Citation Detail: Ding Jianqing and Xie Yan. 1996. THE MECHANISM OF BIOLOGICAL INVASIONAND THE MANAGEMENT STRATEGY. in: Conserving China's Biodiversity (II) (PETER Johan Schei, WANG Sung and XIE Yan eds.). China Environmental Science Press. Beijing. 125-156p.

THE MECHANISM OF BIOLOGICAL INVASION
AND THE MANAGEMENT STRATEGY

Ding Jianqing1 Xie Yan2

★1 General situation of invasive alien species★2 Impact of exotic invading species★3 Pathway of exotic invading species in China★4 The spread mechanism in exotic invading species in China★5 Measures for controlling exotic invasive species★6 Countermeasures★Appendix

Biodiversity is the material basis for the survival and development of human. It creates the value of 33 billion of US dollar per year (Costanza et al, 1997). However, it has faced severe threats in recent years. That the extinction rate successively increases and the genetic diversity is to be sharply impoverished as well as the severe degeneration of ecosystem has taken a turn for the worse in the crises of resource, environment, food and energy. And, the invasion of ecological environment by alien species has become one of the main reasons for the loss of biodiversity.

In nature, the survival and development of each species is limited within a definite space. These species are called "native species". Although the migration of native species itself may occur, but the natural migration rate will be very slow, if it is beyond the impact of human activity. The "exotic species" is the species which is directly or indirectly introduced into the region through human activities, where the exotic species hasn't been distributed in history. The exotic species and the invasive alien species are of different definition and coverage, the former merely represents the species which enters or is introduced into the region without confirmation of disadvantage of the entering species to the region, and the later represents the species on which emphasis is placed that the entering or introducing species is bringing forth damage to the region.

Although the study and control of invasive alien species has been developed for at least over 100 years, but more and more people begin to attach value to the problems of impact of invasive alien species to biodiversity of their ecosystem, especially, the problem of invasive alien species becomes hot spot of researches in recent years. In China, there has been some lag in the development of research on invasive alien species. Most of the researches only focused on the cases of individual species of plant or animal though many surveys and only preliminary investigations were carried out. None of series of review of the impact of invasive alien species to biodiversity was made. The research reports only involved biological invasion in some aspect, such as the occurrence and distribution of exotic species or the damage of exotic species and its control, less researches involved the mechanism of the entry and spread of invasive species. On the bases of summing up the data concerning the invasive alien species in China, the analysis of some invasive alien species in combination with the latest international achievements in the field of control of exotic species. The present paper is putting forward a comprehensive countermeasures for overall control of invading species in the aspects of science, society, culture and education. Therefore, the present study is of great importance either in the theoretical study and the practical application.

1 General situation of invasive alien species

China is one of the countries which have very rich resource in biodiversity on the world. It is known that, there are 2554 species of terrestrial vertebrate (Xie Yan et al., 2001), 3862 species of fish, 30000 species of higher plants (Chen Ling-zhi, 1994 and "Researches on Biodiversity in China", Editor Group, 1988) as well as a great variety of species of invertebrate including insects, lower plants and fungi, bacteria and actinomycetes in China. That in such a plenty of species what actual number of the exotic invasive species is, hasn't reported yet. Especially in recent 20 years, along with the increasing international intercourse, what an exact number of exotic species has entered in China and how many entered exotic species has set up population and thus brought about damage to ecological environment are difficult to be answered accurately owing to various reasons. Since the eighties of 20th century, as the damage of invasive alien species were running wild in China, the works of control of invasive alien species has been stressed. The effective measures for controlling pest insects as North American pinewood nematode (Bursaphelenchus xylophilus), loblolly pine mealybug (Oracella acuta), fall webworm or American white moth (Hyphantria cunea), American rice water weevil (Lissorhoptrus oryzophilus) and vegetable leaf miner (Liriomyza sativa) and for controlling exotic injurious plants, as alligator weed (Altemanthera philoxeroides), water hyacinth (Eichholmia crassipes), ragweed (Ambrosia) and Crofton weed (Eupatorium adenophorum)were adopted and achieved success in different degrees. As to the control of invasive alien species in general, the results of the control of pests in some cases were not too well though a lot of man power and financial funds were invested, owing to that the Chinese government didn't work out the exact regulations of prevention, control and administration of exotic invasive species and owing to the lacks of necessary technical guide for control and coordination of actions in China as a whole. The entered invasive species successively spread its damage and newly entered dangerous invading species occurred and formed potential threats in ecological environment.

1.1 Exotic species
1.1.1 Plants
A survey of exotic invasive species in plants was initiated in the middle nineties of 20th century. It was found that at least more than 58 exotic plant species brought about damages in agriculture and forestry in China, according to an initial preliminary survey and calculation in species of plants in the habitats in farmlands, pasturelands and waters on the basis of literature, conducted by DING Jianqing et al., in 1995 and the details of the survey was published in " China's biodiversity: a Country study"(Ding Jianqing and WANG Ren, 1998). In recent 3 years, great advances in the researches on exotic plant species have been made. The report of a survey by QIANG Sheng et al. (2000), indicated that there were 108 species of weed being identified as exotic weeds,, which are subordinated to 76 genera and 23 families, and 15 of them were believed as countrywide or regional exotic weeds. In addition, a general survey of the exotic species of plants in China, conducted by the Institute of Botany and the Institute of Zoology of the Chinese Academy of Sciences showed there were about 300 exotic plants in China (XIE Yan et al., 2001).

1.1.2 Animals
So far, no systematic report on exotic invasive animal species was published yet. Presently, according to a summary of a number of collected data concerned, there were about 40 species of exotic animal species causing severe damage to agriculture and forestry in China. The pest insects include Fall webworm, pine scale (Hemiberlesia pitysophila), loblolly pine mealybug (Oracella acuta), American rice water weevil, vegetable leaf miner, North American pinewood nematode, banana moth (Opogona sacchan), woolly apple aphid (Eriosoma lanigerum), Grape root louse (Phylloxera vitfolii), Leptinotarsa decemlineata, Dacus dorsalis, white ant or termite and red opentine beetle (Dendroctonus valens) and (LI Xingyu, 1997; FENG Mingxiang, 1992; LIU Yuanzhi et al., 1998; HE Chunhua et al., 1992; CHENG Guifang et al., 1997; WEI Hongjun, 1997). The other exotic animal species are the Amazonian snail (Ampullaria gigas) originated from South America and giant Africa snail (Achatina fulica) originated from East Africa (CHEN Deniu and ZHANG Guoqing, 1996), musk rat (Ondatra zibethicus) originated from North America, squirrel, brown rat (Rattus norvegicus) and R.flavipectus originated from the former Union of Soviet Socialist Republics(ZHANG Daming et al., 1993) and Nutria (Myocastor coypus) originated from South America (XU Ruiqiu et al., 1997). The introduced exotic fish also caused great threats to native fish species and regional ecosystem (ZHANG Guohua et al., 1997; LIAO Guozhang, 1998).

1.1.3 Microorganism
Comparing with the exotic invasive species of animals and plants, the survey of exotic microbial species was rather rarely seen. Presently, there were 11 species causing more severe damage in agriculture. They are Xanthomonas oryzicola Fang, et al. in rice, Peronospora spp. in corn, Synchytriium endobi-oticum (S. chilberszky) percivadl in potato, Phytophthora megasperma (Drechs.) f.sp.glycinea in soybean, Verticillium alboatrum Reinke et Berth in cotton, Citrus huanglungbin , Xanthomonas citri (Hasse) Dowson in citrus, Xanthomonas campestris pv. manihotis in cassava, tobacco ring spot virus , Clevibacter michiganensese sub-sp. Mishiganen in tomato and Ditylenchus spp.in bulb

1.2 Situation of administration: legislation, quarantine and regulation of introduction
At present, there are no specific law and regulation of exotic invasive species in China. Approved by the Chinese State Council, a trial regulation "Trial Implementation of the Domestic Quarantine of Plants in China" was issued by the Chinese Ministry of Agriculture on 4th December, 1957. On 3rd January, 1983, the "Regulation of Plant Quarantine" was issued by the Chinese State Council, and issued once again on 13th May, 1992 after revised. The Standing Committee of the 10th National People's Congress of China adopted the "Law of Entry and Exit Quarantine of Animal and plant of People's Republic of China" on 30th October, 1992 and was implemented on 1st April, 1992 (noted by YU Dahai and CUI Yanlin, 1997). The purpose of the legislation and implementation of the Law of Quarantine is to prevent the domestic animals and plants in China from infectious diseases and parasitic diseases and from the disease- or pest-carrier animal and plants of injurious insects and microorganisms and other injurious biological organisms due to the entry of the foreign diseased animals and plants and the disease- or pest-carriers. And, on the other hand, the Law of Quarantine also checks the exit of diseased animals or plants and disease- or pest-carrier animal and plant from China. The most important task is to protect the development of agriculture, forestry, animal husbandry and fishery to guarantee the safety of agricultural production. The target of quarantine focus on the dangerous biological organisms which brings about damage to the economic development in agriculture, forestry, animal husbandry and fishery, but doesn't think highly of the invasive species which may form threats to the ecological environment and biodiversity.

For example, for plant introduction, the "Regulation of Plant Quarantine" stipulates that "for introduction of seeds and seedlings from abroad, the unit of introduction should submit the application to the institution of plant quarantine in province, autonomous region and city directly under the central government, where the introduction unit is located, and go through the procedures of examination and approval". "the seeds, seedlings and other reproductive materials introduced from abroad should be grown on a trial basis under isolation manner because of their latent danger caused by carrying diseases and injurious insects, and could be released for growing only after investigation, observation and quarantine of the isolated animals and plants and are proved free from the dangerous diseases and pests". That is to say that, according to the Regulation, the targets which need to be quarantined will be those which carry dangerous organisms in the course of introduction of exotic plant species; and, the Regulation doesn't involve the clear measure to make examination and administration of the ecological safety of the introduced plant itself. At present, among the invasive species in China, great quantity of plant was introduced consciously, owing to the lack of definite law and regulation concerned to impose restriction on the blind and unscientific introduction in many places of China.

As for the problem of control of invading species which has entered in and brought about damage, there are also no specific policy and law and regulation at present yet. The article "Control" is one of eight articles in the "Agricultural Constitution of Eight Words". The "plant control" that represents the control of disease, pest and weed in agricultural and forestry economy, doesn't involve the control of exotic invading biological organisms which injuries ecological environment and thus leading to the loss of biodiversity. So, no law or regulation concerning the control of exotic invasive species has been worked out accordingly.

