Systematic revision of the genus Psithyristria Stål (Hemiptera: Cicadidae) with seven new species and a molecular phylogeny of the genus and higher taxa

The cicada genus Psithyristria Stål (Hemiptera: Cicadidae), endemic to Luzon, the Philippines, is reviewed, and its higher taxonomic affiliations are determined using morphology and molecular phylogenetics. Seven new Psithyristria species, P. grandis, sp.n. , P. albiterminalis, sp.n. , P. incredibilis, sp.n. , P. paraspecularis, sp.n. , P. peculiaris, sp.n. , P. moderabilis, sp.n. and P. genesis, sp.n. , are described. A key to the 12 known species is provided. The molecular phylogenetic analyses of Psithyristria and putatively related taxa showed some unexpected generic relationships, leading to changes in higher taxonomic placement for a number of Asian cicada genera. Psithyristria falls within the tribe Cicadini Latreille, 1802, and the tribe Psithyristriini Distant, 1905 syn.n. is therefore synonymized with Cicadini. The subtribe Psithyristriina Distant, 1905 stat.n. is recognized within Cicadini and defined for the genera Psithyristria, transferred from Psithyristriini, and Basa Distant, Pomponia Stål and Semia Matsumura, transferred from Cicadina, synonymizing Pomponiina Kato, 1932 syn.n. with Psithyristriina. The Cicadini subtribe Leptopsaltriina Moulton, 1923 is redefined to include the genera Terpnosia Distant, Euterpnosia Matsumura, Leptosemia Matsumura, Neocicada Kato, Puranoides Moulton, Leptopsaltria Stål, Tanna Distant, Purana Distant, Formosemia Matsumura, Maua Distant, Nabalua Moulton, Taiwanosemia Matsumura, Gudaba Distant and Calcagninus Distant, synonymizing Terpnosiina Kato, 1932 syn.n. The tribe Cicadatrini Distant, 1905 is recognized and redefined to include the genera Cicadatra Kolenati, Psalmocharias Kirkaldy, Mogannia Amyot & Audinet‐Serville, Nipponosemia Kato and Emathia Stål, synonymizing Moganniini Distant, 1905 syn.n. The nine Psithyristria species included in the molecular analyses have an uncorrected mitochondrial genetic distance of 2–9%, and most species appear to be related through a single radiation event that occurred approximately 5–10 Ma. No phylogenetic structure was found in two unusually divergent characters, the forewing venation and the shape of the uncal lobes. Psithyristria is found in the northern Luzon mountains and is closely related to Semia of Taiwan and eastern China, Pomponia of east Asia and the Indonesian/Malaysian islands, and probably most closely to Basa of India. Psithyristria may be a cicadid example of a small number of Philippine organisms that trace their ancestry directly back to the temperate Asian mainland, rather than through the island chains to the south of the country.     

Out of Africa? A dated molecular phylogeny of the cicada tribe Platypleurini Schmidt (Hemiptera: Cicadidae), with a focus on African genera and the genus Platypleura Amyot & Audinet‐Serville

The Platypleurini is a large group of charismatic cicadas distributed from Cape Agulhas in South Africa, through tropical Africa, Madagascar, India and eastern Asia to Japan, with generic diversity concentrated in equatorial and southern Africa. This distribution suggests the possibility of a Gondwanan origin and dispersal to eastern Asia from Africa or India. We used a four‐gene (three mitochondrial) molecular dataset, fossil calibrations and molecular clock information to explore the phylogenetic relationships of the platypleurine cicadas and the timing and geography of their diversification. The earliest splits in the tribe were found to separate forest genera in Madagascar and equatorial Africa from the main radiation, and all of the Asian/Indian species sampled formed a younger clade nested well within the African taxa. The tribe appears to have diversified during the Cenozoic, beginning c. 50–32 Ma, with most extant African lineages originating in the Miocene or later, well after the breakup of the Gondwanan landmass. Biogeographical analysis suggests an African origin for the tribe and a single dispersal event founding the Asian platypleurines, although additional taxon sampling and genetic data will be needed to confirm this pattern because key nodes in the tree are still weakly supported. Two Platypleurini genera from Madagascar (Pycna Amyot & Audinet‐Serville, Yanga Distant) are found to have originated by late Miocene dispersal of a single lineage from Africa. The genus Platypleura is recovered as polyphyletic, with Platypleura signifera Walker from South Africa and many Asian/Indian species apparently requiring assignment to different genera, and a new Platypleura concept is proposed with the synonymization of Azanicada Villet syn.n. The genera Orapa Distant and Hamza Distant, currently listed within separate tribes but suspected of platypleurine affinity, are nested deeply within the Platypleurini radiation. The tribe Orapini syn.n . is here synonymized while the tribe Hamzini is pending a decision of the ICZN to preserve nomenclatorial stability.     

