Invasive alien species

An alien species – animal, plant or micro-organism – is one that has been introduced as a result of human activity to an area it could not have reached on its own. Some alien species, such as the potato and the tomato, which are originally from South America, have been economically important to Europe for hundreds of years. Others, known as invasive alien species, create serious problems when entering new territories as for example pests in agriculture and forestry or vectors of diseases.

Many of the invasive species present in Europe were introduced intentionally, including trees, crops, ornamental garden plants, and pet animals. Other visitors have arrived accidentally, as “stowaways” in airfreight or shipping containers or even crustaceans carried on the hulls of ships. They often pose no threat until they reach natural habitats where there are no competitors or predators.

Whatever their means of transport, the threat posed by invasive species is increasing as a result of climate change, the growth in human travel and the globalisation of trade. The Millennium Ecosystem Assessment rates them as one of the major causes of biodiversity loss, alongside factors such as habitat destruction, climate change and pollution.

What’s the problem?

Native species have resistance to local pests or diseases, but they often have no natural defences against “foreign” organisms and can suffer catastrophic decline. In addition, animals or insects that are kept under control by predators in their natural surroundings can reproduce rapidly and overwhelm a new environment where there are no such checks and balances.

The destructive consequences of rabbit infestations and the introduction of the American grey squirrel into Europe are well known, but there are many other examples: the Harlequin ladybird, from Asia, poses a deadly threat to native ladybirds and other insects in Europe; coypu, mink and musk rat, brought from America for their fur, are now wild in Europe, damaging canals and flood protections systems and decimating indigenous species such as water voles; Japanese knotweed (Fallopia japonica), which was introduced to Europe from eastern Asia as an ornamental plant in the 19th century, is causing damage to natural plant and insect species across the continent; and there is widespread agreement that the alarming decline in global bee numbers is at least partially attributable to the spread and impact of pests such as the Varroa mite.

The EU-financed research project Delivering Alien Invasive Species Inventories for Europe (DAISIE) lists more than 10,000 alien species as present in Europe’s countryside, waterways and marine environments. Although not all are invasive, it is estimated that up to 15% are potentially dangerous to European diversity. Since 1950, more than one species per year has become established, a rate that shows no sign of declining.

Invasive species and human health

As well as inflicting significant damage to the environment and ecological services, invasive species can pose a threat to humans. The Asian tiger mosquito (Aedes albopictus), which arrived in Europe through the trade in used car tyres, has been linked to the transmission of more than 20 human pathogens, including yellow fever and dengue. Alien plants such as the ragweeds (Ambrosia sp.) and the giant hogweed (Heracleum mantegazzianum) can cause allergies, skin irritation and burns. Invasive species have also been implicated in the spread of viruses such as flu and HIV.

The financial cost

Invasive alien species can be expensive for their new host countries. For example, Dutch elm disease — caused by an introduced fungus — has devastated elm trees in Europe, and the pine wood nematode (Bursaphelenchus xylophilus), thought to have originated in North America, has worked its way to Portugal and is causing severe damage to certain species of pine. The American grey squirrel not only out-competes the native red squirrel – it carries parapoxvirus, which is devastating to red squirrels – in Italy and the UK but damages coniferous trees and reduces their value as timber.

The cost to Europe in terms of controlling and eradicating invasive alien species, and repairing the damage they cause is estimated at more than €10 billion a year. This does not take into account the cost of major human pathogens or outbreaks of animal diseases.

What is being done?

The UN Convention on Biological Diversity requires member states “as far as possible, and as appropriate, [to] prevent the introduction of, control or eradicate those alien species which threaten ecosystems, habitats or species”. One of the Convention’s aims, adopted in 2010, is that “by 2020, invasive alien species and pathways are identified and prioritised, priority species are controlled or eradicated, and measures are in place to manage pathways to prevent their introduction and establishment”.

The UN target is also included in the EU biodiversity strategy. To help achieve this target, the EU has agreed a new Regulation on the Prevention and Management of the Introduction and Spread of Invasive Alien Species (see EU regulatory framework below).

In June 2011 the PLH Panel­ concluded that there was “a risk of further entry and establishment” of sudden oak death (Phytophthora ramorum) in the EU and that the recent outbreaks – which affected an estimated 1,900 hectares of Japanese larch, or 500,000 trees, in England and Wales alone – represented a “major step change” in the epidemiology of P.ramorum. It suggested a number of options to reduce the likelihood of further spread.

In March 2012 an opinion on the risks posed by South American potato cyst nematodes (Globodera pallida and Globodera rostochiensis) to solanaceous plants such as potatoes and tomatoes concluded that existing phytosanitary measures are important to prevent entry of new virulent genotypes of the pest.

