Migratory locusts: They can run marathons and also love to race 100 meters

Do you remember the global locust plague in early 2020? At the beginning of the human battle against the new coronavirus, a locust plague caused by desert locusts quietly crossed the Red Sea from East Africa, entered Europe and Asia, and reached Pakistan and India.

Its thousand-mile journey brought panic to the countries it passed through, and made many people worry whether the invading locusts would threaten my country's food security.

The desert locust, which relies on tropical and subtropical desert habitats, will not bring harm to our country, but its "relatives" - the migratory locusts have caused many locust plagues in our country's history, making life difficult for the people.

The marathon-like long-distance migration of swarms of locusts is the main cause of locust outbreaks; solitary locusts rarely do this, they prefer short-distance travel.

Why do locusts adjust their flying strategies according to their population density?

Now, the answer is here. In a study published in the Proceedings of the National Academy of Sciences of the United States on January 4, the team led by Kang Le, an academician of the Chinese Academy of Sciences and a researcher at the Beijing Institute of Life Sciences of the Chinese Academy of Sciences, revealed the reasons why locust population density affects flight strategies, providing a new perspective for the study of animal flight adaptation behavior.

Locusts in flight. Photo courtesy of the Beijing Institute of Life Sciences, Chinese Academy of Sciences

“Holding together” can help you fly far

Many animals are masters of long-distance migration, which is important for their survival and reproduction.

Birds migrate to avoid adverse climates and find suitable breeding grounds; the North American monarch butterfly is the only migratory butterfly in the world, with a migration journey of up to 4,800 kilometers.

The migration of swarms of locusts is less romantic: a swarm of one square kilometer can devour the food rations of 35,000 people in a day.

When a swarm of locusts passes through an area, all vegetation is destroyed, often causing serious economic losses and even leading to food shortages and famine. Locust plagues, droughts, and floods are considered the three major natural disasters in my country's history.

Over the past 2,000 years, large-scale locust plagues have occurred more than 800 times.

"When a locust plague breaks out, large-scale, high-density gregarious locusts can gather and fly more than 2,000 kilometers within a generation, and the maximum single flight time is more than 10 hours," said Kang Le in an interview with China Science Daily.

In fact, whether or not locusts "gather" has a substantial impact on their flight distance. When the locust density is very low, scattered locusts rarely migrate long distances, and only fly short distances when courting or avoiding natural enemies.

The same locust species has different population densities and their flight distances vary so much. How do they adjust their flight strategies according to density? In the new study, Kang Le's team found through flight behavior analysis that the population density during the growth period of locusts determines the flight characteristics of the adult stage, and the differentiation of this characteristic just fits the life characteristics of gregarious and solitary types.

"Short-distance running" and "long-distance running"

Does not grouping locusts mean that they cannot fly? Not really.

The new research breaks some of the inertial thinking of the past and finds that low-density solitary locusts are not bad at flying, but rather have strong explosive power and fast flying speed, but lack endurance, showing flight characteristics similar to those of "sprinters".

On the contrary, high-density gregarious locusts do not take off quickly, but instead fly continuously for a long time at a lower speed, showing flight characteristics similar to those of "long-distance runners".

In Kang Le's opinion, locusts can determine their behavior strategies according to their purpose. These small insects are not simple. "Living in groups is like a marathon, while living in dispersed groups is like a 100-meter race." He compared the flight characteristics of the "sprinter type" and "long-distance runner type" to the life characteristics of the two types of locusts.

Under high population density, the "long-distance" flight characteristics are conducive to gregarious locusts to fly for a long time and long distance, and to maintain huge migratory swarms in order to find sufficient food and suitable egg-laying sites.

The "sprinting" flight characteristics of the scattered solitary locusts help them find mates and quickly avoid predation by natural enemies, because they want to stay in the local area to reproduce and have no need to migrate.

When the population density increases, locusts can change their flight characteristics to adapt to the needs of migration.

“More haste, less speed”

How can such a small insect have such a perfect regulation and conversion mechanism? Scientists used to believe that the difference in flight characteristics between the two types of locusts was caused by the use of different energy substances.

Through forced flight treatment and multi-omics analysis, Kang Le's team found that there was no obvious difference in the types of energy substances used by the two types of locusts.

In their opinion, differences in energy metabolism processes in locust flight muscles are the main reason for the differentiation of flight characteristics and abilities between gregarious and solitary locusts.

Compared with gregarious locusts, solitary locusts exhibit a higher energy metabolism pattern both at rest and in flight.

Further analysis of energy metabolism-related gene expression, respiratory metabolism detection, RNA interference and pharmacological function verification showed that the high-energy metabolism mode of flight muscles of solitary locusts provides more energy required for flight, but more reactive oxygen is produced during the flight, causing oxidative stress accumulation and inhibiting its long-distance flight ability.

In contrast, the relatively low energy metabolism of gregarious locusts enables them to maintain less reactive oxygen production during long-term flight, thereby maintaining the oxidative stress balance of flight muscles.

By changing the locust population density, they found that the flight characteristics of the two types of locusts, the expression of genes related to flight muscle energy metabolism, and the production of reactive oxygen during flight can change in opposite directions.

This clearly demonstrates that the population density that locusts experience during their growth shapes this flight characteristic.

So why are there obvious differences in the long-distance flight capabilities of locusts with different population densities? Many people believe that this may be caused by differences in energy storage between the two.

New research has found that although gregarious locusts have more triglyceride lipid storage than solitary locusts, when there is a significant difference in their long-distance flight ability, there is no obvious consumption of triglycerides for energy storage during their flight.

Based on this, they proposed a hypothesis: this difference in flight ability is determined by the balance between flight muscle energy metabolism supply and stable oxidative stress.

"The findings of this study are quite interesting," said one reviewer.

Other reviewers also said that the study linked behavioral, transcriptomics, metabolomics and protein function data, providing a new perspective for the study of the polymorphism of migratory locusts.

The authors said the new research revealed that locusts change their flight characteristics through the plasticity of flight muscle energy metabolism and the generation of oxidative stress, thereby adapting to the life history strategies of future adults.

This adaptive strategy of changing flight characteristics may also exist in other insects and animals.

At the same time, the results of his research have changed people's understanding of the relationship between energy metabolism and long-distance flight ability, provided a theoretical basis for the study of long-distance flight of migratory locusts, and also provided a new perspective for the study of animal flight adaptation strategies. "That is to say, those who fly fast cannot fly far, and those who fly far cannot fly fast," said Kang Le.

Related paper information:

https://doi.org/10.1073/pnas.2115753118

Source: China Science Daily (2022-01-05, Page 1, original title: "Marathon of Group Living, Hundred-meter Race of Dispersed Living")

Author: Feng Lifei

Editor | Zhao Lu

Typesetting | Guo Gang