Home / Science / Caterpillar's devastating march across China spurs hunting for native predators

Caterpillar's devastating march across China spurs hunting for native predators

A farmer displays the caterpillar of a fall armyworm

The invasive legionnaire of autumn has devastated crops around the world.Credit: Waldo Swiegers / Bloomberg / Getty

A hungry caterpillar ravaging crops is advancing across China and threatening the country's huge corn supply. Scientists are studying ways to minimize the damage caused by the invasive military worm, which was first detected in China in January, including experimenting with native predators capable of controlling the insect. Some researchers say that the spread of the insect may have been slowed down if the country had cultivated genetically modified food crops.

The legionnaire of autumn (Spodoptera frugiperda), native to Central and South America, has spread around the world in recent years, devastating crops in parts of Africa and South Asia. Since arriving in China, it has been found in 18 provinces, regions and municipalities, according to the Chinese Ministry of Agriculture.

Until now, the damage done by the caterpillar – mainly to maize (corn), but also to other crops such as sugar cane – in China is considered manageable. Hu Gao, entomologist at the Nanjing Agricultural University, monitors the spread of the insect. Researchers and farmers are worried about what will happen when the pest probably arrives later this month in the northern plains of China. China is the world's second-largest maize producer and the northern lowland produces nearly 30% of the country's crop.

Losses in billions

Recent outbreaks of fall legionnaires in Africa and South Asia have resulted in corn yield losses of up to 50%. And in Africa, where the pest came in 2016, it is costing the top 12 maize producing countries a total of USD 1 to 4 billion of lost crops a year.1. China is also still struggling with an epidemic of highly contagious virus affecting pigs, African swine fever, which has led to the slaughter of more than one million animals.

"The spread of the fall armyworm in China will have a significant impact on Chinese consumers, as well as the spread of swine fever," said Cong Cao, an innovation researcher at the University of Nottingham in China. China. Rising food prices will put tremendous pressure on the government to control the pest, Cao said.

According to Hu, plant protection centers in provinces and cities are focused on monitoring and controlling the spread of the armyworm in the fall. Adult moths, responsible for the spread of the pest, can travel hundreds of kilometers during successive nights. Control measures include traps and pesticides.

Biological control

Scientists, meanwhile, are working on other strategies. According to Hu, researchers at his university and other Chinese universities are studying chemicals likely to attract insects to traps, as well as native insects that can be used as a means of biological control.

A report from the United States Department of Agriculture, released in May, on the spread of the fall armyworm in China, indicated that the insect had no natural predator in the country, but Hu disputes this conclusion.

Parasitic wasps of Chinese Braconid are already killing other species in Spodoptera the kind to which the fall legionnaire belongs, including the cotton leaf worm (Spodoptera litura) and the Beet Legionnaire (Spodoptera exigua), So Hu thinks that the wasp could also target the fall armyworm caterpillar. In Africa, some parasitoids – whose young feed on and end up killing their hosts – attack the African cotton leaf worm (Spodoptera Littoralis) have already gone on to feast on the legionnaire in the fall.

In recent field trials in Yunnan Province, where the pest was first identified, researchers from the Institute of Plant Protection (IPP), which is part of the Chinese Academy Beijing Agricultural Science, also discovered that the bedbug Arma chinensis kill the caterpillar.

Zhong Guohua, a researcher at South China Agricultural University in Guangzhou, could attack many natural parasites or predators that attack the pest, but it's hard to predict They can be used for control purposes. . To find out, repeated tests would be needed to ensure that the predator is effective in large areas and that it can be high in large enough numbers, Zhong explains.

Defense of GM crops

In some countries, such as Brazil, the pest has been managed by growing transgenic food crops containing genes from the bacteria. Bacillus thuringiensis (Bt). The genes provide crops with resistance to certain pests, including the fall armyworm.

However, Bt food crops have not been approved for commercial purposes in China, partly because of strong public opposition to genetically modified foods, says Du Li, a specialist in biotech law at the University of Macau. .

The growth of Bt corn in much of China would have certainly contributed to pest control, said Li Yunhe, a biotechnology researcher at IPP.

But Hu said it was not clear whether the crop could keep the parasite at bay in the long run. In countries such as the United States, the insect has developed resistance to Bt crops, he notes.

According to Hu, eradication in China is now unlikely and farmers will have to learn how to manage this pest. Other crop producing countries are also on the way to the insect – researchers predict that it will likely enter Japan and South Korea by next month.

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