Also in 2012, the PLH Panel delivered an evaluation of the pest risk analysis for the Spanish territory of the island apple snail (Pomacea insularum), prepared by the Spanish Ministry of Environment and Rural and Marine Affairs. Apple snails, originating in South America, are serious pests of rice and can have devastating effects on natural wetlands. The Panel subsequently published a detailed assessment of the potential establishment of the apple snail in the EU territory, followed in April 2014 by an environmental risk assessment of the apple snail, which showed potentially strong negative impacts on biodiversity, ecosystem functioning and ecosystem services in the wetlands of southern Europe.

The Panel reviewed several measures to limit or prevent spread within the EU of silverleaf whitefly (Bemisia tabaci) in an opinion published in April 2013. Bemisia tabaci is a serious pest that feeds on almost all vegetable crops and is considered to be one of the most serious threats to crop cultivation worldwide, predominantly because of the large number of viruses it transmits.

EFSA’s Panel on Animal Health and Welfare (AHAW Panel) published a scientific opinion in March 2013 on the risk of entry to the EU of the small hive beetle (Aethina tumida) and Tropilaelaps mites and the identification and evaluation of risk reduction options. Risk reduction options with a high effectiveness and technical feasibility were identified in all risk pathways except “accidental import of bees” and “dispersal of the pest via natural means and/or flight”. The Panel identified a need for validated rapid detection methods for both pests and for handling and sampling of imported bees in an insect-proof environment at the designated destination.

EFSA’s Panel on Plant Health (PLH Panel) started its work in the summer of 2006. On request from the European Commission the Panel assesses the risk to plant health of plant pests. Using this scientific advice the European Commission considers the pest for inclusion in the European Union’s lists of harmful organisms. The initial step is the preparation of a pest risk assessment, or the evaluation of a pest risk assessment document produced by the party requesting measures. To harmonise and clarify its approach, the Panel has published a number of guidance documents.

In January 2010 the PLH Panel agreed a set of principles for assessing risks from pests to plant health. This followed guidance on the process and criteria used by the PLH Panel for evaluating pest risk assessment documents received from third parties. These documents often follow different formats, and vary in terms of methodology and level of detail, so the guidance was developed to ensure consistency and clarity.

In June 2012 the PLH Panel published a major guidance document on the evaluation of the effectiveness of options for reducing the risk of introduction and spread of harmful organisms in the European Union.

In addition to these outputs, the PLH Panel has also published a methodology for assessing the environmental risks posed by harmful organisms that may enter and establish in the EU. This new approach includes methods for assessing the impact on ecosystems both in terms of biodiversity and provision of ecosystem services. The scheme was used for the first time in the PLH Panel’s environmental risk assessment of the apple snail, Pomacea maculata, which was published in April 2014.

Invasive alien species: In 2014 the Council of the European Union approved a Regulation on the Prevention and Management of the Introduction and Spread of Invasive Alien Species. The Regulation lays down rules to prevent, minimise and mitigate the adverse effects of the introduction and spread, both intentional and unintentional, of invasive alien species on biodiversity, related ecosystem services, and other areas of economic and social importance. To this end, the European Commission maintains an open list of invasive alien species of concern, which will be regularly updated and reviewed. Species on the list may not be intentionally brought into the territory of the EU, nor may they be kept, bred, transported to, from or within the Union, placed on the market, grown or released into the environment.

Plant health: Protective measures against the introduction into the European Union (EU) of organisms harmful to plants or plant products and against their spread within the EU are established by Council Directive 2000/29/EC. It contains lists of harmful organisms that threaten plant health in the EU. The Directive covers living plants and living parts of plants, including fruit, cut flowers and seeds. The European Commission is currently working to revise legislation in the area of plant health. The new legislation will place more focus on high-risk trade coming from third countries and increased traceability of planting material. It will also introduce better surveillance, and measures to enable the early eradication of outbreaks of new pest species. In addition, the draft new Plant Health regime includes elements relating to the natural environment and the effects that pests have on native plants, biodiversity and ecosystem services.

Animal health: To avoid the introduction into the EU of the small hive beetle and the Tropilaelaps mite through the import of live bees, in 2003 the Commission implemented Decision 2003/881/EC on animal health import requirements for live bees, bumble bees and bee products destined for use in apiculture. Decision 2003/881/EC has been superseded by Regulation (EU) No 206/2010, which incorporates the import requirements for live queen bees and queen bumble bees and colonies of bumble bees coming from controlled environments. These requirements only allow the introduction into the EU of queen bees with a limited number of attendant bees from third countries listed in Part 1 of Annex II to Regulation (EU) No 206/2010 (i.e. countries whose veterinary services are approved to certify to the EU) and also provides for strict controls upon import into the EU.