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As part of an Urban Buzz scheme, strips of teasel (Dipsacus fullonum) and greater knapweed (Centaurea scabiosa) have been established along a sea wall flood defense in the UK to provide a corridor of flower-rich habitat for pollinators such as bees and butterflies. The cutting of tall grassland and planting of dicotyledons also created a suitable short sward environment (c. 30 cm height) for Orthoptera nymphs in the establishment year (2018). However, by 2019, the grassland in the pollinator strips was taller (c. 75 cm) and suboptimal for grasshoppers; in contrast to Roesel's bushcricket (Roeseliana roeselii), which inhabited the taller vegetation in greater abundance. The progression to established grassland with flowering D. fullonum saw the pollinator strips attract significantly higher numbers of bees and butterflies than the floristically poor control strips. This small-scale study illustrates that pollinator strips can have multi-functional benefits for ecosystems beyond pollination, with Orthoptera of tall grassland (R. roeselii) likely to persist alongside planted wildflowers. [ABSTRACT FROM AUTHOR]

Spotted knapweed, Centaurea stoebe L. (Asteraceae), is an invasive perennial forb that has become economically and ecologically damaging in North America. The weevil Larinus minutus Gyllenhal (Coleoptera: Curculionidae), a biological control agent of invasive knapweeds, was introduced to 37 sites in northwest Arkansas since 2008 as part of a biological control program for spotted knapweed. In 2011 and 2012, 25 of these release sites were surveyed to monitor how L. minutus infestation rates changed in relation to distance and time from release. The initial L. minutus introductions at these sites occurred from 2008 to 2011. Transects were used from the point of initial weevil introduction to establish sampling quadrats in which capitula were collected to document weevil presence and infestation rates. The mean maximum distance of weevil colonization and mean local abundance (within the first 50 m from the release point) were calculated in relation to time (yr) since release. Five sites had >10 quadrats in both sampling years and were analyzed with an exponential decay function to model localized population growth and spread. Annual increases in mean local abundance and maximum distance of colonization were observed. These results were substantiated by localized growth (at 3 sites) and spread (at 2 sites) that occurred at the 5 sites analyzed with the exponential decay function. These findings suggest that in years following L. minutus introduction, assuming similar release strategies and environmental conditions, consistent increases in weevil infestation rates and spread from the release site may be expected in about half the sites at which populations establish. [ABSTRACT FROM AUTHOR]

Background: Exotic species can rapidly develop adaptations to their non-native regions, such as increased size and competitive ability. Although these traits are believed to be responsible for invasive success, some non-invasive exotic species display them too. This suggests that increased size and competitive ability might be necessary but not sufficient to turn an exotic into a successful invader. Aim: To assess size and competitive ability of the exotic non-invasive weedCentaureasulphurea, and of inter-regional hybrids between native and non-native populations. Methods: We experimentally produced a cohort ofC.sulphureaindividuals from the native range of the species in Spain, from its non-native range in California, as well as hybrids between the two regions. We grew these plants in pots in competition with the grassBromus hordeaceus, or alone in control pots. Results: Individuals from California were larger and better competitors than individuals from Spain. Furthermore, inter-regional hybrids showed competitive responses similar to that of individuals from California. Conclusions: Our results confirm that increased competitive ability might be more frequent than previously thought among introduced species, since it can be detected in at least some exotic non-invasive species. They also illustrate the importance of maternal effects, how locally adapted traits are conserved and spread in the non-native ranges of exotic species, and suggest that plant size and competitive ability are not directly associated in this species. [ABSTRACT FROM PUBLISHER]

Atractylodes macrocephula Koidz ( A. macrocephula , also known as Baizhu) is an important ingredient in several traditional Chinese herb complexes for the treatment of abdominal pain and gastroenterology diseases for thousands of years. We previously demonstrated the induction of ROS-mediated apoptosis by methanol extract of A. macrocephula in human leukemia cells. After purification and assessment of those active compounds from A. macrocephula ethanol extracts, in this study, we focused on the major active compound, atractylenolide I (ATL-I). Through MTT assay and morphology observation, we found cytotoxic effect of ATL-I in human K562 chronic myeloblastic leukemia (CML), U937 acute myeloblastic leukemia (AML) and Jurkat T lymphoma cells. In addition, ATL-I-induced apoptosis was demonstrated by sub G1 and fragmented chromosomal DNA detection using flow cytometry, enzyme-linked immunosorbent assay (ELISA) and agarose electrophoresis. Finally, we found ATL-I also induced caspase-3 and caspase-9 activation through the detection of procaspase-3, procaspase-9 and caspase-3 substrate poly(ADP-ribose) polymerase (PARP) by immunoblotting. Interestingly, we found that ATL-I induced not only apoptosis but also differentiation, as upregulation of CD14 and CD68 surface markers and increase of phagocytosis ability were discovered in ATL-I-treated K562 CML and U937 AML cells. Our study thus suggests the potential of developing new leukemia therapies by using ATL-I for leukemia treatment in the future. [ABSTRACT FROM AUTHOR]

