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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. [ABSTRACT FROM AUTHOR]

Predicting plant distributions under climate change is constrained by our limited understanding of potential rapid adaptive evolution. In an experimental evolution study with the invasive common ragweed (Ambrosia artemisiifolia L.) we subjected replicated populations of the same initial genetic composition to simulated climate warming. Pooled DNA sequencing of parental and offspring populations showed that warming populations experienced greater genetic divergence from their parents, than control populations. In a common environment, offspring from warming populations showed more convergent phenotypes in seven out of nine plant traits, with later flowering and larger biomass, than plants from control populations. For both traits, we also found a significantly higher ratio of phenotypic to genetic differentiation across generations for warming than for control populations, indicating stronger response to selection under warming conditions. As a measure for evolutionary rate, the phenotypic and sequence divergence between generations were assessed using the Haldane metric. Our approach combining comparisons between generations (allochronic) and between treatments (synchronic) in an experimental evolutionary field study, and linking population genomic data with phenotyping analyses provided a powerful test to detect rapid responses to selection. Our findings demonstrate that ragweed populations can rapidly evolve in response to climate change within a single generation. Short‐term evolutionary responses to climate change may aggravate the impact of some plant invaders in the future and should be considered when making predictions about future distributions and impacts of plant invaders. [ABSTRACT FROM AUTHOR]

Invasive alien species (IAS) can substantially affect ecosystem services and human well-being. However, quantitative assessments of their impact on human health are rare and the benefits of implementing IAS management likely to be underestimated. Here we report the effects of the allergenic plant Ambrosia artemisiifolia on public health in Europe and the potential impact of the accidentally introduced leaf beetle Ophraella communa on the number of patients and healthcare costs. We find that, prior to the establishment of O. communa, some 13.5 million persons suffered from Ambrosia-induced allergies in Europe, causing costs of Euro 7.4 billion annually. Our projections reveal that biological control of A. artemisiifolia will reduce the number of patients by approximately 2.3 million and the health costs by Euro 1.1 billion per year. Our conservative calculations indicate that the currently discussed economic costs of IAS underestimate the real costs and thus also the benefits from biological control. Invasive plants can adversely affect ecosystems and economic costs. Here, the authors quantify the impact of the invasive plant Ambrosia artemisiifolia on seasonal allergies and health costs across Europe, finding that the costs are considerably higher than what previously reported, and estimate also the reduction in the number of patients and health costs that may be obtained with biological control [ABSTRACT FROM AUTHOR]

One of the biggest challenges in classical biological control of invasive weeds is predicting the likelihood of success. Ambrosia artemisiifolia, a North American plant species that has become invasive in Europe, causes economic losses due to health problems resulting from its huge amount of highly allergenic pollen and as a weed to agricultural crops resulting from high seed densities. Here we assessed whether the pollen and seed output of the annual A. artemisiifolia (at the end of the season) is related to in-season abundance of, or damage by, the accidentally introduced biological control agent Ophraella communa. We monitored the growth and leaf damage of individually labelled A. artemisiifolia plants at four locations in Northern Italy and recorded abundance of different O. communa life stages at regular intervals. We found that the in-season level of leaf damage by O. communa consistently helped to explain seed production in combination with plant volume and site throughout the season. Feeding damage, plant volume and site also explained pollen production by A. artemisiifolia six weeks before male flower formation. At three out of four sites, plants with more than 10% leaf damage in mid-June or early July had a very low likelihood of seed formation. Leaf damage proved to be a better explanatory variable than O. communa abundance. Our results suggest that the monitoring of the in-season leaf damage can help to project the local impact of O. communa on A. artemisiifolia at the end of the season and thus inform management regarding the needs for additional measures to control this prominent invader. [ABSTRACT FROM AUTHOR]

