Biocontrol of invasive weeds under climate change: progress, challenges and management implications

The preemptive control strategy for invasive plant seed banks triggering ecological threats through synchronized germination

Invasive alien plants threaten global ecosystems by disrupting biodiversity and degrading ecological functions. Soil seed banks-the reservoirs of viable seeds in the soil-play a crucial role in the persistence and spread of plant populations. However, current control measures for invasive plants predominantly target above-ground vegetation, neglecting these underground seed reserves, thereby allowing invasive plants to re-establish their populations. Inducing synchronous germination to deplete seed banks offers a potential preemptive control strategy. This study hypothesizes that seeds of invasive plants secrete secondary metabolites to promote the synchronous germination of conspecific seeds. Focusing on Ambrosia trifida L., a globally harmful annual invasive plant, where the soil seed bank plays a crucial role in its continued impact. We used metabolomics to identify such metabolites and found that Angelicin significantly enhances germination rates by up to 116.9 % (P < 0.01). Field experiments conducted in the native habitat demonstrated that applying Angelicin at concentrations of 0.015 μg ml-1 or higher depleted over 85 % of the seed bank (P < 0.01) without harming indigenous plant communities. These findings confirm the feasibility of depleting underground seed banks through induced germination. Integrating this strategy with traditional above-ground control methods can develop a comprehensive management system, offering a promising new approach for the widespread control of invasive plants.

Natural products for biocontrol: review of their fate in the environment and impacts on biodiversity

Biocontrol solutions (macroorganisms, microorganisms, natural substances, semiochemicals) are presented as potential alternatives to conventional plant protection products (PPPs) because they are supposed to have lower impacts on ecosystems and human health. However, to ensure the sustainability of biocontrol solutions, it is necessary to document the unintended effects of their use. Thus, the objectives of this work were to review (1) the available biocontrol solutions and their regulation, (2) the contamination of the environment (soil, water, air) by biocontrol solutions, (3) the fate of biocontrol solutions in the environment, (4) their ecotoxicological impacts on biodiversity, and (5) the impacts of biocontrol solutions compared to those of conventional PPPs. Very few studies concern the presence of biocontrol solutions in the environment, their fate, and their impacts on biodiversity. The most important number of results were found for the organisms that have been used the longest, and most often from the angle of their interactions with other biocontrol agents. However, the use of living organisms (microorganisms and macroorganisms) in biocontrol brings a specific dimension compared to conventional PPPs because they can survive, multiply, move, and colonize other environments. The questioning of regulation stems from this specific dimension of the use of living organisms. Concerning natural substances, the few existing results indicate that while most of them have low ecotoxicity, others have a toxicity equivalent to or greater than that of the conventional PPPs. There are almost no result regarding semiochemicals. Knowledge of the unintended effects of biocontrol solutions has proved to be very incomplete. Research remains necessary to ensure their sustainability.

Heat Wave Adaptations: Unraveling the Competitive Dynamics Between Invasive Wedelia trilobata and Native Wedelia chinensis

Heat waves (HW) are projected to become more frequent and intense with climate change, potentially enhancing the invasiveness of certain plant species. This study aims to compare the physiological and photosynthetic responses of the invasive Wedelia trilobata and its native congener Wedelia chinensis under simulated heat wave conditions (40.1 °C, derived from local historical data). Results show that W. trilobata maintained higher photosynthetic efficiency, water-use efficiency (WUE), and total biomass under HW, suggesting that its ability to optimize above-ground growth contributes to its success in heat-prone environments. In contrast, W. chinensis focused more on root development and antioxidant protection, exhibiting a decrease in total biomass under heat wave conditions. These results indicate that W. trilobata employs a more effective strategy to cope with heat stress, likely enhancing its competitive advantage in regions affected by heat waves. This study highlights the importance of understanding species-specific responses to extreme climate events and underscores the potential for heat waves to drive ecological shifts, favoring invasive species with higher phenotypic plasticity.

Climate-Smart Invasive Species Management for 21st Century Global Change Challenges

Addressing the global challenges of climate change and biotic invasions requires understanding their interactions and implications for natural resource management. To facilitate and support invasive species management in a changing climate, we review how climate change and invasions interact to impact the planning, action, and outcomes of invasive species management. Climate change is facilitating the introduction of new potential invasive species and altering pathways of introduction and spread, with implications for which species natural resource managers need to assess, monitor, and target. Climate-driven shifts in invasive species phenology require more flexible management timelines. Climate change may reduce the efficacy and feasibility of current treatment methods and make native ecosystems more vulnerable to invasion. Additionally, disturbance caused by extreme climate events can compound the spread and impacts of biological invasions, making invasive species management a necessary part of extreme event preparation and response planning. As a solution to these challenges, we propose climate-smart invasive species management, which we define as the approaches that managers and decision-makers can take to address the interactive effects of climate change and invasions. Climate-smart invasive species management includes considering potential shifts in species ranges, abundances, and impacts to inform monitoring, treatment, and policies to prevent new invasive species. Climate-smart management may also involve adjusting the timing and type of treatment to maintain efficacy, promoting resilient ecosystems through climate-smart restoration, and considering the effects of climate change when setting management goals. Explicitly considering the interactions of climate change and biological invasions within organizational decision-making and policy can lead to more effective management and promote more resilient landscapes.

