This kind of monster even eats his brothers and sisters when he is hungry

Author: Li Weiwei (Kunming Institute of Zoology, Chinese Academy of Sciences)

The article comes from the Science Academy official account (ID: kexuedayuan)

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Warm reminder: Some of the insect images in this article have been hidden. Readers who are seriously afraid of insects can click to read without worry.

Editor’s Note:

Today is National Land Day, the first national commemorative publicity day designated by the State Council. This year's publicity theme is "Economize and use land intensively, and strictly adhere to the red line of cultivated land." Cultivated land is related to my country's food security. For food security, in addition to protecting cultivated land, we must also fight a war without gunpowder with many pests, such as the protagonist of this article.

In the past three years, a demon moth has been frequently "named" by national ministries including the Ministry of Agriculture and Rural Affairs. Its aggressive momentum has indeed triggered a food war without gunpowder.

Who is it? It is the fall armyworm, which is expected to be found in 40 million mu of land in 2021. Its English name is fall worm, and its Latin name is Spodoptera frugiperda. It belongs to the order Lepidoptera, family Noctuidae, and genus Spodoptera. In addition to knowing its real name, if we want to win the war to protect food, we must first check its "household registration" and find out its "family background".

"This little thing looks really unique" (Photo credit: taken by the author)

Where did this weird thing come from?

In 1797, scientists discovered and named the fall armyworm, which is mainly distributed in tropical and subtropical regions of the Americas and is one of the major food pests in the Americas. It can be said to be an "old enemy" of mankind. As a major global pest reported by the Food and Agriculture Organization of the United Nations, the fall armyworm is very powerful. In the worst-hit years between 2006 and 2018, the fall armyworm caused a 34% reduction in corn production in Brazil, a 40% reduction in corn production in Honduras, and a 72% reduction in corn production in Argentina. In 2018, the fall armyworm caused a 20% reduction in corn production in the United States.

Before 2016, there were no reports of the fall armyworm outside the Americas. But this evil moth is not content to stay in one corner, and when the time is right, it plans to spread all over the world. From 2016 to 2018, the fall armyworm had just left the American continent and ravaged 44 countries in Africa, causing economic losses of more than $13 billion.

In May 2018, the fall armyworm arrived in Asia for the first time. It has reached India, Myanmar, Thailand, Yemen and Sri Lanka. According to incomplete statistics, the affected area is about 2 million hectares, and corn production in some areas has decreased by more than 10%.

The fall armyworm's evil journey continues. At the end of December 2018, the advance team of the fall armyworm came to Yunnan Province, China for investigation. In January 2019, its sneaky advance team was discovered by Chinese scientists. That year, the insects were found in at least 1,524 counties (districts) in 26 provinces (cities, regions) across the country. In February 2020, the area where the fall armyworm was found in my country was 90 times that of the same period. In the spring of 2021, there will be more precipitation in the southwest and less precipitation in Jiangnan and South China, which will help the fall armyworm to continue to reproduce and cause harm in my country. We really can't take it lightly.

The secret weapon of the demon moth

So why can the fall armyworm travel across the ocean to cause harm to a region? Perhaps we can understand the reason by starting with its origin.

The fall armyworm is a completely metamorphosed insect, and its growth process is mainly divided into four stages: egg, caterpillar, pupa, and moth. At different stages, the fall armyworm is equipped with secret weapons. For example, the surface of the fall armyworm's pale yellow eggs is covered with scales, which can block external damage and play a good protective role; in the longest larval stage, as the body grows, the points on its tail like the four barrels of mahjong will become more obvious, the bristles on its body will become denser, and the number of toe hooks on its abdominal feet will also increase, providing a guarantee for its mobility.

Fall armyworm in the caterpillar stage (Image source: author's own)

The strongest defense period of the demon moth is the pupa stage. During this stage, it burrows into the soil or other hidden places, and equips itself with a brown-red pupa shell, which is highly waterproof and greatly enhances its defense. After breaking out of the pupa and becoming a moth, the fall armyworm "achieves its goal" and becomes a veritable demon moth. In addition, the gray camouflage coat provides it with an excellent camouflage suit for nighttime activities. These secret weapons undoubtedly increase the difficulty of prevention and control, and also make the demon moth very rampant.

Monster: When I'm hungry,

He even eats his own brothers and sisters!

In addition to its secret weapons, the fall armyworm can also shed its skin to make itself stronger. After 6 molts, the fall armyworm can make its body bigger. And each molt can double its appetite. When the fall armyworm is 3-6 years old (one molt is one age), it is the stage when it shows its big appetite.

Leaves eaten by fall armyworms (Photo credit: taken by the author)

During this period, it will open its sharp mouth like sepals and frantically eat the core leaves and tender parts of plants. What is more terrifying is that they not only eat plants, but when the density is high, they will kill each other and kill their brothers and sisters. In addition, the fall armyworm has the following characteristics:

1. Special ability to give birth

It only takes one month for the fall armyworm to grow from an egg no bigger than a sesame seed to a moth. Moreover, this moth can reproduce and breed all year round, and the number is amazing. A female moth can produce 100-200 eggs at a time, and 900-1000 eggs in her short life. It can be said that the insect population is prosperous and there are many children and grandchildren. It is really a super-birth guerrilla in the insect world.

2. Special ability to fly

The demon moth also has the ability to fly in the clouds. With the help of air currents, it can fly hundreds or thousands of kilometers every night, and can be called a "fighter" among moths. In addition, although the larvae of moths cannot fly, they can migrate by crawling, hanging on silk between plants, etc. Thousands of larvae spread in the fields like marching, eating crazily, and bringing "catastrophe" to the crops.

