Studies on common ragwort
We used the study species common ragwort to assess possibilities for combining aboveground herbivores as biological control agents and using soil-mediated effects to suppress the species. A desk study analysing data from a mesocosm experiment of 13 plant species and nematode communities showed that soil nematode communities change the outcome of plant-plant interactions, often in favor of common ragwort. Therefore, plant-feeding nematodes are no candidates for ragwort control via the soil. A manuscript has been submitted to Plant and Soil and a revision is now in review.
We identified a bacterium with negative effects on common ragwort seedling growth when roots were inoculated. Inoculation with this bacterium and feeding by caterpillars of the specialist herbivore moth Tyria jacobeae had additive but no synergistic effects on plant growth. The group of Prof. Bezemer continues to study whether this bacterium could be used for suppression in the field.
Observations in the field showed that the spatial arrangement of common ragwort seedlings is affected by conspecific plants that grew there earlier, likely through soil-mediated effects (plant-soil-feedbacks). At short distances, seedling recruitment seems to be suppressed by high densities of conspecific adults. A scientific manuscript is being prepared.
Studies on common ragweed
Two field data sets from common ragweed previously collected were used to analyse the impact of an exotic biocontrol agent in the field. Data constituted the abundance and damage of the leaf beetle Ophraella communa on hundreds of individual common ragweed plants. The results proved that O. communa can strongly reduce seed and pollen production of ragweed and that in-season leaf damage by O. communa helped to explain this impact.
The other data set showed that O. communa reduced ragweed pollen production in the field by ca. 80%. By integrating these data into spatial models, we showed for the first time for Europe that costs of invasive ragweed ( 7.4 billion euro annually) can significantly be reduced (by 1.1 billion euro/ year) by this biocontrol agent.
Scientific papers have been published open access in Neobiota and in Nature Communications.
Studies on invasive Asian knotweeds
A desk study confirmed the host specificity of A. itadori, and the minimal risks for the Dutch flora potentially resulting from a release into the wild. This was used to submit a petition for release to the Dutch government in December 2019, which was approved in July 2020. Mesocosm experiments showed the psyllid performs superior on the hybrid. A manuscript is in preparation for Neobiota. The results have improved the rearing and release program of A. itadori in the NL and have attracted a lot of international media attention.
Training and knowledge transfer
I actively participated in activities of LU, co-supervised (under)graduates, did 2 secondments at the research institute CABI. I was in the Steering Committee of the public-private consortium #uitde1000knoop, realising the implementation of the first exotic weed biocontrol agent in NL, and wrote a follow-up proposal (‘BioCops’) submitted to LIFE+.
I transferred knowledge by teaching/ supervising LU students , and to stakeholders by numerous activities and outreach activities.
Dissemination
Over 10 stakeholder activities such as workshops and webinars in NL and Belgium, 6 articles in professional journals. To the general public a website, tens of posts on social media (Twitter, LinkedIn) and >20 media items (national TV/radio in NL, Belgium and UK), and a class for schoolchildren.