Following its first record in Europe in 2013, the North American ragweed leaf beetle Ophraella communa, used already as a most successful biocontrol agent against common ragweed in China, is spreading rapidly, asking for a detailed analysis of the potential benefit and risk of this introduction for Europe. Here, we report twelve specific and polymorphic tetranucleotide microsatellite markers, which can be used for redrawing its global invasion history and spread across native and introduced ranges. The high level of polymorphism (i.e. from 4 to 18 alleles per locus) and the genetic variation detected within and between one native and two introduced populations provide adequate statistical power for elucidating the beetle's invasion process. [ABSTRACT FROM AUTHOR]

Abstract The North American common ragweed, Ambrosia artemisiifolia , which produces highly allergenic pollen, is invasive in different parts of the world, including Europe. In 2013, common ragweed in northern Italy was found attacked by another accidentally introduced species, the North American leaf beetle Ophraella communa , which is used for biological control of common ragweed in China. Since the establishment of O. communa , ragweed pollen concentrations in northern Italy have significantly dropped. Here we set out to estimate the potential economic benefits of establishment of O. communa in the Rhône-Alpes region in south-eastern France, where detailed data on the economic impact of common ragweed are available. Extrapolating from the change in airborne ragweed pollen concentrations in the Milan area, we estimated that establishment of O. communa in the Rhône-Alpes region will reduce the number of days with ragweed pollen concentrations at which sensitive people express symptoms by 50% and the medical costs due to common ragweed by 5.2–6.8 M € annually. Our findings suggest that investments of public funds are justified to conduct a complete assessment of the potential risks and benefits associated with the accidental establishment of O. communa in Europe. [ABSTRACT FROM AUTHOR]

Roadsides are an important habitat for invasive common ragweed, Ambrosia artemisiifolia L., by facilitating seed dispersal. Reducing the size of roadside populations is therefore essential for confining this highly allergenic species. Here, we aim to determine the cost-effectiveness of mowing regimes varying in frequency and timing, by analysing population-level effects and underlying demographic processes. We constructed population models of A. artemisiifolia parameterised by demographic data for four unmanaged reference populations across Europe in two years. We integrated the effects of four experimental mowing regimes along Austrian road sides on plant performance traits of five years and experimental data on seed viability after cutting. All four experimental regimes reduced the projected intrinsic population growth rates (r) compared to the unmanaged controls by reducing plant height and seed viability, thereby counteracting increased size-dependent fecundity. The prevailing 2-cut regime in Austria (cutting during vegetative growth, here in June and just before seed ripening, here in September) performed least well and the reduction in r was mainly due to reduced seed viability after the second cut. The efficacy of the two best experimental regimes (alternative schemes for 2 or 3 cuts) was mainly due to cutting just before female flowering (here in August) by decreasing final adult plant height dramatically and thereby reducing seed numbers. Patterns were consistent across reference populations and years. Whether regimes reduced r below replacement level, however, varied per population, year and the survival rate of the seeds in the soil bank. Our model allowed projecting effects of five theoretical mowing regimes with untested combinations of cuts on r. By plotting r-cost relationships for all regimes, we identified the most cost-effective schemes for each cutting frequency (1-3 cuts). They all included the cut just before female flowering, highlighting the importance of cutting at this moment (here in August). Our work features i) the suitability of a modelling approach for the demography of an annual species with a seed bank, ii) the importance of seed viability in assessing mowing effects, iii) the use of population models in designing cost-effective mowing regimes. [ABSTRACT FROM AUTHOR]

