Vincetoxicum Rossicum Research Articles

Excising the ghosts of invasions past: restoring native vegetation to soil infested with invasive swallow-worts

Abstract Invasive plants can gain a foothold in new environments by manipulating soil conditions through allelopathy or through the disruption of associations between native plants and their mycorrhizal associates. The resulting changes in soil conditions can affect the recovery of habitats long after the invasive plant has been removed. We conducted a series of greenhouse experiments to examine the effects of soil conditioned by pale swallow-wort [Vincetoxicum rossicum (Kleopow) Barbarich; Apocynaceae], on the growth of native plants. Additionally, we tested the effects of aqueous extracts of common milkweed (Asclepias syriaca L.; Apocynaceae), a related plant with known allelopathic effects, on the regrowth of V. rossicum from transplanted root crowns. Soil from a 15-yr-old V. rossicum infestation reduced seedling emergence in A. syriaca as well as in V. rossicum itself. Conversely, the same soil had no effect on the growth of mature A. syriaca plants. Soil conditioned by V. rossicum growth in the greenhouse had no effect on the biomass and percentage cover generated by two restoration seed mixes. Soil conditioned by A. syriaca, however, yielded lower biomass and percentage cover from both seed mixes. In contrast to the allelopathic effects of A. syriaca on seedlings, aqueous extracts of A. syriaca increased aboveground plant growth in V. rossicum. Our results suggest that the effects of V. rossicum–conditioned soil on native plants are concentrated at the seedling establishment phase. Additionally, the use of diverse native seed mixes shows great potential for restoring productivity to ecosystems affected by V. rossicum.

Mass spectrometry-based metabolomics for the elucidation of alkaloid biosynthesis and function in invasive Vincetoxicum rossicum populations

The genus Vincetoxicum includes a couple of highly invasive vines in North America that threaten biodiversity and challenge land management strategies. Vincetoxicum species are known to produce bioactive phenanthroindolizidine alkaloids that might play a role in the invasiveness of these plants via chemical interactions with other organisms. Untargeted, high-resolution mass spectrometry-based metabolomics approaches were used to explore specialized metabolism in Vincetoxicum plants collected from invaded sites in Ontario, Canada. All metabolites corresponding to alkaloids in lab and field samples of V. rossicum and V. nigrum were identified, which collectively contained 25 different alkaloidal features. The biosynthesis of these alkaloids was investigated by the incorporation of the stable isotope-labelled phenylalanine precursor providing a basis for an updated biosynthetic pathway accounting for the rapid generation of chemical diversity in invasive Vincetoxicum. Aqueous extracts of aerial Vincetoxicum rossicum foliage had phytotoxic activity against seedlings of several species, resulting in identification of tylophorine as a phytotoxin; tylophorine and 14 other alkaloids from Vincetoxicum accumulated in soils associated with full-sun and a high-density of V. rossicum. Using desorption-electrospray ionization mass spectrometry, 15 alkaloids were found to accumulate at wounded sites of V. rossicum leaves, a chemical cocktail that would be encountered by feeding herbivores. Understanding the specialized metabolism of V. rossicum provides insight into the roles and influences of phenanthroindolizidine alkaloids in ecological systems and enables potential, natural product-based approaches for the control of invasive Vincetoxicum and other weedy species.

Examination of Manual Removal Strategies for Dog Strangling Vine

In the summer of 2019, the Junior Naturalists posed a question regarding the control of Dog Strangling Vine (DSV), an invasive plant that is present in the Humber Arboretum. This group conducts stewardship activities in the Arboretum to help balance the environment by using non-chemical methods to control some of the invasive plant species there. They had been cutting off the flowers of the DSV to prevent seed production, but this did not affect the survival of the plants. This research project was created in response to the group’s question. Four strategies were studied for their efficacy in controlling the growth of DSV. These strategies were digging out the plant, pulling out the stalk, cutting the crown beneath the soil surface, and cutting the stalk above the soil surface. While each approach has its benefits and drawbacks, digging the entire plant out of the ground was found to be the most effective in preventing the regrowth of the individual plant. The research is intended to guide student gardeners working in ornamental gardens at the Arboretum and stewardship volunteers working in public parks in non-chemical strategies to be used for controlling DSV. The most effective control efforts should be repeated from year to year, which can result in long-term control of DSV in cultivated gardens and natural areas. This study has limitations since it was enacted on natural areas that had already been overtaken by DSV, which means that the numbers of plants, seeds, and other species in each plot were not consistently uniform. In a subsequent investigation, standardized, cultivated plots of DSV could be created and different competitive native species could be added to determine the effects of treatments on these combinations.

