Alien hitchhikers with imported plants

Alien hitchhikers with imported plants

The weevil Phyllobius intrusus is a North American species who typically lives on Thuja (Cedar) trees. It was found outside Kristiansand, in southern Norway a few years ago, as the first record of its kind in Europe. It is one of the many foreign species that cross national borders as stowaways or contaminants with imported plants. Photo: Arnstein Staverløkk / NINA.

Plant imports are a major pathway for the proliferation of alien species into Norway. In collaboration with garden centers, NINA is monitoring plant imports and this pathway for alien introduction.

Over the last 20 years, the import of plants to Norway has increased considerably. Hitchhiking seeds and spores from other plants and fungi, as well as insects, spiders and other invertebrates, are often well hidden in the soil and on the plants themselves.

Since 2014, NINA, commissioned by the Norwegian Environment Agency, has developed a surveillance program of hitchhiking species that accompany imported plants. Such species can pose a threat to both nature and agriculture as pests. So far, we have discovered well over 200 alien species and over 1 million individuals. However, this is only a small proportion of what is coming into Norway via plant imports. What risks this poses, and if all these manage to establish themselves in Norwegian nature, we do not yet know. Monitoring and early detection is therefore essential in order to minimise any negative impacts that these aliens may pose. 

The main purpose of this project is to monitor and calculate how many alien species come to Norway with imported plants, as well as the risks these pose to the indigenous biodiversity, in a cost-effective manner. Through cooperation with various garden centers and the Norwegian Environment Agency, we aim to address this pertinent issue. 

Germination and environmental DNA

The surveillance of such hitchhikers is a comprehensive job: In order to get a good overview, thousands of seeds and animals must be collected and determined to species level. Alien seeds are germinated under conditions simulating the Norwegian environment, to investigate whether they can survive in Norway. We are continually working to improve the methods of discovering all the species and calculating how many enter the country via this pathway. 

Development of environmental DNA (eDNA) is central to the work to streamline this surveillance. This method allows a sustainable and consistent way to determine several species quickly. eDNA also enables us to detect the proliferation of alien genotypes, and detect so-called ‘cryptic invasions’.

This project is connected to other projects on the early detection of foreign species in Norwegian nature  and  environmental monitoring. Connection between projects in this way provides valuable synergies in order to assess the threat of various alien species, create a good warning system and arrive at effective measures.

Database of alien species found in the project

Project info

Project leader: Marie Davey

Time schedule: 2014-2023

Funding: The Norwegian Environmental Agency

Students/interns: Are you interested in working with alien species? The project has many opportunities for bachelor and master theses, as well as internship projects. Contact the project leader.



Norwegian Institute for Nature Research

NINA is an independent foundation for nature research and research on the interaction between human society, natural resources and biodiversity.
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