This account presents information on all aspects of the biology of Ambrosia artemisiifolia L. (Common ragweed) that are relevant to understanding its ecology. The main topics are presented within the standard framework of the Biological Flora of the British Isles: distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, floral and seed characters, herbivores and disease, and history, conservation, impacts and management., Ambrosia artemisiifolia is a monoecious, wind-pollinated, annual herb native to North America whose height varies from 10 cm to 2.5 m, according to environmental conditions. It has erect, branched stems and pinnately lobed leaves. Spike-like racemes of male capitula composed of staminate (male) florets terminate the stems, while cyme-like clusters of pistillate (female) florets are arranged in groups in the axils of main and lateral stem leaves., Seeds require prolonged chilling to break dormancy. Following seedling emergence in spring, the rate of vegetative growth depends on temperature, but development occurs over a wide thermal range. In temperate European climates, male and female flowers are produced from summer to early autumn (July to October)., Ambrosia artemisiifolia is sensitive to freezing. Late spring frosts kill seedlings and the first autumn frosts terminate the growing season. It has a preference for dry soils of intermediate to rich nutrient level., Ambrosia artemisiifolia was introduced into Europe with seed imports from North America in the 19th century. Since World War II, it has become widespread in temperate regions of Europe and is now abundant in open, disturbed habitats as a ruderal and agricultural weed., Recently, the North American ragweed leaf beetle ( Ophraella communa) has been detected in southern Switzerland and northern Italy. This species appears to have the capacity to substantially reduce growth and seed production of A. artemisiifolia., In heavily infested regions of Europe, A. artemisiifolia causes substantial crop-yield losses and its copious, highly allergenic pollen creates considerable public health problems. There is a consensus among models that climate change will allow its northward and uphill spread in Europe. [ABSTRACT FROM AUTHOR]

Invasive non-native plants (INNP) cause severe impacts on nature and human well-being, and these are predicted to increase. While management tools have been developed to control early-stage invasions or to clean particular sites from INNP, they are only rarely available to halt and reduce large-scale invasions. Importation biological weed control (IBWC; also termed classical biological weed control) offers a potentially effective tool, especially when combined with other land management interventions. Here, we aim to bridge the gap between IBWC advocates and critics by providing a state of the art of IBWC and exploring untapped opportunities and new ideas to further increase efficacy and safety of this tool. We first present a decision tree to identify the circumstances under which IBWC should be considered, either alone or as part of an integrated weed management approach. We then address concerns raised against IBWC by contrasting historical approaches with recently suggested improvements and outline a path forward. With two case studies, we emphasize that successful reduction of weed densities using IBWC will specifically also contribute to environmental health and human well-being by restoring ecosystem services without pesticide input and reaching areas with otherwise no INNP management options. We hope that our compilation helps to reconcile advocates and critics of IBWC and lead to a more constructive discourse and hopefully closer collaboration between the two groups. A joint effort is needed to further improve IBWC and to consider it more often, as the increasing threats imposed by INNP are urgently awaiting sustainable and affordable solutions. • Management tools to reduce large-scale plant invasions are often not available. • Importation (classical) biological weed control (IBWC) can be an effective tool. • We analyze benefits of IBWC, list untapped opportunities and outline a path forward. • We advocate to use IBWC more often, but also more rigorously. [ABSTRACT FROM AUTHOR]

Studies on plant growth and trait variation along environmental gradients can provide important information for identifying drivers of plant invasions and for deriving management strategies. We used seeds of the annual plant invader Ambrosia artemisiifolia L. (common ragweed) collected from an agricultural site in Northern Italy (226 m. a.s.l; Mean Annual Air Temperature: 12.9 °C; precipitations: 930 mm) to determine variation in growth trajectories and plant traits when grown along a 1000-m altitudinal gradient in Northern Italy, and under different temperature conditions in the growth chamber (from 14/18 °C to 26/30 °C, night/day), using a non-liner modeling approach. Under field conditions, traits related to plant height (maximum height, stem height, number of internodes) followed a three-parameter logistic curve. In contrast, leaf traits (lateral spread, number of leaves, leaf length and width) followed non-monotonic double-Richards curves that captured the decline patterns evident in the data. Plants grew faster, reaching a higher maximum plant height, and produced more biomass when grown at intermediate elevations. Under laboratory conditions, plants exhibited the same general growth trajectory of field conditions. However, leaf width did not show the recession after the maximum value shown by plants grown in the field, although the growth trajectories of some individuals, particularly those grown at 18 °C, showed a decline at late times. In addition, the plants grown at lower temperatures exhibited the highest value of biomass and preserved reproductive performances (e.g., amount of male inflorescence, pollen weight). From our findings, common ragweed exhibits a high phenotypic plasticity of vegetative and reproductive traits in response to different altitudes and temperature conditions. Under climate warming, this plasticity may facilitate the shift of the species towards higher elevation, but also the in situ resistance and (pre)adaptation of populations currently abundant at low elevations in the invasive European range. Such results may be also relevant for projecting the species management such as the impact by possible biocontrol agents. [ABSTRACT FROM AUTHOR]

