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Yellow starthistle ( Centaurea solstitialis L) ( YST) is an invasive weed native to the Mediterranean region with a geographical centre of diversity in Turkey. It is widely established in Chile, Australia, and western North America. It arrived in California as a contaminant in alfalfa seed in 1859 and, by 2002, had infested >7.7 million hectares in the U.S.A., Biological control of YST using capitula feeding weevils, picture wing flies and a foliar rust pathogen has been ongoing in the western U.S.A. for more than three decades with limited success. Modelling and field research suggest natural enemies that kill whole plants and/or reduce seed production of survivors are good candidates for successful biological control. A candidate species with some of these attributes is the rosette weevil Ceratapion basicorne ( Illiger)., In the present study, a model of the rosette weevil is added to an extant system model of YST and its capitula feeding natural enemies and, in a GIS context, is used to assess YST control in the Palearctic region and the weevil's potential impact on YST in western U.S.A., The results obtained suggest densities of mature YST plants in western U.S.A. would be reduced by 70-80% in many areas. [ABSTRACT FROM AUTHOR]

A 2-yr (2014-2015) field study in eastern Washington State quantified the effect of environmental factors on the overwintered Eustenopus villosus (Boheman) and Larinus curtus (Hochhut) adults in relation to phenology of Centaurea solstitialis L. (Asteraceae: Cardueae), the feeding and breeding host for these two weevil biocontrol agents. We recorded in the study area: ambient and soil temperatures, soil moisture, percent cover and developmental stage of C. solstitialis, and presence of adults of each weevil species. Sampling took place from early May to mid-August. Weevil activity for both species in both years was segregated into three phases: 1 - a pre-appearance phase in which neither species was detected, 2 - appearance and increase in frequency, and 3 - decrease in frequency. Eustenopus villosus increase in frequency was most strongly associated with warming temperatures both years. Larinus curtus increase in frequency in 2014 was most associated with increasing C. solstitialis cover and in 2015 with warming temperatures and drying soils. In both years, both weevil species' decline in frequency was likely due to the advancing C. solstitialis phenology. This pattern indicates that the appearance and increase in frequency of the overwintered E. villosus and L. curtus adults was likely a function of warming temperatures. Both species' decline in frequency was likely a function of the weevils completing their life cycle in synchrony with the phenological advancement of C. solstitialis and decline of abundant breeding and foraging sites (buds and flowers). [ABSTRACT FROM AUTHOR]

Centaurea solstitialis (yellow starthistle) has invaded rangelands and natural areas in the western USA. There is evidence that mowing is a more effective method of reducing growth and seed production, compared with the well-established and distributed bioagents. To test this hypothesis we measured C. solstitialis's growth and reproduction following two treatments (late spring and early summer bud/capitula destruction and shoot mowing) and measured C. solstitialis's growth and reproduction. We measured changes in soil moisture content to test the hypothesis that these manipulations differentially affect water usage by the invasive plant. Mowing produced shorter plants that weighed less. Bud damaged plants were not statistically different from untreated controls. The number of developed capitula was reduced 67% by mowing but was unaffected by bud damage. Mowed plants redistributed resources from root to flower production. Both treatments reduced mean capitulum diameter. This resulted in reductions of 76% and 21% in estimated seed number for mowed and bud damaged plants respectively. Root abundance decreased and root life-span was reduced by both treatments. Soil moisture depletion was greatest from mid-May to mid-July (from 21% to 9%) and occurred after maximum root abundance. Mowing resulted in a delay in soil moisture depletion compared with the bud damaged plants or the untreated controls. Bud/capitula damage did not affect C. solstitialis's requirement for soil water. Overall, this study supported the hypothesis that mowing reduced C. solstitialis growth and reproduction more than bud damage alone. This information will aid managers in selecting a strategy for managing C. solstitialis in a particular habitat. [ABSTRACT FROM AUTHOR]