However, there is indications that the Chinese central government begins to attach importance to the problem of biological invasion. An international symposium on "Biodiversity and administration of exotic invasive species", the first international symposium concerning the problem of biological invasion in China, was held in Zhuhai Special Economic District, China on 22nd-23rd May, 2001 by Nature Conservation Department of the State Bureau of Environmental Conservation of China. In addition, on 6th June, 2001, "Regulations of Administration of The Safety of Agricultural Transgenic organisms(Genetic Modified Organisms)" was formally issued by the State Council of China.

1.3 Situation of Control in China
At present, the artificial control, biological control, chemical control, agricultural control, mechanical control as well as the integrated control measure with the previous measures combined are applied in control of. exotic invasive plant species in China.

Artificial control: The application of the measure of artificial control of noxious plants has a long history in China. It was also used in control of exotic invasive plants, such as water hyacinth (Eichhomia crassipes), alligator weed (Althemanthera philoxeroides), common cordgrass (Spartina anglica) and South American climber (Mikania micrantha). In past 10 years, the governments of Yunnan province, Zhejiang province, Fujian province and Shanghai city used labor power to clean up water hyacinth from the waters in these regions. More than 100 thousand people was organized in Kunming city of Yunnan in 1991 and 10 million RMB were paid for labor power by Wenzhou city of Zhejiang in 1999 for artificial removal of water hyacinth from the local waters; in Putian city of Fujian, a specified office of controlling water hyacinth was set up and an annual budget of 5 million RMB was funded for the control In 1999-2001, the government of Shenzhen city many times organized labor power to remove South American climber. In Xi'an city and Xianning xian of Shaanxi province and in Jingzhou city of Liaoning province, successful control of fall web worm was achieved through cutting off the larva web curtain of moth and cropping the tree crown at high level by labor power.

Mechanical control: In Kunming city of Yunnan prov. and Ningde city of Fujian prov., a kind of special salvage boat and mower were designed and manufactured for controlling water hyacinth and common cordgrass in these two regions, but the activities failed because the low efficiency and inconvenient operation of the facilities.

Biological control: Successful control of the pest, pine scale, was implemented in Guangdong in 1988 through introducing a parasite, Coccobius azumai from Japan. The area, where the parasite was released, reached a coverage of 738,300 hectares making up around 80% of the total of the epidemic-stricken area. The colonization rates of parasite were 97.8-100% and the parasite rates of female pine scale were 40-50% (PAN Wuyao et al., 1993; HE Guofeng, 1995; CHEN Yongge and GU Dexiang, 1998). By the end of 2000, seven insect species had been introduced for controlling the noxious plants: alligator weed, common ragweed, ragweed, water hyacinth and crofton weed. The populations of the five of the seven natural enemy insect species were set in local regions. The alligator weed in the waters of Southern China was basically controlled (CHEN Xudong and HE Dayu, 1990; WAN Fanghao et al., 1993; DING Jianqing et al., 2000).

Chemical control: In China, the most effective measure of the control of American vegetable leaf miner and American rice water weevil is the use of chemical insecticides . The used insecticides include cartap Fenpropathrin, 杀虫双and Avermectin. The spray of Dilfubenzuronand Delamethrincan also effectively control the American white moth, The herbicides, Round upand Glyphosateshowed certain effects in control of water hyacinth, alligator weed and South American climber. Some effect was shown in control of Crofton weed by using Paraquate.

integrated control: The great success in control of water hyacinth through coordination of integrated way of biological and chemical control measures led to a very important consideration in international academy circle in the field of environmental conservation. An international symposium, the 2nd Symposium of International Organization of Biological Control on the control of water hyacinth through biological and integrated measures, was successfully held in Beijing on October 2000, hosted by the Institute of Biological Control, Chinese Academy of Agricultural Sciences. In addition, "Prize of Scientific and Technological Achievements "was awarded to the Technique System of Integrated Control in control of crofton weed and ragweed by the Chinese Ministry of Agriculture.

2 Impact of exotic invading species

The most important characteristic in exotic invasive species, which is different from the ordinary exotic species, is that the former brings about the consequences of invasion to the local ecosystem. The invasive species always brings forth negative effects on the structure and functions of local ecosystem thus endangering the survival of native species, especially the rare endangered species and leading to the loss of biodiversity. Some invasive species even forms tremendous damage to local economy and community. Viewing from the angle of ecology, the invasive alien species was shown disadvantageous to the stability of native ecosystem; however, some exotic species indeed showed certain economic value for the native community as viewing from the angle of economic and social demands. Some exotic species appeared advantageous when introduced and became harmful after spread without restraint. Some was advantageous in one region and harmful in another. Therefore, the assessment on the advantage and disadvantage of exotic species involves both the time and space significance as well as involves both the ecological and socio-economic significance.

2.1 Ecological impact of exotic invading species
In the processes of the long term evolution in nature, the restraint and coordination to each other among organisms is formed, the populations of individual organism are limited within a certain habitats and sizes, and thus forming stable balanced ecosystem. If a kind of organisms is transferred into a new habitat, and is free from artificial limitation, it will be easy to spread due to the favorable climate, soil, moisture content and other spread conditions. And, then, a large size of population of unique dominance of this exotic species, which survives in larger area in its new habitat, will be formed. This exotic species will then destroy the phases of native fauna and flora in the new habitat that threatens the survival of endangered species and thus causing the loss of biodiversity. The mechanism of the effects of exotic invasive species on ecosystem and the ecological impacts are described as follows
2.1.1 Occupying the ecological niche of native species causing the loss of survival space of the former
In Guangdong , the banana, litchi, longan, wild citrus and some shrubberies and arbors were frequently covered by South American climber which presented an obstacle to the normal photosynthesis of the plants in large coverage thus leading to death of those plants (HUANG Zhongliang et al., 2000); in the suburbs of Shanghai, the tall goldenrod (Solidago altissma) frequently formed a population of unique dominancy that made the other plants hard to grow up (CHE Jingdian and GUO Xihong, 1999). In Caohai, part of Dianchi Lake of Yunnan province, there had been 16 species of higher plant existing there in sixties of last century, but as the vigorous growth water hyacinth without restraint of, the great majority of native hydrophytes, such as Ottelia spp., lost their survival space and died finally, only 3 higher plants survived till the nineties of 20th century (WU Keqiang, 1993).
2.1.2 Competing in food with native species or directly killed the native species that impact the survival of native species
There was lot of examples in China indicating that the exotic fish competed in food with the native fish and swallowed the eggs of the latter that resulted in decrease of the species and the number of native fish. For example in Erhai Lake in Yunnan there were 17 species of native fish originally, but 5 of them, such as the unique Erhai Lake-specific carp and Schizothorax spp. , were in the endangered manner up to present, since 13 exotic fish were introduced into the Lake(WANG Xianpu, year? ); in Lugu Lake, the introduction of exotic fish species, as topmouth gudgeon, also resulted in extinction of Schizothorax spp. (ZHANG Guohua, 1997). The feeding habit of exotic pest insect species endangered native plants that resulted in decrease of species and number of plant, and, in the meantime, the exotic invading pest insect species also competed in food and survival space with the native phytophagous insects that results in the decrease of insect-diversity too. (greater threat to the rare endangered insect) and thus bringing about the changes of species and number of insect in predatory animal and zooparasites that led to the change of the structure and function in ecosystem.
2.1.3 Suppressing the growth of other species with the chemicals released
Ragweed might release the hydroxybenzene acids, polyacetylene, sesquiterpene lactone, and sterol significantly inhibiting and excluding the annual herbs of Graminaceae and Composite (LI Diqiang, 1994; WANG Dali et al., 1995; ZHU Xinru et al., 1997). South American climber could also secrete chemicals affecting the growth of other plants (HUANG Zhongliang et al., 2000).
2.1.4 Lowering biodiversity caused through the formation of large size population of unique dominancy in large area failed to maintain a favorable habitat environment for other species whose survival depends on the diversity of local species
The coverage of invading water hyacinth in river courses, lake and pond in China where the occurred invasion frequently reached 100%, it decreased soluble oxygen in water that led to the death of aquatic animals (DING Jianqing et al., 1995). According to a survey on the habitats at the barren hills, flood lands, either sides of railway and highway in eight cities including Shenyang, the degree of dominance of ragweed was 0.85-1.0 and that of population-diversity was 0.0-0.62 (WAN Fanghao and WANG Ren,1994). At present, because of the lack of food, the survival of rhesus monkey on Lingding Island (nearby the coast of South Sea by Guangdong ) has just been maintained by means of artificial feeding. The spread of siam weed (Eupatorium odoratum) in Xishuangbanna Nature Reserve Area (in Yunnan Province) has pushed the native plants, as Polygonum perfoliatum, to the verge of extinction (DING Jianqing, unpublished).
2.1.5 Consuming soil moisture in quantities resulting in loss of soil and water
The eucalyptus tree, which was introduced from Australia and has grown widely in a number of forestry centers in Hainan Island (present Hainan province) and Leizhou Peninsula of Guangdong is unavailable to soil-and-water conservation. Continuous growing this tree on the same spot will make the crop-producing power of soil being lowered and lowered and then the land wasted in large scale thus leading to the whole forestry center falling into difficult position (WANG Xianpu, 1997).
2.1.6 Damaging natural landscape Four species of the genus Opuntia which had been introduced early in late Ming Dynasty of Chinese history (XIE Yan et al.,2001), formed populations with dominancy and distributed in coastal regions of Southern China and in arid and torrid river valley separately. And, now, the landscape of original natural vegetation is difficult to be found. Some invading species, especially the liane, completely destroyed the well-developed and stratum-rich forests. As the invading species of grass and shrub occupied the space of the forests, the other arbo than the invaded grasses and shrubs became impossible to grow up. After the previous vegetation was destroyed by various exotic invading species, the original vegetation of the forest was turned into short vegetation of unitary stratum
2.1.7 Affecting genetic diversity As the fragmentation of habitat is going on, the survived secondary vegetation was often separated, surrounded and permeated by invading species that caused the vegetation further tattered and thus causing close breeding and genetic drift in some vegetations. Hybridization of some invasive species occurred with kindred species of the same genus, even with the plants of different genera, for example, the Canadian tall goldenrod (Solidago canadensis) was crossed to Aster ptarmicoides. The gene exchange between invading and native species resulted in genetic erosion in native species. Furthermore, related problems existed in recovery of vegetation through growing exotic species and native species in mixed manner, the latter which is a kindred of the former, as the inter-specific hybridization of the species between these genera has been reported (XIE Yan et al., unpublished). For examples, the Japanese larch (Larix kaempferi) was grown in Northern and Northeastern China, where the native larch (Larix) grows; and, in Hainan, Sonneratia apetala, which was originated from Bangladesh ,
It is worth noting that, the exotic invading species made lasting destroy of the environment and gave long term and sustained threats to the ecosystem, that were quite different from the destroy caused by human. When human stopped making contamination to certain environment, the contaminant would be decreased rapidly and the environment would be recovered gradually, while an entered exotic species wouldn't automatically disappear from the ecosystem once it entered, though it stopped entering later. Utilizing the opportunity of the dominancy that the entered species has already shaken off its original natural enemy, most of them would reproduce themselves and spread without restraint, i.e. the control the or elimination of them is often very difficult, while the native species which is once facing extinction due to the exclusion and competition, is irrecoverable from the damage. Accordingly, we should spare no efforts to attach enough importance to the threats from the exotic species on the biodiversity.

