Sick Series: The Asian longhorn beetle’s insatiable appetite

21st June 2019

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Sick Tree Series

We’ve written quite a few articles on the pests that can spell disaster for your garden trees, but the Asian longhorn beetle is a rather worrying menace in the UK, so do look out for it and report it to the Forestry Commission, should you find them in your garden.

What does it look like?
The Asian longhorn is around 2 to 4 cm in length, quite big for a beetle, oval in shape, and coloured a shiny black, dotted with bright white spots and splodges on its back. It has long black and white striped antennae that can be up the twice the length of its body and sturdy black legs that make it look a little like a plastic model of a beetle. These beetles are most active between May and October, so watch out for them then.

A threat avoided, for now
The beetle was first reported in the UK and recognised for the threat it posed in 2012 in Maidstone, Kent. The Food and Environment Research Agency, a government body, was called in and a decision was made to eradicate the problem by felling over 2,000 trees in the woodland where the beetle had been spotted. This may seem like an extreme action to take, but it looks like it was effective because there have been no confirmed sightings of the beetle since.
In the felled trees, 3% contained the beetle and the most commonly attacked species was the sycamore – with 98% of adult beetles found having emerged from sycamore trees and 70% of larvae found in sycamore trees.
They may well return
The beetle originates from China; with the climate changing on a global scale, many species of insect are finding their way from warmer climes to the UK on ships and in containers and thriving once they arrive.

What harm can this bug cause?
We’ve already mentioned that the tree most preferred by this beetle is the sycamore, but all broadleaf woodland is at risk from it. This includes alder, oak, ash, beech, birch, elm, hazel, apple, willow and many others.

The larvae of the beetle feeds on the tree’s living wood tissue, boring tunnels in the trunk and branches as they feed, slowly killing the tree from the inside. When the larvae grows to adulthood it burrows its way out, leaving a circular exit hole around 1 cm wide.
The beetle was accidentally introduced to North America in the 1990s, causing significant damage to the country’s tree population and more recently outbreaks have been reported throughout Europe.

Signs of an Asian longhorn beetle infestation

  1. Holes in the trunk of your tree approximately 1 cm in diameter
  2. Piles of sawdust at the bottom of the tree
  3. Sap bleeding from holes

How to get rid of this beetle

Insecticides don’t seem to work, so there is little choice but to fell infected trees and either burn them or chip them to lengths no longer than an inch.

If you are worried that your trees may be infested, if you’ve seen a beetle you suspect may be an Asian longhorn, or if you’re looking for help to maintain the good health of your garden trees, call us on 0208 292 8992. We’re always happy to pop round or to help with a little advice or assistance.

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