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Simple Summary Yellow starthistle (Centaurea solstitialis) is an invasive annual plant that has infested multi-million ha in the western United States, causing multi-billion dollars of losses and management costs. The rosette weevil (Ceratapion basicorne) has recently been approved for biological control of this weed. However, this weevil reproduces only once a year, which hinders mass-rearing for release. Here, we tested whether insect hormones can break the reproductive diapause of female weevils. We found that applying two insect hormones, 20E and methoprene, can consistently terminate diapause of female weevils to enable them to lay eggs. Thus, topically applying insect hormones could be used to induce females to lay eggs at any time of year, which would permit rearing more than one generation per year. This could greatly increase the number of weevils produced per year in a mass-rearing program to accelerate the release of rosette weevils to help suppress yellow starthistle in the United States. These insects would revert to having one generation per year after release in synchrony with their host plant. Abstract Classical biological control is an important method for controlling invasive alien weeds. Univoltine insects can be highly effective biological control agents of annual weeds because they are well synchronized with their host plant. However, having only one generation per year makes it difficult and slow to multiply them in the laboratory for initial field releases. If it were possible to terminate reproductive diapause early, then we could rear multiple generations per year, which would greatly increase annual production. We used a recently approved biocontrol agent, Ceratapion basicorne (a univoltine weevil), for yellow starthistle (Centaurea solstitialis) as a model system to study the use of two insect hormones, 20-hydroxyecdysone (20E) and methoprene, to terminate reproductive diapause. Methoprene (1 μg applied topically) terminated reproductive diapause of female weevils, whereas doses of 0.0, 0.01 and 0.1 μg did not. The combination of methoprene and 20E had a stronger effect and induced an increase in eggs (1.51 ± 0.16 eggs/day, mean ± SE) compared with a methoprene only group (1.00 ± 0.13 eggs/day), and a control group (0.21 ± 0.04 eggs/day). Thus, topical application of these hormones should enable us to rear the weevil out of its normal season and produce more than one generation per year, which will increase productivity of mass-rearing it for field release. Once released in the field, the insect would continue as a univoltine agent that is well-synchronized with its host plant.

Simple Summary The exotic thistle, Centaurea solstitialis, has become overly abundant in the western USA. A seed weevil, Eustenopus villosus, was released in the early 1990s to reduce seed production and abundance of the thistle. A first step in evaluating success of the biological control program is to evaluate the amount of seed destroyed by the weevil in its new area of infestation. At two sites for two years, we found that adult weevils killed 60–70% of young flower buds, forcing plants to regrow new buds which delayed flowering by 9 days and extended flowering by 4 weeks at season end. Flower heads varied in size and seed production increased linearly by size of the flower head. The seed weevil attacked larger flower heads more frequently than smaller flower heads but the probability of a flower head being attacked did not vary with plant size. Weevil larvae occurred in 27% to 49% of seed heads and resulted in 34% to 47% of the annual seed crop being destroyed. We recommend that another survey be performed to see if the seed weevil has increased in abundance since its introduction. Abstract The impact of the capitulum weevil Eustenopus villosus on Centaurea solstitialis seed production was examined at two field sites in central California. The study occurred in 1993–1995 during the early phases of the biological control program on C. solstitialis and before the current guild of capitulum insects had become widespread. Results showed that adult feeding on early flower buds resulted in 60–70% of buds failing to develop. Regrowth delayed capitulum production by 9 days and extended production by 4 weeks at season end. Between 69% and 92% of capitula were punctured from feeding or oviposition but the occurrence of larvae in capitula ranged from 27% to 49%. Seed production in C. solstitialis capitula increased linearly with size. The occurrence of larvae was proportionally higher in larger capitula (>8 mm) but the probability of attack for individual capitula did not vary with plant size. Total seed loss from larval feeding ranged from 34 to 47%. It is recommended that another survey be performed to determine if the level of infestation of E. villosus has increased since its initial introduction.

