Citrus longhorn beetle
Anoplophora chinensis
Background
The citrus longhorn beetle, Anoplophora chinensis (Forster), is a non-native pest that is
extremely damaging to a wide range of broadleaved trees and shrubs. It is a quarantine
pest for the European Union. The natural range of the beetle includes China, Japan and
other countries in South East Asia. The main pathway of introduction of this pest into
Europe has been with ornamental trees from Asia. It poses a serious threat to horticulture,
forestry and native trees in the UK.
Figure 1. Citrus longhorn beetle adult (21-37 mm in length) and exit hole (6-11 mm across).
Plant Pest Factsheet
Why the concern?
Citrus longhorn beetle has been intercepted in the UK at nurseries and at premises
involved in importing bonsai and ornamental trees from China, Japan and South Korea.
The pest has also been found associated with imported trees in private gardens. The most
common hosts have been maples especially Acer palmatum (Japanese maple).
An outbreak of citrus longhorn beetle was detected in Parabiago, Lombardy, Italy in 2000
and since then two other outbreaks have been detected in Lombardy at Montichiari (2007)
and Gussago (2008). Between 2001 and 2013, Lombardy plant health service spent €180
million on eradication measures, including the removal of over 25,000 trees, however the
pest may have spread too far for eradication to be practical. Outbreaks of the pest have
also been discovered in Soyons, France (2003), Turanj / Sveti Filip I Jakov, Croatia
(2007), Westland, the Netherlands (2007), Rome (2008), Boskoop, the Netherlands (2009)
and Prato, Italy (2014). In and around Boskoop, there is a high concentration of nurseries
supplying trees and shrubs to the rest of Europe.
Although there are no known outbreaks of the citrus longhorn beetle in the UK, the
numerous interceptions in the UK since 2005 and outbreaks in Europe demonstrate that
there is a significant threat to the UK.
What does it look like and what are the symptoms?
Adult beetles are large and black with variable white markings. Particularly distinctive are
their antennae, which are longer than their bodies (between 1.2 and 2 times the body
length) and are black with white/light blue bands. The larval stage of the beetles is the
most damaging. The larvae feed internally on the pith and vascular systems of the lower
trunk and root. The tunnels created by the feeding leave trees susceptible to diseases and
wind damage. The adults cause much more limited damage by feeding on foliage and
eating the bark of young shoots.
Figure 2. Citrus longhorn beetle adult (21-37 mm in length). Fifty pence coin provided for scale.
Citrus longhorn beetles spend most of their life as larvae inside the main trunk or root, and
hence there can be little or no external sign of their presence to anyone inspecting a host
tree. Their lifecycle can be one to two years in Asia, however in the UK the lifecycle is
likely to be three or more years as in the Netherlands. The most obvious symptoms of
citrus longhorn beetle damage are adult exit holes (see photo on front page) which are
typically 6-11 mm in diameter and are generally found towards the base of trunks and
exposed roots. These holes are circular and on smooth barked trees resemble drilled
holes. Other less obvious symptoms include scars/slits on the bark at the site that eggs
have been laid and piles of frass (sawdust like droppings) at the base of an attacked tree.
In thin stemmed trees bulges in the trunk can indicate the presence of a pupal chamber.
What are the hosts?
Citrus longhorn beetle has an extensive host range of deciduous trees and shrubs
including many species native to the UK and species grown as ornamentals. In March
2012, the EU published emergency measures to reduce the risks of the introduction and
spread of A. chinensis. These include requirements concerning the importation of plants
from China and other third countries where the pest is native, plus the production and
movement of plants produced within demarcated areas in the EU. They also set out the
measures that member states are required to take to eradicate or contain populations of
the pest. This includes a list of ‘specified plants’ to which measures apply, and which are
known to be the most significant hosts of citrus longhorn beetle. They are: Acer spp.
Figure 3. A citrus longhorn larva within its cut
open host plant. The larvae grow up to 56
mm in length.
Figure 4. The tunnel and exit hole left within a
young Japanese maple tree that had been
infested by a citrus longhorn beetle.
(maples), Aesculus hippocastanum (horse chestnut), Alnus spp. (alder), Betula spp.
(birch), Carpinus spp. (hornbeam), Citrus spp., Cornus spp. (dogwood), Corylus spp.
(hazel), Cotoneaster spp., Crataegus spp. (hawthorn), Fagus spp. (beech), Lagerstroemia
spp., Malus spp. (apple), Platanus spp. (plane), Populus spp. (poplar), Prunus
laurocerasus (cherry laurel), Pyrus spp. (pear), Rosa spp. (rose), Salix spp. (willow) and
Ulmus spp. (elm).
What time of year have citrus longhorn beetles been
seen?
Adult beetles have most commonly been found in the UK in July and August, but findings
have occurred as early as May and as late as October.
How can citrus longhorn beetles be controlled?
As well as being difficult to detect, citrus longhorn beetles are difficult to control because
the larvae and pupae are protected from foliar insecticide treatments and most predators,
by the surrounding trunk or roots. Currently, the only totally effective way of controlling
larvae is to remove the infested trees and roots systems and to safely dispose of the
material by chipping, burning or by deep burial. Foliar insecticide sprays can be effective
against adults, but are not effective against larvae and pupae. Pheromone traps have
been used to monitor populations in Lombardy.
Advisory Information
If you suspect the presence of this pest or see a beetle you suspect to be a citrus longhorn
beetle, trap it if possible, and immediately report the finding to the relevant authority:
Figure 5. Tree felling in Italy for citrus longhorn beetle control.
For England and Wales, contact your local APHA Plant Health and Seeds Inspector or
the PHSI Headquarters, Sand Hutton, York. Tel: 01904 405138
Email: planthealth.info@apha.gsi.gov.uk
For Scotland, contact the Scottish Government’s Horticulture and Marketing Unit:
Email: hort.marketing@gov.scot
For Northern Ireland, contact the DAERA Plant Health Inspection Branch:
Tel: 0300 200 7847 Email: planthealth@daera-ni.gov.uk
For additional information on UK Plant Health please see:https://secure.fera.defra.gov.uk/phiw/riskRegister/https://www.gov.uk/p…
Authors
Original: Dominic Eyre and Neil Giltrap (Defra) February 2010
Update: Helen Anderson, Dominic Eyre and Neil Giltrap (Defra) May 2016
© Crown copyright 2016
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