2.2 Impacts of exotic species on the society and culture
Through alteration in the natural ecosystem and the decrease of biodiversity in the invading habitat, the exotic invasive species brought about severe damage to local society and culture, even to the health of human. China is a country of multiple nationalities. The people of the nationalities live in compact communities as settlements and there are plenty of special resources of animals and plants and various specific ecosystems around there. The special natural resources and the specific ecosystem of their own communities played important role in the formation of the special culture and life style of various nationalities, especially those of Thai, Miao, Puyi Nationalities. However, the biological invasion was soundlessly weakening the foundation of national culture, the exotic invasive species was substituted for native plant resource because of the continuous competition of exotic invasive species, such as siam weed and crofton weed. For example, water hyacinth often covered the waters (river course, lake, reservoir and pond) that influenced the residents and livestock in utilization of the water, people was difficult to travel by waterway for participating in social events; large quantity of water hyacinth in waters provided nice surviving environment for pest insects, as mosquitos and flies that formed threats to the health of human; in some regions, water hyacinth even influenced public safety in community, because that the heavy coverage of plant provided natural conceal place for criminals

The exotic species can form direct threats to human health. The pollens of ragweed is one of the essential pathogens of allergy in human, which causes hey fever bringing about great world-wide damage to human in many countries. A special survey in 1993 in Shenyang, Liaoning province reported that the incidence of hey fever in population of Shenyang city reached as much as 1.25%, the syndromes of asallythma, sneeze, running water-like nasal mucus occur in pollination season in sensitive patients and the patients with specific sensitive and weak constitution died of other severe complications (XIA Fenfyun, 1983). As exotic animals, the Amazonian snail (Ampullaria gigas), is the intermediate host of zoonotic parasitic disease and the musk rat (Ondatra zibethicus) can spread hare fever that and brings about health problem for local residents. Besides, the mad cattle disease foot and mouth disease and acquired immunodeficiency syndrome(AIDS) are also known to all up to date that the existence of them greatly challenged the survival of human being and their pathogens were carried by exotic organisms or part of those carrier.

2.3 Economy
The exotic invading species can bring about direct and indirect damage to economy of human community. On the basis of a conservative estimate, an economic loss of several thousand billions of RMB per year was brought forth in China by exotic invading species.
2.3.1 The exotic invasive animals and plants turn into injurious animals and directly endanger the economic development in agriculture and forestry of China
The exotic invasive animals and plants can bring about direct economic damage to agronomy, horticulture, lawns, forests animal husbandry and aquaculture.

The loss of yields of whole developmental period of plant in 5 crops, rice, wheat, corn, sweet potato and lettuce, which were caused by exotic invasive species reached 45%, 36%, 19%, 63% and 47%, respectively (TAN Wanzhong, 1994). The toxin contained in Crofton weed can induce asthma in horse, which broke out in 1979 in 179 xiangs (governmental unit of rural area under xian) of 52 xians (county, governmental unit under province) in Yunnan province, killed 3486 of 5015 affected horses just within one year (some xians even turned into "horseless xian"); similarly, the population of cattle and sheep in those regions sharply decreased in size because that there has been no enough safe forage to be used in feeding (LIU Lunhui, l985). In Guangdong, Yunnan, Jiangsu, Zhejiang and Fujian and Shanghai , great quantity of budgets were costed for removing water hyacinth. The exact funds in removal of water hyacinth in Wenzhou city, Zhejiang and Putian city , Fujian in 1999 were 1000 and 500 million yuan of RMB, respectively, but the exact total costs for this task in China wasn't yet calculated at present, maybe at least over one billion RMB on the basis of estimation,. And, much greater economic loss in aspects of agricultural irrigation, cereal transportation, aquatic production and tourism was brought forth by the exotic water hyacinth. Vegetable leaf miner, a kind of exotic invasive insect, was firstly found in Hainan Island in 1993, but up to 1998, it had been found in 21 provinces and cities distributing on a total area of over 2000 mu (mu≈667m2). 110 species of 22 families of plant were parasitized by vegetable leaf miner and caused severe damage to its hosts, especially vegetables and melons including cucumber, musk melon, water melon, summer squash, tower gourd, tomato, hot pepper, egg plant, cow pea, kidney bean, pea and lentil. At present, the costs for controlling vegetable leaf miner were up to 4 billion yuan of RMB (WANG Fuxiang, 1997). The pinewood nematode disease, in the name of "pine cancer", which is caused by North American pinewood nematode, has spread over an epidemic-stricken area covering exceeding 100 million mu in China, and made tremendous threat to scenic spots as Huang Shan Mt.a and Zhang Jia Jie.

In international trade activity of China, the exotic specific always gave rise to problem or trade conflict among countries and thus turning into an important pretext or a means for applying sanction. In recent years, economic loss numbering millions upon millions of RMB in exports in wooden packing box for USA was brought about owing to that the harmful insect, asian longhorned beetle, was found in infested wooden box. This events made the state leaders to attach great importance to the problem of biological invasion.
2.3.2 The invasive alien species brought about loss in tourism in China through impact on the ecosystem in scenic spot.
In Kunming, Yunnan, province, an ideal tour route along Zhuantang of Daguanhe River-Dianchi Lake-West Mt. was established in 70s-80s and tourists can make the tour by boat starting from Kunming (dock is inside the city) for Dianchi and West Mt.. But, having no alternative it was closed since the early 90s because that the growth of water hyacinth in Daguanhe River and Dianchi Lake ran wildly without restraint that caused covering over the whole course of Daguanhe River .and part of Dianci Lake. AT present, the Daguanhe River has been remodeled into subterranean river.
2.3.3 The invasive alien species brought about a series of negative effects on water and soil and climate through change of ecosystem and thus bringing forth the indirect economic loss
Comparing with direct economic loss, the calculation of indirect economic loss was always very difficult in China, but it didn't represent that the indirect loss in economy was less. The indirect loss in economy remained tremendous. For examples, the dead water hyacinth in quantities deposited in the river bed of waters and was mixed with silts that made the river bed to be raised up and thus leading to gradual development of marsh in river course, pond and lake and then going into discarded. This conditions brought forth disadvantageous changes to environmental climate and natural landscape and intensified the drought and flood in local places. Moreover, due to that the living water hyacinth has the ability to absorb heavy metals and the deposited dead plants of the former on the river bed, which bore many poisonous matters including heavy metal, to form the secondary contamination to the waters, and , the contamination degree was once more intensified. Anyway, such a situation shouldn't allow to be ignored at all though those indirect loss in economy is difficult to be calculated precisely.
2.3.4 The economic value of exotic species itself
There is certain economic value in the exotic species, especially in the exotic plant. Water hyacinth itself has many utilities: the big beautiful inflorescence shows its ornamental value; its root system can absorb heavy metal ions, that can be used to purify water quality; containing certain nutrients, the plant biomass of the water hyacinth can be used as forage in raising livestock and domestic fowl; in addition, the water hyacinth can also be used in papermaking, producing marsh gas and manufacturing fertilizer; even so, the possible value in utilities of food, cosmetics and disposable tableware is assessed on trial basis. Someone attempted to transform and utilize the moisture content (95%) in plant biomass of water hyacinth into standard clean water through processing. Besides, the common cordgrass was utilized in papermaking and forage on trial.

However, the judgment of whether an exotic invasive species is useful or injurious should be formed according to giving the integrated consideration to the conditions: the place of occurrence, extent and time of the invasion, various advantages and disadvantages as well as the cost of control or utilization. For example, the water hyacinth could be used as ornamental plant and purifying plant of water quality, if the utility of it is under control, while it would bring about disaster if the introduction is out of the control without restraint. Actually, in most countries on the world (including China), the intensified introduction, reproduction and spread of water hyacinth in large scale without restraint was the principal reason resulting in the present situation of severe damage of the exotic invasive species, water hyacinth. As to the places where the growth of water hyacinth has turned into disaster, the local exact conditions and the economic factors should be fully considered for answering the question: whether utilizing or controlling? The scenic spot, Dianchi Lake of Yunnan, China could be taken as an example for explaining this problem. There was great divergence of opinions on the problem of water hyacinth. The people who held the point of view believed that the water hyacinth is a valuable biological resource in Kunming, and proposed to invest big fund in millions upon millions of RMB for developing the integrated utilization of water hyacinth. But they forgot that such a long term project requires supply of endless flow of raw materials and Dianchi isn't a possible raw material base; and, moreover, most major problem is that the returns on such an investment are unknown at all. Because there has been no lack of lesson in this aspect in world communities. Sudan had import technology and facilities for integrated utilization of water hyacinth, but failed owing to the small returns on great costs. In short, the best option of strategy taken for the control of water hyacinth in the lake, reservoir, river course and pond causing linked disaster areas, is that various measures should be immediately applied in order to inhibit the growth of water hyacinth at a level under the damage and achieve the sustainable success.

3 Pathway of exotic invading species in China

The entry of the most of exotic species relates to the human activities. The exotic species was introduced intentionally or unintentionally in China by the people, when external contact goes , but some entered in natural manner without relation or without significant relation with human activities.

3.1 Intentional introduction
The main purpose of introducing was for development of economy and conservation of environment. The introduction of fine plant variety has given important play to the promotion in development of various industries in agriculture and forestry in China, though artificial introduction of new variety also led to some ecological consequences. According to some calculated data up to 1970, 837 plant species under 267 families had been introduced into China, making 25-33% of the total of cultivated plants. Those plants were introduced from the flore of India-Malasia region, Central America (including Mexico) of Neotropical region, Siberia region of Europe, sub-region of Africa, coastal regions of North Atlantic Ocean, sub-region of Mediterranean Sea and Iran-Turkey region (XIE Xiaofu,1994). Besides, in recent 20 years, the number of entering exotic plant (including weeds) greatly increased as the exchange of external economy and science and technology was increasingly extended, but, so far, it is difficult to get accurate data and information concerning introduction of new variety at present owing to the lack of labor power and the difficulty in these works.

