Invasive Vine Research Articles

Defensive Mechanisms of Mikania micrantha Likely Enhance Its Invasiveness as One of the World's Worst Alien Species.

Mikania micrantha Kunth is native to tropical America and has invaded tropical and subtropical Asia and numerous Pacific Islands. It forms dense thickets and reduces native species diversity and populations in its introduced range. This invasive vine also seriously impacts many agricultural crops and is listed as one of the world's 100 worst invasive alien species. Its life history characteristics, such as the production of large numbers of wind-dispersed seeds, vegetative reproduction, rapid growth, and genetic diversity all contribute to its invasiveness. In this review, we focus on how mechanisms to defend against its natural enemies boost the invasiveness of M. micrantha. It possesses potent defenses against natural enemies such as pathogenic fungi, herbivorous insects, and parasitic nematodes, and exhibits allelopathic potential against plant competitors. These defensive abilities, in concert with its formidable life history characteristics, contribute to the invasiveness of M. micrantha, potentially leading to further naturalization. Several other reviews have summarized the biology and management of the species, but ours is the first review to focus on how the defensive mechanisms of M. micrantha likely enhance its invasiveness. Relatively little is known about the array of defensive capabilities of M. micrantha; therefore, there is considerable scope for further research on its chemical defenses.

Flexible Resource Allocation-Efficient Water Use Strategies Facilitate Invasion of Invasive Vine Sicyos angulatus L.

The invasive vine Sicyos angulatus L. destroys the natural ecosystem of invaded areas. Understanding the differences in growth and development between S. angulatus and other plants is necessary to explore the invasion mechanisms of S. angulatus and implement appropriate prevention and control measures. Thus, this study compared the growth, photosynthesis, and root characteristics of invasive liana S. angulatus and other three vine plants, Ipomoea nil (L.) Roth, Ipomoea purpurea (L.), and Thladiantha dubia Bunge, at different growth stages: seedling, flowering, and fruiting. The results showed that the total biomass of S. angulatus in the fruiting stage was 3-6 times that of the other three plants, and the root biomass ratio and root-shoot ratio decreased throughout the growth stage. Throughout the growth stage, the total leaf area of S. angulatus was significantly higher than that of the other three plant types, and the specific leaf area of S. angulatus at the seedling and flowering stages was 2.5-3 and 1.4-3 times that of the other three plants, respectively. The photosynthetic rate, stomatal conductance, and transpiration rate of S. angulatus at the fruiting stage were significantly higher than those of the other three plants, and its water use efficiency was higher than that of the other three plants at the three growth stages, indicating its strong photosynthetic capacity. The root activity and root pressure of S. angulatus were also significantly higher than those of the other three plants at the seedling and flowering stages. These results show that S. angulatus flexibly allocates resources to its aboveground parts during the growth stage to ensure that the plant obtains the space necessary for its growth and development and that with the help of higher root pressure and root activity, S. angulatus can maintain higher photosynthesis and water use efficiency with fewer resources. Therefore, the prevention and control of S. angulatus requires a combination of aboveground and underground measures. Spraying conventional weedicide/herbicide and manually removing aboveground plants may lead to its resurgence.

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.

Long-term interactive impacts of the invasive shrubLonicera maackiiand white-tailed deer (Odocoileus virginianus) on a deciduous forest understory

AbstractWhite-tailed deer (Odocoileus virginianus) (hereafter, ‘deer’) and invasive plants affect forest understories, but few studies have investigated their interaction. We investigated long-term (11-yr) effects of excluding deer and removing the invasive shrub, Amur honeysuckle [Lonicera maackii(Rupr.) Herder], on plants in southwest Ohio. Deer exclusion enhanced tree seedling richness and density, but reduced annual and bare ground cover. Vine density was reduced byLonicera, especially where deer were excluded. Seedlings of several tree species, the invasive shrub, burning bush [Euonymus alatus(Thunb.) Siebold], and the invasive vine, winter creeper [Euonymous fortunei(Turcz.) Hand.-Maz.], were indicator species of the deer exclosure byLoniceraremoval treatment combination. The effect of deer on cover of native species depended onLoniceratreatment: where shrubs were removed, cover was higher where deer were excluded, but where shrubs were present, cover was higher where deer had access. We attribute these interactions to the reduced growth of, and shading by,Lonicerawhere deer had access and browsed this invasive shrub. Some of these effects were evident in the first 6 yr, but are now larger. Other effects were not evident in the earlier evaluation. These findings inform management of areas with high densities of deer and invasive shrubs palatable to deer. Control of only invasive shrubs will reduce native cover and not improve tree regeneration. Managing only deer will increase woody plants but reduce native cover. Management of both stressors is needed to promote tree regeneration and restoration of plant communities.

