Urs Schaffner

Invasive exotic arthropods and weeds pose a growing threat to biodiversity, food security, and the functioning of whole ecosystems, resulting in significant socioeconomic and ecological impacts. Classical biological control—the importation of specialist natural enemies from the native range—can lead to long-term, sustainable pest suppression, but it is typically implemented reactively after the invasive species is established and is causing significant negative impacts. Proactive biological control offers an anticipatory approach, developing biological control agents before or shortly after establishment and enabling rapid response to new incursions. This review examines current applications, opportunities, and challenges of proactive strategies and proposes steps to advance proactive management of invasive arthropod pests and weeds.

Ambrosia artemisiifolia L. (common ragweed, Asteraceae), native to North America, is a highly invasive weed causing substantial agricultural losses and serious human health problems due to its allergenic pollen. In several countries, legal regulations require its active management. The North American leaf beetle Ophraella communa (Coleoptera: Chrysomelidae) is a biological control agent that can suppress ragweed growth and pollen production. This study evaluated the effectiveness of a synthetic herbicide, a bioherbicide, mowing, and O. communa releases at different densities and timings, applied alone or in combination under field conditions. Three field experiments were conducted in a major European hotspot of A. artemisiifolia in the Pannonian region of Hungary during the 2024 and 2025 growing seasons. Both herbicides, as well as mowing, reduced A. artemisiifolia growth and, to some extent, flower head formation, but not flowering intensity. Ophraella communa established at low densities regardless of the number and timing of released beetles, and despite the hot and dry summer climate of the region. The highest abundance and most damage were observed following medium-density early-season releases (4 beetles per m²) and high-density mid-season releases (32 beetles per m²). The results suggest that repeated or more intensive management may be required for an effective season-long suppression of A. artemisiifolia, and that early, higher-density O. communa releases under different local climates may warrant further investigation.

Prosopis juliflora is a highly invasive tree species in semi-arid and arid regions in eastern Africa. Its ability to displace herbaceous and woody species has been attributed to allelopathic effects, but this has rarely been tested in competition experiments on natural soil and experimentally binding potentially allelopathic substances. We tested the effect of soil collected underneath and outside of P. juliflora canopy, or treated with P. juliflora leaf litter, on the survival, growth, and competitive ability of three resident tree species in the presence and absence of activated carbon. Survival and growth of tree seedlings were reduced on soil collected underneath P. juliflora canopy and on soil collected outside P. juliflora canopy mixed with leaf litter, compared to seedlings growing on soil collected outside P. juliflora canopy. When activated carbon was added, seedling performance increased on soil collected underneath P. juliflora canopy and particularly on soil collected outside P. juliflora canopy mixed with leaf litter. Competition reduced seedling height irrespective of the type of competitor (P. juliflora or resident tree species). There was no significant interaction between soil type and competition, indicating that the effect of competition was independent of soil type. The results suggest that P. juliflora releases allelochemicals into the soil, which have allelopathic effects on resident tree species, and that at least part of these allelochemicals originate from leaf material.

Prosopis juliflora is a highly invasive tree species in semi-arid and arid regions in eastern Africa. Its ability to displace herbaceous and woody species has been attributed to allelopathic effects, but this has rarely been tested in competition experiments on natural soil and experimentally binding potentially allelopathic substances. We tested the effect of soil collected underneath and outside of P. juliflora canopies, or treated with P.julilfora leaf litter, on the survival, growth and competitive ability of three resident tree species in the presence and absence of activated carbon. Survival and growth of tree seedlings was reduced on, compared to seedlings growing on soil collected outside P. juliflora canopies. When activated carbon was added to the soils, seedling performance significantly increased and did not differ anymore from that on soil collected outside P. juliflora canopies. Competition significantly reduced seedling height irrespective of the type of competitor (P. juliflora or resident tree species). There was no significant interaction between soil type and competition, suggesting that the effect of competition was independent of soil type. The results suggest that P. juliflora releases allelochemicals into the soil which have allelopathic effects on resident tree species and that at least part of these allelochemicals originate from leaf material.

