Emerald Ash Borer

Image courtesy of Wikipedia

Emerald Ash Borer (EAB, Agrilus Planipennis)

EAB is an exotic beetle pest. It is a member of the beetle family Buprestidae, and causes significant damage to ash trees (Fraxinus species).

Not yet present in the UK, this wood-boring beetle, native to Asia, has been found in Russia and North America, where it’s most likely to have arrived in imported wooden packing material. It has killed hundreds of millions of ash trees in the United States alone since the 1990s, so its introduction into the UK would cause devastation to ash populations which are already under threat from ash dieback. What’s concerning to us in the UK is that this particular beetle is known to be moving west from Russia at a distance of 25 miles every year. Furthermore, the increases in the global movement of wood and wood packaging means it poses a significant and immediate risk to UK woodlands.

Emerald Ash Borer is a small bark boring insect which causes ash trees to die within two to three years of infestation.

In China the beetle develops through its full life cycle in one year over most of its range, and this appears to also be the case in North America. In colder, northern areas of China, the cycle can take two years.

Adults appear from mid-May to late July, and feed on ash foliage. They are slender beetles between 7.5 - 13.5mm long, and characterised by their metallic emerald green colour. Adult females live for about 22 days, and males slightly less. The females each produce 60-90 eggs which are laid singly or in small clusters into bark crevices, and hatch in 7-10 days.

The larvae (grubs) burrow through the bark after hatching from the eggs, and begin feeding in the living water- and nutrient-conducting tissues of the tree. They produce sinuous tunnels as they feed through four larval stages (called instars), and their tunnels reach a final length of 26-32mm. Feeding tunnels can be 20-30cm long. As the larvae increase in size, the galleries enlarge and fill with brown excretions, and they can eventually girdle and kill branches and entire trees. Larvae feed aggressively until temperatures fall in the autumn. After that they spend the winter in the inner bark in thick-barked trees, or in the outer wood of trees with thinner bark, before emerging as adult beetles between May and July.

Whilst there have been no discoveries of the pest in the UK, we remain vigilant. Symptoms to look out for include the following:

  • Thinning or yellowing of foliage
  • Fissures in bark, 5-10 cm in length
  • Woodpecker activity, as the birds strip away bark to get at the beetles
  • D-shaped holes, 3mm in diameter, produced by emerging adults

A statement in a recent BBC news article says "Our European ash is very susceptible to the beetle. It is only a matter of time before it spreads across the rest of Europe - including Britain - and the beetle is set to become the biggest threat faced by ash in Europe, potentially far more serious than ash dieback."

Read the full report here - Ash Tree Set For Extinction in Europe

More about how to recognise the symptoms of Ash Dieback Disease can be found in our recent blog - Ash Dieback Disease

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