Herbivore damage often deters pollinator visitation and many invasive plants in North America are pollinator-dependent. This has important implications for the biological control of invasive plants because it means that agents that deter pollinators may have a larger than expected impact on the plant. Yet interactions between pollinators and biocontrol agents are rarely evaluated. Centaurea solstitialis, one of the most problematic invasive species in California, is dependent on pollinators for reproduction. I factorially manipulated infection by a biocontrol pathogen and pollen supplementation to test for (1) pollen limitation in C. solstitialis, (2) whether infection increased pollen limitation, and (3) whether this varied across a soil moisture gradient. Plants growing on north-facing slopes where soil moisture was higher experienced mild pollen limitation in the absence of the pathogen and more pronounced pollen limitation when they were infected. Plants on drier south-facing slopes did not suffer from pollen limitation but instead appeared to suffer from resource limitation. Pathogen infection directly reduced seed set in C. solstitialis by 67-72 %. On north-facing slopes, infection had an additional, indirect effect by increasing the degree of pollen limitation plants experienced. The trait that mediates this indirect pathogen-pollinator interaction is the number of inflorescences plants produced: infected plants made fewer inflorescences which led to greater pollen limitation. Although in the present study this outcome is dependent on abiotic factors that vary over small spatial scales, exploiting other invasive plants' dependence on pollinators by selecting agents that deter visitation may enhance agent impact. [ABSTRACT FROM AUTHOR]

Ceratapion basicorne is a weevil native to Europe and western Asia that is being evaluated as a prospective classical biological control agent of Centaurea solstitialis (yellow starthistle) in the United States. Choice oviposition experiments were conducted under laboratory conditions to help assess host-plant specificity of the insect. Mean oviposition rates were highest on C. solstitialis (66% of eggs, on a per replicate basis) followed by Centaurea cyanus (bachelor's button 22%), Centaurea melitensis (6%), Centaurea americana (1%), Saussurea americana (3%) and Carthamus tinctorius (safflower 2%). Adult feeding damage followed a similar pattern; however, there was less oviposition relative to the amount of adult feeding on each of the non-target species than on the target host plant, C. solstitialis. Thirteen safflower varieties were tested, and oviposition occurred on eight of them, at low rates. Adult feeding occurred on all safflower varieties tested, although at rates much lower than on yellow starthistle. The results were intermediate between those of previously reported no-choice laboratory and open field experiments. Overall, the combined results support the hypothesis that C. basicorne is not likely to attack any of the non-target plant species tested here except possibly C. cyanus and C. melitensis, which are both invasive alien plants. [ABSTRACT FROM PUBLISHER]

Centaurea solstitialis (yellow starthistle, Asteraceae) is an invasive annual weed in the western USA that is native to the Mediterranean Region and is a target for classical biological control. Aceria solstitialis is an eriophyid mite that has been found exclusively in association with Ce. solstitialis in Italy, Greece, Turkey and Bulgaria. The mite feeds on leaf tissue and damages bolting plants, causing stunting, witch's broom and incomplete flower development. Field experiments and laboratory no-choice and two-way choice experiments were conducted to assess host plant specificity of the mite in Bulgaria. Mites showed the highest degree of host specificity in the field and lowest in the no-choice experiments. In the field, highest densities of mites occurred on Ce. solstitialis and Ce. cyanus (bachelor's button), and either no mites or trace numbers occurred on the other test plants: Ce. diffusa (diffuse knapweed), Carthamus tinctorius (safflower) and Cynara scolymus (artichoke). In no-choice experiments, mites persisted for 60 days on Ce. diffusa, Ce. cyanus, Ce. solstitialis, Ca. tinctorius and Cy. scolymus, whereas in two-way choice experiments mites persisted on 25% of Cy. scolymus plants for 60 days and did not persist on Ca. tinctorius beyond 40 days. The eight other species of plants that were tested in the laboratory were less suitable for the mite. These results suggest that although A. solstitialis can persist on some nontarget plants for as long as 60 days in the laboratory, it appears to be much more specific under natural conditions, and warrants further evaluation as a prospective biological control agent. [ABSTRACT FROM AUTHOR]