Species distribution models can predict the suitable climatic range of a potential biological control agent (BCA), but they provide little information on the BCA's potential impact. To predict high population buildup, a prerequisite of biocontrol impact, studies are needed that assess the effect of environmental factors on vital rates of a BCA across the environmental gradient of the BCA's suitable habitats, especially for the region where the BCA is considered for field release. We extended a published species distribution model with climate‐dependent vital rates of Ophraella communa, a recently and accidentally introduced potential BCA of common ragweed, Ambrosia artemisiifolia in Europe. In field and laboratory experiments, we collected data on climate‐dependent parameters assumed to be the most relevant for the population buildup of O. communa, i.e., temperature driving the number of generations per year and relative humidity (RH) determining egg hatching success. We found that O. communa concluded one generation in 334 cumulative degree days, and that egg hatching success strongly decreased from > 80% to < 20% when RH drops from 55% to 45% during the day. We used these values to spatially explicitly project population densities across the European range suitable for both A. artemisiifolia and the beetle and found that the present distribution of the beetle in Europe is within the range with the highest projected population growth. The highest population density of O. communa was predicted for northern Italy and parts of western Russia and western Georgia. Field observations of high impact on A. artemisiifolia with records of 80% aerial pollen reduction in the Milano area since the establishment of O. communa are in line with these predictions. The relative importance of temperature and RH on the population density of O. communa varies considerably across its suitable range in Europe. We propose that the combined statistical and mechanistic approach outlined in this paper helps to more accurately predict the potential impact of a weed BCA than a species distribution model alone. Identifying the factors limiting the population buildup of a BCA across the suitable range allows implementation of more targeted release and management strategies to optimize biocontrol efficacy. [ABSTRACT FROM AUTHOR]

Common ragweed (Ambrosia artemisiifolia L.) is a widely distributed and harmful invasive plant that is an important source of highly allergenic pollen grains and a prominent crop weed. As a result, ragweed causes huge costs to both human health and agriculture in affected areas. Efficient mitigation requires accurate mapping of ragweed densities that, until now, has not been achieved accurately for the whole of Europe. Here we provide two inventories of common ragweed abundances with grid resolutions of 1 km and 10 km. These "top-down" inventories integrate pollen data from 349 stations in Europe with habitat and landscape management information, derived from land cover data and expert knowledge. This allows us to cover areas where surface observations are missing. Model results were validated using "bottom–up" data of common ragweed in Austria and Serbia. Results show high agreement between the two analytical methods. The inventory shows that areas with the lowest ragweed abundances are found in Northern and Southern European countries and the highest abundances are in parts of Russia, parts of Ukraine and the Pannonian Plain. Smaller hotspots are found in Northern Italy, the Rhône Valley in France and in Turkey. The top-down approach is based on a new approach that allows for cross-continental studies and is applicable to other anemophilous species. Due to its simplicity, it can be used to investigate such species that are difficult and costly to identify at larger scales using traditional vegetation surveys or remote sensing. The final inventory is open source and available as a georeferenced tif file, allowing for multiple usages, reducing costs for health services and agriculture through well-targeted management interventions. Unlabelled Image • An approach for distribution modelling of anemophilous species using pollen data • Validated against plant observations of ragweed and cross validation • European-wide coverage revealing many new invaded regions. • 1 km & 10 km inventories covering all of Europe. [ABSTRACT FROM AUTHOR]