Shoot herbivory on the invasive plant, Centaurea maculosa, does not reduce its competitive effects on conspecifics and natives

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.     

Host plant differences in arbuscular mycorrhizae: Extra radical hyphae differences between an invasive forb and a native bunchgrass

Arbuscular mycorrhizae affect grassland plant community composition and host plant nutrient uptake, and can mediate shifts in competitive outcome between plant species. Centaurea maculosa, an invasive forb from Eurasia, dominates more than 4 million hectares in the Rocky Mountain region of North America. We examined the role of AM for phosphorus (P) acquisition from a distant source for C. maculosa and Festuca idahoensis, a native bunchgrass. Plants were grown individually in pots divided by a barrier that either excluded plant roots and AM hyphae, or only plant roots. In the half of the pot without a plant, 1 of 3 P treatments was applied: no P, phosphate rock (PR) or triple superphosphate (TSP), applied at a rate of 144 mg P kg^–1 soil. After 14 weeks of growth, C. maculosa was twice as large as F. idahoensis, and neither species biomass was affected by barrier type. Phosphorus fertilizer, and especially PR, moved across the barrier to the plant side of the pot. Tissue P concentration for C. maculosa was highest with the PR treatment, and was not affected by the barrier type. In contrast, F. idahoensis tissue P concentration did not vary with barrier or P treatments. There was more AM extra radical hyphae (ERH) associated with C. maculosa than F. idahoensis, suggesting that C. maculosa provides more carbon for the AM fungi, resulting in greater ERH production, ERH soil exploration and potential for soil nutrient pool exploitation. Although not tested in this study, differences between host plants may be the result of different physiological characteristics of the host plant or differences in AM fungal species that colonize the invader, with different fungal species accessing P from different distances.     

Novel weapons and invasion: biogeographic differences in the competitive effects of Centaurea maculosa and its root exudate (±)-catechin

Recent studies suggest that the invasive success of Centaurea maculosa may be related to its stronger allelopathic effects on native North American species than on related European species, one component of the “novel weapons” hypothesis. Other research indicates that C. maculosa plants from the invasive range in North America have evolved to be larger and better competitors than conspecifics from the native range in Europe, a component of the “evolution of increased competitive ability” hypothesis. These hypotheses are not mutually exclusive, but this evidence sets the stage for comparing the relative importance of evolved competitive ability to inherent competitive traits. In a competition experiment with a large number of C. maculosa populations, we found no difference in the competitive effects of C. maculosa plants from North America and Europe on other species. However, both North American and European C. maculosa were much better competitors against plants native to North America than congeners native to Romania, collected in areas where C. maculosa is also native. These results are consistent with the novel weapons hypothesis. But, in a second experiment using just one population from North America and Europe, and where North American and European species were collected from a broader range of sites, competitive interactions were weaker overall, and the competitive effects of C. maculosa were slightly stronger against European species than against North American species. Also consistent with the novel weapons hypothesis, (±)-catechin had stronger effects on native North American species than on native European species in two experiments. Our results suggest that the regional composition of the plant communities being invaded by C. maculosa may be more important for invasive success than the evolution of increased size and competitive ability. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Structural analysis of the phytophagous insect guilds associated with the roots of Centaurea maculosa Lam. C. diffusa Lam., and C. vallesiaca Jordan in Europe:

Summary During extensive field surveys in central and eastern Europe, 21 herbivorous root insect species were found on Centaurea maculosa ssp. rhenana Boreau, 12 species on C. diffusa Lam. and 11 species on C. vallesiaca Jordan, representing 12 families in 4 orders. The large geographic distribution (species-area function), the high number of Centaurea spp. present (host speciation rate), and the high apparency of the rosettes and the rich food resources offered by the roots during winter, together with their poor accessibility, correlate with the high number of specialist feeders associated with the roots of C. maculosa and C. diffusa. The members of the taxonomically diverse root entomofauna exploit specific structures of the tap root (food niches). Interspecific competition among members of food niches, as well as species-specific responses to different phenological stages (for oviposition) and tissues (for larval development) are thought to be responsible for the high predictability in guild structure. The relatively low levels of host plant attack (two thirds of the roots were unattacked) and the fact that food niches remained unoccupied in most of the regions suggest, however, that the majority of the studied guilds do not represent equilibrium assemblages. Ecological (different habitats), climatic (transitional zone) and historical (ancient pre-Pleistocene communities) factors could account for the highest values of species diversity, infestation levels, species packing and food niche utilization, which are found on C. maculosa in E. Austria/NW. Hungary, compared to other regions. A positive correlation between species packing (number of root-feeding species per population) and infestation rates (percent of roots attacked) was only found for the more stable, semi-natural habitats. A comparative analysis of the regional root insect guilds of C. maculosa with corresponding data for the phytophagous insects associated with the flower heads revealed distinct taxonomical differences, but a high degree of numerical and structural similarity. The different geographical regions are similarly ranked for host plant attack, herbivore pressure, average species packing and level of food niche utilization.     

Invasive plant architecture alters trophic interactions by changing predator abundance and behavior

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.     

Response of the invasive Centaurea maculosa and two native grasses to N-pulses

Nitrogen is often a limiting resource on semi-arid grasslands. During the growing season, N is often only available during short-term pulses associated with wetting events. The Eurasian forb Centaurea maculosa Lam. has invaded millions of hectares of semi-arid grasslands in western North America. C. maculosa's success could be attributed to greater use of N-pulses, or more efficient use of N supplied in those pulses compared with native grasses. In a glasshouse, C. maculosa and two native grasses, the caespitose Pseudoroegneria spicata [Scribn. and Smith] A. Love and the rhizomatous Pascopyrum smithii [Rybd.] A. Love, were established in mixed- and monoculture combinations, and then conditioned to weekly N-pulses of 8, 24, or 72 h for 8 weeks. These pulse durations are typical on semi-arid grasslands. At the end of the 8 weeks, plants were exposed to ¹⁵N-labeled nitrate (¹⁵NO₃ ^–) for 8 h and harvested 16 h later to compare short-term root uptake of ¹⁵NO₃ ^–. C. maculosa did not have greater enrichment (atom % ¹⁵N), rate of ¹⁵N-uptake (mol g^–1 h^–1), or ¹⁵N acquired (relative to ¹⁵N applied) than the grasses. C. maculosa's ¹⁵N-uptake per unit mass was relatively consistent across pulse durations, whereas ¹⁵N-uptake was lower at the longer pulse durations for the grasses. In general, C. maculosa acquired more of the applied ¹⁵N than P. spicata but less than P. smithii. ¹⁵N acquired was often influenced by the neighbour's identity. Regarding growth responses, C. maculosa produced more total biomass than the grasses, except for P. smithii plants growing with C. maculosa conditioned to 72 h pulses of N. Root mass ratios varied depending on the neighbor. Overall, C. maculosa used nitrogen less efficiently than the grasses. C. maculosa's success as an invasive species cannot be explained wholly by a greater response to N-pulses or more efficient use of N-pulses compared with native grasses with which it competes.     

Effects of the Invasive Forb <Emphasis Type="Italic">Centaurea maculosa</Emphasis> on grassland Carbon and Nitrogen Pools in Montana,USA

Invasions by exotic forbs are changing large areas of North American grasslands, but their biogeochemical impacts are not well characterized. Additionally, although many invasive plants may alter biogeochemistry, an invasive species effects have rarely been evaluated across physically diverse sites. We sampled nine sites containing the perennial Eurasian forb Centaurea maculosa to determine if this invasive species alters soil C and N pools in native grasslands in Montana, USA. We sampled surface soil in adjacent microsites with C. maculosa and native grasses and analyzed soil C and N pools with slow to rapid turnover. None of the pools evaluated in the laboratory showed significant differences between C. maculosa and grass microsites when analyzed across all sites. Some differences were found at individual sites, but they were infrequent and inconsistent: Four sites had no differences, four had differences in one or two pools with intermediate (particulate organic matter C or N) or rapid turnover rates (potentially mineralizable N), and just one site had differences encompassing pools with rapid, intermediate, and slow (total C and N, silt-and-clay-associated N) turnover rates. Where they differed, pools were usually smaller under C. maculosa plants than under native grasses, but the opposite was found at one site. In situ N availability, estimated using ion exchange resins, was significantly lower under C. maculosa than under grasses at one of three sites sampled. Results indicate that C. maculosa may sometimes reduce soil C and N pools, including those related to N availability, but they argue against generalizing about the impacts of C. maculosa in grasslands.     