3. Hitchhiking

In 2016, the fall armyworm first escaped from the Americas and invaded Africa. According to the analysis of climate conditions, the monsoon blows from Africa to the Americas, which is inconsistent with the spread direction of the fall armyworm. Whether the adult flies independently or with the help of air currents, this distance does not support the migration of the moth. Therefore, scientists speculate that the fall armyworm invaded Africa from the Americas by "hitchhiking" through international trade and was accidentally introduced. This way of quietly riding on the human logistics network without buying a ticket helped it realize its ambition to spread widely in more than 100 countries.

4. Especially able to “take a beating”

In 2020, the author collaborated with Yunnan Agricultural University to complete an experiment on the types of culturable bacteria in the intestines of fall armyworm larvae in Mangshi City, Yunnan Province, and their sensitivity to antibiotics. The experiment found that there were 6 species of 3 phyla, 5 families, 5 genera, and 6 species of bacteria that could be cultured in the intestines of the fifth-instar larvae of fall armyworm. Among them, Klebsiella variegata was the dominant bacterial species in the intestines of fall armyworm larvae. Klebsiella variegata was significantly resistant to penicillin, erythromycin, and ampicillin, which also indicated that fall armyworm had natural resistance genes.

Is there really no way to deal with this evil moth?

Although the fall armyworm is extremely evil, it can be prevented and controlled. Since it chose to come to my country to cause trouble, it cannot escape the test of scientific and technological strength and biodiversity resources. For example, the black egg wasp studied by the author is a major nemesis of the fall armyworm. The black egg wasp can lay its eggs inside the eggs of the fall armyworm, strangling this evil moth in the cradle.

Noctuidae black egg wasp parasitizing fall armyworm eggs (Image source: self-made by the author)

In addition, the author cooperated with the State Key Laboratory of Conservation and Utilization of Biological Resources in Yunnan to study the predation of Harmonia axyridis larvae on eggs and young larvae of Spodoptera frugiperda. It was found that the maximum daily predation of Harmonia axyridis larvae on eggs of Spodoptera frugiperda was 25.6 on average, and the maximum daily predation of Harmonia axyridis larvae on 2nd instar larvae of Spodoptera frugiperda was 33.3. This shows that Harmonia axyridis larvae have a good control effect on eggs and young larvae of Spodoptera frugiperda, and can be used in the prevention and control of Spodoptera frugiperda. Some readers may ask, can we summon cute chicks and ducklings to deal with the demon moth? Unfortunately, because the cunning Spodoptera frugiperda hides in the heart leaves, poultry generally cannot eat it and cannot do anything about it.

From the excavation of parasitic insects to the discovery of predators, to the research and development of sex attractants and pesticides, researchers have developed a combination of measures to prevent and control the fall armyworm from all directions. Therefore, it is only necessary to optimize monitoring and prevention measures in accordance with the requirements of early detection, early layout, comprehensive monitoring, full-scale killing, regional implementation, joint prevention and control, and vigorously promote unified prevention and control and emergency prevention and control, combined with biological and ecological control, to minimize the damage and losses caused by the fall armyworm. In 2021, the country proposed a special prevention and control technical plan for the fall armyworm to ensure that the fall armyworm does not cause large-scale northward migration damage and control the overall damage and loss of corn production to less than 5%.

If I encounter this weird moth, can I just catch it with my hands?

In 2019, I collaborated with the Wuhan Institute of Virology of the Chinese Academy of Sciences to complete a study of the virus of the fall armyworm. Fortunately, although the moth is hateful, it does not contain any virus that is harmful to humans, so you will not be harmed by the virus if you catch it with your hands. Of course, don't think of killing the moth by eating it. (They don't look that delicious either)

In the blink of an eye, we will usher in a critical period for the prevention and control of fall armyworms. A war of "fighting for food from insects" will start again, and various forces including scientific researchers will once again fight on the front line of protecting food. You may ask, how can we contribute to winning this food war? Perhaps, timely reporting of the moths, actively participating in the promotion of prevention and control knowledge, and cherishing the hard-earned food are all worthy answers.

References:

[1] Li Weiwei, Liu Jiani, Gui Furong, He Shuqi, Chen Quanyan, He Guiwu, Chen Bin. Research on the challenges and prevention and control strategies of alien species invasion faced by China: Taking the fall armyworm as an example[J]. Chinese Agricultural Science Bulletin, 2020, 36(12): 120-126.

[2] Xu Tianmei, Fu Chengyue, Su Zaotang, Xiao Guanli, Li Weiwei, Chen Bin. Comparison of the composition and diversity of intestinal bacterial communities between the populations of Fall Armyworm in the diffusion area and the first release site in Yunnan Province[J]. Plant Protection, 2020, 46(04): 116-125.

[3] Zhao Yingjie, Fu Chengyue, Li Weiwei, Zhang Limin, Du Guangzu, Chen Bin, Li Zhengyue. Predation of Harmonia axyridis larvae on eggs and young larvae of Spodoptera frugiperda [J]. Plant Protection, 2020, 46(01): 51-54+86.

[4] Shi, J., Li, W., Wang, Y. et al. Meta-Transcriptome Profiling of Novel Invasive Pest Spodoptera frugiperda in Yunnan, China. Virol. Sin. 35, 240–244 (2020). https://doi.org/10.1007/s12250-019-00188-z