Among the known exotic injurious plants, more than 50% of them were originated from artificially introduced variety, the major route through which the damage is brought forth and the species were noted as follows: (XU Xiaogang et al.,1999; QIANG Sheng, 2000):

3.1.1 Herbage or forage:
Alligator weed, Trifolium spp., white sweet clover, Coromendel coast false mallow (Malvastrum colomendelianum), Timothy grass (Phleun pretense), carpet grass (Axonopus compressus), Ramose scouring rush (Equisetum ramosissimun), Brachiaria erucaeformis , caterpillar grass (Paspalum dilatatum), Pennisetum setosum , Setaria palmifolia , Sudan grass (Sorghum sudanensis), Lolium persicum , Lolium temulentum , Hordeum jubatum , water hyacinth and alfalfa (Medicago sativa).
3.1.2 Ornament plants:
Gomphrena celosioides, Agertum conyzoides, Mexican ageratum (Ageratum houstonianum), Coreopisis lanceolata, tinctorial coleopsis (Coleopsis tinctoria), lance coleopsis(Coleopsis lanceolata), Cosmos sulphureus, Helenium autumnale, Leucanthemum vulgare, Pyrethrum parthenifolium, marigold (Tegetus erecta), Tagets patula, Solidago canadensis, Silybum marianum, Zinnia peruviana, white-edge morning glory(Ipomoea nil), common morning glory (Ipomoea purpurea), common lantana (Lantana camara), four-o'clock (Milabilis jalapa), pink wood sorrel (Mimosa pudica) and Corym wood sorrel (Oxalis corymbosa).
3.1.3 Medicinal plants:
Sensitive plant-like senna (Cassia mimosoides), sickle senna (Cassia tora), Panicled fameflower (Talinum paniculatum), coffee senna (Cassia occidentalis), Phytolacca americana and Datura metal.
3.1.4 Vegetables:
Amaranthus caudatus, Amaranthus retroflexus, Chrysanthemum coronarium, Coriandrum sativum and erusalem artichoke?Cichorium intybus .
3.1.5 Lawn plants
Catepillar grass (Paspalum dlatatum), carpet grass (Axonopus compressas), Brachiaria mutica and Italian ryegrass (Lolium multiflorum) were introduced.
3.1.6 Environmental plant
Common cordgrass (Spartina anglica) was introduced for protecting shallows from soil erosion.
3.1.7 Exotic invasive species entered as animal protein-By consciously introduced exotic animal, the route through which the damage was brought about.
Amazonian snail (Ampullaria gigas) was introduced consciously for eating in Guangdong, Zhejiang, Fujian and Guangxi provinces, Southern China.
3.1.8 Aquaculture
Exotic fish, Ctenogobius cliffordpopel, and clay fish (Procambius clarkii) were introduced into Erhai Lake, Yunnan province and Shanghai, respectively, in earlier years (YAO Gendi et al., 1995).
Although a number of exotic insects of natural enemy were introduced into China for controlling pest insects or injurious weed, but there was no information on the damage caused by those natural enemy to be published.

It need to emphasized that the invasion by exotic species was often aggravated owing to the unscientific ideology in people. Some believed that "the foreigner is certainly better than the native", so, happened the blind introduction of new variety without paying consideration to analysis of actual conditions. For examples, in introduction of foreign grass variety for lawns in development of city construction, and introduction of exotic species in quantities without paying attention to utilization of native species for an agricultural policy-withdrawing crop cultivation from claimed forest land and prairie and returning forest and grassland, thus, probably caused increase of invasive species.

3.2 Unconscious entry alongside human activities
Unconscious entry of many invading species occurred in China alongside human activities. As international trade successively increased, external exchange continuously expanded and international tourism was rapidly warmed up in recent years, more and more exotic species entered China via various routes.
3.2.1 The exotic species entered China along with the means of transportation
Most of ragweed often occurred both sides of railway and highway and entered China alongside with the train from Korea (GUAN Guangqing et al., 1993); the brown rat (Rattus norvegicus) entered Xinjiang Uygur AR via railway from the interior of China too (ZHANG Damin et al., 1993). The ballast water carried nearly hundred exotic marine organisms into China, especially, the exotic red tide species aggravated the performance of phenomenon of red tide in coastal waters (LIANG Yubo, 2001).
3.2.2 The exotic species entered China along ESwith the imported international agricultural products and goods
Sorghum halepense entered into China in 70s-80s alongside the imported cereals of American countries. The North American pinewood nematode ( in name of "pine cancer") was detected and seized 59 times by Chinese Customs in July, 1999 in wooden packing box of imported mechanical and electrical equipment and electrical home appliances from Japan and U.S.A. and, in 2000, the same nematode was many times detected again from the wooden packing boxes of imported goods from U.S.A. and Japan; seeds of common and giant ragweeds；Sinoxylon conigerum was intercept and seized in 红檀木from Mozambique (XIA Youfu, 2001).
3.2.3 Carried alongside the introduction of animal and plant species or cultivated varieties
Darnel ryegrass (Lolium temulentum) entered China alongside the introduction of new variety in wheat, the seeds of this plant is very similar to that of wheat in morphology is and easy to be mixed in introduced wheat.
3.2.4 Carried by tourist
Many times two fruit flies Ceratitis capitata and, Dacus dorsalis were seized in carried fruits by tourists; the Hoary Plantain , Plantago virginica (Plantaginaceae) might be stuck on tourists' luggage, via which the exotic plant entered China.
It is necessary to indicated that some invasive specie, whose entries weren't just via unique route, might enter twice, even more or through multiple routes, and thereby causes the permanent planting and the spread of invading species.

3.3 Entry via natural conditions other than those above-mentioned
The exotic invasive species might enter China by wind power and waters in natural manner. The seeds of weeds were also carried by birds, for example, the Crofton weed crossed over Sino-Burma or Sino-Vietnam borders and spread in natural manner (LIU Lunhui and XIE Shouchang, 1985). South American climber might be the exotic invasive species which entered Guangdong, China via air current; American rice water weevil might enter Chinese continent in the way of migratory flight by means of air current.

4 The spread mechanism in exotic invading species in China

4.1 The processes of spread of exotic invading Species
In general, the course of spread in exotic species is divided into entering, permanent planting (reproduction) and spread stages. But more detailed division mode has been designed and used: introduction, climatization (naturalization), facilitation, time-lag , spread. interacting with native organisms and stable stages (Williamson, 1996; Cock, 1998; Edward et al., 1998). Although some authors suggested that there existed so called "time lag stage'', the period of the occurrence of time lag stage remained uncertain: some authors believed that there exists time lag stage between introduction and permanent planting (reproduction), while another authors believed that the time lag stage exists in the period between permanent planting phase and spread stage. In fact, each invading organism has its own property of invasion, and differs each other in the length of their spread courses. That means that it is impossible to assure a definitive mode for demonstrating every individual invading species.

Introduction stage: The exotic species just enters a new region, doesn't set up enough size of population for permanent planting or growing that take shorter time in general. If artificial or mechanical measures are applied for controlling the exotic species during this stage, the invader would be eliminated thoroughly-it is the best time for preventing the environment from invasion and for controlling the invasive organisms.

Permanent planting (reproduction) stage: After being adapted to the local climate and environment for a certain period of time, a certain size of population of the exotic invasive organism is set up, the exotic invader begins to undergo climatization or naturalized, and turns into native species. During this stage, the artificial and mechanical measures can still be applied for effective controlling the spread of exotic species, it can yet be regarded as an ideal time for control.

Time lag stage: some exotic species doesn't immediately spread in large scale and runs invading, but appears in static manner. For example, the South American climber entered Guangdong, China in early 80s, last century but initiated to form damage until recent 2 or 3 years. The stagnant stage of this invading plant lasted for almost 20 years (HUANG Zhongliang et al., 2000), the exotic species didn't form "burst" situation though it maintained the population at a level of certain size in certain period of time and in a certain region. This related to the properties of both its own reproduction and climate. If there exists the condition of longer periods of time required for seed production and sexual reproduction cycle and the period of more longer climate cycle, which is available to seed germination, the stagnant stage would last much longer. Generally, the stagnant stage in herbs is shorter than that in woody plants. The stagnant stage is the transition period indicating that whether the exotic species would bring about heavy damage or not. So, to develop effective controlling work during the stagnant stage can still play the role in prevention in environment from the heavy damage brought about by exotic species. Otherwise, the unavoidable damage would come up at last if the final option of an available opportunity of effective control over invading species in the stagnant stage of the population development is missed.

Spread stage: During this stage, the expansion of the population size is unavoidable because that, being adapted to the local climate and environment and forming strong competition system with native species, the exotic species forms its own reproduction system. And, owing to that the seeds of the invasive species develop into ripening stage and spread in quantities without restraint by means of external dispersion condition, thus forming "ecological burst". Under this situation, adoption of any measures for control is difficult to achieve success in effective control within short term implementation. Moreover, if unavailable control measure is adopted (artificial measures under unavailable guide), these measures would further promote the wild spreading and expansion of the invading species, instead of going down. The unique way leading to success in control is to adopt integrated measure: setting up the long term aim of project, adopting the integrated measure with the biological control as major measure (recovering the effect of natural enemy and attaching importance to it) and supplemented with chemical, mechanical and species-substitution measures.

4.2 The main factors promoting the spread and expansion of invading species
After introduction , the exotic invading species begins permanent planting (reproduction) and forms population in a certain size under certain density of individual, suitable temperature, humidity, height above sea level, soil, moisture, nutrition, and environmental conditions and spreads through human activities or by means of natural forces. So, the main factors that promote the spread and expansion of the exotic invasive species are as follows:
4.2.1 Characteristics of high reproduction, ecological adaptation and competition of invading species itself:
For example, in plants, water hyacinth has both sexual and asexual reproduction modes. In aspect of sexual reproduction, there are 300-500 seeds to be produced in one inflorescence and the dormancy of the seed in water can reaches a length of 15-20 years; on the other hand, this species can reproduce itself through asexual way by growing creeper of the plant, a new plant can be formed by growing the creeper under the temperature 30 oC for 5 days. It has also high ecological adaptation- can be adapted to many habitats, the reservoir, lake, pond, irrigation channel and ditches, and river with slow current velocity are the most suitable habitats for this plant. It often occurs and grows vigorously in rice fields and becomes pest and can also grow and reproduce itself in marshes and other low and humid places (Waterhouse, 1994).

