Mugwort ambrosia is particularly troublesome for hay fever sufferers in Europe, because the pollen from this introduced plant species is an aggressive source of allergies. However, a helper from nature could perhaps remedy the ever-expanding plant: A study shows that a beetle imported from Europe to Asia in 2013 prefers to eat mugwort anvils. In northern Italy, this has already drastically reduced the pollen count and the spread of the plant, as the researchers report. At least for Southeast Europe and the foothills, this could also apply in the future.
It grows on roadsides, in gardens and even on rubble heaps: Mugwort ambrosia (Ambrosia artemisiifolia) is an undemanding and hardy herb that is spreading ever further in Europe. After the plant was imported from North America in the 19th century, it first established itself primarily in Southeastern Europe because it needed mild winters to survive. In the meantime, however, mugwort ambrosia has adapted itself to frosty temperatures thanks to a mutation and is now occurring more and more frequently in Central and Northern Europe. “The plant is now regarded as an invasive species in more than 320 countries and it is expected that its spread and impact will increase due to climate change,” explain Urs Schaffner from the CABI research center in Switzerland.
Responsible for 23 million allergy cases in Europe
The problem with this: Ambrosia artemisiifolia produces a particularly allergic pollen. Even a few pollen grains in the air are enough to trigger hay fever, asthma and other allergy symptoms in appropriately sensitive people. As part of their study, Schaffner and his team investigated the level of exposure to this allergy trigger in Europe. To do this, they used data from the European pollen monitoring program for 256 locations in the European Union and evaluated allergy data from the various countries. “We have determined that around 23.2 million people in Europe are currently allergic to mugwort pollen,” the researchers report. However, one has to take into account that not all people with a positive reaction to this allergen come into contact with mugwort pollen. For example, the highest pollen densities and most allergy cases can be found in the Po Valley, in the Carpathian Basin and in the Rhone Valley, as Schaffner and his team determined.
After Schaffner and his team had taken into account the distribution of the plant and its pollen, they came to 13.5 million people in Europe who actually suffer from an allergy to the invasive mugwort ambrosia. This invasive plant therefore causes considerable costs for the European health systems, as they report. Based on average treatment costs of 565 euros per year and patient, the researchers determined Europe-wide costs of around 7.4 billion euros per year. That is significantly more than estimated in previous studies, they say. In addition, the number of people affected could continue to rise because mugwort ambrosia benefits from global warming and also produces more pollen per plant at higher temperatures than it already does. Studies therefore assume that mugwort pollen levels could increase by at least four times by 2050.
Beetle feeding stops pollen production and spread
But there could be something that stops this trend, as Schaffner and his team now report. In 2013, another non-native organism was accidentally introduced – this time a beetle. The leaf beetle Ophraella communa comes from Asia and is already actively bred and used against mugwort ambrosia in China. In Europe, this beetle has so far been particularly widespread in northern Italy – and the first effects can already be seen there: “Up to 100 percent of mugwort ambrosia are attacked by the beetles, and to an extent that is sufficient to allow them to flower fully prevent, ”the researchers report. “Pollen monitoring in the Milan area has revealed that since Ophraella communa was established there has been a substantial drop in mugwort pollen density in the air that cannot be explained by meteorological factors.”
To check this effect, Schaffner and his colleagues carried out a field experiment in which they specifically examined the feeding damage caused by the beetle infestation in Ambrosia artemisiifolia. The result: “We found that Ophraella communa reduced the plant’s pollen production by an average of 82 percent,” they report. Additional tests have shown that this beetle largely spares other native plants. According to the researchers, Ophraella communa could therefore be a possible biological helper against mugwort ambrosia. In order to find out in which regions of Europe the newly introduced beetle could establish and hold in the future, the scientists carried out field tests in which they kept the beetles at different altitudes to be determined in Europe.
The model simulation showed that Ophraella communa could spread mainly in Southeastern Europe, in the northern Alpine region and in the south of France – pretty much in the areas in which mugwort ambrosia has so far been most strongly represented. For the allergy burden from ragweed pollen, this means: “If Ophraella communa colonized its entire environmental niche in Europe, this could reduce the number of people suffering from mugwort pollen allergy to 11.2 million,” said Schaffner and his Colleagues. “This corresponds to a reduction of 2.3 million patients and could lead to a cost reduction of 1.1 million euros annually.” If the researchers are right, allergy sufferers in Germany can only breathe a sigh of relief: the beetle appears in Bavaria and To be able to hold Baden-Württemberg, but not further north.
Source: Urs Schaffner (CABI, Delémont) et al., Nature Communications, doi: 10.1038 / s41467-020-15586-1