Multiple stressors prevent gains in native plant diversity following invasive species removal

AbstractLand managers spend substantial resources managing invasive species to mitigate their negative ecological and economic impacts. However, invasive species management is seldom coupled with empirical assessments of management outcomes or the ecological impacts of the target species. Additionally, the study of invasive species has, until recently, neglected to acknowledge co‐stressors on native communities, which often are the drivers of ecological degradation. We assessed the effects of the invasive plant Vincetoxicum rossicum and its removal on understory plant communities, as well as whether these effects were mediated by deer and invasive earthworms. We used paired fenced and open plots with V. rossicum and an open plot without V. rossicum at each of the three forested sites in New York State Parks from 2017 to 2020. Following a nested design, we located paired sets of open and fenced plots in areas where V. rossicum was experimentally removed and in areas where it was unmanaged. After three years of V. rossicum removal, V. rossicum significantly declined. However, the ultimate goal of management was native plant recovery. Contrary to this aim, native plant diversity and cover increased if V. rossicum was left unmanaged but did not change with V. rossicum removal. Thus, we provide strong evidence that reducing target species abundance does not always translate into native plant recovery. This disparity may be because deer and invasive earthworms are stronger drivers of understory plant communities than V. rossicum, as native plant cover and diversity were lower the more earthworms were in a plot and invasive plant species declined after fencing to exclude deer. Management that prioritizes reducing deer and earthworm impacts over invasive plant removal is therefore worth exploring, especially when coupled with continued monitoring to assess if these actions result in the desired management outcomes. Overall, our findings underscore the need to collect data to test management assumptions: reducing the abundance of an invader may not always result in native plant recovery, especially if other stressors are the ultimate drivers of change in invaded communities.

Quantifying and linking mechanism scenarios to invasive species impact.

Plant species invasion represents one of the major drivers of biodiversity change globally, yet there is confusion about the nature of nonindigenous species (NIS) impact. This confusion stems from differing notions of what constitutes invasive species impact and the scales at which it should be assessed. At local scales, the mechanisms of the impact on local competitors can be classified into four scenarios: (1) minimal impact from NIS inhabiting unique niches; (2) neutral impact spread across the community and proportional to NIS abundance; (3) targeted impact on a small number of competitors with overlapping niches; and (4) pervasive impact that is disproportionate to NIS abundance and caused by modifications that filter out other species. I developed a statistical test to distinguish these four mechanism scenarios based on plant community rank-abundance curves and then created a scale-independent standardized impact score. Using an example long-term dataset with high native plant diversity and an abundance gradient of the invasive vine, Vincetoxicum rossicum, I show that the impact resulted in either targeted or pervasive extirpations. Regardless of whether the NIS impact is neutral, targeted, or pervasive, the net outcome will be the homogenization of ecosystems and reduced biodiversity at larger scales, perhaps reducing ecosystem resilience. The framework and statistical evaluation of impact presented in this paper provide researchers and managers with an objective approach to quantifying NIS impact and prioritizing species for further management actions.

Testing the assumption of environmental equilibrium in an invasive plant species over a 130 year history

Invasive plants are an increasing threat to global biodiversity. Effective management depends on accurate predictions of their spread. However, modelling the geographic distribution of invasive species, particularly with correlative species distribution models (SDMs), is challenging. SDMs assume that species are in equilibrium with their environment (i.e. they occur in all suitable environments); this assumption is likely to be violated for a species that is actively invading new environments. This assumption is rarely assessed, and when violated can have consequences for model reliability. Using the invasive vine Vincetoxicum rossicum, we tested the hypotheses that: 1) invasive species' distribution in environmental and geographic space increase to a plateau over time; 2) this plateau is a useful proxy for equilibrium distribution, a key assumption underlying SDMs. We compare V. rossicum's expansion in environmental and geographic space between historical and current time periods and infer equilibrium when its distribution has remained stable for an extended period. We also compare the performance of SDMs from historical time periods in predicting the current geographic distribution of V. rossicum. We found that V. rossicum has reached equilibrium in environmental space, but is still expanding its geographic distribution. SDM performance was poor in the first 30 years following introduction, but improved as V. rossicum approached environmental equilibrium. Our findings demonstrate the power of including temporal dynamics and the need to consider environmental and geographic equilibrium separately when modelling the distribution of invasive species. In light of our findings, we address shortcomings of the current approach to defining an equilibrium distribution and present a new perspective for reconciling the potentially confounding influence of dispersal limitation when assessing equilibrium distribution.