As for example in animals, Loblolly pine mealybug (Auracella acuta) possesses very high ecological adaptation too. Although a report of a survey on the ecological adaptation and analyses of climate and geology indicated that the most suitable habitats were those located in the Yangtze River Valley but it rapidly spread since invaded in Guangdong in 1988. It can endure low temperature under 20 oC in winter (PANG Xiongfei et al., 1994).
4.2.2 Suitable climate and environmental conditions of entry region:
Water hyacinth could grow in southern part of Yangtze River Valley , the freezing will cause death of the plant in the south but in some regions, only the leaves are affected by freezing and the base part of the plant remained keeping green- not yet died, while in northern China, this plant was difficult to survive through the winter. According to the results of research, it was known that the requirements of nutrient and pH value for the growth of water hyacinth are not so high but the salt content exceeding 0.06% in water will cause the death of the plant. The most suitable conditions for growth are: pH 7.0; phosphorus content, 20 ppm; enough nitrogen; and temperature 28-30 oC. So, since eighties of 20th century, along with the up-speeding industralization course speeding up and leading to ultrophication in the waters of the Southern of China, the water hyacinth grew up more and more vigorously.
4.2.3 Human activities whetted the expansion of population size of exotic invasive species
A country-wide policy of "planting three aquatic plants" was put forward during 50s-60s of 20th century by Chinese government, the water hyacinth, alligator weed and water lettuce (Pistia stratiotes)were introduced and grown all around China in succession (in provinces, xians and xiang). Moreover, great efforts were made to promote the high production of those "three aquatic plants", and thus leading to the artificial spread of water hyacinth (DING Jianqing et al., 1995).

As to invasive animal species, loblolly pine mealybug could spread by means of various way, and enter the new forest region through transportation of nursery stock, scion or cone, the young larva of that mealybug could even enter into human body or attached on animal's body. It was found that the vehicles could serve the fast carrier for this pest insect.
4.2.4 Natural spreading force
In Southern China, the network of rivers, which extends in all directions, is the important route for the spread of water hyacinth; the loblolly pine mealybug could be spread by wind; the seeds of a lot of weed species. Foe examples, ragweed and South American climber, could be carried by wind for distant spread.
4.2.5 Lack of natural control in invaded region
In China, little of natural enemy of water hyacinth has been found at present, only a kind of snail and lepidopteron and few pathogenic bacteria are found as the enemy of water hyacinth, while in South America, the native place of the water hyacinth, there are more than 200 species of insect eating water hyacinth there, this is one of the important reasons that why the water hyacinth didn't cause damage in South America so far but formed damage in China since entered (Waterhouse, 1994). For example of invasive species, in the native area of Loblolly pine mealybug, the number of the species, which eats loblolly pine mealybug is as many as over 30 species, and some parasitic bee are effective in controlling loblolly pine mealybug too, while in China, almost little is the natural enemy which can effect on loblolly pine mealybug in controlling increasing population size and spread of the mealybug (PANG Xiong et al., 1994). One of the important reasons is that those crops lack their own resistance mechanism against the pest insect (ZHANG Runjie and HE Xinfeng, 1997).

4.3 Regions where are easy to be invaded by exotic species
Depending on the entry route of exotic species and the own property of the invasive species, the population of exotic species was easy to burst and becomes invading species making severe damage in some places or habitats (Elton, 1958; Fox and Fox, 1986; Simberloff, 1997):
4.3.1 Important harbor, place nearby port, both sides of railway and highway. The exotic species which were carried via international freight transport, often landed firstly at the harbor and were transmitted to a place nearby the port and created their population in small size as the environmental conditions were suitable, and then began to spread; Those species carried by train and bus were easy to settle down and spread on both sides of railway or highway;
4.3.2 The forests and grasslands where the artificial interfere were severe. The human activity could directly bring about exotic species, that the severe artificial interfere (cutting down trees in forest in a wholly irresponsible way and excessive grazing) led to degeneration of ecosystem and reduction of biodiversity that favored invasion of exotic species;
4.3.3 The island, waters and pasture-land where the biodiversity was lower and the habitat was in simpler construction. Because that the lower biodiversity, lower natural inhibition and the less natural enemy, the exotic species would be easy to survive as well as its population size easy to be expanded.
4.3.4 Habitats destroyed by sudden natural interfere, such as fire or conflagration and flood. In these habitats where the ecosystem were destroyed in short period of time and the species composition and the population structure became simpler, the exotic species was very easy to occupy a large number of ecological site and thus turned into dominant species in the habit.

5 Measures for controlling exotic invasive species

5.1 Artificial control:
The artificial preventive and control measures are suitable to be used in solving the problem of those invasive species which just enters and settles and not yet spread in large area. Due to that China is a country rich in labor resource that can withstand the expense of labor power, the above- mentioned measures could effect in elimination of injurious organisms rapidly in a shorter period of time except the plant seeds sunk in the water and laid in the soil and some injurious animals; the injurious plants with high reproducibility are easy to adventitiously grow up again and to run additional spread, these need control year after year. The remains of injurious plants and animals (body, eggs and plant) after implementation of artificial control should be handled correctly, otherwise they will turn into new resource for spread and objectively speeds up the spreading of exotic organism.

5.2 Mechanical or physical control and removal
Specifically designed mechanical facilities and instruments were used in controlling injurious plants on the world. They are safe to environment and can eliminate the exotic plants in a certain extent in short period of time. Utilization of mechanical salvage boat for removing water hyacinth and other aquatic weeds in Victoria Lake in Africa succeeded in the controlling to certain degree. In China, a salvage boat was specifically designed and manufactured for removing water hyacinth in Dianzhi Lake (nearby Kunming, Yunnan) and a mower was designed and manufactured in Jiande district, Fujian for controlling common cordgrass, but both of them failed in operation at last because of technique reasons. As for the problem in aspect of mechanical control itself, it needs to note that the remains of the injurious plants after realizing mechanical removal must be cleaned out of the habitats otherwise the remains would turn into a new resource of spread of invading plant. Various kinds of other physical control measures could be used in control of exotic injurious organisms, such as destroying by fire in cleaning up injurious plants, trapping pest insects by black light lamp, etc (DING Jianqing et al., 2000).

5.3 Replacing control for exotic invasive species
This method is an ecological control measure mainly used for controlling exotic plants. The essence of it is that the native plant which is of ecological and economic value is utilized as substitute for exotic invading plant on the basis of evolution law in the population of plant itself. The superiority of it consists in :
5.3.1 Once the substitute plant was planted permanently, the exotic invasive species would be controlled for long period of time;
5.3.2 The substitute could conserves the water and soil from erosion and improve the soil, holds the water source and improves environmental quality;
5.3.3 The substitute could provide direct economic value and return planting costs in short period of time as well as the long term benefits;
5.3.4 The substitute could improve the wasted land and turn into the land of economic value and utilization ratio of land might be raised.
The shortcoming of substitution control rests with the high requirement of environment for growing the substitute plant. Many habitats, such as steep mountain slop and waters, aren't suitable to artificial growing of plants; in the mean time, artificial planting native plants for the purpose of recovery of natural eco-environment involves many ecological factors, that forms barrier to actual implementation of growing of substitute plant. Therefore, the investigation on the substitute plants for exotic injurious plants should focus on the ecological property of local native plants: as the competence capability and the allelo-interaction of native plant with the invading plant and the technological essences of the reproduction and cultivation of the substitute plants. Besides, in order to obtain the benefits of economy and ecology, the economic property and market potential of native plant should also be considered. In a cooperation activity of Shenyang University of Agriculture and Administration Bureau of Expressway of Liaoning Province in1989 and 1990, a demonstration region in substitution control for invading ragweed along both sides of the Shen-Da and Shen-Tao expressway was set up and the substitute plants of economic value, including false indigo (Amorpha fruticosa), Hippophae ramnoides), (Poa annua), Coronilla varia , and Chinese artichoke (Helianthus tuberosus) used in control program as substitutes for invading species, ragweed, were cultivated on an area of 3000 mu of the land in demonstration region. Since then, as a result of substiutution control measure, the biomass of invading ragweed in demonstration region decreased from 30 kg/m2 to 0.2 kg/m2.. Those substitute plant also provided great economic benefits in management of forage, green manure, food, medicine, straw weaving, energy and raw materials for chemical industry(GUAN Guangqing et al., 1993).

5.4 Chemical control
The pesticide, or insecticide, is characteristic of fast effect, convenience in applying and popularizing in large extent. However, there are shortcomings as followed:

1) When the insecticide is applied for eliminating exotic organisms, it often kills many native species spontaneously; 2) Much more costs in general when applying insecticide, especially to the large area of mountains and forests and that of ecological environments of lower value, as grassland; and, moreover, 3) To some special environment, such as reservoir, Lake, there is legality-based ban being placed on the application of insecticide (Schroeder,1992).

In addition, as to many species of perennial exotic weeds, the most of the herbicides can only eliminate the upper part of the plant, and the underground part is difficult to be killed, it means the effect of herbicide is not sustainable, though it is used successively

In practice in China, glyphosate and (2,4-D) were referred to systemic herbicide which could be absorbed by weed itself and transferred to other part and effect on whole plant. So, these herbicides were available to be applied to perennial plants but functioned slowly. The contact herbicide, as paraquat and nitrofene, effecting only on the contacting part of plant, it often effected on upper part of the plant and failed to effect on the underground part. So, it is proved suitable to be applied to annual weeds because of its rapid effecting property though it wasn't absorbed and transferred to other part. Due to that many exotic invading plants were referred to perennial plants, the effects of systemic herbicides could be sustained for more longer period of time when applying.

The other chemicals used in control of exotic invading species than above mentioned herbicides, are the chemical insecticide consisting of contact, stomach and taxis insecticides as well as plant hormones and growth regulators which were generally used as agricultural chemicals. Because of that the application of these agricultural chemicals did induce the much stronger drug-resistance of the exotic invading pests, different agricultural chemicals should be applied alternately in an appropriate interval of time or in rotation.

5.5 Biological control
The biological control of invasive alien species means that to introduce natural enemy of the exotic species, which has specific host range and is originated from the native area of exotic species, in order to control the density of population at a level under ecological and economic damage of environment on the basis of ecological balance theory between exotic injurious organisms and its natural enemy. In entering region of exotic organisms, the mechanism of regulation and restraint on each other between exotic injurious organisms and its enemy is re-set up for recovering and holding this ecological balance. So, the biological control of exotic species can result in conservation of biodiversity by utilization of biodiversity (DING Jianqing and FU Weidong, 1996). The general working process consists of: (1) Survey on exotic species and its natural enemy in their native place, collection of natural enemy, assessment of the safety of natural enemy; (2) Involvement of researches related to quarantine, bio-ecological property of natural enemy; (3) Release of natural enemy and evaluation of its effects. Once the population of natural enemy of invading injurious organisms is set up in new habitat, the natural enemy will perform the control of exotic invading organisms through the reproduction and spread of itself automatically and thus realizing long term control of the exotic injurious organisms. That is to say that the biological control measure possesses superiority of sustainable effect of control and relatively low costs (Harley and Formo, 1992).