Studies were made about resting spores of Synchytrium solstitiale, a chytrid that causes false rust disease of yellow starthistle (YST). During evaluation of this fungus for biological control of YST, a protocol for resting spore germination was developed. Details of resting spore germination and study of long-term survival of the fungus were documented. Resting spores from dried leaves germinated after incubating them on water agar at least 7 d at 10-15 C. Resting spores were viable after storage in air-dried leaves more than 2 y at room temperature, suggesting they have a role in off season and long-term survival of the fungus. Each resting spore produced a single sorus that contained a single sporangium, which on germination released zoospores through a pore. YST inoculated with germinated resting spores developed symptoms typical of false rust disease. All spore forms of S. solstitiale been found to be functional, and the life cycle of S. solstitiale has been completed under controlled laboratory and greenhouse conditions. Resting spore galls differ from sporangial galls both morphologically and biologically, and in comparison, each sporangial gall cleaves into several sori and each sorus produces 5-25 sporangia that rupture during release of zoospores. For this reason S. solstitiale should be reclassified as diheterogallic sensu Karling (Am J Bot 42:540-545). Because resting spores function as prosori and produce an external sorus, S. solstitiale is best placed in into the subgenus Exosynchytrium. [ABSTRACT FROM AUTHOR]

Plants interact with numerous enemies and mutualists simultaneously and sequentially. Such multispecies interactions can give rise to trait-mediated indirect effects that are likely to be common in nature but which are also inherently difficult to predict. Understanding multispecies interactions is also important in the use of biological control agents to control invasive plants because modern approaches to biocontrol rely on releasing multiple agents for each target weed. Centaurea soistitialis is one of the most problematic invasive weeds in California, USA, and the weevil Eustenopus vi/losus is its dominant biological control agent. We conducted a field experiment to quantitatively assess the direct effect of the recently approved biocontrol pathogen Puccinia jaceae f.s. soistitialis on plant performance and any indirect effects that might arise by altering the plant's interactions with Eustenopus or its pollinators (principally the nonnative Apis ,nelI fera). We documented both synergy and interference between the two biocontrol agents depending on the life stage of the weevil. Puccinia infection increased the impact of bud-feeding by the adult weevils but reduced the impact of seed-feeding by larval weevils. Neither infection nor Eustenopus attack had an effect on pollinator visitation. The net effect was that attack by both the pathogen and the weevil did not reduce plant fitness relative to plants attacked only by the weevil. Because the consequence to the plant of interacting with one species may depend on the presence or absence of other interacting species, a careful consideration of multispecies interactions may be necessary for the selection of biocontrol agents that act in a complementary manner to reduce plant fitness. Likewise, relatively tractable weed-biocontrol systems allow us to examine multispecies interactions that can be difficult to study experimentally in native systems that are composed of numerous species with well-established populations. [ABSTRACT FROM AUTHOR]

Abstract: The rust fungus Puccinia jaceae var. solstitialis was introduced to California in 2003 for biological control of yellow starthistle (Centaurea solstitialis). To test its effectiveness under field conditions, we examined biomass production, chlorophyll levels, and seedhead production of yellow starthistle (YST) infected with P. jaceae. We also evaluated the effect of P. jaceae on the competitive ability of YST grown with wild oat (Avena fatua), a widespread winter annual grass commonly associated with YST infestations. Chlorophyll levels were reduced by over 50% in severely rust-infested YST leaves. P. jaceae had no effect on growth or reproductive variables in monoculture plots, but caused a modest reduction in YST performance in the competition experiment. In this study, infected plants had fewer leaves than uninfected plants and slightly reduced rosette diameters. P. jaceae also decreased YST biomass from 3.18kgm−2 in non-inoculated competition plots to 2.62kgm−2 in inoculated plots over both years of the experiment. Although not significant, there was a trend towards reduced seedhead production in the inoculated plots. These results indicate that P. jaceae may have some negative effects on YST growth, especially under conditions of interspecific competition. However, the effects of P. jaceae appear to be of minor biological significance and are unlikely to cause major declines in YST populations statewide. [Copyright &y& Elsevier]