Patterns and Pitfalls of Short-cuts Used in Environmental Management Rapid Reviews

Environmental managers and policy-makers need reliable evidence to make effective decisions. Systematic reviews are one way to provide this information but are time-consuming and may not meet the needs of decision-makers when faced with rapidly changing management requirements or transient policy-windows. Rapid reviews are one type of knowledge synthesis that follow simplified or truncated methods compared to systematic reviews. Rapid reviews on environmentally-relevant topics are growing in prevalence, but it is unclear if rapid reviews use similar short-cuts or follow available guidelines. In this methodological review, we assess 26 rapid reviews published between 2002 and 2023. Numerous rapid review short-cuts and approaches were identified, with few consistencies among studies. Short-cuts were present in all stages of the review process, with some of the most common short-cuts including not developing an a priori review protocol, not including stakeholder involvement, or not conducting critical appraisal of study validity. Poor quality in reporting of methods was observed. Fewer than half of assessed rapid reviews reported using available guidelines when developing their methods. Future rapid reviews should aim for improved reporting and adherence to published guidelines to help increase the useability and evidence-user confidence. This will also enable readers to understand where short-cuts were made and their potential consequences for the conclusions of the review.

Integrating biogeographic approach into classical biological control: Assessing the climate matching and ecological niche overlap of two natural enemies against common ragweed in China

Plant invasion is considered a high priority threat to biodiversity, ecosystems, the environment, and human health worldwide. Classical biological control (biocontrol) is a generally safer and more environmentally benign measure than chemical controls in managing invasive alien plants (IAPs). However, the impacts of climate change and the importance of climate matching in ensuring the efficiency of biocontrol candidates in controlling IAPs are likely to be underestimated. Here, based on the ensemble model and n-dimensional hypervolumes concepts, we estimated the overlapping areas between Ambrosia artemisiifolia and its two most effective natural enemies (Ophraella communa and Epiblema strenuana) under climate change in China. Moreover, we compared their ecological niches, further assessing the impact of climate change on the efficiency of two natural enemies in controlling A. artemisiifolia in China. We found that the potentially suitable areas of the two natural enemies and A. artemisiifolia were primarily influenced by temperature and human influence index variables. Under near-current climate, the overlapping area between O. communa and A. artemisiifolia was the largest, followed by E. strenuana and A. artemisiifolia, and both two natural enemies and A. artemisiifolia. The ecological niche between A. artemisiifolia and O. communa was most similar (0.64), followed by A. artemisiifolia and E. strenuana (0.55). The separate control (the niche separation areas of the two natural enemies against A. artemisiifolia) and joint-control (the niche overlap areas of the two natural enemies against A. artemisiifolia) efficiencies of the two natural enemies against A. artemisiifolia will both increase in future climates (the 2030s and 2050s) in northern and northeastern China. Our findings demonstrate a new approach to assess control efficiency and screen potential release areas of two natural enemies against A. artemisiifolia in China without the need for actual field release or experimentation. Moreover, our findings provide important clues for ensuring the classical biocontrol of IAPs worldwide.

Climate warming can reduce biocontrol efficacy and promote plant invasion due to both genetic and transient metabolomic changes

Climate change may affect plant-herbivore interactions and their associated ecosystem functions. In an experimental evolution approach, we subjected replicated populations of the invasive Ambrosia artemisiifolia to a combination of simulated warming and herbivory by a potential biocontrol beetle. We tracked genomic and metabolomic changes across generations in field populations and assessed plant offspring phenotypes in a common environment. Using an integrated Bayesian model, we show that increased offspring biomass in response to warming arose through changes in the genetic composition of populations. In contrast, increased resistance to herbivory arose through a shift in plant metabolomic profiles without genetic changes, most likely by transgenerational induction of defences. Importantly, while increased resistance was costly at ambient temperatures, warming removed this constraint and favoured both vigorous and better defended plants under biocontrol. Climate warming may thus decrease biocontrol efficiency and promote Ambrosia invasion, with potentially serious economic and health consequences.