Evaluation of florpyrauxifen-benzyl for control of Old World climbing fern

Old World climbing fern [Lygodium microphyllum (Cav.) R. Br.; OWCF] is an invasive vine in many Florida wetlands. Management involves poodle cutting the climbing rachis at approximately 120 cm, with a subsequent foliar application of glyphosate to the remaining rooted vines. Recently, there has been increasing interest in synthetic auxin herbicides for OWCF control. Florpyrauxifen-benzyl is a new auxin mimic that was developed for weed control in aquatics and is selective at low use rates. There is limited information regarding its activity on OWCF. We conducted field studies at four wetland sites in south Florida from 2017 to 2020 to evaluate the effectiveness of florpyrauxifen-benzyl for OWCF control. In small-plot studies at two locations, florpyrauxifen-benzyl applied at 0.08 and 0.16 g L 1 reduced OWCFcover to 4%at 3 moafter treatment (MAT) and 21% at 6 MAT.However, florpyrauxifen-benzyl at these concentrations did not consistently control OWCF at 12 MAT. An additional study evaluated banded applications of florpyrauxifen-benzyl or glyphosate compared to poodle cutting for control of the climbing rachis. For both herbicides, banded applications did not control the climbing rachis, whereas poodle cutting provided complete control of all climbing rachis. Finally, an operational field study demonstrated florpyrauxifen-benzyl applied by professional applicators at 0.16 g L 1 reduced OWCF cover to 9% at 17 MAT and was not different from glyphosate applied at 14.4 g L 1. These studies indicate florpyrauxifen-benzyl is active on OWCF and future research should evaluate the effectiveness of repeat applications for longer-term control.

Assessing the status of biological control of air potato (Dioscorea bulbifera) in the southeastern USA

ABSTRACT Air potato, Dioscorea bulbifera L. (Dioscoreaceae), is an invasive vine that climbs into vegetation outcompeting native species and altering ecosystems in the southeastern USA. The biological control agent, Lilioceris cheni Gressitt and Kimoto (Coleoptera: Chrysomelidae), has been released in Florida since 2011 and in other states including Georgia (2015), Louisiana (2016), Texas (2017), Mississippi (2018), and Alabama (2018) to manage air potato. Despite the wide distribution of the weed and mass rearing efforts, there are no studies documenting the establishment of L. cheni outside of Florida. The objectives of this study were to document the beetle release efforts by several agencies and determine the establishment and impact of L. cheni across the southeastern USA. Using community science reports and field surveys, we documented the distribution of air potato and L. cheni. Results demonstrated that the distribution of air potato extends to temperate regions from South Carolina and Georgia to subtropical regions of Louisiana, Texas, and Florida. Surveys showed that the beetle is present across all states with releases, and numbers fluctuated between 6 and 37 beetles counted per 30-surveyor-minutes. Most sites sampled had moderate to high beetle damage (scales of 3–4 out of 5), and air potato cover was low to moderate (2–3 out of 5). However, air potato was still abundant in some areas, which suggests the need for additional beetle releases and/or the use of other tactics to achieve management goals.

Phenolic Acids and Flavonoids Play Important Roles in Flower Bud Differentiation in Mikania micrantha: Transcriptomics and Metabolomics

Mikania micrantha is a highly invasive vine, and its ability to sexually reproduce is a major obstacle to its eradication. The long-distance dissemination of M. micrantha depends on the distribution of seeds; therefore, inhibiting M. micrantha flowering and seed production is an effective control strategy. The number of blooms of M. micrantha differs at different altitudes (200, 900, and 1300 m). In this study, we used a combination of metabolomics and transcriptomics methods to study the patterns of metabolite accumulation in the flower buds of M. micrantha. Using LC-MS/MS, 658 metabolites were found in the flower buds of M. micrantha at three different altitudes (200, 900, and 1300 m). Flavonoids and phenolic acids were found to be the main differential metabolites, and their concentrations were lower at 900 m than at 200 m and 1300 m, with the concentrations of benzoic acid, ferulic acid, and caffeic acid being the lowest. The biosynthesis pathways for flavonoids and phenolic compounds were significantly enriched for differentially expressed genes (DEGs), according to the results of transcriptome analysis. The production of flavonoid and phenolic acids was strongly linked with the expressions of phenylalanine ammonia-lyase (PAL), caffeoyl-CoA O-methyltransferase (COMT), and 4-coumarate-CoA ligase (4CL), according to the results of the combined transcriptome and metabolome analysis. These genes’ roles in the regulation of distinct phenolic acids and flavonoids during M. micrantha bud differentiation are still unknown. This study adds to our understanding of how phenolic acids and flavonoids are regulated in M. micrantha flower buds at various altitudes and identifies regulatory networks that may be involved in this phenomenon, offering a new approach for the prevention and management of M. micrantha.