Background: This study aimed to assess whether current research trends in One Health emphasise zoonotic and foodborne diseases and antimicrobial resistance, as has historically been the case, or whether they increasingly align with a more holistic understanding of the One Health concept. This is achieved by exploring the global trends in One Health-labelled research and examining how these align with the Quadripartite One Health Joint Plan of Action (2022–2026) (OH JPA). Methods: A combination of bibliometric analysis and Social Network Mapping was used to meet the study objectives. Specifically, 6168 publications (January 2010–October 2024) were retrieved from the Dimensions database for bibliometric analysis. A full-accounting approach was used to attribute publications to countries or institutions, while Social Network Analysis centrality measures were used to quantify the scale and impact of collaboration among institutions engaged in One Health research. A topic model was also developed and visualised using the Uniform Manifold Approximation and Projection machine learning algorithm. Results: We found that globally, in the last decade, there has been an increase in the volume of One Health research publications, with the largest annual publication growth occurring after 2018. Half of all 6168 One Health research publications from 2010 are focused on six primary research topics, five of which are a lead topic for one of the six action tracks under the OH JPA. We also found that while there are more outputs on zoonotic epidemics and pandemics, the proportions of other areas of One Health research are increasing, although integrating the environment is still comparatively underrepresented. Although global collaborations exist in One Health research, there exist disparities between countries where One Health research is being conducted (largely in Africa and Asia) and countries leading One Health research (primarily high-income countries). There is some evidence of the use of One Health research in policy making, but the evidence base to determine this is limited, especially for low- and middle-income countries. Conclusions: Efforts are needed to strengthen One Health research capacity in the Global South, while continuing, globally, to conduct collaborative research to better understand changes in One Health research priorities, topical gaps and collaborations. One Health impact statement: This article contributes to ongoing debates on One Health priorities, conceptual thinking and ways of working. The ‘One Health’ approach has galvanised many policy makers, practitioners and researchers across the human, environment, animal and plant health sectors to tackle interconnected health challenges through a more integrated and collaborative lens. However, tendencies towards disciplinary and sectoral silos as well as lack of coordination of One Health in policy persist. This study involved data scientists, social scientists, plant pathologists, ecologists, veterinarians, public health scientists, One Health specialists and policy experts engaged in providing scientific and strategic advice on One Health for institutions working across the globe. This cross-sectoral, transdisciplinary team allowed interpretation of results in ways that would not have been possible with a less diverse team. Research and policy documents self-labelled as One Health were analysed to provide insights that can be used by One Health global scientific and strategic platforms for reform. In addition, insights on One Health research collaborations offer fuel for all stakeholders in the One Health landscape to continue working collectively to tackle complex, global health issues.

Common ragweed, Ambrosia artemisiifolia (Asteraceae), is an invasive weed that causes problems in cropping systems and to human health both in its native range in North and Central America and the introduced range in Europe, Asia, Africa, and Australia. Ophraella communa, an herbivorous chrysomelid beetle from North America, was accidentally introduced into East Asia and Europe, where it significantly reduces weed populations and pollen production. Despite extensive research on its host specificity and risk assessment, the potential environmental risk of this biological control agent in southeastern Central Europe, one of the most heavily invaded areas by A. artemisiifolia, remains to be determined. This literature review attempts to summarize the results of host-range testing conducted so far and identifies plant taxa native to southeastern Central Europe that have not been tested yet. The results suggest that the host range of O. communa is not yet entirely clear, but may include some plant species from the tribes Heliantheae, Inuleae, Anthemideae, Cardueae, Astereae, and/or Coreopsideae. So far, only some of the 21 genera from those tribes with species in southeastern Central Europe have been tested. We therefore suggest further host specificity studies with representatives of these plant genera to fully assess the potential non-target risks by O. communa in agricultural and natural habitats.

Sawfly species of the genus Monophadnus are specialised on Ranunculaceae plants from which the larvae can sequester furostanol saponins into the haemolymph, mainly (25R)-26-[(α-L-rhamnopyranosyl)oxy]-22α-methoxyfurost-5-en-3β-yl-O-β-D-glucopyranosyl-(1→3)-O-[6-acetyl-β-D-glucopyranosyl-(1→3)]-O-β-D-glucopyranoside (compound 1). In this work, TLC, GC-MS, and HPLC-DAD-ESI/MS analyses together with feeding, repeated simulated attacks, and ant deterrence bioassays were conducted to extend the chemoecological knowledge about two sawfly species specialised on H. foetidus L. (Monophadnus species A) and H. viridis L. (Monophadnus species B). Larvae of Monophadnus species B were mostly feeding on the squares treated with the n-butanol fraction from H. foetidus, compound 1 being its primary non-nutritional stimulant. In contrast, all H. viridis fractions stimulated feeding, with n-hexane marginally more active. β-sitosterol within n-hexane was determined as the nutritional stimulant. Quantitative analyses demonstrated that leaves of H. viridis but not H. foetidus contain the ecdysteroids 20-hydroxyecdysone and polypodine B. Moreover, the haemolymph of Monophadnus species B larvae reared on H. viridis contained the glycosides of polypodine B and 20-hydroxyecdysone at a concentration of 2.5 to 6.8 µmol/g fresh weight of haemolymph. This concentration is several thousand times higher than the concentration range of the aglycones in their host plant (3.63 × 10⁻⁴ to 2.23 × 10⁻⁴ µmol total ecdysteroids/g fresh weight of leaves), suggesting bioaccumulation. The larvae of both species fed on H. foetidus do not show any traces of ecdysteroids in their haemolymph, indicating a facultative role of these compounds in their defence as well as their inability to endogenously synthesise these compounds. The haemolymph containing ecdysteroids was a significant feeding deterrent against Myrmica rubra L. ant workers (one of their natural predators) at 0.8 mg/mL. The larvae kept effective deterrent levels of glycosylated ecdysteroids (≅175 mM) between simulated attacks on days 1 and 2, but the levels clearly decreased on day 3 (≅75 mM). Most larvae (89%) survived a first attack but only 23% a consecutive second one. As a conclusion, we report for the first time that two Monophadnus species feeding on H. viridis sequester phytoecdysteroids into the larval haemolymph in the form of glycosides. In addition, compound 1 possesses defensive and phagostimulant activities, and we present evidence for a combined effect of furostanol saponins and ecdysteroids as repellents against ants.