Prioritizing sites for terrestrial invasive alien plant management in urban ecosystems

Abstract Rapid urbanization is placing increased pressure on natural, restored and designed ecosystems to provide services to growing human populations. The establishment and spread of invasive alien species within and around urban areas threaten biodiversity and ecosystem functioning, and the services they provide. Consequently, there is a need to protect and manage areas where invasions will have the greatest socio‐ecological impact. Limited resources call for the strategic prioritization of these areas, yet there are few widely adopted, standardized approaches for prioritizing sites vulnerable to species invasions in urban areas. We applied multi‐criteria decision analyses in a geographic information system to develop a strategic, spatial prioritization approach for identifying those sites most sensitive to terrestrial alien plant invasions. To test this approach, we use the Toronto region as a case study, the most populous metropolitan area in Canada and one of the fastest growing urban centres in North America. Through consultation with local conservation authorities, we developed an objective, hierarchical set of 19 criteria grouped into two categories: biodiversity and ecosystem functioning, and ecosystem services. Spatial data layers were assigned to each criterion and used to map areas most important for biodiversity and ecosystem functioning and providing ecosystem services. We overlayed these priority areas with distribution data of Vincetoxicum rossicum, one of the Toronto region's most widespread and damaging invasive alien plant species (IAPs) to determine the potential threat species’ invasions pose to these important areas. High‐priority sites identified by our prioritization model include areas of significant biodiversity conservation value such as intact forests, meadows and wetlands which are crucial for providing regulating and supporting services. Our IAPs distribution map showed that these high‐priority sites are heavily invaded (92.9% of the area occupied by V. rossicum comprises medium‐high‐priority sites) and should be prioritized for management to ensure biodiversity and ecosystem functioning and the provision of ecosystem services are maximized. The approach applied in this study can be useful for conservation practitioners in guiding the selection of high‐priority, socio‐ecologically significant sites for management action in urban landscapes across different geographic regions and spatial scales.

Soil Characteristics of North American Sites Colonized by the Non-Native, Invasive Vines Black Swallow-Wort and Pale Swallow-Wort

Vincetoxicum nigrum (Black Swallow-wort) and V. rossicum (Pale Swallowwort) are non-native, perennial vines that are spreading across North America. We collected soil samples from invaded sites in the northeastern United States and southeastern Canada. We also performed GIS analyses using the site locations, locations from iMapInvasives, and soil data from SSURGO. We found that Black Swallow-wort tended to occupy Inceptisols while Pale Swallow-wort occupied soils with more silt and clay, including Alfisols. Mean soil pH was lower at Black Swallow-wort sites compared to Pale Swallow-wort sites. However, both species colonized soils that varied widely in pH, fertility, texture, and taxonomy. We conclude that abiotic soil characteristics do not strongly constrain swallow-wort distributions in North America.

Prioritizing terrestrial invasive alien plant species for management in urban ecosystems