The parasitic fly Nemorilla maculosa exploits host‐plant volatiles to locate the legume pod borer,Maruca vitrata

Nemorilla maculosa Meigen (Diptera: Tachinidae) is a solitary endoparasitoid of the legume pod borer, Maruca vitrata Fabricius (Lepidoptera: Crambidae), a key pest of cowpea, Vigna unguiculata (L.) Walp. (Fabaceae) in Africa. A colony of N. maculosa, introduced for experimental purposes from Taiwan to the laboratories of the International Institute of Tropical Agriculture (IITA) in Benin, was used for our studies. Olfactory reponses of N. maculosa to leaves of infested or uninfested cowpea and yellow peabush, Sesbania cannabina (Retz.) Pers. (Fabaceae), and to M. vitrata larvae were evaluated in a four‐arm olfactometer. For all combinations of odor sources, responses between naïve and oviposition‐experienced female flies did not differ. Nemorilla maculosa females were attracted by odors from uninfested leaves of yellow peabush and flowers of cowpea when compared with clean air, and they were attracted to plants damaged by M. vitrata with larvae removed. However, the female fly did not discriminate between odors from infested and uninfested plants. The parasitic fly N. maculosa proved well able to use volatile compounds from various host plants (peabush and cowpea) to locate its host, with a more pronounced attraction by the combination of host larvae and infested host plant parts. These findings are discussed in light of the prospective use of N. maculosa as a biological control agent against the legume pod borer.     

Identification of Planococcus citri (Homoptera: Pseudococcidae) and the description of a new species

Planococcus pacificus sp.n. is described from the South Pacific, Australia and South East Asia. P.citricus is synonymized with P.citri. A key and illustrations are given to separate the species discussed from each other and from the similar P.ficus group.     

Agamococcidiorida ord. n. and Rhytidocystidae fam. n. for the Coccidian Genus Rhytidocystis Henneguy, 1907

Agamococcidiorida ord. n. and Rhytidocystidae fam. n. are established in the apicomplexan subclass Coccidiasina for the genus Rhytidocystis Henneguy, 1907. Dehornia Porchet-Henneré, 1972 is synonymized with Rhytidocystis.     

Generic revision and phylogeny of Microweiseinae (Coleoptera: Coccinellidae)

The monophyly and phylogenetic relationships of the subfamily Microweiseinae were investigated. Twenty‐three in‐group taxa, representing all known genera of Microweiseinae (except for Microcapillata Gordon) were included in a cladistic analysis, based on 45 adult morphological characters. The parsimony analysis of the resulting data matrix supported the monophyly of Microweiseinae, Carinodulini, Serangiini and Microweiseini (inclusive of Sukunahikonini). The recognition of Sukunahikonini renders Microweiseini paraphyletic, and consequently both tribes were synonymized, retaining Microweiseini as a senior family‐group name ( syn.n. ). Genera and tribes of Microweiseinae are diagnosed thoroughly, illustrated and keys to their identification are provided. The following nomenclatural changes were made: Hikonasukuna Sasaji and Orculus Sicard are synonymized with Scymnomorphus Weise ( syn.n. ); Gnathoweisea Gordon is synonymized with Microweisea Cockerell ( syn.n. ); Hikonasukuna monticola Sasaji and Orculus castaneus Sicard are transferred to Scymnomorphus ( comb.n. ); Smilia planiceps Casey, Gnathoweisea hageni Gordon, Gnathoweisea ferox Gordon, Gnathoweisea micula Gordon and Gnathoweisea texana Gordon are transferred to Microweisea ( comb.n ). Three new genera are described: Allenius gen.n. for Allenius californianus sp.n. (type species) from Mexico and Allenius iviei sp.n. from U.S.A.; Gordoneus gen.n. (type species Gnathoweisea schwarzi Gordon from U.S.A.); and Cathedrana gen.n. (type species Cathedrana natalensis sp.n. from South Africa). The first African member of Carinodulini, Carinodulina ruwenzorii sp.n. is described. The genera Microweisea, Coccidophilus, Serangium and Delphastus are well‐known predators of sternorrynchous Hemiptera, such as scale insects (Diaspididae) and whiteflies (Aleyrodidae), and play a significant role in agricultural ecosystems as biocontrol agents. Host data and biological records are summarized for each genus.     

