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A Successful Search

On the origin of the horse-chestnut leaf miner – a talk with Professor H. Walter Lack, Director of the Botanic Garden and Botanical Museum, Berlin-Dahlem

Aug 18, 2011

Die Kastanienminiermotte befällt seit rund 20 Jahren massenhaft Kastanien in Europa.

For the past 20 years the horse chestnut miner has been causing major damage to chestnut trees in Europe.
Image Credit: David C. Lees

Professor H. Walter Lack im Herbarium des Botanischen Gartens.

Professor H. Walter Lack in the herbarium of the Botanical Garden.
Image Credit: Ch. Hillmann-Huber, Botanischer Garten und Botanisches Museum Berlin

These days, walk down any avenue lined with chestnut trees and you can’t miss the signs: brown leaves falling from the trees long before autumn. The cause of this premature leaf fall is the horse-chestnut leaf miner, an invasive leaf-mining moth that has been conquering Europe since the early 1990s. The voracious insects were first found in 1984, on Macedonia’s Lake Ohrid, and in 1986 they were given the scientific name Cameraria ohridella. But this unassuming moth already lived in the Balkans over a century before that – a fact that came to light only recently, in a study performed by an international, interdisciplinary team of researchers headed by Professor H. Walter Lack, of the Botanic Museum of Freie Universität Berlin. Campus.leben spoke with Lack, a professor of biology.

Professor Lack, the debate over the origin of the horse-chestnut leaf miner lasted about 20 years. Why did it take so long to solve the puzzle of where this pest came from?

Since the horse-chestnut leaf miner is a relatively large moth, the experts simply could not imagine that zoologists and entomologists in the Balkans had not discovered the insect much earlier. In fact, though, the horse-chestnut leaf miner makes its home in narrow, forested gorges in Macedonia and Albania that remain difficult to access to this day. The theory that the invasive moth could also come from Southeast Asia or the United States was proposed because those regions are also home to related chestnut species that could serve as hosts for the leaf miner. Our findings on the moth’s origins were so notable to the experts, at any rate, that CORDIS, the research information service operated by the European Union, reported on them just a few days after the study came out.

You have found evidence that the moth was present in scientific collections of dried plants that are over 120 years old. How could the larvae remain preserved for so long in these herbarium specimens?

The tiny larvae of the leaf miner moth live inside tunnels that they eat through the interior of the leaf, called mines. When the chestnut leaves were pressed and dried, the botanists simply preserved the larvae along with them, without noticing. As long as the leaves do not get wet, herbarium specimens can be preserved in this way for hundreds of years.

What did the genetic study of the larvae show?

Through the sequencing process, we were able to prove conclusively that the caterpillars we found were in fact horse-chestnut leaf miner larvae. We were also able to compare historical moth populations with those of the moth living today. In the process, we found new variants, which lets us document the evolutionary development of the populations.

Might your findings help stem the mass invasion of horse-chestnut leaf miners, and with it the damage they do to trees?

Conclusively determining the specific area where they originate may help us look for natural predators of the leaf miner in that area. Those predators in turn could then be used to control these moths as pests.

Our successful search in herbaria throughout Europe has shown the tremendous untapped store of knowledge that still exists in the specimens kept in botanical collections. Herbaria are like an archive of nature, one where we can trace evolutionary processes as if on a timeline. We botanists have a lot of work still to do in this area.

Interviewer: Ortrun Huber

Further Information

Prof. Dr. H. Walter Lack, Botanic Garden and Botanical Museum Berlin-Dahlem, Freie Universität Berlin, Tel.: +49 (0)30 838-50136, Email: h.w.lack@bgbm.org

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