Zigzag elm sawfly attacking trees in UK, warn experts

Elm leaf-eating pest has gradually travelled across Europe from Japan, leaving mark reminiscent of that by Zorro’s sword

Press Association

Thu 21 Jun 2018 18.27 BSTLast modified on Thu 21 Jun 2018 23.33 BST

A pest which leaves a signature trail of destruction on elm leaves reminiscent of the mark of the fictional sword-wielding hero Zorro appears to have arrived in the UK, experts have warned.

The zigzag elm sawfly, originally found in Japan, feeds only on elm leaves and has been progressing steadily through Europe.

Now scientists at the Royal Botanic Garden Edinburgh (RBGE) have confirmed the tell-tale zigzag feeding trail left behind by the sawfly larvae has been found on leaves collected in Surrey during autumn 2017.

The discovery has raised concerns it could pose another blow to the UK’s elms, which have already been devastated by Dutch elm disease, and threaten wildlife that rely on the trees.

Elm leaf-feeding insects such as the rare white-letter hairstreak butterfly, which suffered in the 1970s due to the loss of trees to Dutch elm disease, could be hit by the new pest’s arrival.

While the zigzag elm sawfly rarely kills trees, large populations can completely defoliate elms, which could be disastrous for the white-letter hairstreak whose populations are sometimes restricted to single trees, the experts said. 

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