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