Geographical distribution and detection of two potyviruses occurring in Momordica charantia (Cucurbitaceae) in Puerto Rico

Transmission dynamics of viruses within and among cultivated plant species are often well known. Much less studied, especially in the tropics, is the dynamic of virus exchange between cultivated and nearby wild or weedy species, even though such exchanges are known to occur. To develop the best strategies for crop protection and general disease control, spatial distribution of viruses in non-cultivated plants needs to be understood. This research focuses on the potyviruses that infect Momordica charantia (Cucurbitaceae), an alien naturalized invasive vine in Puerto Rico. A total of 390 symptomatic and asymptomatic plants were sampled throughout Puerto Rico, including adjacent islands of Culebra and Vieques. Samples were subjected to an enzyme linked immunosorbent assay (ELISA) for general potyvirus screening, and to ELISAs specific for Papaya ringspot virus (PRSV) and Zucchini yellow mosaic virus (ZYMV). The species distribution model algorithm MaxEnt was used to predict suitable environments for the potential presence of potyvirus symptoms, potyvirus, PRSV or ZYMV in M. charantia. Almost half of the samples of M. charantia tested positive for ZYMV, PRSV or both viruses. Twice as many samples were positive for PRSV (39%) than for ZYMV (21%). About 14% of samples were positive for both potyviruses. Plants that tested positive for PRSV were three times more likely to be positive for ZYMV than were plants that were negative for PRSV. Plants that tested positive using the general potyvirus ELISA were much more likely to exhibit symptoms than plants testing negative for potyvirus. In comparison, PRSV and ZYMV samples testing positive or negative were equally likely to exhibit virus-like symptoms. When we classified samples according to habitat (agricultural, rural-nonagricultural, or urban), the presence/absence of symptoms and test results for potyvirus, PRSV and ZYMV were not dependent on habitat classification. By contrast, a MaxEnt model using 20 environmental variables was able to predict areas of Puerto Rico where environmental conditions are favorable for the potential presence of virus symptoms, potyvirus, PRSV or ZYMV in M. charantia. Conditions predicted by our model to be moderately to strongly suitable for the presence of PRSV in M. charantia covered a much larger area of Puerto Rico than they did for ZYMV. The vegetable growing region in the central to eastern south coast was predicted to have highly suitable environmental conditions for the presence of both potyviruses in M. charantia.

The invasive Tradescantia zebrina does not inhibit germination of the native Hymenaea courbaril but does modulate its growth

ABSTRACT Background Invasive plant species can modify ecosystem structure and function, potentially leading to the loss of native species, environmental and biotic homogenisation, changes in nutrient cycling, impairment of ecosystem services, and decrease in the rate of regeneration of plant recruits. Aims We assessed the effects of the non-native and invasive vine Tradescantia zebrina on the germination and development of the native tree Hymenaea courbaril in north-eastern Brazil. We hypothesised that the invasive species would negatively impact the germination and development, and, via competition, the growth of the native species. Methods We conducted a germination experiment for six months in seven forest patches. Seeds of H. courbaril were cultivated in four possible combinations of two treatments: under a cover with and without T. zebrina, and on soil that originated from places with and without T. zebrina present. Results Neither T. zebrina cover or soil affected the germination or biomass of H. courbaril during the experiment. H. courbaril seedlings were taller and had longer roots when cultivated in soil that originated from places with T. zebrina. Conclusions T. zebrina presence alters soil properties in a way that triggers morphological responses in H. courbaril, which can be associated to a perceived competition context.

Attraction of the Air Potato Leaf Beetle, Lilioceris Cheni, (Coleoptera: Chrysomelidae) to leaf Volatiles of the Air Potato, Dioscorea bulbifera.

