It may seem like a hopeless place, but locusts find a way to breed in the scorching heat of the Sahara at midday.
The biblical voracity of these insects make them among the world’s most destructive pests. They devour agricultural crops in swarms that number in the billions and stretch miles long. While they prefer to lay eggs in the desert’s cooler evenings, new research shows that female desert locusts can manage this even under the burning sun with help from male partners, which keep them cool by climbing on their backs to act as living parasols.
The finding, published in September in the journal Ecology, could contribute to efforts to reduce the use of pesticides while trying to protect agricultural crops from locusts. For as well known as desert locusts are, “we still don’t have particularly sustainable ways to manage massive outbreaks,” said Arianne Cease, a locust expert at Arizona State University who wasn’t involved in the new study. So “any additional information about their behavior can help with improving our capacity to monitor and treat them more sustainably,” she said.
Desert locusts males have long been observed mounting females to guard them from other contenders for mating. But this usually happens at night. Still, many females end up laying eggs during the day, when ground temperatures can reach above 120 degrees Fahrenheit.
“This is an amazing thing for an organism to do,” said Koutaro Ould Maeno, a locust expert at the Japan International Research Center for Agricultural Sciences and an author of the new study, “I am not aware of any animal that lays eggs in the ground in the hot Sahara during the day.”
To understand how female locusts pulled this off without ending up fried under the sun, Dr. Maeno and colleagues embarked on three field expeditions over a decade.
“Locusts do not occur every year, and because they migrate, it was difficult to find a group” in the Sahara, Dr. Maeno said.
When the team managed to find breeding locusts, it noticed that when females were laying their eggs under the sun, around 90 percent of them were being mounted by a male — just like during the night. The scientists were surprised to observe that the coupling insects rotated to follow the sun, staying parallel to its rays much like sunflowers soaking up solar rays. Even more unexpectedly, infrared thermal cameras showed that the body temperatures of the couples during daytime egg-laying remained lower than the ground temperature.
All these clues suggested that the mounting males, while focused on keeping other males away, may also shade the females, helping them endure the burning temperatures.
To test this hypothesis, Dr. Maeno’s team glued dead locusts to wooden sticks and tied them to the ground, alone or in pairs. Then, they recorded their body temperatures under the sun to compare them. The results showed that the dead males serving as sun umbrellas made a difference: Shaded bodies of females had lower body temperatures than exposed females.
Dr. Cease praised the team’s fieldwork and said the study “offers a unique insight into desert locust life history.” While scientists know mate guarding is common among many species, she said, this may be the first time it was shown to have this additional benefit.
Dr. Maeno hopes that his team’s findings will aid in developing techniques to control the pest. He suggested, for example, that spraying locusts as they lay eggs and can’t move could help “control them efficiently and reduce the amount of insecticide used,” he said.
He also thinks studying desert locust behavior could offer other benefits.
“I want to elucidate the locust’s strategy for surviving in the desert,” Dr. Maeno said. “Global warming is making us hotter, but I hope to learn cool-down techniques from desert locusts.”
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