We examined the type and magnitude of invasive plant ( Centaurea stoebe subsp. micranthos (Gugler) Hayek) effects on the demographic parameters of a rare plant ( Cirsium pitcheri Torr. & A.Gray), using two seed addition experiments with three treatments in two dune habitats - lakeshore linear dunes and high perched dunes on Lake Michigan, USA. Treatments were near Centaurea stoebe subsp. micranthos, near a native plant, or in the open. Seedling emergence, establishment, and juvenile survivorship were significantly higher on perched dunes, with higher surface soil moisture, than on lakeshore dunes. Treatment effects varied significantly with habitat and life stage. Seedling establishment decreased near Centaurea stoebe subsp. micranthos on lakeshore dunes, but increased near any neighbor on perched dunes. However, juvenile survival was significantly lower near Centaurea stoebe. subsp. micranthos in both habitats. The probability of reaching the adult flowering stage was much lower, and occurred later, for plants near Centaurea stoebe subsp. micranthos, especially on lakeshore dunes. Thus, Centaurea stoebe subsp. micranthos had a strong negative effect on establishment, survival, and flowering of Cirsium pitcheri, but interaction intensity varied with habitat and life stage. The results suggest that coupling seed addition with watering and invasive plant removal could bolster populations of this rare endemic plant. [ABSTRACT FROM AUTHOR]

The article explores the innovative restoration in ecological area which were occupied by spotted knapweed, a non-native perennial forb in North America. Topics discussed include use of herbicide treatments, long term restoration for knapweed and establishing a study on the development of native warm-season grasses in Michigan. Other topics include the use of single annual mowing methods and experimental management strategies to prevent knapweed.

Invasive species frequently need to be controlled as part of efforts to reestablish native species on degraded sites. While the effectiveness of differing control methods are often reported, the impacts these methods have on the establishment of a native plant community are often unknown. To determine methods that effectively reduce spotted knapweed (Centaurea stoebe) while enhancing native species establishment, we tested 12 treatment combinations consisting of an initial site preparation (mowing, mowing + clopyralid, or mowing + giyphosate), in factorial combination with annual adult knapweed hand pulling and/or burning. We established 48 plots and applied site preparation treatments during summer 2008, seeded 23 native forbs and grasses during spring 2009, pulled adult knapweed annually from 2009-2012, and burned in the early spring 2012. During July of 2011 and 2012, percent cover of all species was visually estimated. By 2011, seeded species had established in all treatment plots, including plots that retained greater than 50% knapweed cover, indicating that native species successfully established despite knapweed dominance. Mowing alone had no longterm impacts on community development. Clopyralid favored non-native grass establishment, while giyphosate encouraged non-native forbs. Clopyralid had minimal impacts on native forb establishment, but did effectively control knapweed. Pulling reduced knapweed cover, increased non-native grass cover and enhanced native species establishment. Burning had little impact, possibly due to low intensity and unseasonable weather. On the heavily invaded site we studied, combining the use of clopyralid with hand pulling effectively controlled knapweed and favored the establishment of seeded native grasses and forbs. [ABSTRACT FROM AUTHOR]

Highlights: [•] The methane yields of nine novel plants were measured. [•] The specific methane yields varied 170–381Nm3/t VS and TS yields 9–23tTS/ha. [•] Highest methane yield was achieved brown knapweed 6100Nm3 CH4/ha. [•] The cultivation and sustainability of novel plants have to be studied more carefully. [ABSTRACT FROM AUTHOR]

Biological invasions are inherently demographic processes, but trait differences between native and introduced genotypes are rarely linked to population growth rates. Native European Centaurea stoebe occurs as two cytotypes with different life histories (monocarpic diploids, polycarpic tetraploids); however, only tetraploids have been found in its introduced range in North America. In a common garden experiment using artificial populations, we compared the demographic performance of the three geo-cytotypes in the presence and absence of a specialist herbivore using periodic matrix models. We found no difference in population growth rate between the two European cytotypes and no significant effects of herbivory in all geo-cytotypes. However, there was a pronounced increase in population growth rate for North American compared with European tetraploids due to increased seed production and juvenile establishment. These results suggest that genetic drift or rapid evolution, rather than pre-adaptation through polyploidy may explain the invasion success of tetraploids. [ABSTRACT FROM AUTHOR]

Nigropallidal encephalomalacia was diagnosed in two horses in northern Victoria that had a history of long-term pasture access to a dense growth of Rhaponticum repens. The region in which the affected horses lived had received well above average rainfall for several months preceding the poisoning. Affected horses had sudden onset of subcutaneous oedema of the head, impaired prehension and mastication, dullness, lethargy and repeated chewing-like jaw movements. Diagnosis was confirmed at necropsy, with characteristic malacic lesions in the substantia nigra and globus pallidus of the brain. This is the first documented case of nigropallidal encephalomalacia in Australian horses associated with R. repens. [ABSTRACT FROM AUTHOR]

