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Quick facts

Common name: elm zig-zag sawfly

Scientific name: Aproceros leucopoda

What does it affect?: English elm, wych elm, field elm

Areas affected so far: the south-east and East Midlands

Origin: Japan and parts of China

What does elm zig-zag sawfly damage look like?

The most distinctive symptom of the pest is the zig-zag feeding pattern made by the larvae. As the larvae become older, they just eat the whole leaf and the pest is harder to identify.

What is the elm zig-zag sawfly?

The elm zig-zag sawfly is a non-native species of sawfly. The adult is a small black, wasp-like sawfly with white legs. The larvae are tiny green caterpillars.

Adult sawflies lay their eggs into the serrations at the edges of elm leaves and the larvae hatch within 4-8 days. The larvae develop over a further 15-18 days, spending this time feeding on the leaves. They then cocoon on the underside of the leaf, emerging as adults within 7 days.

As the lifecycle is very short, the elm zig-zag sawfly can produce several generations in one summer and infestations can happen very quickly. Adding to this, no males of the species have been recorded which means the sawfly might reproduce by parthogenesis (reproduction without fertilisation) so its numbers can increase rapidly.

Where has the elm zig-zag sawfly impacted?

The elm zig-zag sawfly is currently in the south-east of England and the East Midlands but spreading. It was introduced to Europe in 2003, spreading rapidly and reaching the UK by 2017.

Elm zig-zag sawfly larva feeding trail

Credit: © Forest Research

How did the elm zig-zag sawfly get here?

We don’t know how this pest got here. It is likely that the elm zig-zag sawfly spread by ‘hitch-hiking’ on vehicles as the spread seems to follow major roads across continental Europe. They might have also spread through imported elms for planting.

We also don’t know the full distribution of the sawfly in the UK, but it is expected that it will continue to spread.

What impact will the elm zig-zag sawfly have?

If the populations get so high that trees are defoliated year after year, it can become weakened and more vulnerable to attacks from other pests and diseases, as well as environmental stresses like drought.

Defoliation also poses a threat to species that rely on the elm, like the white-letter hairstreak butterfly and the white-spotted pinion moth.

What are we doing about it?

To combat pests and diseases like the elm zig-zag sawfly we have:

  • Developed a UK Sourced and Grown assurance scheme to make sure that all the trees we plant and sell are produced in the UK. This reduces the risk of importing new pests and diseases.
  • 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.
Horse chestnut tree discoloured to yellow after a leaf miner infestation

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What we are doing about tree pests and diseases

We are fighting back against pests and diseases. Find out what we're doing to prevent the spread and protect the UK’s trees. 

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What to do if you spot the elm zig-zag sawfly

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

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