In general, the duration from the release of natural enemy till the success in obvious effects of control will take several years or more. Accordingly, it is difficult to practise biological control measure which give full play to the thorough elimination of invading organisms in a shorter period of time. The practice of biological control of weeds will easily give rise to conflict of interests owing to the different understanding of the weeds, brought about by views from different angles (DING Jianqing and WAN Fanghao, 1992). Besides, there is certain ecological risks exist in the introduction of natural enemy in control of exotic injurious organism. Careful and scientific analysis of the risk in introduction of natural enemy is necessary before releasing, the introduced natural enemy probably turns into a new exotic invasive organism, resulting in the consequence " bringing a wolf into the house".

The biological control of weeds has had a long history of more than 100 hundred years on the world, when it succeeded in control of weeds, also faced new challenge in the safety of natural enemy organism. For example, the insect , Cactoblastid cactorum which had been introduced into Australia, South Africa and Hawaii as natural enemy for controlling the local weeds, cactus (Opuntia spp.) and achieved success. But after than, till 1989, the aforesaid natural enemy insect of cactus turned into one of severe pests in Florida, U.S.A., threatening local horticultural cactus (Simberloff, 1996). In 1993, an convention "International convention about administration of introduction of natural enemy for biological control" was issued by FAO, UN to standardize the introduction of natural enemy. At present, before the natural enemy is released, which is used for controlling injurious plants, the evaluation of safety of natural enemy is to be examined consisting of selective and non-selective examination methods. The tested plant species for analysis of risk consist of: 1) representative species which is referred to the same genus and family or kindred family of the objective plant in taxonomy; 2) The local representative species of economic and decorative value; 3) local endangered species; and 4) The species similar to the objective species in morphology and phenology.

5.6 Integrated control
The integrated control measure is to fuse the individual techniques, as biological, chemical, mechanical, artificial and substitute measures together to give full play to their own superiorities and to remedy their own shortcomings thus attaining the goal of integrated control of invasive organisms. The integrated control is not the simple addition of various techniques but the fusion of them. Various techniques coordinate and promote themselves each other. For example, The utilization of integrated measures of biological and chemical measures for controlling invading plants shows the following characteristics:
5.6.1 Fast efficiency. In the early period of implementation in the region where the injurious plants should be urgently removed, a certain dose of definite herbicide will be used selectively in order to rapidly inhibit the spread of injurious plant and its population within a short period of time and thus speeding up control rate;
5.6.2 Sustainment. Owing to that the herbicides can only give rise to short term control effect, it is difficult to keep up the sustainable effects, so, it is necessary to release a certain number of selected natural enemy which specifically eat objective injurious plants and bring forth a long term reproduction of itself, then, population is set up that results in gradual dynamic balance between the population of species and that of its natural enemy and succeeds in sustainable control finally;
5.6.3 Safety. As compared with the measure of applying single herbicide, the integrated control measure requires more strict limitation to the variety, concentration, dose, and times of applying chemical herbicides. For the safety of other organisms, the applying concentration dose, and times of applying selected herbicide are greatly lower than the routine. So, higher level of safety in integrated control measure is easy to attain and thereby brings about little influence on the environment;
5.6.4 Economy. The biological control measure is the cord of the integrated control system. In practice, the former, after the natural enemy is released, it can reproduce itself automatically and set up population until a definite quantity attained, and, no more labor power will be invested for proliferation of it, i.e. the integrated control measure has the superiority that once investment for long term return with relatively lower costs (DING Jianqing, 1995).

6 Countermeasures

6.1 Legislation and countermeasure of administration
No law or regulations, which is aimed at the exotic species, has been worked out in past in China. So. Law of prevention from invasion of exotic organisms and regulations of administration of invading organisms should be worked out rapidly on the basis of legality. Because the exotic invading organisms threaten the community in various respects, a unified administration and coordinate commission involving the departments of agriculture, forestry, environmental conservation, marine, trade, quarantine, public health, national defence, administration of justice, education and scientific research should be set up to realizing the unified administration of exotic invasive species on whole at the level of national interests instead of one or several departments.

Give full consideration to every link in the course of the entry of invasive species and relevant legal regulations of countermeasure which aim at individual entering routes should be worked out. Especially, the relevant regulations aiming at the introduction of organisms including animals, plants, microorganisms and transgenic animals and plants (genetic modified organisms), traffic transportation, international trade goods and tourism should be put under the strengthened supervision on the basis of legality For example, when a plant is introduced, the purpose of introduction, species of introduced plant, place where the introduced plant comes from, planned planting area as well as the possible region of spread, all of these should be put under strengthened supervision; When insect is introduced for biological control of injurious organism or for pollination , the purpose of introduction, quantity, releasing region and the assessment report of risk analysis should be put under strict examination too.

Either the native species should be protected from the damage brought about by introduced insect and the introduced insect itself should be protected from turning into a new injurious insects. Therefore, a definite and detailed regulations should be worked out at least including:

1) Application for introduction should be submitted by introducer (Report of feasibility analysis before application);
2) The application for introduction is reviewed and demonstrated by the department of administration (Joint Committee of Specialist); Approved or Rejected;
3) Supervision in the course of introducing;
4) Quarantine, planting on trial basis, supervision and analysis and evaluation after introduction;
5) Introducer submits application for release or spread;
6) The application for release is reviewed and demonstrated by the department of administration (Joint Committee of Specialist): Approved or Rejected; and
7) Identification of medium- and long term assessment after release.

6.2 Countermeasures in public involvement and education
The protection of environment from invading organism needs joint efforts devoted by whole society, the public enthusiasm should be fully aroused, awareness of whole society in protection of environment should be enhanced thus encouraging whole society participating in the action of protecting environment from invasion caused by invasive organisms. The activities are as follows:
6.2.1 to educate the public to understand the harmfulness of biological invasion through doing propaganda by means of broadcast, television, newspaper and web.
6.2.2 To work out specified propaganda strategy, as, printing, publishing and releasing popular science article, brochure and pamphlet on biological invasion or audiovisual works in quantities; to provide concerned information for tourists and propose action to demonstrate the relation between tourism of human and biological invasion in order to protect the scenic area from new invading species being carried by tourists.
6.2.3 Specific propaganda, education and training should be conducted for the employed of key professions related to quarantine, biological introduction, traffic and transportation, international trade and tourism.
6.2.4 To strengthen awareness of defense against invading species and enhance the vigilance of occurrence of biological invasion in the employed who is working in the regions of natural reserves where the invasive organisms are easy to enter in.

6.3 Counter measures of utilization - To transform the wasted materials into things of value
After scientific analysis and demonstration of cost/benefit, some economic properties of invading organisms can be effectively utilized and the invasive organism is then to be changed into things of value. But, during this course, new artificial spread of invading organism must be strictly prohibited.

6.4 Countermeasure of prevention
6.4.1 Introduction of new organism should be carefully implemented
Before introduction, fully scientific assessment, forecast and examination on the introduction should be completed. Either the consideration to the present situation or the forecast for the future; either the economic benefit or the ecological damage; either the local or the countrywide problems should be kept in mint at all. And, the observation on the introduced organism should be strengthened after entry, continuous tracing is necessary after releasing. When problem happens, the effective countermeasure must be implemented immediately in order to prevent the environment from the damage in large area.
6.4.2 The quarantine and interception of the border Customs should be further stressed to stop the new invading organism entering
Close inspection at various transportation means entering China, such as trains, automobiles, ships and the luggage carried by tourists, should be further strengthened to prevent the unconscious entry of exotic organisms.

6.5 countermeasure of control and recovery
As for the entered exotic species which has caused damage, the countermeasure of rapid control should be adopted immediately (Techniques are mentioned above). After the invasive species being eliminated, regular inspection should be practiced in the original region where the invading species occurred, and the problem should be handled in time to prevent the re-entry of invading species. In addition, the fast-growing native plants are available to the naked land where the invading species has been eliminated already, that make the original natural figure of the native flore and ecosystem to be recovered from the initial damage.

6.6 Countermeasure of scientific research
Strengthening the researches on biological invasion is the key for resolving the problem of biological invasion in China at present, including the researches on clearing and defining the invading species, its distribution, and mechanism of invasion, the research on evaluation of the ecological damage brought about by invading species as well as the research on countermeasure of control.

6.7 Countermeasure of information exchange
Presently, there are quantities of information in biological invasion in China but fail to get effective exchange of themselves. The establishment of State information center on biological invasion and information bank and the effective utilization of INTERNET and LAN (local area net) will greatly strengthen the information exchange and are of great importance in prevention and control of biological invasion

Appendix

Main representatives of invasive species-
(Taxonomy, Figures and biological description; Native place, Distribution in China; Prolems; Control)

1 Exotic invading plants
Water hyacinth (Eichhomia crassipes)
Water hyacinth belongs to the family Pontederiaceae It is a perennial aquatic plant, a floating herb or with root system in the mud of waters bed. Very short stem with long stolon which can form a new plant after removing off from the maternal plant. The leaf grows in rosette phyllotaxy, leaf blade in oval, obovate and kidney-like round shapes, specular; the base part of petiol shows a little vinaceous color, and is enlarged to form air sac in cucurbit shape. Flower vinaceous, the upper one is larger than the others, yellow dots are shown on the middle flower. The upper part above the water level of the whole plant reaches more than 1 m in length in water hyacinth, there are two reproduction mode, sexual and asexual, and the asexual mode is the major one. The plant mass of water hyacinth can be doubled within 5 days through the asexual reproduction mode depending upon the stolon being separated off from maternal plant. An inflorescence of water hyacinth can produce around 300 seeds which can survive for 5-20 years when deposited on the river bed and under the most favorable condition (Forma and Wright, 1981).

Water hyacinth grows in various habitats and the reservoir, lake, pond, irrigation channel and ditch and river course in slow current velocity are the most suitable habitats. It often occurs in rice field and turns into injurious herb, in addition, in marsh and other humid places, water hyacinth can grows and reproduce too. The growth of water hyacinth requires not so high nutrition and pH value, but it would die if the content of salt in water is over 0.06% . The optimum growth conditions are pH 7.0, phosphorus content, 20 ppm, enough nitrogen and optimum temperature, 28-30 oC. Freezing can cause the death of water hyacinth. But in some regions of China, only the leaves were affected by freezing, the base part remained keeping green and didn't die, so, it could survive through winter there smoothly (Waterhouse, 1994).