* Premise of study: Functional trait comparisons provide a framework with which to assess invasion and invasion resistance. However, recent studies have found evidence for both trait convergence and divergence among coexisting dominant native and invasive species. Few studies have assessed how multiple stresses constrain trait values and plasticity, and no study has included direct measurements of nutrient conservation traits, which are critical to plants growing in low-resource environments. * Methods: We evaluated how nutrient and water stresses affect growth and allocation, water potential and gas exchange, and nitrogen (N) allocation and use traits among a suite of six codominant species from the Intermountain West to determine trait values and plasticity. In the greenhouse, we grew our species under a full factorial combination of high and low N and water availability. We measured relative growth rate (RGR) and its components, total biomass, biomass allocation, midday water potential, photosynthetic rate, water-use efficiency (WUE), green leaf N, senesced leaf N, total N pools, N productivity, and photosynthetic N use efficiency. * Key results: Overall, soil water availability constrained plant responses to N availability and was the major driver of plant trait variation in our analysis. Drought decreased plant biomass and RGR, limited N conservation, and led to increased WUE. For most traits, native and normative species were similarly plastic. * Conclusions: Our data suggest native and invasive biomass dominants may converge on functionally similar traits and demonstrate comparable ability to respond to changes in resource availability. [ABSTRACT FROM AUTHOR]

Abstract: A caged field experiment was used to determine how Centaurea stoebe L. phenostage (rosette, single-stem, multiple-stem) and ploidy level (diploid=2× and tetraploid=4×) influence oviposition and feeding of two biological control agents, Agapeta zoegana (Lep.: Cochylidae) and Cyphocleonus achates (Col.: Curculionidae). Ploidy level did not influence oviposition patterns of A. zoegana but rosette and one-stem plants had significantly more eggs than multiple-stem (4×) plants. Differences in oviposition levels did not translate into differences in larval densities, but 2× plants (particularly large one-stem plants) had significantly more larvae than 4× plants. There was a significant positive correlation between numbers of larvae and root diameter. Ploidy level and phenostage both had a significant effect on C. achates feeding damage, with adults feeding more frequently on multiple-stem plants. No C. achates larvae were observed when the roots were dissected. Furthermore, the generalist herbivore Arion lusitanicus, naturally present in the garden plots, was predominantly associated with young rosette plants, a stage at which survival rate is acknowledged to be the most important determinant of knapweed density. These results indicate that the combined damage caused by A. zoegana and C. achates, superimposed on damage caused by generalist herbivores in the local community, could provide effective control for C. stoebe. [Copyright &y& Elsevier]

Abstract: The role of spotted knapweed phenology on the attack rate of two seed-head insects Urophora affinis and Larinus minutus was assessed in a series of field studies at four study sites in south-eastern British Columbia, Canada. Slow or later developing knapweed plants had more seed heads that contained only single or multiple U. affinis whereas early or faster developing plants had more seed heads containing L. minutus alone or in combination with U. affinis. L. minutus did not distinguish between seed heads with or without U. affinis larvae when laying eggs. However, seed heads with multiple U. affinis present, produced fewer L. minutus adults than expected. The probability of single or multiple U. affinis galls being present increased with seed-head diameter but was not affected by seed-head height. Attack by L. minutus increased with seed-head diameters >5mm and was lower at plant heights above 50cm. These results demonstrate two mechanisms that enable U. affinis to successfully coexist with L. minutus: differences between the species in their response to the developmental phenology of knapweed heads, and increased survivorship of U. affinis in heads with multiple U. affinis galls through niche interference competition. These mechanisms provide a possible explanation for the persistence of U. affinis populations on spotted knapweed, in spite of high levels of within seed-head mortality that have been observed with increasing L. minutus populations. [Copyright &y& Elsevier]

The physiological responses of plants to variable levels of root and shoot herbivory in the field may yield valuable insights regarding potential compensation or tolerance responses for herbivory. In an infestation of Centaurea stoebe (spotted knapweed) located in the Colorado foothills, we measured physiology, biomass, and flower production of individual plants undergoing a natural range of herbivory by the above- and belowground biological control insects, Larinus minutus and Cyphocleonus achates. Over the growing season, net carbon assimilation rate, transpiration, stomatal conductance, and intercellular leaf [CO2] (C i) all decreased, while water use efficiency increased. The decrease in these physiological traits was due to an increase in the intensity of L. minutus damage over time; effects of C. achates root damage to plant physiology, including transpiration were only marginally significant. The effects of these two species on plant physiology were not interactive, and Larinus minutus was found to exert larger negative effects on this invasive plant in terms of plant physiology and potential reproductive output than C. achates. While previous studies have shown C. achates to have significant negative effects on population densities of spotted knapweed, the addition of Larinus minutus to the suite of insects used in biological control of spotted knapweed should facilitate continued or enhanced reduction in densities of this noxious weed. [ABSTRACT FROM AUTHOR]

The article evaluates the responses of Centaurea stoebe knapweed to herbivores. The growth of this plant is greatly reduced by nitrogen limitation and competing vegetation while Centaurea stoebe's seed production in low-nitrogen soils is reduced by Larinus minutus, a seed feeder. The results show that plant growth responses to herbivory can be generated. It was also found that insect herbivores increase the dominance of such invasive plant.

