Prepare for the worst, scope for the pest
Scientists are locked in an ongoing battle to repel invasive alien species that threaten China’s ecosystem, Li Yingxue reports.
Tuta absoluta, or the tomato leaf miner, is a small darkcolored moth and a devastating pest for tomatoes. Feeding damage is caused by its larvae at all of its developmental stages, or instars, and takes place throughout the whole plant except the root. An infestation can quickly occur throughout an entire crop cycle.
They live on and in the leaves, stems, flowers and also in the fruit itself. On leaves, the larvae form irregular burrows — like mines inside the leaf, hence the critter’s moniker — which may become necrotic and cause the leaves to die. In the fruit, as well as being attacked by the larvae, the holes and spaces formed by the voracious eaters can invite secondary pathogens into the tomato, causing it to rot.
If not managed properly, it is capable of causing total yield losses.
Originating in South America, it invaded in Spain in 2006 and rapidly spread across Southern Europe and North Africa engulfing all of the countries in the Mediterranean region.
It has also invaded China, the largest tomato producer in the world.
In August 2017, during field surveillance in Yili, Xinjiang Uygur autonomous region, researchers found infestation of lepidopteran larvae on field- grown tomato plants, which was later identified as the tomato leaf miner.
According to Liu Wanxue, director of the department of biological invasions at the Institute of Plant Protection, Chinese Academy of Agricultural Sciences, it was the first record of the pest in China.
“It means there needs to be detection and monitoring techniques and prevention measures including plant quarantine and studies of its natural enemies to prevent further spread of new invasive insect pests,” Liu says.
China is a country that is in most jeopardy from invasive alien species — ones that are introduced, accidentally or intentionally, outside of their natural geographic range and which become problematic.
Over half of those listed among the 100 of the world’s worst invasive alien species, as published by the International Union for Conservation of Nature, have invaded China.
Each year, more than 600 invasive alien species identified have cost around 200 billion yuan ($ 30.17 billion) in economic losses, according to Chinese Academy of Agricultural Sciences vice- president, Wu Kongming.
They also threaten ecological safety by weakening biodiversity and the health of human beings and animals. With its rich biodiversity, China is especially vulnerable to invasive alien species.
Lifting the public’s awareness of such invaders, and monitoring and detecting them, has become an urgent challenge for China in recent years.
In August, “how to prospectively predict the risk of new invasive alien species in China’s agricultural and forestry ecosystem and control them in a timely manner” was added to the 2020 list of major engineering technical problems to be solved by the Chinese Association for Science and Technology.
Wu thinks it’s necessary to enhance the capability to cope with invasive alien species to safeguard the nation’s food security and ecology.
The invasive alien species in China’s agricultural and forestry ecosystem include insects, plants, viruses, fungi and bacteria. Most of them come through coastal areas and borders. They are introduced under natural, accidental and intentional circumstances, and sometimes a combination of the three.
According to Liu, it was the latter which was the major source of the invasive alien species in China in last century.
“China has a long history of introducing species for multiple purposes, including economic benefit, ornamental value and environmental protection,” he says. “Some species may escape the confines of their enclosures or cultivation and become invasive.”
Alternanthera philoxeroides, or alligator weed, which is a native species of South America, was introduced to China in the 1930s as horse fodder.
It affects both aquatic and terrestrial environments and was put on the list of the first batch of invasive alien species in China in 2003.
Yin Wandong, lecturer at the School of Life Sciences, Henan University, says, these days, a more comprehensive risk evaluation process is held before an exotic species is introduced to China.
In the past couple decades, as international trade, transportation and tourism have grown, more invasive alien species have been introduced to China unintentionally.
Personal pets, particularly aquatic ones, are sometimes a source — for instance, people buy turtles like trachemys scripta elegans, or the red- eared slider, and end up setting them free, which has led to non- native turtle invasions in many places in China.
Even seeds stuck to a tourist’s shoe can become an invasive alien species.
Yin says people should raise their awareness of invasive alien species, which can even be introduced by shopping online from overseas.
“Some invasive alien species threaten people’s health and they are not far away from people’s daily life,” Yin says. “Take ambrosia artemisiifolia, or annual ragweed, as an example, ragweed pollen is a common, powerful allergen and is produced in massive amounts.”
Ragweed invaded China more than 80 years ago and has spread to over 20 provinces and cities. According to a study by Zhang Xiaoli from Beijing Plant Protection Station, among the pollen allergy patients at Peking Union Medical College Hospital between 2016 and 2018, more than one quarter were triggered by ragweed pollen.
Few invasive alien species have arrived naturally. Weeds can spread through airflow, water flow or get carried by migratory birds, insects and animals.
Spodoptera frugiperda, or fall army worm, flew into Southwest China. First detected in Yunnan province in January 2019, the pest had infested over 1 million hectares of land through 2019 and caused an economic loss of 10 billion yuan.
China’s Ministry of Agriculture and Rural Affairs warns that the formidable harm caused by fall army worms could erupt in more places in 2020.
The invasion of non- native species is a complicated ecological process including transport, colonization, establishment and landscape spread.
According to Liu, once a new invasive alien species has been found to significantly affect agroforestry production or ecological environment, it means it has taken root and is almost impossible to eliminate.
“The key is to carry out strict and scientific monitoring, prevention and control at early stage of invasion which can minimize the ecological and economical loss the invasive alien species may cause,” Liu says.
Liu and his team have studied the tomato leaf miner’s distribution history and trend worldwide, especially in Asia, and analyzed the possible ways and areas through which it has invaded China for years.
After continuous fixed- point monitoring in high- risk areas including Yunnan and Xinjiang, they managed to detect the pest at an early stage.
“To monitor and control invasive alien species needs multidisciplinary collaborations including biology, chemistry, agricultural pharmacology and computer science,” he says.
Liu says there is need to build a technology platform for precise detection and intelligent remote monitoring — detection methods using technologies including modern molecular biology, satellite remote sensing, DNA fingerprints and unmanned aerial vehicles.
Liu thinks that, as well as using technology, providing more information and knowledge to farmers about potential invasive alien species can help detect them in a timely manner.