Parasitic “hitchhiking” moths, which infect and destroy the leaves of horse chestnut trees, are moving north and could soon invade Scotland.
The horse chestnut leaf-mining moth, which originates in the Balkans, was first recorded in London in 2002 and has spread throughout England and Wales.
Dr Darren Evans, an expert in conservation biology at the University of Hull and a co-founder of Conker Tree Science, said “it’s only a matter of time” before the species expands further north into Scotland.
The invader feasts on the leaves of the conker-producing trees, turning them brown and causing them to drop in the late summer.
Evans said several million of the caterpillars could be present on each infected tree, adding: “It looks like autumn has come early for the trees. When the leaves have been destroyed, they tend to drop early.”
There is little evidence that the moths can kill horse chestnut trees, but Evans said there were fears they could weaken the tree’s immune system and make them more susceptible to disease, including bleeding canker, a bacterial disease that creates leaking lesions on the trunk.
The horse chestnut tree was introduced to Britain hundreds of years before the Victorians began planting them in large numbers, particularly in parks. Researchers are concerned that the threat of disease has caused a reduction in the numbers being grown.
Anna Platoni, entomologist at the Royal Horticultural Society, said little could be done to combat the moths. She said: “The moth caterpillars overwinter in the leaves under the tree.
“You can rake up, collect and burn fallen leaves in the autumn and that will reduce the population in the vicinity of your tree. But unless you’ve got a very isolated tree, then the next year the likelihood is it will just fly back in from somewhere else.”
She said there was growing evidence that native predators such as dragonflies and birds were starting to recognise the moths as food, which may restore balance.
Evans said the leaf-mining moth was one of a growing number of invasive insect pests spreading throughout UK woodlands, aided by climate change and extensive foreign trade links.
The Conker Tree Science project is urging people to record sightings of moth-infected trees on its website to help track the spread of disease.