Abstract: Molecular analyses can play a primary role in the process of host specificity evaluation at species and population levels. Here we present an example of their application with a promising candidate biological control agent for yellow starthistle, Centaurea solstitialis L. Although it is highly host specific, Ceratapion basicorne (Coleoptera: Apionidae) can develop on safflower in laboratory tests. A field experiment was conducted to further evaluate host plant specificity; however, it was not possible to rear all larvae to the adult stage, which was necessary for species determination. Therefore molecular genetic methods were used to identify immature specimens. A 731bp fragment of mtDNA cytochrome C oxidase I gene (COI) was sequenced from 41 individuals of C. basicorne and four congeners: Ceratapion orientale, Ceratapion onopordi, Ceratapion penetrans and Ceratapion scalptum. Intraspecific variability ranged from 0.0% to 0.2%, and interspecific divergences ranged from 1.7% to 17.6%. All larvae that were sequenced from the field study, clearly matched one of the five species, enabling us to unambiguously identify them. Use of molecular genetics to identify larvae should also help the process of foreign exploration, enabling the identification of field-collected larvae, which often provide more reliable host plant associations than field collected adults. [Copyright &y& Elsevier]

Abstract: In anticipation of large-scale distribution of a Turkish isolate of Puccinia jaceae var. solstitialis in California for biological control of yellow starthistle (Centaurea solstitialis, YST), susceptibility of YST within the state was determined and a protocol for bulk inoculum production was developed. Inoculation was made of 62 field accessions of YST representative of the range of habitats in California. These were determined to be equally susceptible to infection by the isolate approved for release in the United States in 2003. To support a program to speed establishment by release at many locations statewide, protocols for artificial increase of inoculum were developed. Over 64g of urediniospores were produced with a mass-production system under greenhouse conditions from 2003 to 2006. Yield of inoculum varied by season, with peak production occurring from early spring through early summer. A large-scale urediniospore harvest also was made from a field plot at Davis, California. Our results show that susceptibility of YST in California is not likely to limit establishment of P. jaceae for biological control, and that production of this or other obligate pathogenic fungi (biological control agent) is possible for support of statewide release and research programs. [Copyright &y& Elsevier]

We studied the life history, geographic distribution, behavior, and ecology of Larinus filiformis Petri (Coleoptera: Curculionidae) in its native range to determine whether it is worthy of further evaluation as a classical biological control agent of yellow stat-thistle, Centaurea soistitialis (Asteraceae: Cardueae). Larinus filiformis occurs in Armenia, Azerbaijan, Turkey, and Bulgaria and has been reared only from C. soistitialis. At field sites in central and eastern Turkey, adults were well synchronized with the plant, being active from mid-May to late July and ovipositing in capitula (flowerheads) of C. solstitialis from mid-June to mid-July. Larvae destroy all the seeds in a capitulum. The insect is univoltine in Turkey, and adults hibernate from mid-September to mid-May. In the spring, before adults begin ovipositing, they feed on the immature flower buds of C. soistitialis, causing them to die. The weevil destroyed 25-75% of capitula at natural field sites, depending on the sample date. Preliminary host specificity experiments on adult feeding indicate that the weevil seems to be restricted to a relatively small number of plants within the Cardueae. Approximately 57% of larvae or pupae collected late in the summer were parasitized by hymenopterans [Bracon urinator, B. tshitsherini (Braconidae) and Exevistes roborator (Ichneumonidae), Aprostocetus sp. (Eulophidae), and unidentified species of Eurytomidae and Ormyridae]. This weevil may be a better choice than the other capitula insects already established in the United States, particularly in colder parts of the plant's range. [ABSTRACT FROM AUTHOR]