Centaurea cyanus occurs mostly in middle-high regions of Czech Republic. It prefers light soils with low calcium content. As an arable weed, this species can be found mainly in winter cereals and in the stands of winter oilseed rape. Achenes can germinate well immediately after harvest so they can emerge the same year during autumn from various soil depths with maximum of 8 cm. This species deCSeased its occurrence in the past and was classified as an endangered one. But it is spreading in recent years especially in relation to inCSeased sowing areas of winter oilseed rape. It is common in field margins but we can record also whole-field area occurrence. Centaurea cyanus is relatively sensitive to many herbicides commonly used in cereal stands. More problematic is its control in oilseed rape stands. Even if active ingrediences dimethachlor and propachlor show good efficacy on this weed, when the field is highly infested and C. cyanus emerge in high numbers from deeper soil layers, these herbicides can be less effective. In such cases it is cases it is suitable to use spring treatment with herbicide with active ingredience clopyralid. [ABSTRACT FROM AUTHOR]

Russian knapweed ( Acroptilon repens) and Spotted knapweed ( Centaurea maculosa) are allelopathic weeds invasive in North American grasslands. Both species contain at least one phytotoxic flavonoid root exudate with demonstrated negative influences on other plants. Previous findings indicated that Silky lupine ( Lupinus sericeus), among other legumes, was relatively resistant to Spotted knapweed invasion and allelochemistry. We hypothesized that legume species may exhibit resistance to flavonoids in knapweed root exudates and may serve as candidate species for management efforts. Because legumes form symbiotic relationships with rhizobia, these bacteria must also be evaluated for allelochemical resistance before legumes can be recommended for restoration. In this study, we examined four legume species for effects of 7,8-benzoflavone (from Russian knapweed) and (±)-catechin (from Spotted knapweed) on rhizosphere interactions involving legume roots and associated rhizobia. Pure cultures of four rhizobia strains exhibited varied responses when grown with 7,8-benzoflavone or (±)-catechin. Alfalfa ( Medicago sativa) and its bacterial symbiont, Sinorhizobium meliloti, exhibited allelochemical resistance that varied with (±)-catechin concentration when grown in vitro. Four legume species were grown under greenhouse conditions. Plants that were inoculated and nodulated generally exhibited no response to 7,8-benzoflavone or (±)-catechin treatments. Plants that were not inoculated exhibited stronger responses. Therefore, inoculation and nodulation may confer resistance to allelochemicals. These results, when coupled with previous research and field observations, suggest that legumes may not be susceptible to knapweed allelopathy and may be good choices in restoration of knapweed infestations when inoculated, particularly on sites with low soil nitrogen. [ABSTRACT FROM AUTHOR]

Quantitative determination of flavonoids from the aerial part of greater knapweed ( Centaurea scabiosa L.) has been carried out by differential spectrophotometry in combination with a modified method of forming flavonoid complexes with aluminum chloride in HCl. Depending on the plant collection site, the quantitative content of flavonoids in the aerial part of greater knapweed varied within 1.3 – 2.0% (calculated as rutin). The random error of measurement did not exceed 3% at a confidence probability of 0.95. The systematic error of the proposed metohd did not exceed the error of determination. The accumulation dynamics of flavonoids in the aerial part of greater knapweed during the 2006 vegetative peroid have been tracked for plants growing in Tomsk and Kemerovo regions. The maximum content of flavonoids (1.70 ± 0.04% calculated as rutin) was observed in the stage of full flowering, which is therefore the optimum period for collecting the aerial part of the plants for the maximum yield of flavonoids. The maximum amount of flavonoids was accumulated in leaves (1.96 ± 0.04%), which is somewhat greater than the content of flavonoids in the entire aerial part of greater knapweed (1.70 ± 0.04%). [ABSTRACT FROM AUTHOR]

As primary producers, plants are known to influence higher trophic interactions by initiating food chains. However, as architects, plants may bypass consumers to directly affect predators with important but underappreciated trophic ramifications. Invasion of western North American grasslands by the perennial forb, spotted knapweed ( Centaurea maculosa), has fundamentally altered the architecture of native grassland vegetation. Here, I use long-term monitoring, observational studies, and field experiments to document how changes in vegetation architecture have affected native web spider populations and predation rates. Native spiders that use vegetation as web substrates were collectively 38 times more abundant in C. maculosa-invaded grasslands than in uninvaded grasslands. This increase in spider abundance was accompanied by a large shift in web spider community structure, driven primarily by the strong response of Dictyna spiders to C. maculosa invasion. Dictyna densities were 46–74 times higher in C. maculosa-invaded than native grasslands, a pattern that persisted over 6 years of monitoring. C. maculosa also altered Dictyna web building behavior and foraging success. Dictyna webs on C. maculosa were 2.9–4.0 times larger and generated 2.0–2.3 times higher total prey captures than webs on Achillea millefolium, their primary native substrate. Dictyna webs on C. maculosa also captured 4.2 times more large prey items, which are crucial for reproduction. As a result, Dictyna were nearly twice as likely to reproduce on C. maculosa substrates compared to native substrates. The overall outcome of C. maculosa invasion and its transformative effects on vegetation architecture on Dictyna density and web building behavior were to increase Dictyna predation on invertebrate prey ≥89 fold. These results indicate that invasive plants that change the architecture of native vegetation can substantially impact native food webs via nontraditional plant → predator → consumer linkages. [ABSTRACT FROM AUTHOR]

A new species of Centaurea, Centaurea sicana , endemic to Sicily, is described. This new taxon is close to Centaurea parlatoris and Centaurea giardinae (Sect. Dissectae), the former occurring at Palermo and in the Madonie Mountains, while the latter occurs on the Etna volcano. The new species has so far been found only on the Sicani Mountains, a limestone mountain range in western Sicily, while the related species occur in the surrounding mountains. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 157, 785–788. [ABSTRACT FROM AUTHOR]

