On the ‘celebrity’ insect trail: Researchers have outfitted squirrel hawk moths with tiny transmitters, showing that these seasonally migratory butterflies use highly sophisticated flight strategies similar to those of migratory birds. You can even adapt to unfavorable wind conditions to stay on track over long distances. The results of the groundbreaking study also show that migratory insects can be guided by a complex navigation system.
In the spring they move north to their summer quarters – in the fall they return to the warm south. Migratory birds not only follow this concept: many flying insects also migrate seasonally, sometimes covering vast distances. Thus the many species from different families represent the smallest and most numerically widespread migratory animals on Earth. However, their migratory behavior has been less researched than that of birds. Above all, more detailed information is missing: “Understanding what individual insects do during their migration and how they interact with the weather is one of the main challenges of research on the migratory behavior of animals,” says lead author Miles Means of the Max Planck Institute for Behavioral Biology in Radolfzell.
Insect celebs are equipped with transmitters
In order to provide new information in the research field, Mains and his colleagues conducted studies on a special representative of the migratory moth: the squirrel hawk moth (Acherontia atropos) known for its distinctive markings on its back, which resemble a human skull. This trait earned him an appearance in The Silence of the Lambs. However, the reason for using the squirrel hawk moth as a test animal is its large size and complex migratory behaviour. Its wingspan is more than ten centimeters and covers enormous distances in its annual migrations from Africa to Central Europe. However, as is usual with many insects, the entire migration cycle is covered over several generations. But individual samples also cover long distances.
For the study, the researchers reared the caterpillars of squirrel mites to adulthood in the laboratory. Then the butterflies were equipped with miniature wireless transmitters weighing only 0.2 grams. As the scientists explain, this corresponds to less than 15 percent of their body weight, and thus represents a reasonable burden for the mites: “The food they often eat is probably more than that weight,” Mains says. He and his colleagues then let the test animals, fitted with “backpacks,” fly out of Constance.
In order to be able to record information from transmitters at a relatively close distance, the scientists escorted southward migratory butterflies with a light aircraft. In total, the team tracked 14 butterflies for a maximum of four hours and distances of up to 80 kilometres. In this way, the researchers were at least able to record the trajectory of individual nocturnal flight phases. As they explain, this is the longest distance to date an insect has been continuously observed in the wild.
Not only with the tailwind
Analysis of the data showed that the moths followed perfectly straight flight paths over long distances during their nighttime flight. However, as the weather data recorded in parallel showed, this was not due to the fact that they waited until the winds were favorable on their backs. Instead, they apparently used a variety of flight strategies to counter the prevailing winds and thus stay on track. The researchers reported that when there was a strong headwind or a headwind, they flew very low and increased their speed to maintain control over the course.
However, butterflies also benefit from favorable winds: when there is a tailwind, they fly high and slowly, and therefore can be effectively carried by the air. “For years, it has been assumed that insects primarily allow themselves in this way during long-distance migration. However, we have been able to show that insects can be true navigators on an equal footing with birds and that they are much less susceptible to headwind conditions than we thought,” Mains says.
The study also shows once again that migratory insects can orient themselves in complex ways. In further investigation, the scientists will now investigate this aspect more closely: They want to show how squirrel hawk moths determine direction to their destinations in order to fly to them in a straight line. “Based on previous laboratory work, there is a possibility that insects use internal compasses, both optical and magnetic, to map their global flight paths,” Mains says. Overall, the team now sees the success of the research methodology as a basis for further research. „Durch den Beweis, dass es technisch möglich ist, einzelne Insekten während ihrer Wanderung durchgängig zu verfolgen und ihr Flugverhalten im Detail zu beobachten, hoffen wir, weitere ähnzfenant vieagenwite benz” a lock.
Source: Max Planck Institute for Animal Behavior, Article: Science, doi: 10.1126 / science.abn1663
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