Small fire ants "invade" my country! Is it related to red fire ants?

A new invasive pest has been discovered in China. Recently, the Red Fire Ant Research Center of South China Agricultural University said that for the first time, a wild population of the famous invasive species, the small fire ant, was recorded in mainland my country. What harm does the small fire ant do? Why do the invasions of alien species continue despite repeated bans? What are the prevention and control methods?

Written by reporter Liao Mailun Edited by Liu Zhao

New Media Editor/Li Yunfeng

Interview experts

Liu Quanru (Professor, School of Life Sciences, Beijing Normal University)

Yang Hongzhen (Researcher, Beijing Museum of Natural History)

Xie Yan (Associate Researcher, Institute of Zoology, Chinese Academy of Sciences)

On April 8, a paper published online in the Journal of Agricultural Sciences stated that the invasive fire ant has been found in China. The warning has been reported in accordance with regulations, and the research report has been published in the academic journal Journal of Integrative Agriculture. What is the current status of invasive alien species in my country? What are the prevention and control measures?

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"Tiny" fire ants cause great harm, destroying crops and hurting people

The small fire ant discovered this time is an invasive ant species with similar destructive power to the red fire ant, and is also listed as one of the 100 most destructive invasive species by the World Conservation Union (IUCN).

"Like the red fire ant, the small fire ant is also native to South America and is rapidly spreading around the world." Chen Siqi, a doctoral student at the Red Fire Ant Research Center of South China Agricultural University, told reporters, "The scientific name of the small fire ant is Chrysomelidae, which is not a true fire ant. It is called the small fire ant because it can cause pain to people through stings like the red fire ant, but its body size is much smaller."

"The venom of the small fire ants can cause a lot of trouble." Professor Lu Yongyue of the research center further explained that humans, livestock and animals bitten by them may suffer from punctate keratopathy, which threatens health. According to foreign research, the activities of small fire ants can destroy biodiversity, hinder tourism, reduce agricultural productivity, and cause huge ecological and economic losses.

▲A specimen of a small fire ant worker. (Photo source: Red Fire Ant Research Center of South China Agricultural University)

According to Professor Xu Yijuan, co-corresponding author of the paper, the researchers confirmed through morphological identification and DNA barcoding technology (with a matching degree of more than 99.5%) that the collected samples were indeed small fire ants.

"At present, we have only recorded the invasion of small fire ants. We have not yet determined whether this is just an isolated incident or has already colonized. We cannot be sure whether there are small fire ants invading other areas." Xu Yijuan said, "Generally speaking, once any kind of alien pest is discovered, it has often gone through the stages of introduction, successful colonization, and even spread. Relevant departments should strengthen plant quarantine, distribution range and degree of harm investigation, biological and ecological characteristics research, monitoring and prevention and control technology development of this kind of invasive ants, so as to actively respond to the threat of small fire ants to my country's social and ecological security."

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my country has enacted laws to prevent the invasion of alien species

China is one of the countries in the world that suffers the most from biological invasions. In recent years, invasive alien species have caused economic losses of hundreds of billions of yuan almost every year. In addition to the small fire ants and red fire ants, the familiar crayfish, apple snails, water hyacinths, etc. are all invasive alien species that cause serious damage.

The 2019 China Ecological Environment Bulletin shows that more than 660 alien invasive species have been found in the country. Among them, 71 species have caused or have potential threats to natural ecosystems and are included in the "List of Alien Invasive Species in China". The survey results of alien invasive species in 67 national nature reserves show that 215 alien invasive species have invaded national nature reserves, of which 48 alien invasive species are included in the "List of Alien Invasive Species in China".

Preventing biological invasions is urgent. On April 15, 2021, on the occasion of the sixth National Security Education Day, the "Biosafety Law of the People's Republic of China" was officially implemented, which clearly stipulates the prevention of alien species invasions and the protection of biodiversity.

However, preventing the invasion of alien species is not easy. Because alien species invasion has a time lag, alien species need to undergo a period of adaptive evolution before large-scale expansion, so many biological invasion events are difficult for people to detect quickly.

