Biological invasion has existed since ancient times and is more frequent in modern times. Especially in recent years, with the increasing international exchange and trade, the vigorous development of tourism and the convenient development of transportation, the barrier function of natural barriers such as oceans, mountains, rivers and deserts is getting smaller and smaller, and more and more species cross the barrier with the help of human activities, making biological invasion more successful. According to incomplete statistics, there are more than 400 alien species invading China, among which more than 100 species are harmful. Among the most threatened alien species in the world 100 published by IUCN, there are more than 50 species in China.

Biological invasion, also known as alien species invasion, refers to the phenomenon that alien organisms (including microorganisms, plants and animals) are introduced into the native land, and the population quickly spreads out of control, leading to the extinction of native species and other hazards. It is divided into several stages: introduction, settlement and diffusion.

In recent years, there are generally three ways of alien invasion: one is artificial introduction and evolution into invasive species, that is, conscious introduction. Due to the imperfect introduction evaluation system and the limited level of research and understanding of alien species, some alien invasive species were introduced as beneficial species from the beginning, causing irreparable losses. Second, with the introduction of trade, transportation, tourism and other activities, that is, unconscious introduction. For example, alien invasive organisms may be inadvertently brought in with international trade, the introduction of animals and plants, tourists' belongings and human vehicles. The third is self-diffusion, that is, natural invasion. Species migrate from their place of origin to another area with wind, rain, rivers and self-movement. For example, rice weevil can migrate with monsoon and light, and naturally spread with water flow, and Eupatorium adenophorum can be introduced naturally through the surrounding wind and water flow. According to the analysis, more than half of the alien invasive harmful species in China are caused by human factors.

Second, the invasive species of alien organisms.

It is reported that more than 400 alien species have invaded China, including mammals, birds, reptiles, amphibians, fish, crustaceans and plants. The following is a list of some alien invasive creatures:

1, mammals:

Otter, muskrat, Rattus norvegicus;

2. Birds:

Small sunflower cockatoo, rainbow sucking parrot, Canada goose;

3. Reptiles:

Brazilian tortoise;

4. Amphibians:

Bullfrog;

5, fish fish:

Bighead carp, goby fish, spike fish, mosquito fish, fetal giant salamander, perch and silver carp;

6. Crustaceans:

Crayfish;

7. Mollusca Mollusca:

Amphibia canaliculata, African snail;

8, insect insert:

Termites, Hemiberlesia pitysophila, Hyphantria cunea, Pinus elliottii, Liriomyza sativae, Periplaneta americana, Blattella germanica, cotton aphid, grape root worm, nematode and pine wood nematode;

9. Fungi Fungi:

Sweet potato long beak shell fungus;

10, Wild Animal Diseases:

Infectious pancreatic necrosis of salmon;

1 1, plants:

Chenopodium ambrosioides, Alternanthera philoxeroides, amaranth, cactus, forsythia suspensa, Solanum spinosum, plantain, star anise, Pogostemon rugosa, ragweed, Sedum, Erigeron Erigeron, Eupatorium adenophorum, Mikania micrantha, Hedyotis diffusa, poisonous wheat, water hyacinth, golden dragon with five claws, melon, lantana, etc. Lantana, leek, tall fescue, crow's mouth, flying grass, cactus, sunflower, Leymus chinensis, carpet grass, festival grass, paspalum, Pennisetum, Setaria viridis, Sudan grass, ryegrass, bulbous barley, alfalfa, Hedyotis diffusa, Hedyotis diffusa and Hedyotis diffusa.

Third, the harm of alien biological invasion

The harm of biological invasion is mainly manifested in three aspects: destroying the ecological environment, threatening human health and endangering economic development.

First of all, alien invasive species will cause serious ecological damage and biological pollution. Most exotic species broke out after successful invasion, and their growth was difficult to control, resulting in serious biological pollution and irreversible damage to the ecosystem. For example, water hyacinth, which originated in South America, has now spread all over rivers, lakes and ponds in North China, East China, Central China and South China. In Dianchi Lake, with a continuous area of 1 1,000 hectares, water hyacinth grows wildly, covering the water surface, seriously destroying the structure and function of aquatic ecosystem, resulting in the death of a large number of aquatic animals and plants. Alien invasive species form a single dominant population by suppressing or crowding out local species, which endangers the survival of local species and eventually leads to the loss of biodiversity. For example, Eupatorium adenophorum, which originated in America, has spread all over most parts of southwest China, and always appears in the form of a single superior plant community in its place of occurrence, which has led to the decline and disappearance of the original plant community.

Secondly, it threatens human health. Alien invasive species not only bring great losses to the ecological environment and national economy, but also directly threaten human health. Ambrosia and Ambrosia trifoliata are now distributed in Northeast China, North China, East China and Central China 15 provinces and cities. The pollen produced by ragweed is the main pathogen causing human pollen allergy, which can cause hay fever. Apart from mad cow disease and foot-and-mouth disease, the disasters brought to human beings are very painful, because harmful organisms are endangering human health and the safety of agricultural organisms all the time. In the second half of the fifth century, the plague invaded the Middle East from Africa and then reached Europe, killing about 654.38 billion people. 1933 China classical swine fever epidemic, resulting in the death of 9.2 million pigs. 197 avian influenza occurred in Hong Kong, and 6,543,800+4,000 chickens had to be destroyed. Only the losses of chicken farmers and chicken vendors were compensated, totaling HK$ 654.38+0.4 billion.

In addition, biological invasion leads to frequent outbreaks of ecological disasters, causing serious damage to agriculture and forestry and endangering economic development. In recent years, the serious occurrence and damage area of forest invasive pests such as Bursaphelenchus xylophilus, Pinus elliottii, Hemiberlesia pitysophila and Hyphantria cunea have increased year by year. Ragweed, Eupatorium adenophorum, Eupatorium odoratum, Mikania micrantha, Alternanthera philoxeroides, Eichhornia crassipes, Spartina, etc. It has spread wildly and has reached an uncontrollable level. According to experts' estimation, the annual losses caused by biological disasters in China account for 10%- 15% of grain output, 15%-20% of cotton output and 20%-30% of fruit and vegetable output.

Four. The Status of Alien Invasion in China

According to the latest statistics of the Ministry of Agriculture of China, at least 380 species of plants, 40 species of animals and 23 species of microorganisms have invaded China. These exotic creatures are huge in number and multiply rapidly, causing economic losses of more than 57 billion yuan to China's agriculture and forestry every year. Alien invasive species often become the absolute dominant species in new invasive areas, while local species suffer devastating rejection. Second, dangerous alien pests invaded one after another, and new epidemics broke out constantly. Thirdly, with the globalization of global economy and the development of international trade, the frequency of alien pests' invasion has increased dramatically, and the danger has been increasing. For example, before the 1990s, there were only 1 species of alien pests that invaded China in almost 8- 10. After the 1990s, there were 1-2 species of newly discovered invasive organisms every year.

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