Abstract Invasive alien plant species (IAPs) in urban areas can have detrimental effects on biodiversity, ecosystem services and human well‐being. Urban areas are complex social management mosaics with high land‐use diversity, complex land tenure patterns and many different stakeholder groups, some of which derive benefits from invading species. Urban conservation practitioners face complex decisions about which IAPs require management. Yet most IAPs prioritization frameworks have been designed for and implemented in natural or rural areas and are generally inadequate for guiding effective and sustainable interventions in urbanized areas. We modified an existing prioritization scheme to develop a framework for prioritizing terrestrial IAPs in urban areas which applies evidence‐based (data‐driven) and stakeholder‐based (local knowledge) assessments to score and rank alien plant species in terms of their priority for management using an objective set of criteria. The framework consists of 46 criteria, grouped into eight modules which assess invasion status, habitat requirements, biological characteristics, dispersal ability, distribution, impacts (positive and negative) and potential for control for each alien plant species under consideration. We use the city of Toronto, Canada as a case study to test our framework—a list of 50 IAPs were effectively scored and ranked in order of high to low priority for control. Species with the highest total prioritization scores were Vincetoxicum rossicum (Dog Strangling Vine), Convolvulus arvensis (Field Bindweed) and Taraxacum officinale (Common Dandelion, ranked 1, 2 and 3 respectively). Many of the identified high priority species align with those previously flagged as of management concern by conservation practitioners, but also include those that are not actively managed due to their perceived lower ecological impacts. These species still require high resource investment for other objectives such as aesthetics. This highlights the complexity of alien plant species management in urban areas. Synthesis and applications. Prioritizing invasive alien plants for management in urban areas is particularly challenging due to often conflicting ecological, economic and social objectives. We use available evidence and local stakeholder knowledge to develop an objective and systematic prioritization tool which can assist conservation practitioners in selecting priority species for management action in complex urban landscapes.

Southern blight of perennial swallowwort (Vincetoxicum spp.) in New York

AbstractPale swallowwort [Vincetoxicum rossicum (Kleopow) Barbar.; syn.: Cynanchum rossicum (Kleopow) Borhidi] and black swallowwort [Vincetoxicum nigrum (L.) Moench; syn.: Cynanchum louiseae Kartesz & Gandhi] are invasive perennial viny milkweeds that have become prevalent across natural and managed habitats in northeastern North America. Southern blight of V. rossicum caused by the fungus Athelia rolfsii (Curzi) C. C. Tu & Kimbr. was reported at a New York county park in 2008, resulting in a decline in V. rossicum stands. The disease outbreak and persistence of the pathogen highlighted the potential of A. rolfsii for Vincetoxicum spp. control. To better characterize A. rolfsii’s pathogenicity and biology, we studied virulence to adult Vincetoxicum spp., spatiotemporal attributes of the Southern blight epidemic at the discovery site over 4 yr, and sclerotial survival over 2 yr. Disease incidence and severity were high for both Vincetoxicum spp. in misting chamber experiments. The spatiotemporal spread patterns of Southern blight in V. rossicum suggest the epidemic in the first year of monitoring (2016) was already highly aggregated and that subsequent spread was limited and resulted in significant local aggregation. Sclerotial survival studies at two locations (Pittsford and Ithaca, NY) demonstrated the A. rolfsii isolates can overwinter in upstate New York and are pathogenic to Vincetoxicum spp. the subsequent season. However, shallow burial of sclerotia more rapidly reduced survival compared with placement on the soil surface. Overwinter survival of A. rolfsii sclerotia in New York is notable, as this pathogen is typically associated with subtropical and tropical regions. Broadcast applications of the pathogen would be needed for widespread Vincetoxicum control at a site, but even restricting releases to select locations would not prevent pathogen movement off-site via water or machinery. The known risks of the A. rolfsii isolate to other broadleaf plants in natural and agricultural settings suggest a low feasibility of use for the biological control of Vincetoxicum spp.

Does the Presence of the Biological Control Agent, Hypena opulenta (Lepidoptera: Erebidae) on Swallow-Worts Deter Monarch Oviposition?

Invasive black and pale swallow-worts (Vincetoxicum nigrum (L.) Moench, and Vincetoxicum rossicum Kelopow), which are related to milkweeds, can act as ecological traps for monarch butterflies (Danaus plexippus L. (Lepidoptera: Nymphalidae)) as they lay eggs on them that fail to develop. A recently approved biological control agent against swallow-worts, Hypena opulenta Christoph, occupies the same feeding guild on swallow-worts as monarch larvae and could be perceived as a competitor to monarchs. We tested how the presence of this defoliating moth on swallow-worts may influence monarch host selection. In a two-year field experiment, we placed pale swallow-wort plants that were either infested with H. opulenta or noninfested as well as common milkweed (Asclepias syriaca L.), into monarch habitats to assess oviposition rates. In the laboratory, monarchs were either given a choice or not between milkweeds and black swallow-worts with or without H. opulenta. While monarchs strongly preferred common milkweed in the field, up to 25% of the eggs we observed were laid on pale swallow-wort, without preference for swallow-wort with (10.7%) or without (14.3%) H. opulenta. In laboratory choice and no-choice tests, monarchs did not lay any eggs on black swallow-wort, likely because of the long-term laboratory rearing on common milkweeds. Our results confirm that pale swallow-wort may act as an oviposition sink to monarchs in Michigan as well. Since the biological control program is still in its infancy, the nature of interactions between monarchs and H. opulenta may change as the biocontrol agent becomes more widespread.