Water ,hyacinth originates from South America. It was introduced into the mainland of China in 30s of 20th century as forage for domestic animal and fowl, and had been popularized as ornamental plant and decontaminating plant for purifying water quality, and then escaped and spread out of the introducing regions later and turned into wild-grown exotic plant. Because of the very high rate of asexual reproduction,water hyacinth now widely distributes in areas of 17 provinces and cities in North, East, Central and South China; especially in Kunming, Yunnan, Jiangsu, Zhejiang, Fujian, Sichuan, Hunan and Hubei provs. and the southern part of Henan province, the situation of invasion of water hyacinth is severe at present (DING, Jianqing et al., 1995). In those regions, water hyacinth mainly distributed in river, lake and pond, always formed unique dominant population and excluded native aquatic plant in those waters, on which the local aquatic animals rely for survival in the same waters. In Dianchi Lake, a high land lake located by Kunming city,Yunnan, on which Kunming city and its citizen rely for existence, water hyacinth covered over near 1000 hectares of the waters at a coverage near 100%. Owing to the contamination of water quality and thus causing fast-growth of water hyacinth, many aquatic organisms were on the verge of extinction. A reference paper noted that there were 16 species of aquatic plant and 68 species of aquatic animal in Dianchi Lake before 60s, 20th century, and, till 80s, the most of aquatic organisms were successively eliminated -only 30 odd species left. Artificial removing is the major measure for control. In 1995, natural enemy insects specifically eating water hyacinth, Neochetina eichhormiae and N. bruchi were introduced into China by the Institute of Biological Control, Chinese Academy of Agricultural Sciences (CAAS) from U.S.A. and Argentine, and were released in Zhejiang and Fujian provs. The release attained preliminary success in effect of control (DING Jianqing et al., 1998b; DING Jianqing et al., 2001); Utilization of chemical herbicides, glyphosate, Round upand paraquat, achieved success in controlling water hyacinth in shorter period of time (DING Jianqing et al., 1998a), coordinative utilization of chemical measure (herbicide) and biological measure (natural enemy) in control of water hyacinth also achieved success in advancement of research in this aspect (DING Jianqing et al., 1999). However, in short, the control of water hyacinth in China, lacks united scientific technological guide, in most of invaded regions, actually, as the growth rate of water hyacinth exceeded the efficiency of control, ideal effect of control isn't come yet.

South American climber (Mikania micrantha)
South American climber belongs to the genus Mikanas under the family Compositae and is a perennial herbaceous or slight woody vine. Stem slender and long, prostrate or climbing, multiple-branched; leaf on the middle part of stem in triangle oval to oval shape, leaf on the base part in heart shape; White flower,head inflorescence. Both asexual and sexual reproduction modes. The stem node and internode can generate roots and the leaf axil of each node can generate a pair of new branch forming new plants, so, the another name for south American climber in English is "one mile takes one minute", symbolizing the fast growth and spread of it. In Guangdong, China, South American climber was often found at the border of destroyed forest, wasted agricultural land, roadside, orchard neglecting to take reasonable administration, reservoir and both sides of irrigation channel and ditch etc.It favored the habitat which has porous soil rich in organic matters and sunshine (HUANG Zhongliang et al., 2000).

South American climber originates from Central America, and is widely spread over the Asian tropical regions including India, Malaysia, Thailand, Indonesia, Nepal, Philippine, and Papua New Guinea, Solomon Island, Christmas Island on Indian Ocean and some islands on the Pacific, including Fiji and West Samoa, and Queensland of Australia. As an exotic weed, South American climber occurred in Hong Kong early in 1919, found in Shenzhen, China in 1984, and was widely distributed in Hong Kong and the regions of the delta of the Pearls River. This plant is a vine plant of super reproducibility and fond of climbing, once climbing on shrub of arbor, it will soon cover over the whole shrub or arbor tree which stifled to death owing to the lack of photosynthesis. Besides, South American climber also can produce allelopathic substanceto inhibit the growth of other plants and brings forth damage to almost all the species of the natural secondary forest, artificial fast-growing forest, economic forest and Scenic forest whose height are below 6-8 m, especially that to some secondary forest and scenic forest, it will cause the most severe damage of invaded plant- died of withered in large scale. Since 90s of 20th century, South American climber spread from southeast Asia to Hong Kong and the region of whole delta of the Pearls River. An area of 80% of the range (7000 mu) of Nei Lingding Island National Nature Reserve Area suffered the damage brought about by South American climber, and in a 7000-mu Area, 1200 mu of it suffered the most severe damage of disaster which was caused by .the invading South American climber. In this Nature Reserve Area, where the key conservative animals including more than 600 rhesus monkeys, pangolins and pythons lives, the plants, such as banana, litchi, longan (Euphoria longana), wild citrus and some shrub and arbor were covered by South American climber in large scale. The affected plants were difficult to run normal photosynthesis and their existing environment was undergoing great destruction endangering the survival of rhesus monkey, mangrove and birds. If no emergency measure is adopted, not only the state key conservative animals, as rhesus monkey etc are threatened with extinction but the natures reserve area at national level is also facing the danger of destruction. In recent two years, many times of artificial control measure -removing by labor power- was adopted and implemented in Guangdong province (Shenzhen and Zhuhai Cities) but produced very little effect. At present, the trials on chemical control and survey on the population of natural enemy of south American climber are proceeding.

2 Exotic pest insects
Fall web worm (Hyphantria cunea)
American white moth , or fall web moth, belongs to the family Arctiidae under the order Lepidoptera. White Adult, body length 12-15 mm, wing expansion, 25-28 mm.. Several brown dot on fore-wing. Antanna of carcharodont type in female moth, candodous fore-wing. Spherical egg, light green in early development and brownish before hatched. Egg laid on the back of the leaf blade forming irregular egg mass, 300 odd eggs per mass. The body color of larva varies greatly, two kinds of larva, red-headed and black-headed types, depending on the color of head. dark fusco-rufous pupa in long spindle shape, brown or red cocoon constituting of loose silks confounded with the body hairs of young larva (FANG Chenglai, 1985).

American white moth hibernates beneath the bark of tree or hidden inside the litter on the ground to survive through the winter, young larvas fusule and make web after hatched. The larvas gather inside the web and eat leaf blade, after the leaf blade is eaten to the end, young larvas move to another part of branch crotchet or tender branch and make another new web. The 1- 4 instar larva makes web causing damage to plant, web in milky yellow color can be made as big as 50 cm in size. Leaving the web after 5th instar, the larva continues to injure the plant and even comes to the stage of violent eating. American white moth begets two generations of offspring a year in the areas in Lioaning province.

American white moth is an important object of international quarantine in plant. It originates from North America, entered Europe in 1940, Japan in 1945, Korea in 1958, the areas of Dandong city, Liaoning, China in 1979 and was found in Shaanxi province in 1984. And, now, it spread and causes severe damage in Liaoning, Hebei, Shandong, Shaanxi and Tianjin city and it is the matter of cause that American white moth will probably invade Beijing in recent days. This invasiveding species is believed one of the most dangerous invading pest insects causing disaster of destruction in agriculture and forestry. It can injure more than 200 species of agricultural and forest plant including mulberry, tree of heaven (Ailanthus altissima), Fraxinus chinensis, elm, hawthorn, apple, pear, cherry, willow, apricot, paulownia (Paulownia fotunei), grape, poplar, Chinese toon (Toona sinensis), plum, Chinese scholartree, peach, potato, sunflower, strawberry, chive ( Allium tuberosum), Corn, Cucumber, egg plant, persimmon, black date(黑枣), soybean, cabbage, towel gourd, castor-oil plant, Chinese ilex. pumpkin, peanut, hot pepper, Chinese cabbage, muskmelon, tobacco, summer squash, bluish dogban (Apocynum venetum), hemp, sesame, datura, carrot, tomato and cotton. This moth has strong reproducibility and spread rapidly that it can spread by a rate of 30-50 km a year in radiate manner. Chinese Governments at all level attach the most to it. Early in 1981, the Office of the State Council of China had transmitted a notice on strengthening the works of quarantine and control or American white moth made by Chinese Ministry of Agriculture and Forestry; In 1984, the State Council of China and Central Military Commission jointly issued a urgent notice on "rapid elimination of American white moth in the areas of Shaanxi", and the governmental leading groups for controlling American white moth at all levels were set up, importance in which leaders of local governments at various levels participated. As American white moth was found in Tianjin city in 1995, the "Headquarter of strict control of America white moth " was set up in Beijing to prevent this moth entering Beijing. In Xi'an and Xianyang cities, Shaaxi and Jingzhou city, Liaoning, application of artificial mechanical and chemical measures for controlling American white moth achieved success in controlling. In practice. The adult moths were trapped and killed by using black light lamp; in addition,artificially cutting off web; digging out pupas in autumn and winter by labor power; spraying chemical and biological insecticides, deltamethrin and Diflubenzuronwere also realized in previous invaded regions in China.

Vegetable leaf miner (Liriomyza sativa)
Vegetable miner (Liriomyza sativa Blanchard) belongs to the family Agromyzidae under the order Diptera. It has small conformation in adult, yellow head and black posterior orbit; Mesonotun, black and specular, most part of mesopleura, yellow; light brown bilateral mottling on yellow feet; wing length, 1.3-1.7 mm; white egg, semi-opaque; maggot-like larva, semi-opaque in initial hatching and turns into flesh aurantiacus later; illiptic pupa aurantiacus, 1.3-2.3 mm in length.

The adult has strong phototaxis and weak flight capacity. It sucks sap from the leaf blade of plant and forms engraving-dot-like concave, near round in shape; eggs are laid in mesophyll between the upper and lower epiderm, young larva moves stealthily under the epiderm, eats the mesophyllus and forms tunnel, the end of the turnel slightly expanded to allow the elder larva biting the upper epiderm and getting out of the tunnel to pupate. The occurrence of vegetable leaf miner varies depending upon the geological and climate conditions. In Hainan province, China, it occurred in whole year, and, occurred severely on August, September and October in Hubei, Jiangsu and Anhui provinces, and, in the areas of Beijing City, Hebei province and Tianjin city, relatively severe injury of it occurs on July, August and September (WANG Fuxiang, 1997).

Vegetable leaf miner originates from America, and distributes in more than 30 countries and regions of America, Oceania, Africa and Asia at present. In China, this insect was found early in 1993 in Hainan province (Hainan Island), China and spread over 21 provinces, disricts and cities in China till 1998. The total of the areas in more than 20 million mu which distributes in previous provinces, cities and districts, had suffered injury of this insect. 110 species of plants under 22 families can be parasitized by vegetable leaf miner, especially the vegetables including cucumber, muskmelon, water melon, summer squash, tomato, hot pepper, egg plant, cowpea, kidney bean, pea, and hyacinth bean. The damage rate of this invading insect in injuried leaf blade could reach 10-80%, causing decrease in production of vegetables and melons and in quality of those products, even reached total yield failure. At present, the main measures for controlling vegetable leaf miner consist of:
1) Agricultural control (artificial control) - at the peak of injury, remove and destroy the leaf blade carrying insect;
2) Physical control - yellow plate was used for trapping and killing the insect according to the yellow-tactic property of vegetable leaf miner,;
3) Chemical control - Significant effects could be obtained by using insecticides, Cartapand Shachon Shuang;
4) Biological control - A survey on utilization of natural enemy, parasite bee, without using insecticide could achieve a certain parasite rate of parasite bee above-mentioned. So, effective protection of utilized natural enemy could obtain certain effects of control (XU Zaifu and Zeng Ling, 1989).

