Producer: Popular Science China
Producer: Zhao Xumao (Young Researcher, Lanzhou University)
Producer: Computer Network Information Center, Chinese Academy of Sciences
On 11 February 2020, the Food and Agriculture Organization of the United Nations (FAO) issued an early warning to the world, saying it hoped that the world would be on high alert for the locust plague that is now raging and prevent a food crisis in the invaded countries.
Desert locust outbreaks in Kenya. (Image source: Food and Agriculture Organization of the United Nations)
It is reported that the locust plague began in Africa, then flew across the Red Sea into Europe and Asia, and has now reached Pakistan and India, which can be said to be only one step away from China.
Map of the migration path of the desert locust (Source: Food and Agriculture Organization of the United Nations)
<h1 class = "pgc-h-arrow-right" > to form a locust plague, there must be a large number of locusts, but also to gather in swarms</h1>
Everyone should have seen locusts, and many people caught locusts when they were young.
In the field, you can often see the figure of locusts (Image source: Veer Gallery)
Locusts, belonging to the order Orthoptera, include: The whole family Tetrigoidea, the family Eumastacoidea, the locustoidea family , there are more than 10,000 species in the world, and there are more than 1,000 species in China.
Most of the locust plagues recorded in ancient Chinese books are caused by East Asian flying locusts, which are the most harmful of locusts, although there is only one species, but there are many subspecies. There are three main subspecies that are harmed in China - the East Asian Flying Locust, the Asian Flying Locust and the Tibetan Flying Locust.
Image source: Baidu Encyclopedia
Many people may be curious, how did the locusts commonly found in the field suddenly erupt and become a plague?
Generally speaking, the occurrence of locust plagues must meet two conditions: one is a sudden increase in numbers; the other is a large-scale cluster.
In fact, locusts have always existed, under normal circumstances, locusts are limited by natural conditions, and the population is maintained in a relatively stable state. On weekdays, locusts fly in pairs between farmland and fields, which cannot constitute a disaster. Hazards can only occur if there is a sudden explosion of quantity.
< h1 class = "pgc-h-arrow-right" > warm winters after drought and overgrazing may lead to locusts multiplying</h1>
Locust eggs will be hidden in the egg sac, overwintering in the soil, and the number of generations (the number of generations that occur) in a year has a lot to do with the annual effective temperature, food, light and the growth and development of each insect stage.
In ancient China, there was a saying that "locusts are in the extremes of drought", believing that locust plagues are often accompanied by droughts.
Locusts are insects that prefer warmth and dryness, and the arid environment is conducive to their growth and development, and in dry years, due to the decline in water levels, the soil becomes relatively solid, and the number of eggs laid by locusts is greatly increased. Academician Kang Le believes that the locust plague caused by drought mainly refers to flying locusts, not the more serious the locust plague is. After the drought, it often causes the exposure of river beaches and lake beaches, forming a very popular spawning place for flying locusts, so that locusts overwinter to lay high eggs and increase population density sharply. In addition, if there is a warm winter again, the following spring rain is relatively abundant, and the temperature rises faster, which can easily lead to the outbreak of locust plague in the locust breeding area.
Now, Africa, the Arab countries, India, and Pakistan are suffering from locust plagues, and They are close to China. However, according to the analysis of Academician Kang Le, the locust plague was caused by desert locusts, and China is not a distribution area of desert locusts. Therefore, the probability of forming a serious threat to our country is relatively small.
Modern scientific research has shown that due to the relatively large number of locust species, the causes of locust plagues are also complex and not exactly the same. Some locust plagues are not only related to the climate, but also lead to overgrazing.
The great harm to China is the Asian car locust (Oedaleus asiaticus), which has more than 30 species in the world and is an important grassland and agricultural pest in Europe, Africa, Australia and Asia.
Asian cart locusts prefer to feed on foods with low nitrogen content, and high nitrogen foods will reduce their size and viability. The depletion of nitrogen content in heavy grazing soils reduces the nitrogen content of plants, providing an excellent opportunity for the growth and development of Asian car locusts.
<h1 class= "pgc-h-arrow-right" > in the legs of locusts, there is a swarm of "switches"</h1>
The sudden increase in locust populations due to environmental conditions and human activities is only the first step in the formation of locust plagues. The next step is to gather in groups and act collectively.
In fact, locusts usually like to live alone, and only after the sudden large-scale cluster can they cause greater harm. So why do locusts gather? This is also a hot topic studied by many insect experts.
Zoologists at the University of Oxford in the United Kingdom have found that when a certain part of the hind leg of locusts is touched, they will change their original habit of being alone and become like to live in groups.
Locusts may have some sort of "button" that allows them to cluster, and certain tactile factors cause them to change their habits. Scientists at oxford university have experimented with the desert locust in the solitary stage, repeatedly touching multiple parts of its body in search of buttons that allow the locust to form clusters.
They did find that the button that gave the locust swarm was somewhere in the leg, and when that area was stimulated, they suddenly became gregarious, and touching the rest of the body would not have the effect. The occasional gathering of locusts in a natural environment when their hind legs touch each other, which may cause them to change their habits and begin to live in groups, and their members increase in the same way, forming a locust plague.
So what chemical signals are the ones that stimulate the locust's nervous system to cause its behavior to change?