To put it simply, there are three necessary elements for the invasion of alien species: first, they are not native to the area and spread naturally or are introduced intentionally or unintentionally by humans; second, they survive in the wild, establish populations, and reproduce from generation to generation; and third, after a successful invasion, they threaten native species and local ecosystems, and may also cause damage to agricultural, forestry, animal husbandry, fishery production, human health, etc.

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The crimes are too numerous to list

Destroying biodiversity, threatening agricultural, forestry, animal husbandry and fishery production, affecting human health...the "claws" of invasive alien species have extended to all fields and their "crimes" are too numerous to list.

Biodiversity is an important material basis for the survival and development of human society and is the common wealth of all mankind. However, the world's biodiversity is facing many threats, among which biological invasion is considered to be the second largest cause of global biodiversity reduction, second only to habitat destruction.

The reduction in biodiversity caused by invasive animals is relatively easy to understand. They "stand out from the crowd" with their excellent hunting ability and reproductive capacity, quickly occupying ecological niches and competing with local species for resources, while gradually assimilating local species through "marriage".

So how do invasive plants "bully" native plants? In fact, they have a killer weapon to achieve "bullying" - allelopathy.

Allelopathy refers to the phenomenon that plants release some chemicals to inhibit the growth and development of neighboring plants. "Invasive alien plants such as ragweed, ragweed trilobate, and purple loosestrife have strong allelopathy. They produce some exclusive compounds to affect or inhibit the growth of other plants, and preferentially obtain resources in the local area, thereby achieving the purpose of invasion." Liu Quanru, a professor at the School of Life Sciences of Beijing Normal University, said in an interview with reporters.

Relying on the "killer weapon" of allelopathy, invasive alien plants have achieved their desire to "harm others and benefit themselves" and created their own monodominant communities. The ecological niches of local plants have been occupied by these invasive alien plants, resulting in a decrease in plant species. Imagine what it would be like to see a flowerbed that was originally full of flowers during the festival become a lonely one.

At the same time, the reduction in plant species may also lead to a decrease in animal diversity. Different insects eat different types of plants. If only one type of plant is left, it is likely that many insects will face the dilemma of not being able to find food, which will lead to a decrease in animal diversity and further affect the ecology.

In addition to affecting biodiversity, invasive alien species also cause harm to agriculture, forestry and animal husbandry. Take the example of Eupatorium adenophorum, which ranks first on the list of China's first batch of invasive alien species. It has huge ambitions and not only excludes and replaces local species, but also further expands, invades farmland and forest land, competes with crops for sunlight, water and nutrients, causes crop yield reduction, and affects tea trees, mulberry trees and fruit trees, causing significant economic losses.

The "ruthless" purple loosestrife not only harms plants, but also animals. Its pollen can cause asthma in horses, and its plants contain aromatic and spicy chemicals, as well as some toxic substances, which can cause poisoning or death to livestock after being eaten by mistake.

Faced with rampant invasive species, humans cannot "stay out of it" because many "invaders" can harm human health in various ways. Pollen produced by ragweed and ragweed is the main pathogen that causes human pollen allergies; toxins from marine organisms such as algae enter the human body through the food web and cause poisoning; after being bitten by red fire ants, red spots or blisters may appear on the skin, and those who are allergic to them may go into shock or even be in danger of their lives; the invasion of gypsy moths indirectly leads to the outbreak of Lyme disease...

▲The Lyme disease pathogen Borrelia burgdorferi completes its life cycle in a variety of hosts (Image source/NCBI)

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Establish blacklists and whitelists to prevent problems before they happen

The numerous crimes committed by invasive alien species have made people further realize the importance of preventing and controlling biological invasions. Liu Quanru, a professor at the School of Life Sciences of Beijing Normal University, believes that prevention is more important than treatment, because once a biological invasion is formed, it takes a lot of manpower, financial resources, and material resources to control it, and even so, it is difficult to completely eliminate it. Therefore, it is crucial to strengthen entry quarantine, prevent the entry of invasive alien species carried by inbound tourists or international mail parcels, and strictly guard the country's borders.