Understanding the functional traits that allow invasives to outperform natives is a necessary first step in improving our ability to predict and manage the spread of invaders. In nutrient-limited systems, plant competitive ability is expected to be closely tied to the ability of a plant to exploit nutrient-rich microsites and use these captured nutrients efficiently. The broad objective of this work was to compare the ability of native and invasive perennial forbs to acquire and use nutrients from nutrient-rich microsites. We evaluated morphological and physiological responses among four native and four invasive species exposed to heterogeneous (patch) or homogeneous (control) nutrient distribution. Invasives, on average, allocated more biomass to roots and allocated proportionately more root length to nutrient-rich microsites than did natives. Invasives also had higher leaf N, photosynthetic rates, and photosynthetic nitrogen use efficiency than natives, regardless of treatment. While these results suggest multiple traits may contribute to the success of invasive forbs in low-nutrient environments, we also observed large variation in these traits among native forbs. These observations support the idea that functional trait variation in the plant community may be a better predictor of invasion resistance than the functional group composition of the plant community. [ABSTRACT FROM AUTHOR]

Little is known about how exotics influence the ecophysiology of co-occurring native plants or how invader impact on plant physiology may be mediated by community diversity or resource levels. We measured the effect of the widespread invasive forb spotted knapweed (Centaurea maculosa) on leaf traits (leaf dry matter content, specific leaf area, leaf nitrogen percentage, leaf C:N ratios, and δ13C as a proxy for water use efficiency) of two co-occurring native perennial grassland species, Monarda fistulosa (bee balm) and Koeleria macrantha (Junegrass). The impact of spotted knapweed was assessed across plots that varied in functional diversity and that either experienced ambient rainfall or received supplemental water. Impact was determined by comparing leaf traits between identical knapweed-invaded and noninvaded assemblages. Virtually all M. fistulosa leaf traits were affected by spotted knapweed. Knapweed impact, however, did not scale with its abundance; the impact of knapweed on M. fistulosa was similar across heavily invaded low-diversity assemblages and lightly invaded high-diversity assemblages. In uninvaded assemblages, M. fistulosa δ13C, leaf nitrogen, and C:N ratios were unaffected by native functional group richness, whereas leaf dry matter content significantly increased and specific leaf area significantly decreased across the diversity gradient. The effects of spotted knapweed on K. macrantha were weak; instead native functional group richness strongly affected K. macrantha leaf C:N ratio, δ13C, and specific leaf area, but not leaf dry matter content. Leaf traits for both species changed in response to spotted knapweed or functional richness, and in a manner that may promote slower biomass accumulation and efficient conservation of resources. Taken together, our results show that an invader can alter native plant physiology, but that these effects are not a simple function of how many invaders exist in the community. [ABSTRACT FROM AUTHOR]

A recent decline in spotted knapweed, Centaurea stoebe L. subsp. micranthos (Asteraceae), has been observed in parts of western Montana. The release of the biological control agent Cyphocleonus achates (Fahraeus) is thought to contribute to the decline, but persistent drought since at least 1999 may be an additional factor. We conducted outdoor plot experiments to test the relative impacts of C. achates weevils and summer drought relief on spotted knapweed survival and growth. Groups of spotted knapweed transplants were assigned to one of four weekly water addition treat- ments (no added water, and 0.25, 0.5 or full recovery of plant water deficit, where ‘deficit’ refers to potential evapotranspiration minus rainfall) in May to August 2004 and June to August 2005 and to either exposure to or protection from C. achates. In June of each subsequent year (2005 and 2006), plants were harvested and growth attributes that reflect plant vigor were measured. Drought indices showed that throughout the time of the study until January 2006, western Montana was in drought alert or severe drought. Summer drought relief had no effect on aboveground biomass and plant height of knapweed plants in subsequent years, but feeding by C. achates larvae reduced these two measures of plant vigor. Knapweed plants resuming growth after the drought ended in spring 2006 were significantly larger than those resuming growth under drought conditions in spring 2005. Spring drought may reduce knapweed growth, but C. achates reduced knapweed growth regardless of drought conditions. [ABSTRACT FROM AUTHOR]

Abstract: Allelopathy as a mechanism of invasion in plant communities remains a debated topic, partly due to lack of techniques to measure allelochemical output and stability in the field. Evidence has arisen to support allelopathic mechanisms in several invasive knapweeds, including Russian knapweed. Previous studies have shown that a phytotoxin, 7,8-benzoflavone, is produced by Russian knapweed roots under soil-free conditions. Here we describe a high performance liquid chromatography (HPLC) method to detect this compound in soil and we present the first observations of this compound from Russian knapweed infested soils. [Copyright &y& Elsevier]