Soil physical properties associated with the invasive spotted knapweed and native grasses are similar

Centaurea maculosa Lam. (spotted knapweed), a Eurasian perennial forb, has invaded disturbed and undisturbed semiarid grasslands in the western United States. In the past, success in controlling C. maculosa and restoring invaded areas has been limited. Most research has addressed chemical aspects of invasive species interactions with soils, while potential impacts of altered soil physical properties on C. maculosa's success has not been studied. We hypothesized that the persistence of C. maculosa in semiarid rangelands might reflect an ability to alter site conditions. The objective of this study was to compare selected soil physical properties under C. maculosa-dominated and native perennial grass-dominated areas on semiarid grassland. We used six field sites in western Montana containing adjacent plots dominated by C. maculosa and by native perennial grasses. Soil physical properties including particle size fractions, bulk density, and hydraulic and thermal properties, as well as total organic carbon content, of near-surface soils were measured for each vegetation type. Soil physical properties seldom differed between C. maculosa- and native grass-dominated areas. When soil physical properties differed, the differences were inconsistent within and among sites. Presence of C. maculosa did not alter surface soil characteristics at our six sites, thus its persistence on these semi-arid grasslands cannot be explained by an ability to alter near-surface soil characteristics.     

Neighboring plant influences on arbuscular mycorrhizal fungal community composition as assessed by T-RFLP analysis

Controls on root colonization by arbuscular mycorrhizal fungi (AMF) include host nutrient status, identity of symbionts and soil physico-chemical properties. Here we show, in the field, that the subset of the AMF community colonizing the roots of a common grass species, Dactylis glomerata, was strongly controlled by neighboring roots of a different plant species, Centaurea maculosa, an invasive forb, thus adding a biological spatial component to controls on root colonization. Using an AMF-specific, 18s rDNA-based terminal restriction fragment length polymorphism (T-RFLP) analysis method, significant differences were found between AMF community fingerprints of samples derived from roots of grasses with (G_Cm) and without (G₀) neighboring C. maculosa. There were also significant differences between samples derived from C. maculosa roots (C_mac) and both G_Cm and G₀ roots. Sample ordination indicated three generally distinct groups consisting of C_mac, G_Cm and G₀, with G_Cm samples being of intermediate distance between G₀and C_mac. Our results indicate that, with the presence of C. maculosa, AMF communities of D. glomerata shift to reflect community composition associated with C. maculosa roots. These results highlight the importance of complex spatial distributions of AMF communities at the scale of a root system. An additional dimension to our study is that C. maculosa is an aggressively invasive plant in the intermountain West. Viewed in this light, these results suggest that pervasive influences of this plant on AMF communities, specifically in roots of its competitors, may represent a mechanism contributing to its invasive success. However, further work is clearly required to determine the extent to which AMF genotypic alteration by neighboring plants influences competitive relationships.     

Two new and three redescribed species of Viscosia (Nematoda,Oncholaimidae)

Viscosia coomansi sp. nov. and Viscosia heterolaina sp. nov. are described from Lake Grevelingen and Eastern Scheldt (The Netherlands). Viscosia glabra (Bastian, 1865) de Man 1890, Viscosia franzii Boucher 1977, and Viscosia viscosa (Bastian 1865) de Man 1890 are redescribed, taking into account new important characters. Juvenile specimens are depicted for V. viscosa. Viscosia carnleyensis Ditlevsen, 1921 is synonymized with Viscosia glabra (Bastian, 1865). Mononcholaimus viscosus Allgén, 1930 and Mononcholaimus elegans sensu Schuurmans-Stekhoven, 1942, 1950 (nec. Kreis, 1924) are synonymized with Viscosia viscosa (Bastian, 1865).     

The invasive plant species Centaurea maculosa alters arbuscular mycorrhizal fungal communities in the field

While several recent studies have described changes in microbial communities associated with exotic plant invasion, how arbuscular mycorrhizal fungi (AMF) communities respond to exotic plant invasion is not well known, despite the salient role of this group in plant interactions. Here, we use molecular methods (terminal restriction fragment length polymorphism analyses based on the large subunit of the rRNA gene) to examine AMF community structure in sites dominated by the invasive mycorrhizal forb, Centaurea maculosa Lam. (spotted knapweed), and in adjacent native grassland sites. Our results indicate that significant AMF community alteration occurs following C. maculosa invasion. Moreover, a significant reduction in the number of restriction fragment sizes was found for samples collected in C. maculosa-dominated areas, suggesting reduced AMF diversity. Extraradical hyphal lengths exhibited a significant, on average 24%, reduction in C. maculosa-versus native grass-dominated sites. As both AMF community composition and abundance were altered by C.maculosa invasion, these data are strongly suggestive of potential impacts on AMF-mediated ecosystem processes. Given that the composition of AMF communities has the potential to differentially influence different plant species, our results may have important implications for site restoration after weed invasion.     