The impact of the capitulum weevil Eustenopus villosus on Centaurea solstitialis seed production was examined at two field sites in central California. The study occurred in 1993–1995 during the early phases of the biological control program on C. solstitialis and before the current guild of capitulum insects had become widespread. Results showed that adult feeding on early flower buds resulted in 60–70% of buds failing to develop. Regrowth delayed capitulum production by 9 days and extended production by 4 weeks at season end. Between 69% and 92% of capitula were punctured from feeding or oviposition but the occurrence of larvae in capitula ranged from 27% to 49%. Seed production in C. solstitialis capitula increased linearly with size. The occurrence of larvae was proportionally higher in larger capitula (&gt, 8 mm) but the probability of attack for individual capitula did not vary with plant size. Total seed loss from larval feeding ranged from 34 to 47%. It is recommended that another survey be performed to determine if the level of infestation of E. villosus has increased since its initial introduction.

Many plant invasion studies in grasslands suggest that resident plants that share functional traits with invaders can reduce invasion by competing for limiting resources. However, since invasion studies often occur in highly controlled plots or microcosms, it is unclear how heterogeneous site conditions alter competitive interactions under realistic scenarios. To explore how landscape heterogeneity affects biotic resistance provided by competitive resident plants, we conducted a field‐based experiment across four sites in California grasslands. Plots contained naturally occurring populations of native Hemizonia congesta, but differed in other characteristics, including litter cover, annual grass cover, soil moisture, and species richness. We invaded plots with the functionally similar nonnative Centaurea solstitalis (yellow starthistle) and, at one site, supplemented one‐half of the established plots with water to test the effects of increasing a limiting resource. As in simplified plots and microcosms, increasing H. congesta abundance reduced starthistle biomass by competing for limited soil moisture, but only in plots with high starthistle germination. We conclude that higher abundances of native H. congesta can reduce starthistle invasion in heterogeneous grasslands, but competition is also affected by both abiotic (soil moisture) and biotic (starthistle germination number) conditions that vary across sites.

Transcriptome sequences are becoming more broadly available for multiple individuals of the same species, providing opportunities to derive population genomic information from these datasets. Using the 454 Life Science Genome Sequencer FLX and FLX-Titanium next-generation platforms, we generated 11−430 Mbp of sequence for normalized cDNA for 40 wild genotypes of the invasive plant Centaurea solstitialis, yellow starthistle, from across its worldwide distribution. We examined the impact of sequencing effort on transcriptome recovery and overlap among individuals. To do this, we developed two novel publicly available software pipelines: SnoWhite for read cleaning before assembly, and AllelePipe for clustering of loci and allele identification in assembled datasets with or without a reference genome. AllelePipe is designed specifically for cases in which read depth information is not appropriate or available to assist with disentangling closely related paralogs from allelic variation, as in transcriptome or previously assembled libraries. We find that modest applications of sequencing effort recover most of the novel sequences present in the transcriptome of this species, including single-copy loci and a representative distribution of functional groups. In contrast, the coverage of variable sites, observation of heterozygosity, and overlap among different libraries are all highly dependent on sequencing effort. Nevertheless, the information gained from overlapping regions was informative regarding coarse population structure and variation across our small number of population samples, providing the first genetic evidence in support of hypothesized invasion scenarios. Fil: Dlugosch, Katrina M.. University of British Columbia; Canadá Fil: Lai, Zhao. Indiana University; Estados Unidos Fil: Bonin, Auélie. Indiana University; Estados Unidos Fil: Hierro, Jose Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Ciencias de la Tierra y Ambientales de La Pampa. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales. Instituto de Ciencias de la Tierra y Ambientales de La Pampa; Argentina Fil: Rieseberg, Loren H.. University of British Columbia; Canadá. Indiana University; Estados Unidos

