This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Researchers from Eötvös Loránd University (ELTE) and Semmelweis University have investigated what happens to horse chestnut leaves when they are attacked from within by the horse chestnut leaf miner. Their findings show that the functioning of the leaf changes while the damage is still barely visible to the naked eye.
The results have been published in the journal Plant Stress. The horse chestnut leaf miner (Cameraria ohridella) is a widespread pest of horse chestnut trees across Europe. The larvae feed inside the leaves, and as they consume increasingly large areas of tissue, the leaves turn brown and fall prematurely.
The damage, however, begins much earlier: changes are already taking place in the leaf's tissues and cells when there are barely any visible signs on the outside. The findings provide a more detailed picture of how horse chestnut trees respond to leaf miner damage and what changes occur before visible symptoms appear. Detecting these early signs could in the future help identify damage sooner and improve the timing of plant protection measures.
The invasive moth species, the horse chestnut leaf miner, was first described in North Macedonia in 1986 and has since spread across almost the whole of Europe. Its larvae create so-called mines inside horse chestnut leaves, where they feed on the leaf tissue. They primarily consume cells of the palisade parenchyma, a tissue layer located in the upper part of the leaf whose cells contain numerous chloroplasts, which play a key role in photosynthesis.
The researchers found that the damage is not limited to the tissue directly consumed by the larvae. Changes also occur in the leaf tissue surrounding the mines, even when these areas still appear healthy to the naked eye: the structure and functioning of cells and chloroplasts are altered, and photosynthetic activity decreases. "We collected samples from horse chestnut trees in 10 urban parks in Budapest and Szombathely between 2021 and 2025.
We compared tissue from healthy, intact leaves with visually intact areas surrounding larval mines, as well as with leaf sections showing early- and late-stage damage," explained Enkhjin Enkhbileg, a Ph.D. student and first author of the published paper. The changes in the surrounding leaf tissue are not limited to photosynthesis: the plant's defense-related metabolism also changes in response to the presence of the larvae. Among other things, the researchers tracked changes in phenoloid metabolism.
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