Knapweeds ( Centaurea spp.) are among the most invasive of non-indigenous plant species that have colonized western North America over the last century. We conducted a 4-year experiment in a reconstructed grassland to test hypotheses related to the ability of grasslands to resist the invasion of diffuse knapweed ( C. diffusa). We experimentally invaded C. diffusa and three native species into areas where we manipulated soil nitrogen (N) and phosphorus (P) availability and removed extant grasses to reduce competition. We evaluated the growth response of these species to these resources and competitive manipulations. Of the native species that were experimentally added, only one species, Ratibida pinnata (prairie coneflower), established in any numbers. Establishment values in intact vegetation were low for both species, but establishment by C. diffusa (0.02%) clearly outperformed that of R. pinnata (0.001%). Under reduced grass competition, establishment was enhanced, but the values for C. diffusa (0.68%) were not statistically different from those of R. pinnata (0.57%). Neither species performed better under higher soil nutrients in the presence of competing grasses. In plots with both species, biomass of the two planted species was positively correlated, but the biomass of both species was negatively correlated with non-added weedy species. Subsequent harvests of C. diffusa indicated that establishment was enhanced in treatments with higher soil nutrients but that the biomass of these plants could only be enhanced when plant competition was also reduced. These results indicate that C. diffusa can establish in intact grasslands at rates higher than natives, but opportunism rather than competitive ability best describes the invasiveness of C. diffusa. Thus, the mechanisms contributing to the establishment of this knapweed species are different from factors identified as contributing to the dominance of this invader. [ABSTRACT FROM AUTHOR]

Abstract: We studied the variation in the responses of brown knapweed (Centaurea jacea) ecotypes from Finland and Switzerland to elevated O3 and CO2 and, the possible role of CO2 as a factor modifying O3 sensitivity. Individuals of four C. jacea ecotypes were exposed to elevated O3 (40ppb) and CO2 (450ppm) alone or in combination in open-top chambers (OTC) in the summer 2003. Open-field plots served as controls for the chamber effect. Ozone effects were mainly manifested as visible injuries: O3-specific light brown flecks and non-specific purple pigmentation. The proportion of O3-specific visible injuries was highest in the Swiss plants, where they correlated positively with early flowering, high dry matter production and high stem dry weight. CO2 ameliorated the severity of O3-specific visible injuries only in the most O3-sensitive ecotype, but diminished the differences between the different ecotypes. Ozone exposure also accelerated plant senescence, which was seen as enhanced development of purple pigmentation. The lack of growth responses may be explained by the low exposure concentrations. The intraspecific differences in O3 sensitivity may limit the use of C. jacea as a bioindicator for intact vegetation. [Copyright &y& Elsevier]

Abstract: Spotted knapweed (Centaurea maculosa Lam.) is an invasive plant that alters species composition and grazing value of rangelands in the northwestern United States. The spread of invasive plants may be reduced by using livestock as a biological control. We determined if mature ewes and their lambs (n =34ewe/lamb pairs) consume more spotted knapweed when ewes and/or lambs are conditioned to fresh-cut spotted knapweed. Ewe/lamb pairs were randomly assigned to one of four conditioning treatments: ewes and lambs not conditioned to spotted knapweed (N), conditioned ewes with non-conditioned lambs (E), non-conditioned ewes with conditioned lambs (L), or conditioned ewes and lambs (both—B). Then, ewes and lambs were observed together for 5 days (Trial 1); 11 days later, lambs were observed for 4 days without their mothers (Trial 2). During conditioning, intake by conditioned and non-conditioned ewes and lambs varied over time (as-fed basis, treatment by day interaction; ewes P =0.03; lambs P =0.05). Overall, non-conditioned lambs (N, E) consumed more than conditioned lambs (L, B; P =0.02). In Trial 1, N ewes consumed similar amounts of spotted knapweed and bromegrass (Bromus inermis Leyss.) as the E, L, and B ewes (P =0.67). E ewes spent more time eating spotted knapweed than L ewes (P =0.001), and E ewe/lamb pairs consumed more spotted knapweed than L ewe/lamb pairs (P =0.02). In Trial 2, N lambs consumed less spotted knapweed than E, L, and B lambs (P =0.06). L lambs consumed more than E lambs (P =0.007). Conditioning ewes, lambs, or ewes and lambs did not increase time spent eating spotted knapweed when both grazed together in a drylot, but conditioned lambs, without their mothers present, consumed more spotted knapweed 11 days later than non-conditioned lambs. Conditioning lambs only in a group setting with their peers may have the greatest potential to enhance consumption of spotted knapweed, because of social facilitation and the predilection for young animals to try novel feeds. [Copyright &y& Elsevier]

Herbivory can have negative, positive, or no effect on plants. However, insect biological control assumes that herbivory will negatively affect the weed and release natives from competition. Centaurea maculosa, an invader in North America, is tolerant to herbivory, and under some conditions, herbivory may increase its competitive effects on natives. Therefore, we investigated two hypotheses: 1) herbivory stimulates compensatory growth by C. maculosa, which increases its competitive effects, and 2) herbivory stimulates the allelopathic effect of C. maculosa. In the greenhouse, Trichoplusia ni shoot herbivory reduced C. maculosa biomass when shoot damage exceeded 40% of the total original leaf area. Conspecific neighbors had no effect on C. maculosa biomass, and the presence of the natives Festuca idahoensis and F. scabrella had a positive effect on C. maculosa. Neighbors did not alter the effects of shoot herbivory. More importantly, even intense shoot herbivory on C. maculosa did not benefit neighboring plants. In a field experiment, clipping 50% of C. maculosa aboveground biomass in the early summer and again in the late summer reduced final biomass by 40% at the end of the season; however, this clipping did not affect total biomass production or reproductive output. Festuca idahoensis neighbors did not increase the effects of clipping, and aboveground damage to C. maculosa did not release F. idahoensis from competition. In the greenhouse we used activated carbon to adsorb allelochemicals, which reduced the competitive effects of C. maculosa on F. idahoensis but not on F. scabrella or other C. maculosa. However, we found no increase in the allelopathic effects of C. maculosa after shoot herbivory. In summary, our results correspond with others indicating that exceptionally high intensities of herbivory are required to suppress C. maculosa growth and reproduction; however, even intense herbivory on C. maculosa does not insure that native bunchgrasses will benefit. [ABSTRACT FROM AUTHOR]

