Hardly any other plant is as allergenic as Ambrosia. But now there is a glimmer of hope – thanks to an accidentally introduced beetle. A study, in which the University of Fribourg was a participant, has shown that a natural enemy of the weed can relieve more than two million European allergy sufferers of their symptoms.

Ophraella communa with its conspicuous stripes down its wing cases actually has no business being in Switzerland at all. Originally endemic to North America, it may have landed as a stowaway at the Milano Malpensa airport around 2013. From there it began to spread out in Northern Italy and Switzerland.

Such intruders – a by-product of globalisation – are usually unwelcome; after all they often represent a threat to domestic fauna and flora. However in this case it’s different: the main food source for the Ambrosia leaf beetle is a plant which was originally not found here either and is regarded as a particularly dangerous weed. Its name: common ragweed or Ambrosia. Its highly allergenic pollen makes it one of the main triggers for hay fever and itchy eyes; it can also lead to illnesses such as eczema or allergic asthma.

Drastic reduction in pollen production
The way this beetle, only measuring four millimetres, affects the spread of Ambrosia and the consequences this has for the health costs of the whole of Europe, has now been investigated by an interdisciplinary team of researchers. The study was directed by the Centre for Agriculture and Bioscience International (CABI); a principal role was also played by the University of Fribourg. The results have just been published in the journal Nature Communications.

The study’s results were astonishing: before the arrival of the leaf beetle in Europe, there were around 13.5 million sufferers of allergies induced by Ambrosia, but now the situation is changing – thanks to the Ambrosia leaf beetle. Field studies in Italy have shown that the damage the beetle can do to the plant by feeding on it is so considerable that its pollen production is reduced by 80 percent, and in some cases even 100 percent. In terms of the beetle’s potential range, “Ophraella communa could relieve more than two million European allergy sufferers of their ailments,” says the leader of the study, Urs Schaffner of the CABI.

7.4 billion euros per year
The scope of the study also included a calculation of the consequences of the increasing spread of Ambrosia for health costs – with and without the effect of the beetle. This part of the study was initiated and directed by Heinz Müller-Schärer, Professor of Ecology und Evolution at the University of Fribourg. He says: “we were able to show that the economic effects of Ambrosia had until now been vastly underestimated.” According to Müller-Schärer, the invasive plant causes immense costs to the whole European economy, namely 7.4 billion euros annually, but thanks to Ophraella, this is going to change: “Our calculations show that the costs may well go down by 1.1 billion euros per year.” The faster the beetle spreads, the greater the effect.

Informing the public
Müller-Schärer’s view of the presence of the beetle is correspondingly positive. “To start with, we were not sure whether this foreign species was useful or harmful.” Laboratory tests had shown that it was possible that the beetle was harmful to sunflowers. However field tests in China and Europe could not confirm this finding.

On the basis of these insights, the leader of the study, Urs Schaffner, is calling for “politicians and authorities to be better informed in future about the effects of invasive species on human health. This is the only way to ensure that appropriate resources are invested and measures against invasive species are coordinated and implemented.”

Further information
The project’s website and http://internationalragweedsociety.org/smarter/
Paper on nature.com, DOI: 10.1038/s41467-020-15586-1​
Study on Ophraella in Ticino
Blog article on CABI.org
Article on universitas
Presentation on YouTube
Pictures