As one of the countries most seriously affected by invasive alien species, my country should strengthen research on risk analysis of alien pests, collect information on the occurrence and prevalence of pests, fully understand and master the occurrence, spread and transmission of alien pests, and achieve "knowing ourselves and the enemy, and fighting a hundred battles without danger". Once an important alien pest is found to have invaded, it can be detected quickly and accurately, reported to relevant departments in a timely manner, and early warning notices can be issued.

"In nature reserves, there are special rangers to carry out monitoring, and invasive species can often be discovered relatively early. However, in unmanaged areas, we can only organize corresponding alien invasive species monitoring work on a regular basis, and we may miss the good opportunity to 'nip the invasive species in the bud.' So for invasive species that have already appeared in other countries or regions, we can widely publicize them so that more people can understand and recognize them, and report them as soon as they are discovered." said Xie Yan, an associate researcher at the Institute of Zoology, Chinese Academy of Sciences.

In addition, the intentional introduction of alien species cannot be ignored. At present, my country has published four lists of alien invasive species in China and established a "blacklist" system. However, there is a time lag in biological invasions, and it may take some time for us to discover the "true face" of alien species, so some species that are not on the "blacklist" are still at high risk of invasion and cannot be prevented.

Some alien species have achieved good results in the short term, but have caused greater harm, which is not worth the cost:

The introduction of Spartina alterniflora to Chongming Dongtan was initially intended to promote sedimentation, protect riverbanks and maintain land. Since the roots of Spartina alterniflora are particularly long and grow horizontally, they can fix the sand and prevent it from being carried away by the waves, and it has indeed achieved certain results. However, as it develops, it begins to pose a serious threat to many native reeds and plants on the river bank, destroying the succession process of the inherent natural plant community in the wetland and seriously changing the spatial distribution pattern of the native vegetation in the wetland.

Spartina alterniflora has also had an impact on animals in the area. Xie Yan said: "The beach used to be home to animals such as sandworms, but after being invaded by Spartina alterniflora, they could not survive and gradually disappeared. At the same time, various birds that feed on these small animals have also lost their prey, and they are no longer seen feeding on the beach." In addition, Spartina alterniflora has also caused huge economic losses to local fishermen.

▲Spartina alterniflora at Chongming Dongtan (Photo credit: East China Normal University)

Therefore, we should consider establishing a "white list" system to include alien species that are frequently introduced and have been proven to pose no risk of invasion. In principle, species on the "white list" can be introduced. For species that are neither on the "white list" nor on the "black list", "case by case" is required. In this regard, Xie Yan said: These "gray list" species that are neither black nor white need to be strictly evaluated before introduction, that is, to see whether they have the characteristics of invasive species, and score them according to their characteristics. If they exceed a certain score, they cannot be introduced. If the score meets the conditions for introduction, a small amount of introduction can be allowed and monitoring can be done well. Introduction is allowed only after it is proven to be harmless.

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Three ways to control invasive species

Although we hope to keep all invasive alien species out, it is inevitable that some will slip through the net. For the alien species that have already invaded, we cannot just leave them alone, but must actively control them.

There are three main traditional methods for the “treatment” of invasive alien plants. The first method uses physical control, which is simply “pulling”, that is, pulling out and eradicating invasive plants with the help of manual or mechanical means. However, you should not pull them out randomly. You should pay attention to choosing the right time and complete the pulling out before the seeds are hardened. Once they bloom, they must be pulled out immediately. Pulling them out after they have fruited will only make things worse and help the invasive plants spread further. However, even if you choose to pull them out at the right time, it is tantamount to trying to stop the boiling water by adding more water, because the ecological niche is still vacant, and as long as the invasive plants are “still alive”, they may still make a comeback later.

The second option is chemical control, which is to use herbicides to kill invasive alien plants. However, in the process of killing, it may cause soil and water pollution, thus causing new ecological and environmental problems.

