Quick facts

Common names: Asian longhorn beetle and citrus longhorn beetle

Scientific name: Anoplophora glabripennis and Anoplophora chinensis

What does it affect?: many broadleaf trees

Areas affected so far: not currently widespread in the UK, one outbreak in Kent in 2012

Origin: Southeast Asia


What does Asian and citrus longhorn beetle damage look like?

Asian and citrus longhorn beetles both harm the trees they infest at all stages of their lifecycle. The adult beetles look very similar; they are very large black and white beetles that grow up to 37mm in length. They can be seen feeding on leaves in tree canopies. Signs of damage include:

  • Large, round exit holes on tree trunks, around 10mm in diameter.
  • Damaged leaves from adults feeding on foliage. They often eat the central part of the leaf and leave the rest of the leaf untouched.
  • They also strip areas of young bark from shoots as they feed which is a distinctive pattern of damage not seen in many other pests.
  • Frass (sawdust-like waste) caused by larvae tunnelling in the tree which can drop from the tunnels and collect at the base of the tree or at the forks of branches.
  • Fissures, vertical cracks and splits running up the length of the bark which are a result of the tree repairing the damage caused by larvae boring underneath.

What are Asian and citrus longhorn beetles?

The Asian and citrus longhorn beetles are non-native beetles with boring larvae. Adult beetles lay eggs in notches under the bark. These eggs hatch and the larvae burrow into the tree. Due to the very large size of the larvae (between 30 and 60mm long by the time they reach maturity) they cause extensive damage inside the tree as they feed on the wood. This damage can cut off water and nutrient supplies to the leaves and therefore cause the death of the tree. The damage can also cause structural failure of the tree.

They target a range of broadleaf trees including:

  • Alder
  • Birch
  • Hazel
  • Beech
  • Poplar
  • Plane 
  • Willow
  • Rowan 
  • Whitebeam
  • Hornbeam
  • Ash
  • Cherry
  • Apple
  • Pear
  • Sycamore
  • Horse chestnut
  • Field maple

Credit: Heiko Küverling / Alamy Stock Photo

Where have the Asian and citrus longhorn beetles impacted?

These beetles aren't present in the UK at the moment. There was an outbreak of Asian longhorn beetles in the UK in 2012, but it was eradicated and there have been no cases of the citrus longhorn beetle reported.

Globally, both species have spread from Southeast Asia to Central Europe and North America.

How did they get here?

While these pests aren’t currently in the UK, the highest risk of spread comes from wood packaging from China. Their larvae are moved around in wood packaging material, wooden products and within infected plants, especially bonsai trees. The adults emerge and lay eggs on native trees to establish a new population.

Both species have become more prevalent in their native range after policy change in China to mass-plant hybrid poplar trees in public areas. These hybrids are particularly susceptible to the beetles, causing their numbers to increase dramatically. This has only helped the spread across Europe and North America.

Credit: Purestock / Alamy Stock Photo

What impact will the Asian and citrus longhorn beetles have?

Trees infested by the beetles are killed slowly over a number of years as the population builds up. Management of the pests during an outbreak involves felling of thousands of trees to stop it spreading. Asian longhorn in particular is causing serious problems to trees in the United States since its introduction in 1996.

As the climate continues to warm, these species will be able to establish more easily and quickly in the UK because the climate will become more like the climate from which they originate, therefore the problem is likely to get worse. These beetles are often intercepted by port authorities around Europe so it is only a matter of time before they are introduced again.

What are we doing about it?

To combat the introduction of pests and diseases like the Asian and citrus longhorn beetles we have:

  • Developed a UK and Ireland sourced and grown assurance scheme to make sure that all the trees we plant and sell are produced in the UK and Ireland.
  • Lobbied the government to improve biosecurity at border points to stop new pests and diseases entering the UK.
  • Partnered with Observatree, a tree health citizen science project which trains volunteers to spot pests and diseases, thereby helping tree health authorities identify and manage outbreaks early.

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What to do if you spot them

If you spot the signs and symptoms of this pest, report it to the plant health authorities via TreeAlert if you are in Britain and TreeCheck if you are in Northern Ireland.

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