Abstract: Since the introduction of Puccinia jaceae var. solstitialis into California in 2003, multiple urediniospore generations have been observed, along with teliospores and pycnia, on yellow starthistle (Centaurea solstitialis). A field and laboratory study of urediniospore viability was conducted to determine the potential of using infected plant material for redistribution of inoculum into new areas. To better understand the life history of P. j. solstitialis, urediniospore viability was measured during the summer and fall when the host plant is usually senescent. Latent period (time from inoculation to pustule eruption) after field and laboratory inoculations was measured in order to determine the potential number of urediniospore generations that occur per year. Viability of urediniospores stored in the laboratory gradually declined over a period of 10 weeks; spore hydration increased germination. Based on the results obtained in this study, introductions of harvested infected plant material would have to be done quickly to offset losses in urediniospore viability. Urediniospore viability in the field decreased exponentially 86% near the coast and 97% in the Central Valley three weeks after production, and was negligible (0–0.2%) thereafter. Latent period ranged from four to five weeks at cool winter temperatures to two to three weeks at warm summer temperatures in both the laboratory and field. Results of this study suggest that urediniospores are not likely to remain viable through the summer and fall dry season. Teliospores, therefore, serve as the inoculum source when YST seedlings germinate in the winter. Approximately six urediniospore generations can be expected to occur each year in central-northern California under suitable conditions for disease. [Copyright &y& Elsevier]

Abstract: The rust fungus Puccinia jaceae var. solstitialis (P. j. solstitialis) was first approved for release in California in 2003 as a classical biological control agent for Centaurea solstitialis (yellow starthistle, Asteraceae). It is difficult to produce large quantities of this obligate pathogen so it was necessary to develop an optimal release strategy for the efficient use of urediniospores. In 2005–2006 field experiments were conducted in two distinct habitats types, the coastal hills and Central Valley, CA, to determine the optimal month for introductions, and to determine if enclosing plots in tents at the time of inoculation was necessary to achieve high levels of infection. All releases resulted in infected plants at both sites for both years. At the Central Valley site near Woodland CA, disease incidence was higher than at the coastal hills, tent enclosures had no effect on infection, and the pathogen persisted throughout the growing season. One year after the 2005 release, P. j. solstitialis had reappeared in most Central Valley plots, although early season releases in 2005 resulted in greater severity in 2006 than the late season releases. In the coastal hills near Napa, CA, tent enclosures improved disease incidence and severity after January and May releases, perhaps by retaining moisture, but the pathogen did not persist in all plots until plant senescence, and there was no reinfection (the following spring) at this site. The rust fungus did not have a negative affect on plant mortality, biomass, or flower production at either location. Our results show that infection can be achieved from January to June, and tent enclosures sometimes appeared to increase infection; however, reinfection is probably limited by local environmental conditions. [Copyright &y& Elsevier]

The fungus Synchytrium solstitiale is a candidate for use as a biocontrol agent against Centaurea solstitialis. This obligate parasite can be propagated only in planta, which necessitates development of a method for preserving cultures for longer periods of time for routine biological studies and shipment to other laboratories. Normally, sporangia embedded within the plant tissue release zoospores when submersed in water at temperatures above freezing. To examine what chemicals might inhibit zoospore release, infected tissue was exposed to different suspensions of fungicides. Cycloheximide and benomyl completely inhibited zoospore release or immediately induced encystment from tissue stored in these two chemicals, respectively. A few zoospores were released in suspensions of iprodione and propionic acid but were not motile. However, when tissue stored in iprodione or propionic acid was transferred to fresh distilled water, abundant active zoospores were released. Freezing the infected tissue at different temperatures in different cryoprotectants also affected the release of motile zoospores. Infected C. soistitialis tissue was immersed in water, water plus iprodione, methanol, ethylene glycol, dimethyl sulfoxide, glycerol, skim milk, trehalose, or sucrose and subjected to different temperatures for various periods of time. Some treatments protected the viability of the fungus for a shorter period of time whereas other treatments completely inhibited release. The best results were obtained when infected tissue was stored at -2°C in 0.5 M sucrose where active zoospores were released after 12 weeks of storage. Overall, results obtained from this study demonstrate a technique for long- term storage of S. solstitiale. [ABSTRACT FROM AUTHOR]