Biomass allocation of Vincetoxicum rossicum and V. nigrum in contrasting competitive environments.

Understanding how drought and biomass allocation patterns influence competitive ability can help identify traits related to invasiveness and guide management. Vincetoxicum nigrum and V. rossicum are increasingly problematic herbaceous perennial vines in the northeastern United States and southeastern Canada. Using a greenhouse experiment, we investigated how biomass allocation and competition intensity of Vincetoxicum spp. responded to four competitive regimes at two levels of soil water availability in the presence of conspecific or congeneric neighbors. Soil moisture was the most important influence on growth and biomass allocation. Vincetoxicum nigrum had a greater capacity for growth and reproduction than V. rossicum, especially under drought. Drought reduced the probability of reproduction for V. rossicum. Vincetoxicum rossicum had a higher root-to-shoot ratio than V. nigrum under adequate soil moisture. This difference more than doubled under drought. Under interspecific competition, V. nigrum maximized its biomass, while V. rossicum limited aboveground growth and reproduction. Root-only competition increased shoot and root biomass relative to shoot-only competition. The effects of root and shoot competition were additive under interspecific competition, but interacted under intraspecific competition (negative interaction under drought and positive interaction under sufficient soil moisture). Management strategies targeting mixed populations of V. rossicum and V. nigrum are most important under ample water availability. Under drought conditions, strategies focused on V. nigrum should effectively limit Vincetoxicum growth and seed reproduction. Phenotypic plasticity and the positive competition intensity associated with drought in monocultures may contribute to drought resistance in these invasive species.

Density-dependent impacts of invasive Vincetoxicum rossicum (pale swallowwort) and native Asclepias syriaca (common milkweed) on plant traits and competitive interactions

Density-dependent impacts of invasive Vincetoxicum rossicum (pale swallowwort) and native Asclepias syriaca (common milkweed) on plant traits and competitive interactions

Invasion drives plant diversity loss through competition and ecosystem modification

Abstract Although invasive plants increasingly contribute to the current biodiversity crisis, the mechanisms through which they impact native communities are still poorly understood. Community ecology theory has emphasized direct competitive displacement over common resources, but invasion‐driven ecosystem modifications, such as altered soil pH, might also have consequences for plant diversity. However, the relative importance of ecosystem modification compared to direct resource competition has rarely been tested. Here we studied the invasive vine Vincetoxicum rossicum across invaded meadows in southern Ontario, Canada. In each meadow site, we quantified: (a) the strength of impact on the resident plant community, (b) the potential for competition with resident species (as the degree of niche dissimilarity and competitive superiority to the residents based on their functional traits) and (c) the amount of ecosystem modification related to invasion. We found that impacts on plant biodiversity were more negative where the invader had greater potential to competitively displace species (because it had a similar niche as the residents or was competitively superior), but also where it strongly altered soil N pools, moisture and pH. Synthesis. Our case study suggests that while competition is undoubtedly an important driver of invasion impact, ecosystem modifications can have cascading effects on plant communities, thereby magnifying the impacts of biological invasions.

Fungal endophytes increase biomass production in pale swallow-wort (Vincetoxicum rossicum (Kleopow) Barbar.)

Pale swallow-wort, Vincetoxicum rossicum (Kleopow) Barbar., is an invasive weed in the lower Great Lakes Basin of North America. We investigated the relationship between V. rossicum productivity and several environmental variables across 54 established V. rossicum populations in southern Ontario. Variables included climate measurements, soil characteristics (pH, texture, and nutrient status), habitat type, plant community, and the diversity of root-associated fungi. Vincetoxicum rossicum roots were collected at all 54 sites, and associated fungi were compared using terminal restriction fragment length polymorphism. Aboveground biomass of V. rossicum was measured at 23 sites with similar light regimes, allowing comparison between populations. Results suggested that abiotic soil variables, and habitat type have little effect on V. rossicum productivity. Aboveground biomass production was significantly correlated with precipitation, and the presence of fungal pathogens and dark septate endophytes. Annual precipitation and soil clay content were also positively correlated with the abundance of soil pathogens. Accumulation of these microbes may negatively affect co-occurring native plants and associated fungal partners. The presence of these fungal species in soil could be used as an indicator of site susceptibility to invasion by V. rossicum and assist in the development of management plans for this exotic vine.

