GREAT SPRUCE BARK BEETLE - Dendroctonus micans

What You Need to Know About the Great Spruce Bark Beetle – GREAT SPRUCE BARK BEETLE – Dendroctonus micans

Pests and Diseases

1st March 2021 | Info

Common Name: Great Spruce Bark Beetle

Scientific Name: Dendroctonus micans

Affects: Sitka Spruce, Norway Spruce and Oriental Spruce.

Now commonly found in Western England, Wales and Southern Scotland, the Great Spruce Bark Beetle originates from Siberia and was first discovered in the UK in 1982.

Here is everything that you need to know about the Great Spruce Bark Beetle.

What are they and what do they do?

Great Spruce Bark Beetles are large bark beetles that tunnel into the bark of living trees to lay their eggs.

These eggs hatch and their larvae then proceed to make feeding tunnels and galleries within the bark.

The damage caused by large infestations can cause girdle stems and be fatal. Girdling, also called ring-barking, is where the bark is completely removed from a portion of the trunk. Girdled stems make it difficult for a tree to successfully transfer energy from photosynthesis or take up water up from their roots, which can lead to dieback and the ultimate death of the tree.

The beetles are thought to have entered the UK in untreated, infected wood which unfortunately was not spotted. They were first discovered in the UK in 1982, although it is likely that they have been here longer.

What symptoms/signs should I look out for?

  • Feeding galleriesThe larvae of Great Spruce Bark Beetles form feeding galleries when they bore into bark. Most of the time, you cannot see these galleries unless a tree has been greatly infested and their bark has begun to fall away. You can check to see if there are any feeding galleries in your bark by tapping on the wood and listening for a hollow sound.
  • Resin tubesResin tubes are produced as female beetles bore into a tree to lay their eggs, and as a protective response, a tree will then increase its resin production. Look out for brightly coloured resin tubes that are often white but can also be blue or purple.
  • Exit holes on bark – Look out for minute holes in the bark that have been made by adult beetles coming in and out of a tree’s bark.
  • Powdery frass around bases – Exit holes that are created by the beetles cause powdery frass to be ejected out of the tree which will often collect around its base.

What impact could they have?

Due to global warming, there are increased temperatures around the world, including in the UK. Unfortunately, this is likely to cause a greater spread of the Great Spruce Bark Beetle as, in warmer climates (i.e., temperatures around 22.5°C), they can fly rather than being limited to crawling between trees.

Global warming could also mean that we gain more environmental changes that can cause stress to our infected trees and worsen the effects that the beetles already implement. For example, periods of drought weaken a tree’s natural defences and exacerbates the effects of pests such as the Great Spruce Bark Beetle.

What is being done to prevent them from spreading?

Biological control using the beetle Rhizophagus grandis is currently being implemented to prevent the spread of the Great Spruce Bark Beetle. Rizohphagus grandis are natural predators of the bark beetle, but do not cause damage to the tree. This method is proving to be highly effective.

Biological control is always preferable to other forms of pest control since it does not require the use of chemical agents, which often have unintended off-target consequences. It relies on the use of natural predators to reduce numbers of the pest (e.g., blue tits feeding on Horse Chestnut Leaf Miners). However, it is not guaranteed that all pests can be treated this way as not all of them have natural predators that are suited to the climate and conditions of the UK.

Therefore, it is important to be vigilant about pests such as the Great Spruce Bark Beetle, and if you do spot one, you can report it to the plant health authorities, via TreeAlert.

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