To understand the success of invasive alien species, it is necessary to evaluate the site-specific eco-evolutionary challenges they face in their new environments. We explored whether the rearrangement of genetic diversity is linked to the invasiveness of Prosopis juliflora by (i) comparing different stages of invasion (founding vs invasive populations) in two invaded areas (Afar Region, Ethiopia and Baringo County, Kenya) to evaluate whether different stages are dominated by different genetic attributes (e.g., characteristic genotypes or levels of genetic diversity) and by (ii) evaluating if landscape features affected dispersal between invasive populations in the two invaded areas. We hypothesised that different invasion stages would have unique genetic characteristics due to either site-specific demographic and/or dispersal dynamics. We also compared the genetic characteristics at an ‘invasive–non-invasive congener’ level by studying the non-invasive P. pallida, introduced to Baringo County, and assessed whether it hybridises with P. juliflora. In the Afar Region, the establishment and spread of P. juliflora were characterised by extensive gene flow that homogenised genetic diversity across all populations. In contrast, in Baringo County, invasive populations had lower genetic diversity than founders, and genetic differentiation was lower between invasive populations than between invasive and founder populations. In both invaded areas, we found no evidence that dispersal was hampered by geographic distance, bioclimatic conditions, or distance to roads, rivers and villages, at least at the spatial scales of our study; indicating frequent long-distance dispersal. Allelic richness was higher in P. juliflora than P. pallida founders and hybrids were mainly planted trees probably resulting from the sympatric cultivation of the two species following their introduction. Thus, management actions on Prosopis invasion in eastern Africa should consider site-specific dynamics occurring during the invasion.

A large number of non‐native trees (NNTs) have been introduced globally and widely planted, contributing significantly to the world's economy. Although some of these species present a limited risk of spreading beyond their planting sites, a growing number of NNTs are spreading and becoming invasive leading to diverse negative impacts on biodiversity, ecosystem functions and human well‐being. To help minimize the negative impacts and maximize the economic benefits of NNTs, Brundu et al. developed eight guidelines for the sustainable use of NNTs globally—the Global Guidelines for the Use of NNTs (GG‐NNTs). Here, we used an online survey to assess perceptions of key stakeholders towards NNTs, and explore their knowledge of and compliance with the GG‐NNTs. Our results show that stakeholders are generally aware that NNTs can provide benefits and cause negative impacts, often simultaneously and they consider that their organization complies with existing regulations and voluntary agreements concerning NNTs. However, they are not aware of or do not apply most of the eight recommendations included in the GG‐NNTs. We conclude that effectively managing invasions linked to NNTs requires both more communication efforts using an array of channels for improving stakeholder awareness and implementation of simple measures to reduce NNT impacts (e.g. via GG‐NNTs), and a deeper understanding of the barriers and reluctance of stakeholders to manage NNT invasions. Read the free Plain Language Summary for this article on the Journal blog.

Are there aspects of complexity that are characteristic for research for development projects? Our study shows what are these aspects, how they affect research and what practices seem to be promising for dealing with the increasing levels of complexity. The need to deal with complexity is getting increasingly attention in research for development projects implemented through transboundary research partnerships between organisations from the Global North and the Global South. However, less is known about aspects beyond the systems under study that still affect complexity in the research project. We conducted an experience capitalization of five transboundary research partnerships undertaking research in 14 countries in the Global South. We found that the combination of multiple contexts, the cultural and disciplinary diversity of the transboundary research partnerships, and the set of rules and proceedings from the funding mechanism affect the levels of complexity. We further identified that a transdisciplinary approach and several related practices, like intercultural communication or integrative partnerships, are promising ways of dealing with complexity. Current structures in research for development need to improve in order to fully use the potential of transdisciplinarity for sustainability transformation.