Host plant patch size plays an important role in the distribution and densities of many insect species. Understanding how the host plant patch size influences the population of a biological control agent is necessary to monitor the success of a biological control programme. Urophora quadrifasciata (Dipt. Tephritidae) was released in the early 1970s to control the spotted knapweed, Centaurea biebersteinii (Asteraceae) in North America. The studies reported here investigated the influences of spotted knapweed patch size and stem density on U. quadrifasciata larval populations overwintering within capitula in the Upper Peninsula of Michigan, USA. An inverse relationship was found between the percentage of capitula with U. quadrifasciata larvae and spotted knapweed patch size in 2002 from Houghton county, MI. In 2003, an inverse relationship was also found in the south region of the study area in Houghton and Keweenaw counties, Michigan. The percentage of capitula with U. quadrifasciata larvae and spotted knapweed patch size were positively related for the central region. No relationship was found for the North region in 2003. Dispersal of U. quadrifasciata is directed north-east along the Keweenaw Peninsula, Michigan. With this directed spread, areas with well-established populations of U. quadrifasciata would provide source individuals for new colonization. Spotted knapweed patch size may play an important role in the overwintering populations of U. quadrifasciata as a result of dispersal. [ABSTRACT FROM AUTHOR]

Interspecific competition has been suggested as an explanation for the failure of some insects as biological control agents for weeds. Enclosure and exclusion cages were used, in southern British Columbia, Canada to evaluate the importance of interspecific competition between a seedhead weevil, Larinus minutus , and a gall-inducing fly, Urophora affinis , two biocontrol agents released against spotted knapweed in North America. At the seedhead scale, U. affinis , which is an inferior biological control agent based on knapweed seed mortality, was the superior competitor. Larinus minutus attack rates were significantly lower in the presence of U. affinis compared to release treatments where L. minutus was attacking alone. Reduced L. minutus attack rates were apparent in seed heads expected to contain both species, assuming insect distributions were random, but instead only contained U. affinis . L. minutus did not significantly affect U. affinis density. Although overall attack rates on knapweed seedheads were higher when both species were together at a site, the consequence of the antagonistic interaction is that overall seed destruction was not as high as it could have been if the weevil were attacking on its own. These results support minimizing the number of biocontrol agents released that use similar resources on the target weed, to avoid negative interactions between control agents and potential reductions in biocontrol efficacy resulting from competitive exclusion. [ABSTRACT FROM AUTHOR]

Abstract: Cyphocleonus achates, the knapweed weevil, is an effective biological control agent of the invasive weed, Centaurea maculosa Lam. A meridic diet was developed and tested for the rearing of the larval stage of this insect. Using this diet, C. achates was reared for over three generations, with the adults being offered knapweed plants for feeding and oviposition in greenhouse conditions. Slight or no differences were seen between insects reared on a standard meridic diet formulation and one containing knapweed tissues. The following life history parameters were monitored over the three generations: percent egg hatch (ranging from 42.9 to 59.1%), time to egg hatch (20.0–23.2 days), time to adult emergence (52.0–54.1 days), adult weights 3 days post-eclosion (101.9–117.0mg), percent adult emergence (48.3–58.6%), and percent mortality/deformity in the different stages (with mortality occurring primarily in the early larval stages). Additionally, a study involving low temperature and short day conditions suggested that C. achates could be maintained for longer periods of time in larval diet cells when placed in growth-retarding conditions, although percent adult emergence was lower. External morphology was also studied in order to distinguish between the sexes to ensure that each adult cage had a similar ratio of females to males. Abdominal features were found to be the most dependable characteristics for use when determining the sex of adult C. achates. [Copyright &y& Elsevier]

Semiarid lands of North America are vulnerable to invasion by exotic forbs that frequently have an extended phenology compared with native herbaceous species. We hypothesized that photosynthetic stems, rosette leaves, and cauline leaves of Centaurea maculosa Lam. (knapweed) would differ in ecophysiological specialization and that these differences would enhance plant carbon uptake across seasonal variations in microclimate. Photosynthesis, water relations, and morphological features of C. maculosa were measured under natural variations in temperature and soil water, and under manipulated light environments, in adults compared with seedlings having only rosette leaves. Carbon gain was greater in adults than in seedlings owing to high photosynthesis in cauline and rosette leaves when water was abundant. Otherwise, photosynthesis was relatively lower but persistent through drought in all tissues and ages until senescence. Photosynthesis decreased with water stress in all tissues except stems. Stems comprised up to 36% of photosynthetic area following senescence of rosette leaves during seasonal drought. Seedlings expressed shade acclimation compared with rosette and especially cauline leaves of adults, although adult rosette leaves had flexible photosynthetic light responses. Contrasting ecophysiological specializations of photosynthetic tissues enhance carbon gain of adult C. maculosa as light, water, and temperature vary during its relatively long growth season. [ABSTRACT FROM AUTHOR]