Abstract: Economic analyses are a valuable input into the decision-making process for biological control programs. The challenge though is how to incorporate qualitative risk assessments of biological control programs, or the risk of nontargeted effects into mathematical economic models. A technique known as threshold cost/benefit analysis is presented and an example on how to apply this method is illustrated using the yellow starthistle biological control program. The results show that incorporating uncertainty into the analysis can have a significant impact on the decision to undertake a biological control program. [Copyright &y& Elsevier]

Abstract: The biological control of yellow starthistle (Centaurea solstitialis) by four capitulum-feeding insects (weevils Bangasternus orientalis and Eustenopus villosus, and flies Urophora sirunaseva and Chaetorellia succinea), as affected by plant competition with annual grasses, is analyzed using a weather-driven, physiologically based, age-structured, simulation model. Seed density in the soil seed bank for yellow starthistle and the number of overwintering insects provide between-season links. Seed germination intensity and pattern is determined by the timing and quantity of autumn rains and temperatures, while season-length is mostly determined by soil–water balance. Output from the yellow starthistle systems model was integrated into a geographic information system to examine regional differences in abundance for all species across several ecological zones of California. A marginal analysis of the simulation results was performed to examine the efficacy of each capitulum-feeding insect, their within-capitulum competitive interactions, and the effect of competition from annual grasses on yellow starthistle populations. The model suggests that lack of complete control of yellow starthistle may be due to plant compensation via increased per-plant seed production at lower plant densities and the incomplete destruction of seed in attacked capitula. The model suggests herbivory that reduces the plant’s ability to compensate and/or kills whole plants before seed maturity would most likely lead to control of yellow starthistle. [Copyright &y& Elsevier]

Centaurea solstitialis L., yellow star thistle, is an annual weed that belongs to the family Asteraceae. In Turkey, this weed can be found in pasture areas, along roadsides, in cultivated areas and in field margins. Yellow star thistle is native to Mediterranean and western Asian countries. Alternative management strategies to chemical control have been and still are being studied; for example, management strategies to control this weed in the USA concentrate on the biological control approach. In addition, chemical control methods in pasture areas are banned in Turkey, which led us to carry out this field study. The average percentage cover of yellow star thistle on the selected study sites at an altitude of 0-1623 m in southern Turkey was 22.56%. Three fungi and 15 arthropod species were found on yellow star thistle during the survey and rearing study. These were Helminthosporium sp., Alternaria sp., Puccinia sp., Bangasternus orientalis, Ceratapion basicorne, Ceratapion sp., Phytoecia humeralis, Eustenopus villosus, Haplothrips reuteri, Lixus cardui, Strophosoma melanorammum, Uroleucon jacea, Diplapion detritum, Larinus curtus, Larinus grisescens, Lixus scolopax, Urophora sp. and Aceria solstitialis. Among these species, Ceratapion spp. had the highest infestation rate (18.4%), and 1-6 larvae per attacked plant. An important observation made with regard to Ceratapion spp. was that they do not feed on yellow star thistle seeds, but their larvae mine the root crown of plants that have reached the rosette stage. [ABSTRACT FROM AUTHOR]

In an effort to design a bioassay to screen for biocontrol pathogens and their toxins, procedures were developed to produce calli of yellow starthistle (YST), Centaurea solstitialis (Asteraceae), on solid and liquid media. Three Murashige and Skoog (MS) media with different hormone additives were compared for their effects on the growth of the YST calli. The most effective medium was made of MS salts supplemented with two cytokinins and a low rate of auxin. The growth of the calli slowed when cytokinins were omitted. Similar results were observed in a bioassay setup to compare the reactions of the YST calli with those of detached leaves exposed to potential toxins in the culture filtrates of test fungi. After exposure for 96 h to different concentrations of culture filtrates from three Alternaria alternata isolates, the calli exposed to 100 and 50% concentrations of the filtrates were significantly more damaged than other concentrations tested, based on a visual rating scale. No differences were observed in the damage ratings among the A. alternata isolates tested. An additional bioassay was setup to determine if calli could be used to screen pathogenic fungi. After 48 h, a distinction could be made in a visual rating between calli treated with spores of a pathogen, Phoma exigua, and a nonpathogen, Penicillium sp., confirming that YST calli can be used to screen potential pathogenic fungi against YST. [Copyright &y& Elsevier]

