Asian longhorn beetle is a native of China and the Korean peninsula, and poses a serious threat to a wide range of broadleaved trees. It has caused extensive damage to trees in the USA and Italy since being accidentally introduced there in recent years, and there have been outbreaks in several other European Union countries.
The beetles tend to stay close to the site of original infestation in the early stages of an outbreak. However, experimental data has shown that the beetles can fly hundreds of metres, and are capable of flying distances greater than 2km. Analysis of climate data by scientists at Fera suggests that most of England and Wales and some warmer coastal areas of Scotland are suitable for beetle establishment, but south-east England and the south coast are at greatest risk.
The lifecycle from egg to beetle is one to two years in parts of Asia, and possibly as long as four years in the UK. Beetles emerge during the summer and will mate and lay eggs, after which they die. Because it is often the resulting emergence holes that are the earliest evidence of an outbreak, it is important to survey and monitor the surrounding area to ensure the adults have not already spread to neighbouring hosts.
Individual specimens of Asian longhorn beetle (ALB) have occasionally been found from time to time in the UK, but in March 2012 a breeding population was confirmed by Forest Research scientists in the Paddock Wood area near Maidstone in Kent.
It was discovered during a routine annual survey as part of monitoring the area around a site where one adult Asian longhorn beetle had been found in 2009. The scientists noticed suspicious marks on a sallow tree, the first evidence of possible infestation, and several larvae were discovered inside samples from the tree. Morphological examination and DNA sequencing of the larvae confirmed that they were ALB.
We and the Food & Environment Research Agency (Fera) rapidly implemented measures to eradicate the outbreak and prevent it spreading further afield.
More than 4700 potential host trees were surveyed and 2166 host trees were removed. A total of 66 infested trees were detected, of which only 24 were found by visual inspection, the remaining 42 only being detected after they were felled.
Overall, 354 live larvae, 34 live pupae and two recently emerged adults were recovered from the infested trees. One 12-metre tall sycamore tree possessed 88% of all the exit holes and 40% of the live larvae and pupae found in the outbreak area. Surveys at the outbreak site will continue over the next four years before eradication can be officially declared.
Fortunately this outbreak was detected before the 2012 adult beetle emergence period, which provided time to inspect and deal with infested trees.
It is suspected that the original beetles might have emerged from wood packaging material which had been used to import slate from China to a site next to where the outbreak was located. Untreated wood packing is a known pathway for Asian longhorn beetles, and all wood packaging material imported into the EU should be marked to show that it has been treated to reduce the risk of carrying quarantine pests. It is illegal to import wood into the UK which shows signs of the beetle.
Known hosts (tree species which it can infest) include: Acer (maples and sycamores); Aesculus (horse chestnut); Albizia (Mimosa, silk tree); Alnus (alder); Betula (birch); Carpinus (hornbeam); Cercidiphyllum japonicum (Katsura tree); Corylus (hazel); Fagus (beech); Fraxinus (ash); Koelreuteria paniculata; Platanus (plane); Populus (poplar); Prunus (cherry, plum); Robinia pseudoacacia (false acacia/black locust); Salix (willow, sallow); Sophora (Pagoda tree); Sorbus (mountain ash, whitebeam etc); Quercus palustris (American pin oak); Quercus rubra (North American red oak); and Ulmus (elm). Apple and pear trees can also be attacked.
The lifecycle from egg through larvae to beetle is one to two years in Asia, and possibly longer in the UK. Beetles emerge from spring onwards and will mate and lay eggs, after which they die.
In North America and central and southern parts of Europe, ALB completes its life-cycle in 1-2 years, but in cooler regions the life-cycle can take up to three or four years. It is likely that in southern Britain most individuals will complete their development in two years, and climatic mapping work conducted at Fera suggests that conditions along the south coast and south east England would be suitable for a two-year life cycle. Further north, the beetle is less likely to be able to complete its lifecycle in two years. However, there is always an element of uncertainty about these predictions, which results from very local variations in climate, our changing climate, and uncertainties about the origin of the invasive beetles.
Residents and landowners within a 2km buffer zone around the infestation were asked to hold back from any felling/tree surgery or pruning of woody shrubs in gardens. This is because the beetle's larvae live in trunks and branches, so it is important to make sure these are properly disposed of. Residents in this zone who do need to prune or fell trees or woody shrubs have been asked to ensure that all woody material is taken to an appropriate Kent County Council waste transfer station or recycling site.
The buffer zone area was extended in 2012 to include an infested tree found on the northernmost edge.
We urged everyone within the 2km buffer zone to keep a look out for, and report, the beetle or evidence of its presence to ensure the best prospects for eradicating this outbreak. We are repeating this advice again in summer 2013.
A leaflet about the beetle and what the public can do to help stop it spreading was distributed to homes in the buffer zone, including areas of Paddock Wood and East Peckham.
The only insecticides that could be considered are not completely effective, so there is no real substitute for tree removal as a means of eradicating Asian longhorn beetle.
ALB does not attack wood in houses. The adults only lay their eggs on living trees, and although the larvae can continue to develop in felled wood, the early-stage larvae require the conditions and nutrition found in living wood
This pest is regulated, so movement of plants, logs and wood from infested areas is subject to statutory controls. Movement restrictions on host plants and woody material for two commercial retailers in the affected areas have been implemented by the Fera Plant Health & Seeds Inspectorate and Forestry Commission by way of plant health notices.
We advised local people not to undertake any tree surgery or felling until we had completed our survey, unless it was necessary for safety reasons, or to move any logs or branches which had been recently felled. Movement of infested material could carry the beetle to new locations. Also, the larvae can complete their development in felled trees or branches if left untreated, especially in the summer months, so this material would present an ongoing hazard.
Fera served notices on plant retailers in the affected area to prevent the movement of any potentially infested host plants or host plant material (with stems more than 2cm in diameter).
Larvae within wood will not survive if the wood is chipped to lengths no longer than 25mm. Once the wood has been chipped in this way it is deemed safe and can be disposed of.
There is no reason to restrict people’s movements in the infested area or buffer zone. The only possible restrictions would have been brief local exclusions for safety reasons during any tree felling which became necessary.
Some common native beetles can be mistaken for Asian longhorn beetles. The adult beetles are large (about 20 - 40 mm long) and shiny black with variable white markings. Particularly distinctive are their antennae, which are longer than their bodies (up to twice the body length) and are black with white or light blue bands. They are almost identical in appearance to citrus longhorn beetle (Anoplophora chinensis), another non-indigenous longhorn beetle that threatens trees in Britain.
The most obvious symptoms of Asian longhorn beetle damage are the circular exit holes made by the emerging adult beetles in the trunks and branches, which are about 10 mm in diameter and are usually found in the main trunk and above.
Other signs which might be present, but less obvious, include piles of sawdust-like droppings at the base of infested trees, scraped bark, possibly sap bleeding from sites where eggs have been laid, and feeding damage on the bark of smaller branches and shoots.
We urge the public and industry, especially businesses receiving materials in wooden packaging from China or Korea, to keep a look-out for the beetle or evidence of its presence, and to report any sightings using our on-line form.
Or call us on 0844 2480071.
If possible, the beetle should be caught and placed in a secure container such as a sealed glass jar so that an inspector can collect it. The beetles are not harmful to humans, although they should be handled with caution because they can nip the skin, although the nip is unlikely to penetrate the skin or draw blood. For most people the nip is likely to be no more uncomfortable than a nip by one of our larger native beetles.