Air potato, Dioscorea bulbifera L., is an invasive vine found in the southeastern United States and is native to Asia and Africa. The air potato leaf beetle Lilioceris cheni (Coleoptera: Chrysomelidae), is a host specific biological control agent introduced for D. bulbifera control. In this study, odor cues that control the attraction of L. cheni to D. bulbifera were investigated. The first experiment investigated the response of L. cheni to D. bulbifera leaves versus no leaves in the presence or absence of air flow. The experiment showed a significant response of L. cheni to D. bulbifera leaves in the presence of air flow with leaves placed upwind. When air flow and/or leaves were absent, L. cheni dispersed randomly between the upwind and downwind targets, indicating L. cheni uses volatiles from D. bulbifera in host selection. The second experiment investigated L. cheni response to undamaged, larval-damaged, and adult-damaged plants. Lilioceris cheni showed preference to move towards conspecific damaged plants compared to undamaged plants but did not discriminate between larvae-damaged or adult-damaged plants. The third experiment investigated volatile profiles of damaged D. bulbifera plants using gas chromatography coupled with mass spectroscopy. We found significant differences in volatile profiles between adult and larval damaged plants compared to mechanically damaged and undamaged plants, with increases in 11 volatile compounds. However, larval and adult-damaged volatile profiles did not differ. The information acquired during this study could be used to develop strategies to monitor for L. cheni and improve its biological control program.

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.

Thermal adaptation of photosynthetic physiology of the invasive vine Ipomoea cairica (L.) enhances its advantage over native Paederia scandens (Lour.) Merr. in South China.

This paper reveals that contrary thermal-adaptation strategies expanded the photosynthetic, growing, and physiological advantages of invasive I. cairica over native P. scandens under high temperature.

Response of black swallowwort (Vincetoxicum nigrum) to herbicides plus mowing

AbstractThe invasive vine black swallowwort [Vincetoxicum nigrum (L.) Moench = Cynanchum louiseae Kartesz & Gandhi, Apocynaceae] is difficult to control, and herbicide studies are lacking. This long-lived perennial species is primarily found in high-light environments in natural areas and perennial cropping systems in northeastern North America. We conducted a 3-yr herbicide efficacy study, with or without mowing, in an old-field site infested with V. nigrum in Dutchess County, NY, USA. Experimental plots were either herbicide treated in early July or mowed in early July and subsequently herbicide treated in late August for 2 yr with the potassium salt of glyphosate (2.02 kg ae ha−1), the isopropylamine salt of glyphosate (1.35 kg ae ha−1), or the butoxyethyl ester of triclopyr (1.79 kg ae ha−1). Both glyphosate formulations were effective in reducing V. nigrum aboveground biomass, although they were somewhat less effective in reducing cover or stem densities of V. nigrum plants >10-cm tall after 2 yr compared with untreated plots. Mowing did not always enhance the efficacy of foliar glyphosate applications. Triclopyr, with or without mowing, was generally not effective against V. nigrum in our study. The only significant effect of triclopyr was to increase the cover of grasses in the plots. While annual applications of glyphosate can be useful for management of V. nigrum infestations, higher rates and more frequent applications of triclopyr need to be investigated to determine its usefulness for V. nigrum control.

Use of support influences height and above-ground allometry but not biomass allocation to different aerial organs of an invasive vine

Use of support influences height and above-ground allometry but not biomass allocation to different aerial organs of an invasive vine

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.

Negative impact of new invasive species Dolichandria unguis-cati on the flora in Balh valley of Mandi district, India

India has rich plant and animal diversity. It is amongst twelve mega biodiversity countries of the worldand has ten biogeographical regions. It is rich in wild genetic biodiversity and apart from this also hailsnumber of exotic species. Prehistorically, number of plants were introduced and India harbours around18% exotic flora. Himachal Pradesh is rich in wild as well as exotic plant biodiversity. Approximately, its40% flora is exotic and of American origin. plants. These plants have reproduced, propagated andnaturalized in the new region. Sometimes, these species show aggressive behavior upon finding suitableresources and environmental conditions in a given area. These species have shown high fertility, dispersalrates and it has been reported that they secrete certain allelochemicals that adversely affect the growth andsurvival of native plants. Bidens pilosa, Lantana camara, Eucalyptussp, Parthenium hysterophorus, Populussp,Ageratum conyzoides, Argemone mexicna are some of examples of invasive species in India. This study wasconducted on a new invasive species Dolichandria unguis-cati in Balh valley and its effects on the surroundingflora. This species was introduced as an ornamental climber in the studied area. Within the small durationof time it shows high invasive nature and badly affects the local ecosystem of studied area. Study revealsthat this species shows alarming negative effects on local genetic pool of valley. Government should payattention to eradicate this invasive vine.

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.

