By flying with sphinxes during migration, scientists reveal that insects use sophisticated flight strategies similar to those of vertebrates

Insects are the smallest flying migrants in the world, but they can maintain perfectly straight flight paths even in adverse wind situations, according to a new study from the Max Planck Institute for Animal Behavior (MPI-AB) and the University of Konstanz. The researchers radio-tracked the migrating sphinxes for up to 80 kilometers, the longest distance over which an insect has been continuously monitored in the wild. By closely tracking individuals during migration, the world’s first study reveals a century-old mystery about what insects do on their long journeys. The study, published in Science, confirms that sphinxes can accurately maintain straight paths over long distances, using sophisticated strategies to counter and correct for adverse wind conditions. The results reveal that the insects are capable of precise navigation, confirming that an internal compass guides them on their long journeys.

With thousands Of the billions of people who migrate each year, insects are among the most common migrating animals on Earth. They include species of renown, such as the monarch butterfly, as well as species of enormous societal and environmental value, such as locusts, mosquitoes and bees. But even though migrating insects far outnumber better-known migrants, such as birds or mammals, their migration is the least understood form of long-range animal movement.

The problem, for the most part, has been methodological. “Studying insects in motion is a formidable challenge,” says first author Myles Menz, who conducted the research at MPI-AB and is now a lecturer at James Cook University in Australia. “They are usually too numerous to mark and find, and too small to carry tracking devices.”

Much of what we know about insect migration comes from of studies that sample insects at a given second, such as by radar or direct observation, which have left vast gaps in our knowledge. “Understanding what insects do during migration and how they react to weather situations is the final frontier of migration science,” says Menz.

The current study, which tracked radiolabeled individuals in a light aircraft, is the first to continuously study nocturnal migratory insects in the wild, and represents the longest distance an insect has been continuously tracked in the field. The team, which includes researchers from MPI-AB and the University of Konstanz in Germany and the University of Exeter in the UK, focused on the death’s-head hawk-moth, a large nocturnal migrant which travels up to 4 kilometers between Europe and Africa each year. year. Like many insects, the species is a multigenerational migrant, which means that no individual knows the entire route.

At MPI-AB in Constance, in Germany, the team bred caterpillars to adulthood in the lab to make sure the individuals were naive. When the moths emerged as adults, they were fixed with radio tags weighing, 2 grams, or less than 15% of the adult body weight. “Butterflies would likely eat more weight than that overnight, so these tags are extremely light on insects,” Menz says.

Researchers released the tagged butterflies and waited for the flight to start, after which they chose one individual to follow at a time. The team tracked 14 moths each for up to 80 kilometers or 4 hours – a stretch long enough to be considered like a migratory flight – using antennas mounted on a Cessna aircraft to detect precise locations every five to 15 minutes. The insects were tracked in the south-southwest path from Constance in the Alps, which was the route taken by the sphinxes to the Mediterranean and North-West Africa.

Due to the practical constraints of flying in airplanes, scientists followed the moths continuously until the insects s stop en route. “When you’re on a plane, it becomes extremely difficult to wait for the insects to start migrating again because you would have to be in the air when it happens, which could be any time of the night,” says the lead author. Martin Wikelski, a movement ecologist from MPI-AB and the University of Konstanz, who piloted the aircraft during the study.

The results show that the butterflies have maintained perfectly straight trajectories over long distances during flight. It wasn’t because they were expecting favorable winds. Instead, they used a range of flight strategies to shield themselves from prevailing winds, allowing them to maintain their course throughout the night. When the winds were favorable, they flew high and slow, allowing the air to carry them. But in strong headwinds or crosswinds, they would fly low to the ground and increase their speed to maintain control of their path.

Said Menz: “For years , it was assumed that insect migration consisted mainly of being carried away. But we show that insects are capable of being great navigators, on par with birds, and are much less vulnerable to wind conditions than we thought.

“ By showing that it is technically feasible to continuously monitor individual insects during their migration and observe their flight behavior in detail, we hope to inspire further studies to answer many other great questions in this field. ”

For the authors of the study, the next step is to answer the question of how butterflies are able to maintain such straight lines. “Based on previous lab work, it is possible that insects use internal compasses, both visual and magnetic, to navigate their way around the world,” Menz says.


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