Birch Trees Beset by Bugs Skip to content
Scolioneura betuleti sawfly larvae in birch leaf.
Photo: Sawfly larvae in a birch leaf..

Birch Trees Beset by Bugs

Birch trees in the Reykjavík capital area are struggling following two waves of pests this spring and summer. While the trees made a comeback after moth larvae ate their way through new growth in the spring, they were soon beset by another hungry creature. Sawfly larvae, first spotted in Iceland in 2017, have done a number on local birch this summer, leaving behind brown leaves on many trees in the capital area.

“Many have noticed that the birch trees in our gardens are not doing well,” a press release from the Icelandic Institute of Natural History reads. According to the press release, Eriocrania unimaculella, moth larvae that mine birch leaves, ravaged the trees this spring. “In the short term, the trees managed to regain their foliage,” the release continues, “but a new pest has emerged which is greying the new leaves.”

The new pest is the larvae of the Scolioneura betuleti sawfly. The larvae was first spotted in Iceland in 2017, though it is not known when it first arrived in the country. Experts had noticed, however, damage to birch trees in late summer for several years prior which was similar to moth larvae damage in the spring. It was hypothesised that a second generation of moth larvae was to blame, but it has now been established that sawfly larvae is the culprit.

Scolioneura betuleti larvae behave similarly to Eriocrania unimaculella larvae, though they are not related. The sawfly lays its eggs in birch leaves in midsummer. Larvae live in and eat the leaf tissue, which is known as “mining” the leaves. The pests’ one-two punch can make it difficult for birch to grow healthy foliage all summer, “which will probably reduce the growth of the trees, seed ripening, and necessary preparation for the winter months.”

According to experts, green alder shrubs (Alnus viridis), a relative of birch common in Reykjavík gardens, may also be at risk from the Scolioneura betuleti larvae.

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