The third method is to use biological control, which is to introduce natural enemies of alien invasive plants. However, this method also has certain risks and may inadvertently cause new biological invasions.

(Photo source: Economic Daily)

As for the prevention and control strategies of alien invasive plants, Liu Quanru believes that ecological prevention is the best choice for biological invasion. First, it is necessary to remove alien species at the right time, and then select local plants for replacement planting, replacing annual plants with perennial plants, and replacing herbaceous plants with woody plants. Through replacement planting, the biological ecology is restored, and the alien invasive plants are squeezed out with the help of natural vegetation. Although the effect may not be immediate, after a few years, the results will gradually emerge, and the local ecology will gradually return to its pre-destruction appearance.

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Reasonable resource utilization allows invasive species to “make meritorious contributions”

In addition to various control methods, many people have proposed to utilize invasive alien plants as resources. For example, invasive plants can be processed into livestock feed, fertilizer, or as raw materials for dyes. However, before resource utilization, careful research should be conducted to choose a utilization method that is more beneficial to the ecological environment and economic benefits.

Research has found that the humification coefficient of the invasive alien species water peanut is 0.18, which is 2 to 4 times that of ordinary green manure. The rice yield of 1 hectare of green manure made from 15 tons of fresh grass water peanuts is 300 to 450 kg/hectare higher than that of conventional fertilizers, and 150 kg/hectare higher than that of the same amount of potassium chloride. The raw material of Flaveria can be extracted to make yellow dyes, and Flaveria and indigo can be mixed in different proportions to make different green dyes.

▲Flavour-topped Chrysanthemum (above) and Indigofera tinctoria (below)

These resource utilization methods certainly have certain advantages, but we must also be careful of the dangers. Liu Quanru said in an interview with reporters: If fertilizer plants and dyeing factories want to use invasive alien species as raw materials, they must conduct careful preliminary research to determine whether the total amount of invasive plants in the surrounding area can support operations. If they plant invasive alien plants themselves to supplement raw materials later, it would be putting the cart before the horse.

People often say that "garbage is a resource placed in the wrong place", and this is actually true for some invasive alien plants, which may be beneficial to the ecology in some special areas. For example, Eupatorium adenophorum has the ability to enrich heavy metals such as chromium, cadmium, lead, and zinc, and can be used as an ideal restoration plant for heavy metal pollution areas; the roots of water hyacinth have a strong adsorption capacity for metal ions such as silver, mercury, arsenic, cadmium, and other harmful substances (such as cyanide-containing substances) in water, and can reduce the BOD (biochemical oxygen demand) value in domestic sewage, and can be used to treat a variety of heavy metal-polluted water bodies and domestic sewage.

Biological invasions are becoming more and more serious. This is not the fault of one country or one city. The responsibility should be shared by all mankind. Preventing and controlling biological invasions is a long-term battle. Every tiny action of each person may affect one of the links and trigger a butterfly effect.

During the interview, Yang Hongzhen also said: "Citizens' ecological protection awareness is very important to prevent the invasion of alien species. Therefore, it is necessary to strengthen education and publicity on biological invasion, let people understand the harm of biological invasion, establish new ethical norms for biosafety protection, further regulate their own behavior, and make everyone realize that they have the responsibility to control the invasion of alien species."

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References:

[1] Li Hong, Xu Hui. Introduction to the Science of Alien Species Invasion[M]. Beijing. Science Press, 2016

[2] Fu Weidong, Zhang Guoliang, Huang Hongkun, et al. Questions and Answers on Alien Invasive Species[M]. Beijing. China Agricultural Science and Technology Press, 2020.

[3] Su Wenwen. A brief discussion on the current status, hazards and prevention of biological invasions[J]. Agriculture and Technology, 2020, 40(10): 78-80.

[4] Liu Su. Don’t let good deeds encourage biological invasion. Unreasonable release of animals is more terrible than killing them. Environment and Life, 2013(12):44-48.

[5] Huang Shunjiang. Releasing animals should follow the laws of nature[N]. China Science Daily, 2019-10-15(007).

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