Yellow starthistle (Centaurea solstitialis L.) (YST) is an important invasive plant that infests millions of hectares in the western USA and Canada. Isolates of the exotic rust fungus Puccinia jaceae have been evaluated as a potential biological control for YST. The objectives of this study were to characterize isolates of P. jaceae by amplified fragment length polymorphic (AFLP) DNA analysis and to develop primers that will allow the identification and monitoring of isolates. AFLP analysis indicated that Eurasian isolates of P. jaceae from different hosts exhibited unique fingerprint patterns primarily based on host/pathogenicity preference. Overall similarities in AFLP profiles of isolates of P. jaceae ranged from 68.1 to 94.6%. The three isolates originally collected from YST clustered with similarities of 87.3–94.6%. Simple sequence repeat (SSR) primers were screened for fragments unique to P. jaceae pathogens of YST. Two primers, (GACA)4 and (ACG)5, produced 1170 and 912-bp fragments, respectively, in three isolates of P. jaceae var. solstitialis. The fragments were sequenced, and primers were designed and tested with isolates of Puccinia spp. and accessions of Centaurea spp. Primers from the GACA repeat amplified a 1091-bp product only with the three isolates of P. jaceae that infect YST. Primers from the ACG repeat amplified a 851-bp product with the same three P. jaceae var. solstitialis isolates, and an isolate collected from Centaurea maculosa, which is a weak pathogen of YST. These primers will be useful for monitoring isolates that may be released in future field trials to manage YST populations. [Copyright &y& Elsevier]

The phenological synchrony of Eustenopus villosus (Boheman) with its host, yellow starthistle, Centaurea solstitialis L. (Asteraceae: Cardueae), was studied in Idaho in 1995 and 1996. Field plots were observed for adult weevil activity periodically throughout the growing season, and yellow starthistle capitula were examined for adult feeding damage, oviposition damage, and larval development. At the study site, weevil phenology was well synchronized with C. solstitialis. Immature capitula, fed upon by adults, were abundant when E. villosus began to emerge in late May. During both years, the number of weevils and capitula increased throughout June. Adult females fed on capitula for about 2 wk. Weevil ovary dissections revealed that ovaries were mature after a 2-wk period of feeding. The development of mature capitula during late July corresponded to the initiation of oviposition. Eustenopus villosus, unique among the phytophages introduced for C. solstitialis biological control, attacks four plant stages resulting in observable impact to buds. Damaged buds either died or became distorted. Weevil feeding damage on young and mature capitula may make this insect a highly effective control agent. [ABSTRACT FROM AUTHOR]

The weevil Bangasternus orientalis Capiomont was selected as a candidate for the biological control of Centaurea solstitialis L. (yellow starthistle) in the United States. Its potential host range was studied during 1982, 1983, and 1984 in Rome, Italy, using populations collected from C. solstitialis in Thermi near Thessaloniki and Kozani in northern Greece. Adults laid eggs only on members of the genus Centaurea and the thistle Onopordum acanthium; eggs laid on O. acanthium hatched but 1st instars died before entering buds. There was no significant difference in the number of eggs laid on various U.S. and Italian strains of C. solstitialis included in the tests. Eggs were not deposited on plant species of economic importance such as Cynara scolymus, Helianthus annuus, Carthamus tinctorius, and Lactuca sativa. Larvae completed their larval development only on C. solstitialis from Greece and on U. S. and Italian populations of C. solstitialis among the60 plant species, varieties, and strains (in 7 families) tested: This restricted host range suggested introduction of this weevil as a biological control agent against yellow starthistle in the United States. Releases of B. orientalis were made in California, Washington, Idaho, and Oregon in 1985 and it became established in all states in 1989. [ABSTRACT FROM AUTHOR]