Invasive dominance and resident diversity: unpacking the impact of plant invasion on biodiversity and ecosystem function

AbstractPlant invasions have consistently been shown to cause significant reductions in the diversity of recipient plant communities; an effect that can cascade through ecosystems to impact the stocks and flows of nutrients and energy as well as the diversity of higher trophic levels. However, the manner in which invasive plants alter ecosystem functioning and trophic interactions is highly variable can occur through the direct effects of the invader's abundance and its indirect effects via changes in community diversity. Understanding the nature of these interactions between plant invasion, community diversity and ecosystem functioning can provide insight for ecosystem managers. We evaluated whether plant invasion alters the relationship between biodiversity and ecosystem function (BEF) by comparing BEF models that either include or subtract the diversity and function values associated with the invasive vine,Vincetoxicum rossicum.To do this, we (1) characterizeV. rossicumwithin the functional trait space of the regional species pool, (2) assess how different components of plant biodiversity vary along aV. rossicuminvasion gradient, and (3) examine howV. rossicuminvasion affects BEF relationships and trophic interactions, both at the plot‐scale and incrementally along a site‐level invasion gradient. In general, we found thatV. rossicuminvasion was associated with significant declines in plant community diversity across a suite of biodiversity measures; a consequence ofV. rossicum's functional trait structure (height and specific leaf area). We also found thatV. rossicuminvasion resulted in significantly greater productivity (i.e., dominance effects in the inclusion model), but also that the diversity of the remaining resident community was positively associated with productivity (i.e., niche complementarity in the subtraction model). Further, we observed that while the relationship between flower cover and pollinator diversity was positive for both the inclusion and subtraction models, this relationship was stronger in the absence ofV. rossicum. Our findings suggest that while plant invasion can result in enhanced productivityviadominance effects, this comes at the cost of significant declines in diversity. However, it is also the case that remaining resident diversity can exhibit positive effects on multiple functions and support for higher trophic levels.

Urbanization and plant invasion alter the structure of litter microarthropod communities.

Anthropogenic activity underpins the creation of urban ecosystems, often with introduced or invasive species playing a large role in structuring ecological communities. While the effects of urbanization on charismatic taxa such as birds, bees or butterflies have received much attention, the impacts on small and inconspicuous organisms remain poorly understood. Here, we assess how the community structure of leaf litter-inhabiting microarthropods in city parks varies along an urbanization gradient in Toronto, Canada. At each park, we established paired forest understorey plots which were either dominated by native vegetation or dog-strangling vine Vincetoxicum rossicum, an invasive species that is spreading throughout northeastern North America and abundant in urban areas. We compared microarthropod richness, abundance and diversity in ecological traits between invaded and non-invaded plots as well as compositional dissimilarities among plots across the urbanization gradient. We recorded 123 genera and found (a) there was a negative effect of urbanization on microarthropod richness and abundance but only in invaded plots; (b) richness and abundance increased continuously with urbanization in non-invaded plots, but peaked at intermediate urbanization levels in invaded plots and (c) there was significant turnover with increasing urbanization, with distinct communities represented in highly urbanized areas compared to less urbanized areas, regardless of whether invaded. We also found litter microarthropod richness and abundance increased with soil ammonium and decreased with nitrate. These trends were especially strong for fungivorous microarthropods; however, there was no relationship between soil nutrients and urbanization or invasion. Urbanization and biological invasion drive biodiversity change, and there is a need to disentangle these effects on ecological communities and related ecosystem processes. We show microarthropod communities change with urbanization, with the effects of invasion most prominent in non-urban areas. Here, there is high richness and abundance but low ecological trait diversity, possibly because certain feeding traits are excluded and others overrepresented. Understanding of urban ecological systems must include knowledge of the microarthropods that interact widely across food webs, form distinct communities in highly urban areas and drive many of the important ecological functions upon which people in cities depend.

