what their flight capabilities were.”

The team wanted to solve a paradox: In the wild, genetically similar fruit flies were thousands of miles apart, but when released outside, they buzzed around in circles for short distances, like in our kitchens.

The paradox was identified in the 1940s by the Ukrainian-born geneticist Theodosius Dobzhansky, known for his 1937 book Genetics and the Origin of Species.

One possible explanation was that the flies behaved differently when they searched for food in the wild.

Led by former postdoctoral scientist Kate Leitch, the team made several forays to Coyote Lake, a dry lake bottom 230 kilometers from Caltech in the Mojave Desert, with hundreds of thousands flying in containers.

The goal was to release the flies, lure them into traps at fixed locations, and measure how long it took the insects to fly there.

Coyote Lake is a dry lake bed 140 miles from Caltech in the Mojave Desert, California, USA.

Coyote Lake is a dry lake bed 140 miles from Caltech in the Mojave Desert, California, USA.

To do this, the team placed 10 ‘scent traps’ in a circular ring, each located within a radius of one kilometer (0.6 miles) around the release location.

Each trap featured an enticing cocktail of fermenting apple juice and champagne yeast – a combination that produces carbon dioxide and ethanol, which are irresistible to a fruit fly.

The species has developed a tolerance for alcohol by living in and feeding on rotting and fermented fruit.

The traps also each had a camera and were constructed with one-way valves so that the flies in the trap could crawl to the cocktail, but not back.

In addition, the researchers set up a weather station to measure the wind speed and direction at the release location during each experiment. This would indicate how the flies’ flight was affected by the wind.

The flies released by the team were originally collected from a fruit stand and then grown in the lab, but they were not genetically modified in any way.

At the capture site, flies were lured by a cocktail of fermenting apple juice.  By measuring the time it takes the flies to travel from the release site to these traps, researchers can estimate how fast and far a fruit fly can travel.

At the capture site, flies were lured by a cocktail of fermenting apple juice. By measuring the time it takes the flies to travel from the release site to these traps, researchers can estimate how fast and far a fruit fly can travel.

Map of the researchers' setup.  The team placed 10 'scent traps' in a circular ring, each located within a radius of one kilometer (0.6 miles) around the release site.

Map of the researchers’ setup. The team placed 10 ‘scent traps’ in a circular ring, each located within a radius of one kilometer (0.6 miles) around the release site.

The team floated the buckets flying to the center of the circle with traps. The buckets contain a lot of sugar, so the insects would get full energy for their flight.

However, they do not contain any protein, giving the flies a strong drive to seek out protein-rich foods.

The team estimated that the flies would not be able to smell the traps from the center of the ring, forcing them to disperse and search.

At a precise time, a team member in the center of the circle opened the buckets at the same time and released the flies quickly. The team repeated these experiments under different wind conditions.

It took about 16 minutes for the first fruit flies to travel the mile to reach the traps, which corresponds to a speed of about one meter per second.

The team interpreted this speed as a lower limit, as these first flies may have flown in circles a bit after release or were not flying in a perfectly straight line.

Previous studies from the lab showed that a fully fed fruit fly has the energy to fly continuously for up to three hours.

From this, the team concluded that D. melanogaster can fly about 12 to 15 kilometers (7.4 to 9.3 miles) in a single flight, even in a gentle breeze, and will go further if aided by a tailwind.

Michael Dickinson dives out of the way after releasing buckets of thousands of fruit flies on dry soil in the Mojave Desert

Michael Dickinson dives out of the way after releasing buckets of thousands of fruit flies on dry soil in the Mojave Desert

In 2018, the Dickinson lab discovered that fruit flies use the sun to fly in a straight line in search of food.

Flying aimlessly in circles can be deadly, so there is an evolutionary advantage to navigating efficiently.

Thinking that each fruit fly chooses a direction at random, the team uses the sun to fly straight in that direction, and carefully controls its forward speed as it blows sideways in the wind.

This allows him to cover as many distances as possible and it is more likely to encounter a plume of scent from a food source.

“For any animal, if you find yourself in the middle of nowhere and there is no food, what do you do?” Said Dickinson.

Just hopping around hoping to find some fruit? Or do you say, “Okay, I’m going to take a direction and go as far as I can in that direction and hope for the best”?

“These experiments suggest that’s what the flies do.”

The study is published in the journal Proceedings of the National Academy of Sciences.

TIME FLIES LIKE AN ARROW – BUT FRUIT FLIES LIKE A BANANA

The fruit fly (Drosophila melanogaster) is a small common fly found near ripe and rotten fruit.

It has been used to study genetics and behavior for over a century.

The species has also developed a tolerance for alcohol by living in and feeding on rotting and fermented fruit.

In 2012, researchers from Emory University in Atlanta, Georgia said fruit flies actively search for food containing ethanol to kill parasitic wasps in their bloodstream.

Thanks to a diet of fermented fruits, the flies are accustomed to alcohol and it has little effect on them. But it kills the wasps.

“We found that environmental alcohol protects fruit flies from parasitization by wasps,” said study author Dr. Todd Schlenke.

Even after infection, the consumption of alcohol by fruit flies kills the wasps that grow in them.

‘Surprisingly, fly larvae actively search for ethanol-containing food when they are contaminated, showing that they use alcohol as a wasp medicine.’

While the flies initially prefer foods with a sweet taste, they soon learn to choose less sweet food sources that provide more calories and nutritional value, another team from the University of British Columbia said.

The researchers let fruit flies (Drosophila melanogaster) choose between sources of liquid sugar that varied in their sweetness-to-calorie ratio.

In some cases, it took the flying populations as little as four hours to shift their preference to more nutritious food sources – usually based on sugars such as sucrose, maltose and D-glucose.

Researchers also isolated different molecular pathways in a fly strain that appear to affect taste and nutritional preference, and found that blocking insulin signaling increased preference for nutritious sugars.

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