Opportunities from Unmanned Aerial Vehicles to Identify Differences in Weed Spatial Distribution between Conventional and Conservation Agriculture

Weeds are one of the major issues in agricultural production and they are present in most agricultural systems. Due to the heterogeneity of weed distribution, understanding spatial patterns is paramount for precision farming and improving sustainability in crop management. Nevertheless, limited information is currently available about the differences between conventional agricultural (CV) weed spatial patterns and weed spatial patterns in conservation agricultural systems (CA); moreover, opportunities to use unmanned aerial vehicles (UAV) and recognition algorithms to monitor these differences are still being explored and tested. In this work, the opportunity to use UAVs to detect changes in spatial distribution over time between CA and CV fields was assessed for data acquisition. Acquired data were processed using maximum likelihood classification to discriminate between weeds and surrounding elements; then, a similarity assessment was performed using the ‘equal to’ function of the raster calculator. The results show important differences in spatial distribution over time between CA and CV fields. In the CA field 56.18% of the area was infested in both years when the field margin effect was included, and 22.53% when this effect was excluded; on the other hand, in the CV field only 11.50% of the area was infested in both years. The results illustrate that there are important differences in the spatial distribution of weeds between CA and CV fields; such differences can be easily detected using UAVs and identification algorithms combined.

Biology of an Adventive Population of the Armored Scale Rhizaspidiotus donacis, a Biological Control Agent of Arundo donax in California

Simple Summary

The invasive giant reed, Arundo donax, impacts river ecosystems world-wide. The plant-feeding scale insect Rhizapidiotus donacis is approved for biocontrol use in North America but a wild (adventive) population was found in southern California. We studied the adventive scale to document its distribution, life history, relatedness to European samples, risk to a native reed, and ability of a biocontrol wasp to develop within it. The adventive was found within a single watershed and is genetically closest to the Iberian scale population. Rhizaspidiotus donacis developed on some Phragmites reed types, but at lower densities than Arundo. It produces one generation each year with mobile juveniles from March through June. Aphytis melinus wasps showed similar interest in adventive R. donacis as their usual host with deposited eggs developing into a second generation. Rhizaspidiotus donacis appears limited in distribution by its life history, precluding broad biocontrol implementation through natural dispersal but allowing for targeted application. The genetic differentiation between imported biocontrol samples and adventive populations presents an opportunity for exploring benefits of hybrids and/or alternative genotypes where establishment has been difficult. While likely rare in the wild, spillover to vulnerable endemic Phragmites or deleterious parasitoid effects on scale populations warrants consideration when planning use of this agent.

Abstract

Arundo donax (giant reed) is invasive in Mediterranean, sub-, and tropical riparian systems worldwide. The armored scale Rhizaspidiotus donacis is approved for biocontrol in North America, but an adventive population was recently discovered in southern California. We documented this population’s distribution, phylogeny, phenology, potential host spillover to Phragmites spp., and potential for parasitism by a common biocontrol parasitoid of citrus scale. The adventive scale was found within a single watershed and is genetically closest to Iberian scale genotypes. Rhizaspidiotus donacis developed on Phragmites haplotypes but at much lower densities than Arundo. The adventive population is univoltine, producing crawlers from March-June. Aphytis melinus parasitoids exhibited sustained interest in R. donacis during choice and no-choice trials and oviposition resulted in a small second generation. Rhizaspidiotus donacis appears limited in distribution by its univoltinism and sessile adult females. This presents challenges for broad biocontrol implementation but allows for targeted application. The genetic differentiation between imported biocontrol samples and adventive populations presents an opportunity for exploring benefits of hybrids and/or alternative genotypes where establishment has been difficult. While unlikely to occur in situ, spillover to vulnerable endemic Phragmites or deleterious parasitoid effects on scale biocontrol agents warrants consideration when planning use of R. donacis.

Double trouble: the implications of climate change for biological invasions

The implications of climate change for biological invasions are multifaceted and vary along the invasion process. Changes in vectors and pathways are likely to manifest in changes in transport routes and destinations, together with altered transit times and traffic volume. Ultimately, changes in the nature of why, how, and where biota are transported and introduced will pose biosecurity challenges. These challenges will require increased human and institutional capacity, as well as proactive responses such as improved early detection, adaptation of present protocols and innovative legal instruments. Invasion success and spread are expected to be moderated by the physiological response of alien and native biota to environmental changes and the ensuing changes in biotic interactions. These in turn will likely affect management actions aimed at eradicating, containing, and mitigating invasions, necessitating an adaptive approach to management that is sensitive to potentially unanticipated outcomes.