Acroptilon repens is an invasive weed in North America but also causes problems in disturbed habitats in its native range in Asia. In order to test the effect of simulated biological control and soil disturbance on established A. repens patches and the competing vegetation, two levels of shoot clipping as well as soil tillage were imposed on A. repens patches in an undisturbed meadow and at two fallowland sites in the native range of the weed. At the meadow site, 2 years of partial clipping of shoots and of soil tillage had no influence on A. repens performance, while soil tillage significantly reduced the above-ground biomass of the competing vegetation. At the fallowland sites, which had been continuously cultivated for several years prior to the experiment, A. repens shoot density, biomass and number of seed heads were significantly higher in the undisturbed control than in the tillage plots. The total number of seed heads per unit area increased with shoot density up to 200 shoots m−2. These results indicate that A. repens has considerable regrowth capacities that allow established patches to tolerate substantial losses of above-ground biomass and that the competitive ability of A. repens is favoured both when soil disturbance is imposed on previously undisturbed sites, as well as when repeated soil disturbance is abandoned. The only promising nonchemical herbicide-based approach to reduce the competitive ability and seed output of A. repens appears to be a long-term management that enhances the interspecific plant competition by reducing soil disturbance and selectively damaging A. repens. [ABSTRACT FROM AUTHOR]

Centarea maculosa Lam. (spotted knapweed) is one of the most destructive invasive weeds in the western United States, particularly in pastures and rangelands. One of the components that may contribute to its invasiveness is the naturally produced, root-secreted allelochemical (-)-catechin. This compound has been shown to have broad-spectrum phytotoxic activity, possibly assisting C. maculosa in displacing native plant communities. As a recently characterized phytochemical, little is known about the specific effect of (-)-catechin on either C. inaculosa or other plant species. We have found that, in vitro, C. maculosa begins to secrete phytotoxic levels of (-)-catechin within 2-3 weeks of seedling emergence. Furthermore, (-)-catechin concentrations consistent with those naturally secreted by C. maculosa were sufficient to inhibit germination in all species tested, including C. maculosa. These concentrations were also often either phytotoxic or growth inhibitory to seedlings in a range of plant species, while having no negative effects on the growth of C. maculosa seedlings. However, our results also indicate that different levels of resistance and susceptibility to (-)-catechin exist in plant populations, suggesting that the capability of C. inaculosa to invade an area through allelochemistry may be dependent on the age and species composition of plants in that area. [ABSTRACT FROM AUTHOR]

Release of exotic insects as biological control agents is a common approach to controlling exotic plants. Though controversy has ensued regarding the deleterious direct effects of biological control agents to non-target species, few have examined the indirect effects of a ”well-behaved” biological control agent on native fauna. We studied a grassland in west-central Montana infested with spotted knapweed (Centaurea maculosa) to examine the effects of knapweed invasion and two gall flybiological control agents (Urophora affinis and U. quadrifasciata) on the native deer mouse (Peromyscus maniculatus). Stomach-content analysis revealed that Urophora were the primary food item in Peromyscus diets for most of the year and made up 84–86% of the winter diet. Stomach contents indicated that wild-caught mice consumed on average up to 247 Urophora larvae mouse–1 day–1, while feeding trials revealed that deer mice could depredate nearly 5 times as many larvae under laboratory conditions. In feeding trials, deer mice selected knapweed seedheads with greater numbers of galls while avoiding uninfested seedheads. When Urophora larvae were present in knapweed seedheads, deer mice selected microhabitats with moderately high (31–45% cover) and high knapweed infestation (≥46% cover). After Urophora emerged and larvae were unavailable to Peromyscus, mice reversed habitat selection to favor sites dominated by native-prairie with low knapweed infestation (0–15%). Establishment of the biological control agent, Urophora spp., has altered deer mouse diets and habitat selection by effecting changes in foraging strategies. Deer mice and other predators may reduce Urophora populations below a threshold necessary to effectively control spotted knapweed. [ABSTRACT FROM AUTHOR]

Invading exotic plants are thought to succeed primarily because they have escaped their natural enemies, not because of novel interactions with their new neighbors. However, we find that Centaurea diffusa, a noxious weed in North America, has much stronger negative effects on grass species from North America than on closely related grass species from communities to which Centaurea is native. Centaurea's advantage against North American species appears to be due to differences in the effects of its root exudates and how these root exudates affect competition for resources. Our results may help to explain why some exotic species so successfully invade natural plant communities. [ABSTRACT FROM AUTHOR]

Examines the biology of Larinus minutus Gyllenhal, an agent for biological control of diffuse and spotted knapweeds. Forage losses caused by spotted knapweeds; Host specifity of the species; Onset of oviposition; Effects of temperature on the activity of the species.