1 Yellow starthistle (Centaurea solstitialisL) (YST) is an invasive weed native to theMediterranean region with a geographical centre of diversity in Turkey. It is widelyestablished in Chile, Australia, and western North America. It arrived in California asa contaminant in alfalfa seed in 1859 and, by 2002, had infested>7.7 million hectaresin the U.S.A. 2 Biological control of YST using capitula feeding weevils, picture wing flies and a foliarrust pathogen has been ongoing in the western U.S.A. for more than three decades withlimited success. Modelling and field research suggest natural enemies that kill wholeplants and/or reduce seed production of survivors are good candidates for successfulbiological control. A candidate species with some of these attributes is the rosetteweevilCeratapion basicorne(Illiger). 3 In the present study, a model of the rosette weevil is added to an extant system modelof YST and its capitula feeding natural enemies and, in a GIS context, is used toassess YST control in the Palearctic region and the weevil’s potential impact on YSTin western U.S.A 4 The results obtained suggest densities of mature YST plants in western U.S.A. wouldbe reduced by 70–80% in many areas.

At two field sites that differed in fertility, we investigated how species richness, functional group diversity, and species composition of constructed plant communities influenced invasion. Grassland communities were constructed to be either functionally diverse or functionally simple based on belowground resource use patterns of constituent species. Communities were also constructed with different numbers of species (two or five) to examine interactions between species richness, functional diversity and invasion resistance. We hypothesized that communities with more complementary belowground resource use (i.e., more species rich and more functionally diverse communities) would be less easily invaded than communities with greater degrees of belowground resource use overlap. Two contrasting invasive species were introduced: an early-season, shallow rooting annual grass, Bromus hordeaceus (soft chess), and a late-season, deep rooting annual forb, Centaurea solstitialis (yellow starthistle). Invader responses to species richness and functional diversity treatments differed between sites. In general, the more similar the patterns of belowground resource use between residents of the plant community and the invader, the poorer the invader’s performance. Complementarity or overlap of resource use among species in the constructed communities appeared to affect invader success less than complementarity or overlap of resource use between the invader and the species present in the community.

Yellow starthistle is an exotic invasive weed that is estimated to infest over 14 million acres in California and is considered the most common exotic weed statewide. We reviewed several previous studies and conducted a township survey to provide an up-to-date analysis of the weed's rapid spread throughout the state. A county-by-county comparison between 1985 and 2002 showed increases in yellow starthistle in all regions of the state except for northeast California and the southeast desert region. Currently, most infestations occur in Northern California, but future invasions and spread will likely occur in the coastal counties of Southern California.

The guaianolide type sesquiterpene lactones chlorojanerin, 13-acetyl solstitialin A and solstitialin A were identified as the anti-ulcerogenic components of the chloroform extract of the aerial parts of Centaurea solstitialis ssp. solstitialis (Asteraceae). In this study, these compounds were investigated by using various in vivo ulcer models in rats and mice. Chlorojanerin was shown to be significantly effective in preventing the induction of lesions by ethanol- (EtOH-) (both oral and subcutaneous administration), indomethacin-, indomethacin plus HCI/EtOH-, N-G-nitro-L-ar.-inine methyl ester plus EtOH, N-ethylmaleimide plus EtOH-, water immersion and restraint stress, and serotonin, as well as inhibiting fitratable gastric acidity and acid output, and increasing gastric pH, but was ineffective in the prevention of ulcers induced by pyloric ligation, diethyldithiocarbamate, and cysteamine, and had no effect on gastric secretion volume or peptic activity. A mixture of 13-acetyl solstitialin A (95%) and solstitialin A (5%) was found to be significantly effective against EtOH-induced lesions on oral administration but was ineffective when administered subcutaneously. This mixture was also found to be effective in preventing lesions induced by EtOH, indomethacin, indomethacin plus HCl/EtOH, N-G-nitro-L-arginine methyl ester plus EtOH, N-ethylmateimide plus EtOH, water immersion and restraint stress, serotonin and cysteamine, as well as inhibiting fitratable gastric acidity and fitratable acid output, and gastric pH, but was found ineffective against the pyloric ligation-induced and diethyldithiocarbamate-induced ulcerogenesis models, as well as gastric secretion volume and peptic activity. On the other hand, active compounds did not show any toxic effect on acute toxicity (3 days administration) evaluation tests in mice. (c) 2007 Elsevier Ireland Ltd. All rights reserved.