Plant Functional Group Diversity as a Mechanism for Invasion Resistance

A commonly cited mechanism for invasion resistance is more complete resource use by diverse plant assemblages with maximum niche complementarity. We investigated the invasion resistance of several plant functional groups against the nonindigenous forb Spotted knapweed (Centaurea maculosa). The study consisted of a factorial combination of seven functional group removals (groups singularly or in combination) and two C. maculosa treatments (addition vs. no addition) applied in a randomized complete block design replicated four times at each of two sites. We quantified aboveground plant material nutrient concentration and uptake (concentration × biomass) by indigenous functional groups: grasses, shallow‐rooted forbs, deep‐rooted forbs, spikemoss, and the nonindigenous invader C. maculosa. In 2001, C. maculosa density depended upon which functional groups were removed. The highest C. maculosa densities occurred where all vegetation or all forbs were removed. Centaurea maculosa densities were the lowest in plots where nothing, shallow‐rooted forbs, deep‐rooted forbs, grasses, or spikemoss were removed. Functional group biomass was also collected and analyzed for nitrogen, phosphorus, potassium, and sulphur. Based on covariate analyses, postremoval indigenous plot biomass did not relate to invasion by C. maculosa. Analysis of variance indicated that C. maculosa tissue nutrient percentage and net nutrient uptake were most similar to indigenous forb functional groups. Our study suggests that establishing and maintaining a diversity of plant functional groups within the plant community enhances resistance to invasion. Indigenous plants of functionally similar groups as an invader may be particularly important in invasion resistance.     

Traits of the invasive Centaurea maculosa and two native grasses: effect of N supply

The Eurasian forb Centaurea maculosa (Lam.; spotted knapweed) has invaded millions of hectares of semi-arid grasslands in western North America. It readily colonizes disturbed areas, but also invades pristine grasslands. C. maculosa's success could be attributed to greater use, or more efficient use, of available soil nitrogen (N). Soil N often limits growth on semi-arid grasslands. Greater or more efficient use of soil N by C. maculosa, if this occurred, may inhibit establishment, survival, or reproduction of native grasses. In a glasshouse, C. maculosa and two native grasses, Pseudoroegneria spicata [Scribn. and Smith] A. Love and Pascopyrum smithii [Rybd.] A. Love, were grown in mixed- and monoculture for 8 weeks to determine growth response to two soil N supplies, which mimicked low and high N mineralization rates in semi-arid grasslands. At the end of the 8 weeks, plants were exposed to ¹⁵N-labeled nitrate for 24 h, and harvested to compare uptake of NO₃ ^–. C. maculosa's growth response to N indicated that it was more competitive for N than the tussock grass P. spicata, but less competitive than the rhizomatous grass P. smithii. C. maculosa used nitrogen less efficiently than both of these native grasses. C. maculosa roots took up more ¹⁵N per unit root mass than the grasses, but acquired less N than P. smithii because P. smithii had greater root mass than C. maculosa. Total biomass and ¹⁵N uptake of C. maculosa varied depending on which species it was growing with. C. maculosa's success cannot be explained wholly by greater or more efficient use of soil N than that of the native grasses with which it competes.     

First Stage Zoeas of Quadrella Dana, 1851 [Crustacea: Decapoda: Brachyura: Xanthoidea: Trapeziidae] and their Affinities with those of Tetralia Dana, 1851, and Trapezia Latreille, 1828

The first stages zoeas of Quadrella maculosa Alcock, 1898, Q. serenei Galil, 1986, Tetralia rubridactyla Garth, 1971, and Trapezia richtersi Galil & Lewinsohn, 1983, are described and illustrated. Setal differences between the Quadrella zoeas are not recorded, but they can be separated on the spinulation of the dorsal spine (present in Q. maculosa absent in Q. serenei). The first stage zoea of Q. maculosa is compared with that of Tetralia rubridactyla and Trapezia richtersi. But although Quadrella and Tetralia appear superficially similar in that both have two pairs of lateral carapace spines (vs. one pair in Trapezia), other observations imply that Tetralia zoeas may have closer affinities with Trapezia rather than with Quadrella. However, this appears to contradict recent phylogentic relationships based on adult morphology.