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Male locusts serve as parasols for females during egg laying in the hot sun

A team of entomologists at Center National de Lutte Antiacridienne's Mauritanian National Desert Locust Center has found that male locusts will mount a female when she is laying eggs during the heat of day.

In their study, in the journal Ecology, the group conducted field expeditions and carried out experiments to test for heat protection from male locusts.

Prior research and anecdotal evidence have found that locust swarms can decimate large swaths of croplands in short order and that they reproduce quickly. Some research has also suggested that while females generally lay their eggs in the evening, when it is cooler outside, some have been observed doing so during the hot daylight hours.

The researchers wondered how the females could achieve such a feat, and to find out, they made several trips around the Sahara during times when locusts were swarming. They observed that the males were mounting the females as if to mate while she was laying eggs, but only during the daytime. Similar behavior had been seen in male locusts at night, where the behavior was found to keep other males from interfering with females' egg laying.

To make sure it was not a random event, the researchers searched out pairs during times when the desert floor reached up to 48°C—under such conditions, they found that approximately 90% of the females were being mounted by males. They also noted that pairs moved in tandem as the sun moved across the sky, staying parallel to its rays. Using thermal cameras showed that the bodies of the females were cooler than those few females not being mounted.

The researchers also conducted a simple experiment: They glued dead locusts to sticks and tied them to the ground—some in pairs, some alone. In recording the body temperature of the dead locusts, they found that their bodies served as a shield against the sun's heat—those underneath were cooler.

The research team suggests their findings could lead to new pesticide strategies to combat locust infestations, preventing loss of crops.