A hungry caterpillar that ravages crops is advancing across China and threatening the nation’s vast supply of maize. Scientists are investigating ways to minimize the damage caused by the invasive fall armyworm — which was first detected in China in January — including experimenting with native predators that could keep the pest in check. Some researchers say that the insect’s spread might have been slowed if the country grew genetically modified food crops.
The fall armyworm (Spodoptera frugiperda), a native of Central and South America, has spread around the world in the past few years, causing devastation of crops in parts of Africa and southern Asia. Since its arrival in China, it has been found in 18 provinces, regions and municipalities, according to China’s ministry of agriculture.
So far, damage caused by the caterpillar — mostly to maize (corn), but also to other crops such as sugarcane — in China is considered manageable. But Hu Gao, an entomologist at Nanjing Agricultural University who is monitoring the insect’s spread, says researchers and farmers fear what will happen when the pest arrives, probably later this month, at the North China Plain. China is the world’s second-largest producer of maize, and the northern plain produces almost 30% of the country’s crop.
Losses in the billions
Recent fall armyworm outbreaks in Africa and southern Asia have resulted in maize yield losses as high as 50%. And in Africa, where the pest arrived in 2016, it costs 12 major maize-growing countries a total of US$1–4 billion in lost crops a year1. China is also still battling an epidemic of a highly contagious virus affecting pigs, African swine fever, which has led to the culling of more than 1 million of the animals.
“The spread of fall armyworm in China will have a significant impact, along with the spread of swine fever, on Chinese consumers,” says Cong Cao, a researcher studying innovation at the University of Nottingham Ningbo China. The rising price of food will put tremendous pressure on the government to control the pest, says Cao.
Hu says plant-protection centres in provinces and cities are focused on monitoring and controlling the fall armyworm’s spread. The adult moths, which are responsible for the pest’s spread, can travel hundreds of kilometres over successive nights. Control measures include traps and pesticides.
Scientists, meanwhile, are working on other strategies. Hu says researchers at his and other Chinese universities are studying chemicals that could be used to attract the insect to traps, and native insects that could be deployed as a means of biological control.
A report by the United States Department of Agriculture, released in May, on the fall armyworm’s spread in China said that the insect has no natural predators in the country, but Hu disputes that conclusion.
China’s parasitic Braconid wasps already kill other species in the Spodoptera genus to which the fall armyworm belongs, including the cotton leafworm (Spodoptera litura) and the beet armyworm (Spodoptera exigua), so Hu thinks the wasp could also target the fall armyworm caterpillar. In Africa, some parasitoids — whose young feed on and eventually kill their hosts — that target African cotton leafworm (Spodoptera Littoralis) have already switched to feasting on the fall armyworm.
During recent field trials in Yunnan Province, where the pest was first identified, researchers based at the Institute of Plant Protection (IPP), part of the Chinese Academy of Agricultural Sciences in Beijing, have also found that the stink bug Arma chinensis kills the caterpillar.
There could be many natural parasites or predators that target the pest, says Zhong Guohua, a researcher at the South China Agricultural University in Guangzhou who is working on controlling the fall armyworm, but whether they can ultimately be used for control it is difficult to predict. Finding out would require repeated testing to ensure the predator is effective across large areas, and can be bred in large enough numbers, says Zhong.
GM crop defence
In some countries, such as Brazil, the pest has been managed by growing transgenic food crops that contain genes from the bacterium Bacillus thuringiensis (Bt). The genes offer crops resistance to some pests, including the fall armyworm.
But Bt food crops have not been approved for commercial use in China, in part because of strong public opposition to genetically modified food, says Du Li, a specialist in biotechnology law at the University of Macau.
The growth of Bt maize across a large area of China would definitely have helped to control the pest, says Li Yunhe, a biotechnology researcher at the IPP.
But Hu says that it’s not clear whether the crop can keep the pest at bay in the long term. In countries such as the United States, the insect has developed resistance to Bt crops, he notes.
Hu says eradication in China is now unlikely and that farmers will have to learn to manage the pest. Other major crop-producing countries are also in the insect’s path — researchers predict that it will probably enter Japan and South Korea between now and next month.
Nature 570, 286-287 (2019)