Classical biological control is an important means of managing the increasing threat of invasive plants. It constitutes the introduction of natural enemies from the native range of the target plant into the invaded area. This method may be the only cost-effective solution to control the rapidly expanding common ragweed, Ambrosia artemisiifolia, in non-crop habitats in Europe. Therefore, candidate biocontrol agents urgently need to be assessed for their suitability for ragweed control in Europe. A previous literature review prioritized the host-specific leaf beetle Ophraella slobodkini as a candidate agent for ragweed control in Europe, whereas it rejected its oligophagous congener O. communa. Meanwhile, O. communa was accidentally introduced and became established south of the European Alps, and we show here that it is expanding its European range. We then present a short version of the traditional pre-release risk-benefit assessment for these two candidate agents to facilitate fast decision-making about further research efforts. We selected two complementary tests that can be conducted relatively rapidly and inform about essential risks and benefits. We conducted a comparative no-choice juvenile performance assay using leaves of ragweed and sunflower, the most important non-target plant, in Petri dishes in climatic conditions similar to that in the current European range of O. communa. This informs on the fundamental host range and potential for increasing abundance on these host plants. The results confirm that O. slobodkini does not survive on, and is hence unlikely to cause severe damage to sunflower, while O. communa can survive but develops more slowly on sunflower than on ragweed. In parallel, our species distribution models predict no suitable area for the establishment of O. slobodkini in Europe, while O. communa is likely to expand its current range to include a maximum of 18% of the European ragweed distribution. Based on this early assessment, the prioritization and further assessment of O. slobodkini seem unwarranted whereas the results urgently advocate further risk-benefit analysis of O. communa. Having revealed that most of the European area colonized by ragweed is unlikely to be suitable for these species of Ophraella we suggest the use of such relatively short and cheap preliminary assessment to prioritise other candidate agents or strains for these areas. [ABSTRACT FROM AUTHOR]

• A temperature-dependent numerical model for a weed biocontrol agent is presented. • Temperatures used to drive the model were satellite-derived or measured locally. • Model predictions were compared to observations in a caged field experiment. • Phenology predictions, driven by both temperature sources were similar. • This model can be used to predict weed biocontrol impact. Herbivorous insects play important roles in agriculture as pests or as weed biological control agents. Predicting the timing of herbivore insect population development can thus be of paramount importance for agricultural planning and sustainable land management. Numerical simulation models driven by temperature are often used to predict insect pest population build-up in agriculture. Such simulation models intend to use station-derived temperatures to drive the development of the target insect, although this temperature may differ substantially from that experienced by the insect on the plant. To improve the estimations, it has been suggested to replace air temperature in the model by land surface temperature (LST) data. Here, we use a numerical simulation model of insect population dynamics driven by either air temperature (combined with atmospheric temperature soundings) or land surface temperature derived from satellites to predict the population trends of the leaf beetle Ophraella communa, a potential biological control agent of Ambrosia artemisiifolia in Europe. For this, we conducted an extensive field experiment that included caged O. communa populations at five sites along an altitudinal gradient (125–1250 m a.s.l.) in Northern Italy during 2015 and 2016. We compared our model predictions using air or land surface temperature with observed beetle population build-up. Model predictions with both air and land surface temperatures predicted a similar phenology to observed populations but overestimated the abundance of the observed populations. When taking into consideration the error of the two measurement methods, the predictions of the model were in overlapping timeframes. Therefore, the current model driven by LST can be used as a proxy for herbivore impact, which is a novel tool for weed biocontrol. [ABSTRACT FROM AUTHOR]

