Invasive species whose colonisation and spread have unacceptable economic, social or ecological consequences are now referred to as quarantine pests - whether they are mammals, fungi or insects. The effectiveness of measures to prevent the establishment and/or spread of pests - i.e. eradication or at least containment - is often questioned. The history of Asian longhorned beetle infestation shows that eradication measures are not just a case of tilting at windmills, but can in fact be successful - provided decisive action is taken.

large black beetle with white dots and long antennae

Fig. 1: The Asian longhorned beetle (ALB) Anoplophora glabripennis. Photo: LfL

Invasive species in the forest

Invasive animal, fungal and plant species can cause major ecological and economic damage. There are numerous examples showing the far-reaching consequences of accidentally introduced species.

In Portugal, for example, a quarantine zone had to be set up in 2000 following the discovery of the pinewood nematode Bursaphelenchus xylophilus, an invasive nematode on pine trees (Pinus spp.) originally from North America. In the first few years of the millennium, around 50,000 diseased pine trees were felled and destroyed there each year; by 2004, the infested area already covered 258,000 hectares, and it continued to expand significantly in the following years.

In California and Oregon, the non-native pathogen Phytophthora ramorum was the cause of severe oak dieback in the coastal forests there in the 1990s. Regionally, the disease led to the dying out of entire tree populations, and it became known as Sudden Oak Death (SOD). In the British Isles, the same pathogen destroyed large plantations of Japanese larch (Larix kaempferi) from 2009 onwards. To prevent it spreading further, more than two million larch trees thus had to be felled in the UK in 2009.

According to the German Federal Agency for Nature Conservation, around 900 alien species have spread in Germany in the last 500 years, and a further 2,200 or so have been recorded in isolated cases (1,640 plants, 38 fungi and 460 animals). In order to protect plants from damage caused by invasive insects, nematodes, phytoplasmas, bacteria, fungi, viruses and viroids, so-called quarantine pests have been monitored worldwide for more than 50 years. In the EU, there are corresponding rules and regulations for the import of goods and commodities. Annual surveys in tree nurseries, public green spaces and forests are intended to help prevent the establishment of invasive species and to allow these pests to be eradicated successfully at an early stage.

Detection of a quarantine species - and then?

The introduction of a non-native species takes place in several stages:

  1. Introduction by transport
  2. Establishment
  3. Spread

In order to prevent or at least minimise damage caused by introduced species, each of these phases requires specific measures. Accidental introduction through transport can be avoided through rules and regulations for the import of goods and commodities. If a species is nevertheless able to establish itself, its spread must be prevented through the implementation of suitable eradication measures. The prerequisite for this is that the presence of the quarantine species is recognised, and that the way of life of this species permits “eradication”. Once a species has become established over a large area, it is usually only possible to minimise the harmful effect, e.g. by slowing down or limiting its spread.

In order to achieve eradication, a quarantine zone (QZ) is set up when a quarantine organism is detected. In the case of quarantine pests living on plants, infested or suspected infested plants must be removed, the transport of host plants from the quarantine zone is prohibited, and further control measures are taken. A monitoring system should be implemented in this zone to monitor the introduced species. Depending on the development cycle of the quarantine species, a quarantine zone can only be dissolved several years after the last discovery.

ALB - a beetle with high potential to cause damage

Dead maple, showing a large number of boreholes

Fig. 2: Dead maple in Kelheim after several years of infestation by the Asian longhorned beetle, showing a large number of boreholes (A), fungal fruiting bodies (P) and a broken tip. Photo: Hannes Lemme (LWF)

The Asian longhorned beetle (Anoplophora glabripennis) (Figure 1) is one of the most prominent representatives of invasive harmful organisms on woody plants in Germany. The species has been present in the EU since 2001; it was first detected in Germany in 2004 in Neukirchen am Inn in Bavaria. This longhorned beetle species has been subject to strict precautionary regulations and measures ever since, aimed at preventing its spread within the EU and at controlling it. Since then, the beetle has nevertheless appeared in North Rhine-Westphalia (Bornheim), Baden-Württemberg (Weil am Rhein, Hildrizhausen) and Saxony-Anhalt (Magdeburg), as well as on six further occasions in Bavaria (Feldkirchen (2012), Ziemetshausen-Schönebach (2014), Neubiberg (2014), Murnau (2016) Kelheim (2016) and Miesbach (2019). There it sometimes caused considerable damage to heavily infested trees (Figure 2).

The ALB is a polyphagous beetle species with a wide range of host plants. Under natural conditions, species of maple (Acer spp.) are its preferred host species. In China, however, the ALB has also been causing horrendous damage since the early 1980s to large areas afforested with poplars.

The considerable damage potential of the ALB results from the beetle's biology: it infests vital trees and colonises them until it has exhausted them as a resource (Figure 2). A total of 64 boreholes were found in a field copse near Feldkirchen, for example, 42 of which were on a single tree. In severe infestations, the larvae feed on the cambium and outer sapwood all the way round the trunk, causing the tree to die. Their bore tunnel systems often lead to branches and trunks breaking during storms. 

The species takes several years to develop. This is one factor resulting in its low dispersal rate in western, central and northern Europe, and is favourable for the success of eradication measures. Eradication is supported by felling the host trees to remove eggs, larvae and pupae from the habitat, and by catching beetles with species-specific pheromone traps, i.e. by attacking all stages of the insect’s development.