An experimental application of Hypena opulenta as a biocontrol agent for the invasive vine Vincetoxicum rossicum

Abstract1. Pre‐release testing for biological control agents is focused primarily on assessment of host‐range specificity and safety of potential agents. Agent impact is considered pre‐release; however, the ultimate assessment of an agent must occur following release in the field under the target population levels and conditions of the invaded ecosystems. The invasive Eurasian vine, Vincetoxicum rossicum, has spread aggressively through its invaded range of eastern North America since its initial introduction in the late 1800s. In laboratory tests, the Eurasian moth Hypena opulenta has shown great promise as a potential control agent for V. rossicum.2. We were interested in the defoliating ability of H. opulenta and its subsequent effect on the seed production of V. rossicum under field conditions. To examine this, we established a field site near Kirkfield, Ontario, that consisted of meadow and forest understory plots, both of which were highly invaded by V. rossicum.3. We report highly significant feeding by H. opulenta in both light conditions. Unexpectedly, we observed a significant increase in seed production following folivory in shade conditions. We observed no significant effect of larval folivory on seed production under sun conditions, where V. rossicum seed production is greater by a factor of 10 as compared to shade conditions.4. It is unclear how continuous exposure to folivory by H. opulenta will affect mature V. rossicum stands, although it might be expected that such populations would invest in defenses to herbivory, possibly at the expense of reproductive output. In order to better understand if V. rossicum populations in either light condition could exhibit longer‐term compensatory growth in response to folivory, further experimental work is needed that examines inter‐annual variability in V. rossicum reproduction at variable H. opulenta densities.

Interpreting host-test results for classical biological control candidates: Can the study of native congeners improve the process?

When an insect candidate is identified for classical biological control, the first step is to identify its fundamental host-range. An insect’s fundamental host range, however, is typically broader than its ecological host range. This discrepancy can lead to ‘false positives’ in host testing and hamper the development of potential agents. Here, we propose a novel tool for interpreting host-range tests and identifying ‘false positives’ by studying native insects closely related to the biological control candidate. We conduct a series of laboratory and field studies comparing the fundamental and ecological host ranges of Chrysochus auratus Fabricius (Coleoptera: Chrysomelidae), a beetle native to North America, and present throughout the range invaded by pale swallow-wort, Vincetoxicum rossicum (Kleopow) Barbar. (Apocynaceae). We use the results to re-evaluate the risk associated with releasing the closely-related European beetle, Chrysochus asclepiadeus (Pallas) (Coleoptera: Chrysomelidae), a biological control candidate for V. rossicum that has raised some concerns because of no-choice feeding on North American milkweed species (Asclepias spp.) during laboratory host-testing. Laboratory and greenhouse trials here show that native North American C. auratus adults can feed and complete larval development on several native Asclepias species (fundamental host range), however in the field where both closely-related plant genera are present, this species specialized only on plants in the genus Apocynum. It appears then that Asclepias species generate ‘false positives’ for Chrysochus beetles when only the fundamental host range is assessed in the laboratory, and there is a need to re-evaluate C. asclepiadeus for potential biocontrol in North America taking into account its ecological host-plant range. We advocate for the inclusion of closely-related native congeners, where appropriate species exist, to aid in interpreting host-plant testing for potential classical biological control agents.

Response of pale swallowwort (Vincetoxicum rossicum) to multiple years of mowing

AbstractPale swallowwort (Vincetoxicum rossicum), as well as its congener, black swallowwort (Vincetoxicum nigrum), is a European viny milkweed that has become invasive in natural areas and perennial cropping systems in the northeastern and midwestern United States and southeastern Canada. Mechanical control over 1 to 2 yr has not been effective, but studies of a longer duration are needed. We measured effects of mowing (no mowing or three or six times per growing season) on stem and root crown densities, percent cover, and follicle (seed pod) production of V. rossicum and percent cover of other vegetation over a 7-yr period. Stem density, root crown density, and percent cover of V. rossicum were reduced after 3 to 5 yr of mowing regardless of mowing frequency. Cover of other, mostly nonnative, broadleaf species increased. Follicle production was eliminated in all years of the study. In our environment, mowing three times at monthly intervals during the growing season can prevent seed production. However, mowing must occur for at least 3 yr to reduce, but not eliminate, stands of V. rossicum.