• Performance and survival of Ophraella communa populations differ in their response to temperature. • Variation in thermal reaction norms for survival indicate the potential of O. communa populations to cope with variation in environmental conditions. • We found no risk of increasing non-target effects on sunflower under different temperature regimes. • There was no significant correlation between genetic diversity and phenotypic trait means. Although biological control agents (BCAs) are an effective tool for limiting the impact of invasive alien plants (IAPs), mismatch between the BCA and IAP, exacerbated by future climate change, may affect biocontrol efficacy and the likelihood of there being non-target effects. In a common-environment experiment, we measured leaf consumption, performance (i.e. development time and adult weight), and survival in 11 populations of the leaf beetle Ophraella communa from its native (North America) and introduced (China, Europe) ranges under three temperatures treatments (20 °C, 27 °C, 31 °C) and on two plant species, the target IAP Ambrosia artemisiifolia (common ragweed) and the closely-related crop Helianthus annuus (sunflower) , a potential subsidiary non-target host. Leaf consumption, development time, adult weight and survival differed significantly in the different populations without any significant geographical pattern. Specifically, there was variation in levels of survival at different temperatures between populations, with highest levels of leaf consumption and survival in the Fogang (China) population at all temperatures, while survival was highest in other populations under colder and warmer conditions. In general, we observed faster development and a marginal increase in adult weight, but decreasing survival, with increasing temperatures in all populations. The beetles consumed much more common ragweed than sunflower leaves, with no difference evident in the consumption levels on sunflower under cooler or warmer temperature conditions. Moreover, cold temperatures negatively affected the survival of beetles feeding on sunflower, potentially leading to a reduction of fitness on the non-target host. Genetic composition and diversity, assessed using microsatellite markers, showed higher allelic richness and expected heterozygosity in native US populations compared to introduced Chinese populations and lower allelic richness and expected heterozygosity in US and Italian populations at the edge of the distribution compared to core populations. Overall, Chinese populations showed low genetic diversity, likely due to releases after mass rearing. Although there were differences in genetic diversity among populations, we did not find correlations between genetic diversity and phenotypic trait means. Our results indicate that some of the populations examined might be able to cover areas that are heavily infested by common ragweed or are expected be so under climate warming but are predicted to be presently unsuitable for the beetle. [ABSTRACT FROM AUTHOR]

• Ophraella communa, a biocontrol agent of ragweed, was recently found in Europe. • Risk assessments of non-target effects of this beetle were lacking for Europe. • It is known to be Heliantheae-specific; no European native members of this tribe. • We found spill-over but no sustained attack on members of Inuleae and Coreopsideae. • Risks of non-target attack of European plant species by O. communa appear to be low. In 2013, the North American oligophagous leaf beetle, Ophraella communa LeSage (Coleoptera: Chrysomelidae), was found in Europe for the first time. Recent studies in Northern Italy and Southern Switzerland record extensive defoliation by O. communa on its preferred host, common ragweed, Ambrosia artemisiifolia L. (Asteraceae, Tribe Heliantheae), and reductions in its flowering and seeding. In some regions in Northern Italy, this has reportedly led to a > 80% depletion in airborne A. artemisiifolia pollen concentrations. The potential for non-target damage by O. communa to closely related native European plant species was previously unknown. During extensive field surveys covering 18 populations of nine potential non-target species, we found adult O. communa on a single plant individual. In a common garden field experiment in Northern Italy in an area with high O. communa densities, leaf damage was highest on two other Asteraceae species, Dittrichia graveolens (L.) Greuter and Pentanema helveticum (Weber) D.Gut.Larr. (both in the Tribe Inuleae). While adult feeding was observed on most of the test plant species, only D. graveolens , which has recently extended its range and is now an invasive species in Western Europe , sustained all life stages of O. communa in the common garden and in laboratory experiments. We found no evidence of substantial non-target effects by O. communa that could potentially threaten populations of European native plant species that are taxonomically closely related to ragweed. [ABSTRACT FROM AUTHOR]