With its pink flowers, the alpine rose is one of the most attractive mountain plants. However, it is highly toxic and is avoided by grazing animals and insect larvae. The Tyrolean butterfly researcher Peter Huemer was all the more surprised when he and a Swiss colleague discovered a butterfly species that specializes in the alpine rush this year. Their caterpillars live in the leaves of the plant and eat them, the researchers report in the specialist journal “Alpine Entomology”.
The rust-leaved alpine rose (Rhododendron ferrugineum) is widespread in the Alps, but is considered “completely uninteresting because there are no specialists on it,” said Peter Huemer, head of the natural science collections of the Tyrolean State Museums in Innsbruck, to the APA. The expert was therefore completely perplexed when he parked his backpack for a break in Ardez in the Lower Engadine (Switzerland) in July and discovered a caterpillar in an alpine rose leaf.
“It was immediately clear that it had to be an extraordinary species,” said Huemer. Together with his Swiss colleague Jürg Schmid, he returned a few days later to look for caterpillars and pupae and to find out more about this curious insect. They were able to prove a stable population of the butterfly. But the identification of the species initially presented a complete mystery.
They called the butterfly the “alpine rose leaf miner” because the caterpillar burrows into the interior of an alpine rose leaf immediately after hatching, where it spends its entire life until pupation. So far, no insect was known that specialized in the alpine rose. The caterpillar is well protected from bad weather and predators between the intact leaf membranes and eats the leaf from the inside out. To pupate, the caterpillar leaves the infected leaf and creates a hammock-like web on the underside of the leaf, where it finally pupates. In the laboratory, the researchers observed that after about ten days, a nocturnal butterfly around twelve millimeters in size with white-black-spotted wings hatched.
Based on morphological features such as wing color and pattern and a genetic comparison, Huemer and Schmid found that it was not a new species. Rather, the “Alpine rose leaf miner” is a “Lyonetia ledi” species, a species that is widespread in Northern Europe, Northern Asia and North America. In Northern Europe, the butterfly lives exclusively on swamp porst and hail bush – typical raised bog plants that do not occur in the Alps.
In Austria you can find the butterfly in a small area on the border with the Czech Republic – more than 400 kilometers from the Engadine. Huemer therefore suspects that in earlier cold phases – around 12,000 years ago – the swamp porst and the alpine rose shared a habitat north of the Alps. After the end of the last glacial period and the melting of the glaciers, some populations of the species could have shifted their host preference from the swamp porst to the alpine rose. The separation of the distribution areas of the two plants in the following warm phases could then also have resulted in a separation of the butterfly populations. The alpine population would thus be a relic of the Ice Age.
So far the “alpine rose leaf miner” has only been sighted in the Lower Engadine. There he lives on a northern slope at around 1,800 meters above sea level, where the alpine roses do not bloom due to the high snow cover in winter and the largely shady conditions in summer. The scientists suspect that the butterfly can also be discovered in places with similar conditions in the northern Alps, for example in neighboring Tyrol and Vorarlberg, but assume that the previously overlooked species is not widespread in the Alps. The special microclimate of the Swiss location also means “a great risk for the population in view of climate change,” says Huemer.