3 Nematode

North American pinewood nematode (Bursaphelenchus xylophilus)
North American pinewood nematode is the pathogenic organism of pinewood disease. It belongs to the genus Bursaphelenchus, the family滑刀总科, under the order垫刀, class Nematode and phylum Vermes. The adult has a conformation slender and long, 1 mm in length. The tail part in female adult near cone shape with a round end. The tail part in male adult likes bird talon, bending toward segmental venter.

The pinewood nematode disease is also called pine blight-a kind of destructive diaease in pine. This disease is induced by North American pinewood nematode which is carried and spread by mediating insect, a kind of long-horned beetle, Monochamus altermatus, located in pinewood. After infection, the needle leaf of pine turns into yellowish brown or red-brown (fusco-rufous), withers and bows downward, resin secretion ceases, invading hole of beetle or egg-laying trace could be seen on the trunk, the whole diseased tree died of withered at last, and the timber turns to bluish color.

This disease frequently occurs under high temperature and arid conditions. Almost 100% of beetle, undergone eclosion in diseased pine tree, carries pinewood nematode. Each beetle can carry tens of thousands of nematode, the highest quantity even reached 280 thousands of nematode. When the carrier beetle bites the tree to supplement nutrient, the larva of nematode enters the resin channel of pine tree through the wounds caused by beetle's biting, and then develops into adult nematode through exuviate. The pine tree infected by pinewood nematode often turns to be used as a object base for laying eggs by beetle. So, the parasitized beetle in the diseased pine tree will carry the nematode in quantities again when it undergo hatching and accompanied "inoculation" of the nematode for the healthy pine tree again in next year that leads to the successive spread of nematode disease. The short distance spread of this disease mainly depends upon the beetle carrying nematode and the remote spread relies on the pest-carrier, such as the infected nursery stock, pine timber, pinewood-made packing box and pinewood products by the parasitized beetle or the hidden nematode (mainly the nematode-carrier beetle), which are trade goods or traveler's luggage in long distance allocation or transportation. The nematode lays eggs after copulation, about 100 eggs are laid for each female nematode. Eggs of nematode are hatched under the temperature 25 oC for 30 h. The development of larva lasts for 4 instars. The nematode can complete one generation cycle in 3 days when it is under the temperature 30 oC. The optimum temperature for the growth and reproduction of nematode is 20 oC, the temperature below 20 oC will cause the failure of development and that below 28 oC will cause the inhibition of reproduction of the nematode adult, and that over 33 oC will cause the failure in reproduction (CEN Bingzhan,2001.8.23).

The Pinewood Nematode Disease has occurred in Japan, Korea, U.S.A., Canada, and Mexico. In China, the first case of this disease was discovered in 1982 in the Sun Yat-sen Mausoleum in Nanjing city, and successively it occurred in Anhui, Shandong, Zhejiang, and Guangdong provinces and spread and resulted in disaster, that led to death of withered in pine tree in quantities. The damage cause by pinewood nematode disease has brought about economic loss of near RMB 5 billion yuan in Anhui and Zhejiang provinces. Now, this epidemic disease is classified as the object of emergency which is to be put in Quarantine either in domestic or the external affairs in connection with the control of invading organisms in China.

The Chinese government at various level attach the great importance to the control and administration of pinewood nematode disease and obtained certain success in it, a fund of a total of RMB over fifty seven million yuan (57360000 yuan) has been invested and a total of over eight hundred thousands hectares (80.1418) of land are put under the administration and control of the disease by local governments as well as the Chinese Ministry of agriculture. That is to say, all of these is enough to realize the "Control, Compression and Elimination" of the pinewood .nematode disease. In addition, application of attractant specific to the beetleand trapping apparatus as well as aerial monitoring technique enhance the capability of macro monitoring and controlling the situation of the pests and damage; Techniques of Artificial logging diseased and dead trees, bagging fumigation for killing the beetleand utilizing a wasp (Scleroderma guani) as natural enemy for controlling the beetle gave rise to obvious effects on control of disaster (Xin Hua Web, 2001). In Anhui Province, a project on biological control zone engineering of prevention system for protecting Huang Shan pine from pinewood nematode disease has been initiated recently in an all-round way. The width of the biological control zone is 4 km by the inner boundary 67 km in length and the outer boundary 100 km in length. Such a measure would form an effective separation of the Huang Shan Scenic spot from the pinewood nematode disease to enter (HUANG Xun, 2001).

4 Mollusca

Amazonian snail (Ampullaria gigas Spix)
Amazaonian Snail, belonging to the family Pilaidae under the class Gasopoda, is a molusca of amphibian mussel. Adult is of unisexuality, repent body 3.5-6 cm in length, shell near round disc with 6 spiral whorls in general; egg in spherical shape with a diameter of 2-2.5 mm, dark red color during initial layingwhen early egg-laying, sticky, and turns thin before hatching, egg laid in manner of 3-5 storeyed mass, the number of egg varies between 100-960; body length of young snail 2-2.5 mm, mollusca body, in dark red color, young snail can crawl in the initial period after hatching, after then, the shell enlarged in size along right spiral. The shell aperture of young snail or elder young snail less than 2.2 cm (FENG Weiming, 1994).

The life cycle of Amazonian snail goes in three stages: egg, young snail and adult snail. After mating of female and male, the fertilization performs within the snail body of the female. The egg-laying mainly performed at the place 10-20 cm above the water level where the weeds and crops grow or at the stone sides of ditches. Living independently, the initially hatched young snail separates off and drops down into the water and can immediately floats and swims to look for food. The adult snail lays egg many times within a life cycle with large number of egg. More than 10 times a femal snail can lay after one mating. The adult snail favors the habitat where exist the fertile soils and ditches or paddy fields with very slow current velocity of water,The snail always sank down on the bottom of waters or adheres to the pond sides or gathers beneath the aquatic plants in daytime, and looks for food in night. The temperature gives great influence on the growth of Amazonian snail. In the south areas of Yangtze River, the Amazonian snail can live through winter naturally. It bring forth two generations a year (CAI Weixiong and CHEN Rizhong, 1990).

Amazonian snail, which originates from the river valley of South America, was introduced into Taiwan and Guangdong province, China, in 70s-80s of 20th century. In early days after introduction, it had good sales on the market but the prize dropped down later owing to the local people didn't like the snail's taste which is much less fragrant and crisp than those in native snail (fragrant snail). The snail raiser gave up their enterprises and throw aside the Amazonian snail which soon turned into wild growing organisms in river, irrigation channel and ditche and pond. Because that the Amazonian snail is an omnivore animal and is characteristic of strong reproducibility and fast development, it soon became a harmful animal in Fujian, Guangdong, Guangxi and Zhejian province and Shanghai. This snail bites leaf blade and stem of aquatic plants, and severely influence on the plant growth. In Luzai xian of Guangxi province, the density of Amazonian snail attained to a level as 11300 snails per mu of fieldand the injury rate 7-15% in general, and even reach the top 64% of rice plants in an area of field; Amazonian snail bites the lotus' leaf (floating on the water surface of pond) causing the loss of the lotus' stem (enlarged part which lies on the bottom of pond, is a delicious vegetable in China), it also injures other aquatic plants, as narcissus. Moreover, Amazonian snail is also an intermediate host of zoonotic parasitic disease, easily bringing about the problem of health to human community.

AT present, the control of Amazonian snail mainly aims on the measure of chemical control and supplemented with artificial measure. The biological control measure isn't put on the order. The problems concerning the control of Amazonian snail are: the applied chemicals for killing snail showed toxicity in the water, becoming a severe source of chemical contamination, unsafe to organisms as well as to human being; exceeded dose raise the cost of control; and the technique isn't precise that causes low efficiency of the chemical control measure.

5 Mammal

Nutia (Myocastor coypus)
Nutia, belonging to the family Castoridae under the order Rodentia, has short, thick and round and fat body, in blackish brown color, big head, bigger sinus hair on upper lip, which is in light brown color, body length in adult female nutia 50-60 cm, tail length 30-40 cm, male animal weighs slightly heavier than female, the four limbs thick and short, the hind legs is little longer than the fore two, no web on the fore limbs, there are web on the hind limbs except that between 1st and 2nd toes,hind palms can be used as a support the for the body standing and as paddles when swimming; slow sense of smell, small round ears has sensitive sense of hearing (XU Ruiqiu et al.).

Nutia survives in wild of the areas in South China, is mostly dwells at the sites nearby river, ditche and pond where no freezing is there all the year round and is rich in various aquatic plants growing lushly. Nutia digs hole on steeper slop for constructing nest. Nutia mainly eats plant stem, branch and leaf, also fresh water mussel and other mollusks. Mating and bearing of it perform throughout the year, the adult female nutia bears more than 6-8 young animals at a litter. (XU Ruiqiu et al., 1997).

Nutia, which originates from Argentine, Chili and Uruguay of South America, was firstly introduced into the Northeast Zoo, China as early as in 1953 from former USSR (the Union of Soviet Socialist Republics) for display. Because of that nutia has the characteristics of thick and soft fine hair and good insulation of the fur, this animal was once to be believed as a rare economic animal of commercial value, and, had introduced actively by animal raiser of Fujian province in China in 1989-1994. But, owing to that the fur quality became worse and worse when it was raised in Southern China and the meat was not good in taste, people was gradually disappointed with it. So, there was numbers of nutia escaping to the wild from the farm or to be set free to the wild by the raisers. Then, the nutia in the wild lived and reproduced itself and gradually turned into an important injurious animal endangering agricultural crops. In Gutian xian, Fujian, nutia bit seedlings of rice causing decrease of rice production at the level 25-30% of the total. Severe damage to tomato, water melon, potato, vegetable and fruit tree (such as various varieties of citrus) were also made., the loss rate of the field crop and orchard caused by suffering damage from nutia was greatly exceeded that by suffering damage from disease and injurious insect. The geological climate condition rather favors the natural reproduction of nutia. It is necessary to strengthen the monitoring of the dynamic of the development and spread of nutia population. Killing through hunting or toxin measures are adopted to limit the spread in order to decrease the loss in agricultural production (XU Ruiqiu, 1997).

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