Local grasses for the control of the invasive vine Mikania micrantha

Abstract Mikania micrantha (Asteraceae) is an invasive vine found in tropical and southern subtropical Asian and the Pacific Islands. The current methods used to control this vine are inadequate, which warrants the development of ecologically sustainable methods. Therefore, we investigated the ability of four grass species to prevent the invasion of M. micrantha, with an ultimate goal of developing ecologically sustainable control methods for widespread application. The clumps of native grass species from China (Panicum incomtum, Pennisetum purpureum, Saccharum arundinaceum and Microstegium vagans) were established. We sowed M. micrantha seeds and transplanted the seedlings into the grass clumps to examine whether the clumps could eliminate the new M. micrantha plants. In addition, we transplanted M. micrantha into existing grass clumps to examine whether the grass clumps could prevent the re-invasion of M. micrantha. Furthermore, we grew M. micrantha with P. incomtum and P. purpureum in the field to examine whether the grasses could outcompete M. micrantha. Mikania micrantha seeds germinated hardly in the grass clumps, and all seedlings died within 3 months. It was difficult for the vine to survive in the grass clumps. Our field experiments showed that the coverage of M. micrantha was significantly lower than that of the grass species in the first year, and that the vine was outcompeted after 2 years. To the best of our knowledge, this study is the first to reveal that tall grasses, particularly P. incomtum and P. purpureum, have potential to serve as bio-control agents for M. micrantha.

Potential impact and phenology of the biological control agent, Hypena opulenta on Vincetoxicum nigrum in Michigan

ABSTRACT Pre-release studies indicate that the defoliating moth, Hypena opulenta, can be effective at reducing biomass, survival, and seed production of invasive swallow-wort vines. However, laboratory studies to date report higher defoliation rates and larval densities than are present in the field five years post-release in Canada. To understand the consequences of H. opulenta feeding on black swallow-wort, Vincetoxicum nigrum, at more realistic densities, we conducted experimental cage releases in Michigan. We also evaluated the phenology of the moth. We released 1, 2, or 5 pairs of H. opulenta on caged swallow-wort and measured resulting larval densities, defoliation levels, plant fecundity and survival for two years. To determine which release date may result in two generations of H. opulenta in Michigan, we released adults in June or July at one sunny and one shaded location and followed their phenology. Larval densities and damage increased with release size, but plant survival and fecundity were not affected. Hypena opulenta produced two generations when released in June at >15 h day length. Survival of H. opulenta and defoliation rates were higher in the shaded environment. These results support previous findings regarding better performance of H. opulenta at shaded sites, however, larval densities achieved in the field both in this experiment and at Canadian release sites are still too low to negatively affect swallow-wort fitness. Moreover, we were unable to confirm overwintering success and thus establishment of H. opulenta in Michigan is not yet known.

The Relationships of Habitat Conditions, Height Level, and Geographical Position with Fruit and Seed Traits in Populations of Invasive Vine Echinocystis lobata (Cucurbitaceae) in Central and Eastern Europe

In climbing plants, fruits can be formed at different heights, depending on the height of external support. However, the effect of height on fruit and seed traits in invasive vines of Cucurbitaceae has not been intensively studied so far. In Europe, Echinocystis lobata, a North American member of Cucurbitaceae, is considered one of the most abundant invasive alien plants spreading in natural riparian forests, thickets, and tall herbs, whereas it is a rare species in urban woodlands. In this study, we tested the variability of selected fruit and seed traits of E. lobata in connection with habitat origin (natural, semi-natural, and anthropogenic), habitat type (using the EUNIS habitat classification), height (the distance between the fruit and the ground), and geographical position. The study was conducted in 2018 in 65 sites located in Latvia, Lithuania, Poland, and Slovakia. In each study site, a random sample of 10 fresh mature fruits of E. lobata was collected from subsequent 0.50 m intervals of height. The length, the width, and the weight of the fresh fruits, as well as the total number of seeds and number of undeveloped seeds per fruit, were examined. Moreover, the well-developed seeds from selected study sites were weighed. The statistical analysis showed the significant effect of habitat origin, habitat type, and height on most of the studied fruit and seed traits. The largest range of height (from 0.00 to 4.00 m) was observed in two types of habitats (F—heathland, scrub, and tundra; and G—woodland, forest, and other wooded land). The total number of seeds per fruit was positively correlated with the length, width, and weight of the fresh fruits. The fruits were a little heavier and bigger in natural habitats located in the northeast of the study area. The distribution of fruits at different heights may contribute to better dispersal of seeds by animals and wind, and may also better protect the seeds from being eaten by granivorous animals. The defence against seed-eating animals is expected to be stronger in semi-natural habitats, as well as on banks and shores of inland surface waters, where the seed production is the highest. The influence of seed traits on seed germination and seedling survival in various habitats and their importance in the invasiveness of E. lobata require further study.