Researchers at Oxford and Cambridge in the United Kingdom found that swarms of locusts are affected by a chemical called serotonin. On weekdays, locusts dislike each other, and once their serotonin levels rise, they will abandon the insect stereotype and gather together. Serotonin chemicals are more common in the brains of locusts, like the Martial Fire Order, which can call for locusts to gather together. Michael Anstey and his co-authored serotonin levels in desert locusts showed that serotonin levels in the assembled locusts were nearly 3 times higher than those in the solitary state.
When the locusts meet the above two conditions, the locust swarm will gather larger and larger, and a swarm of up to 40 billion locusts can eat 80,000 tons of food a day, which is equivalent to the annual ration of 400,000 people. After eating up a place, they will take off, migrate, eat up, and migrate again. After the locust swarm can generally move 600 kilometers, some can migrate thousands of kilometers, during this period there will be new locusts to join them, the locust population will become larger and larger, the consequences are unimaginable!
Shilabo, Ogaden, Somalia – Ethiopia – An area where a herd of camels is trying to pass through the invasion of locusts. (Image source: Food and Agriculture Organization of the United Nations)
<h1 class="pgc-h-arrow-right" > how much impact can a locust plague have? </h1>
Humans have been dealing with locusts for thousands of years, and they have also left many records, and it can be seen that the ancient Chinese record of locusts is a history of disasters:
The Book of Rites and Moon Decrees has a record of "locust plagues". After the Tang and Song dynasties, the improvement of papermaking and the popularization of paper provided great convenience for the historical record, and the record of locust plague became more and more detailed.
For example, in the first year of Tang Zhenyuan (785 AD), the Summer Locust, the East Zihai, the West End of the River Long, the Heavens, and the Ten Days Cease. There are relics of grass and trees and animals, and the pillow road is starved. In autumn, the great locusts of Guanfu are exhausted, the people are hungry, and the locusts are hunted for food.
For example, in the twenty-first year of Ming Chenghua (1485 AD), there was a great drought, locusts and locusts, and everyone couldnibalized. Most of the exiles, when the hungry people roared in the mountains and forests. The locusts in Taiping County flew and flew to cover the sky, and the leaves of the grass and ears were exhausted, and the people turned around. It is the year of the Yuanqu people exiled for most of the time, gathering in the mountains and forests. In March, Pingyang Locust. In April, Henan Locust. July Suncheon Locust.
According to records, in the more than 2,600 years from 707 BC (the thirteenth year of Lu Huan) to 1907 (the thirty-third year of Qing Guangxu), there were more than 500 locust plagues.
In short, in ancient China, locust plagues were one of the three major natural disasters alongside floods and droughts, and once the locust plague arose, the locust army that covered the sky and the sun could loot the geographical crops in an instant, and what was even more terrifying was that locust plagues often came after droughts. The ancients relied on the sky to eat, and once the crops in the field were gone, the next thing was hunger and starvation, and even more, it led to the destruction of the country.
In modern times, the impact of locust plagues cannot be underestimated. In the 12 years from 1985 to 1996, East Asian locusts occurred in the Yellow River Beach, Hainan Island, Tianjin and other locust areas year after year. In the autumn of 1985, the East Asian locust swarm in Tianjin Beidagang was about 30 kilometers wide from east to west, affecting an area of 2.5 million mu, which was the first inter-provincial migration of the gregarious East Asian locust since the founding of New China. In 1998, the summer locust of the East Asian flying locust occurred on more than 800,000 hectares in 8 provinces including Shandong, Henan, Hebei and Tianjin. In 1999, more than 800,000 hectares of summer locusts occurred in 9 provinces, including Shandong, Henan, Hebei and Tianjin.
The impact of locusts on humanity knows no borders. In 2016, the Russian government, suffering its worst locust plague in 30 years, declared a state of emergency. Flying locusts passed through southern Russia, and for a time the sun and moon were dark, and the sky and earth were dim, like the end of the world. According to reports, the locust plague destroyed more than 10% of the farmland in Russia, affecting an area of up to 70,000 hectares. This is actually a great migration of locusts, but their numbers are too large, and these locusts are actually from far away North Africa after scientific investigation.
Seemingly inconspicuous insects can explode with amazing energy on the way to migration, their migration is not only to complete the inheritance of their own lives, but also to affect the entire ecosystem, the butterfly effect is very obvious in nature. In recent years, scientists have found that the migration of insects is staggering, and in England alone, the number of insect migrations can reach a staggering 3.5 trillion times a year, and the combined weight can reach 3200 tons, which is equivalent to the displacement of a small destroyer. Such a huge biomass is not a small amount in the entire ecosystem, and their impact is far-reaching. It's a feast for the insect-eating animals in the ecosystem; in turn, these insects can have an impact on plant growth. Therefore, the migration of insects is not only their own business, but also affect predators, prey and competitors. In addition, these insects are themselves a huge amount of energy and nutrients, and may also carry a large number of pathogens for transfer, which has an unusual impact on the species circulation and energy flow of the entire ecosystem.
In the history of mankind, those seemingly powerful beasts, such as lions, tigers, and leopards, did not cause much harm. In contrast, this seemingly weak locust has become one of the historical disasters of mankind. It seems that the forces of the strong and the weak are by no means fixed, the strong may not be permanently strong, and the weak may not be permanently weak. Humans need to pay attention to every species that exists on Earth, even if it seems insignificant.
The article only represents the views of the author and does not represent the position of the China Science Expo