Measures in quarantine zones

A man examines a trunk with many holes

Fig. 3: If the suspicion of infestation with the ALB is confirmed, regular inspections of the affected trees are necessary. Photo: Birgit Gleixner (LfL)

If a beetle discovery, a beetle sighting or a suspected infested tree is clearly assigned to the Asian longhorned beetle, employees of the responsible plant protection service (in Bavaria the Bavarian State Institute of Agriculture (LfL)) inspect the trees in question together with representatives of the local municipality (in the case of public green spaces) or with representatives of the Bavarian Forestry Administration in the forest and, if necessary, the trees are felled. Once felled, they are chipped in a suitable area on the same day and then disposed of by incineration in a large combustion plant. On the following days, a so-called demarcation survey is initiated immediately in the vicinity of the “initial discovery site”, to determine the size of the infested zone. Depending on the size of the trees, ground search teams (hedges) or aerial platform search teams made up of specially trained tree climbers (treetops) are deployed to do this, as well as certified ALB and CLB (Citrus Longhorn Beetle) sniffer dog teams. They look out for typical symptoms of infestation, such as coarse bore dust, gnaw marks, egg-laying sites and holes drilled by the beetle.

In close consultation, the State Institute of Agriculture LfL and - if the forest is affected - the State Institute of Forestry LWF use the initial data to draw up one or more general rulings based on EU Commission Implementing Decision (EU) 2015/893, and designate a demarcated area or quarantine zone. The quarantine zone is a safety zone in which regular checks are carried out (Figure 3). It consists of an infested zone surrounded by an infestation-free buffer zone. In the QZ, personnel from the Offices for Food, Agriculture and Forestry monitor the quarantine pest (e.g. by means of pheromone traps and an annual monitoring survey); in addition, any handling of the host tree species is severely restricted, by banning the transport of hardwood out of the QZ, for example. The measures to be implemented for the QZ are set out in the general ruling(s). If new symptoms or beetles spotted on trees, host trees in this area are destroyed as described.

In addition to this, and in accordance with the EU Commission Implementation Decision, all other specified plants within a radius of 100 metres of the infestation point are removed as a precaution if living stages are found. The responsible plant protection service must monitor all steps of the action taken. Through consistent implementation of these measures, the ALB has been successfully eliminated from six out of seven Bavarian quarantine zones (Figure 4).

tabel

Fig. 4: Overview of quarantine zones for the control of the Asian longhorned beetle (Anoplophora glabripennis) in Germany; as of 30 April 2023.

The eradication of an invasive species is possible!

Successful eradication of an introduced and invasive species such as the ALB is not an exception. A summarising study shows that, of 672 eradication programmes carried out between 1880 and 2010 against 130 invasive arthropod species, 395 (59 %) were successful; only 110 eradication programmes (16 %) were classified as having failed. In the remaining 167 programmes, eradication had not yet been completed at the time of the study. A detailed analysis of the reasons for successful eradication is revealing. The following factors were identified as being decisive:

  • the size of the infestation area,
  • it being possible to find the species through characteristic signs of the infestation or species-specific attractants, and
  • effective measures for removing the species from the newly colonised habitat

The prerequisites are met in the case of the ALB. There are currently 38 known introductions of the ALB in Europe (Figure 5). Of these, 26 (68 %) are considered to have been eradicated. Several points are striking here:

  • Seven of the twelve introductions that have not yet been eradicated are in Italy, with two further introductions each in Germany and France respectively.
  • For all introductions before 2010, it took more than 10 years from discovery of the infestation to eradication.
graphics

Fig. 5: Number of known introductions of the Asian longhorned beetle in Europe, differentiated by country (a) and time of discovery (b), as well as the current status of the introduction: “eradicated” or “not eradicated” as of April 2023. Source: Branco et al 2022, updated according to EPPO Reporting Service 2022 and 2023

In all cases discovered after 2010, the eradication period was reduced to an average of six years. On the one hand, this reflects increasing experience in dealing with the ALB beetle species; on the other hand, a clear legal framework for the cooperative and consistent implementation of control measures has been in place since 2015 in the form of Commission Implementing Decision (EU) 2015/893. In Hildrizhausen, Kelheim and Murnau, for example, this led to the quarantine zone designations being lifted after the minimum period of five years (Figure 4).

Key measures for eradication are rapid and consistent action and strict compliance with the requirements for monitoring the tree population, monitoring measures implemented by the responsible authorities, and the ban on the removal of plant material and wood from the quarantine zones. Comprehensive public relations work and educational campaigns to raise awareness in the municipalities and cities concerned also contribute greatly to the success of the measures. Only through transparency of action and open communication can the eradication measures be implemented effectively, as private property is usually involved. Experience to date has also shown that if the ALB is recognised early in new areas, this shortens the duration of the quarantine period in the quarantine zone and the associated measures.

Despite the promising eradication measures, the primary goal must be to prevent the ALB from being introduced in the first place. This is why the Food and Agriculture Organisation (FAO) has adopted ISPM 15 (IPPC 2002), a phytosanitary standard that regulates the handling of packaging wood in international trade. When used properly, treated wooden packaging is no longer a means for insects developing in the wood to spread. It has also been possible to identify some high-risk goods that have increasingly been associated with infested packaging wood. The federal and state governments have thus drawn up so-called risk lists of goods, on the basis of which the responsible plant protection services are increasingly monitoring international shipments of goods, and container shipments in particular, more closely.

thick white larva

Fig. 6: Larva of the Asian longhorned beetle - under the right conditions it can also develop in packaging material. Photo: LfL

Summary

The introduction of invasive species takes place in several stages: Introduction by transport is followed by establishment - and if this is not prevented, the species will continue to spread. The primary goal is therefore to prevent their introduction. If a species is nevertheless able to establish itself, eradication measures must be taken to prevent its spread. These are explained here, using the Asian longhorned beetle (ALB) as an example. The experiences of the last 20 years, with eradication measures against the ALB carried out in Germany and other EU countries, shows that successful eradication is possible before major ecological and economic damage occurs. However, this requires early detection of the infestation and rapid, consistent action.