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The management of biological invasions is a worldwide conservation priority. Unfortunately, decision‐making on optimal invasion management can be impeded by lack of information about the biological processes that determine invader success (i.e. biological uncertainty) or by uncertainty about the effectiveness of candidate interventions (i.e. operational uncertainty). Concurrent assessment of both sources of uncertainty within the same framework can help to optimize control decisions.Here, we present a Value of Information (VoI) framework to simultaneously analyse the effects of biological and operational uncertainties on management outcomes. We demonstrate this approach with a case study: minimizing the long‐term population growth of musk thistle Carduus nutans, a widespread invasive plant, using several insects as biological control agents, including Trichosirocalus horridus, Rhinocyllus conicus and Urophora solstitialis.The ranking of biocontrol agents was sensitive to differences in the target weed's demography and also to differences in the effectiveness of the different biocontrol agents. This finding suggests that accounting for both biological and operational uncertainties is valuable when making management recommendations for invasion control. Furthermore, our VoI analyses show that reduction of all uncertainties across all combinations of demographic model and biocontrol effectiveness explored in the current study would lead, on average, to a 15.6% reduction in musk thistle population growth rate. The specific growth reduction that would be observed in any instance would depend on how the uncertainties actually resolve. Resolving biological uncertainty (across demographic model combinations) or operational uncertainty (across biocontrol effectiveness combinations) alone would reduce expected population growth rate by 8.5% and 10.5% respectively.Synthesis and applications. Our study demonstrates that intervention rank is determined both by biological processes in the targeted invasive populations and by intervention effectiveness. Ignoring either biological uncertainty or operational uncertainty may result in a suboptimal recommendation. Therefore, it is important to simultaneously acknowledge both sources of uncertainty during the decision‐making process in invasion management. The framework presented here can accommodate diverse data sources and modelling approaches, and has wide applicability to guide invasive species management and conservation efforts., Our study demonstrates that intervention rank is determined both by biological processes in the targeted invasive populations and by intervention effectiveness. Ignoring either biological uncertainty or operational uncertainty may result in a suboptimal recommendation. Therefore, it is important to simultaneously acknowledge both sources of uncertainty during the decision‐making process in invasion management. The framework presented here can accommodate diverse data sources and modelling approaches, and has wide applicability to guide invasive species management and conservation efforts.

The biotic resistance hypothesis asserts that native species may hinder the invasion of exotic species, which can occur either directly or indirectly by influencing interactions between exotic and local species. Aphid-tending ants may play a key role in the indirect biotic resistance to plant invasion. Ants may protect aphids, thus increasing their negative effect on exotic plants, but may also deter chewing herbivores, thus benefiting exotic plants. We studied native aphid-tending ants (Dorymyrmex tener, Camponotus distinguendus, and Dorymyrmex richteri) on exotic nodding thistles (Carduus thoermeri), which are attacked by thistle aphids (Brachycaudus cardui) and thistle-head weevils (Rhinocyllus conicus). We evaluated the impact of ants, aphids, and weevils on thistle seed set. We compared ant species aggressiveness towards aphid predators and weevils and performed ant-exclusion experiments to determine the effects of ants on aphid predators and weevils. We analysed whether ant species affected thistle seed set through their effects on aphids and/or weevils. The ant D. tener showed the most aggressive behaviour towards aphid predators and weevils. Further, D. tener successfully removed aphid predators from thistles but did not affect weevils. Excluding D. tener from thistles increased seed set. Analyses supported a negative indirect pathway between the aggressive D. tener and thistle seed set through aphid populations, while the other ant species showed no indirect effects on thistle reproduction. Therefore, aggressive aphid-tending ants may enhance biotic resistance by increasing aphid infestation on exotic invasive plants. This study highlights the importance of indirect biotic resistance in modulating the success of invasive species.

One of the main obstacles of classical biological control is that biological control organisms cannot be recalled once they are released in nature. It is particularly true for the flowerhead weevil, Rhinocyllus conicus Frolich, which was released as a biological control organism for the invasive musk thistle, Carduus nutans L. (MT). While weevils successfully suppressed introduced populations of musk thistles and other invasive thistle species, non-target attacks have been reported on multiple native thistles including federally listed threatened and endangered (T&E) thistle species. To investigate the foraging behavior of female weevils on invasive and native thistles, we examined volatile organic compounds (VOCs) emitted from MT and a T&E plant species, Sacramento Mountains thistle, Cirsium vinaceum Wooton & Standley (SMT) in the Lincoln National Forest, New Mexico. We used a dynamic headspace volatile collection system and gas chromatography-mass spectrometry to compare volatile profiles between MT and SMT. Female weevils reacted to 7 electrophysiologically active chemical compounds in the blends based on gas chromatography-electroantennography. The behavioral response of female weevils was indifferent when VOCs from both thistles were offered in y-tube olfactometry experiments. Yet, they preferred VOCs collected from MT to purified air. The searching time of female weevils was longer to VOCs collected from SMT over controls. Investigating signals during the initial host recognition of released biological control organisms may open new opportunities to reduce non-target attacks on T&E plant species.

Whether plant populations are limited by seed or microsite availability is a long-standing debate. However, since both can be important, increasing emphasis is placed on disentangling their relative importance and how they vary through space and time. Although uncommon, seed addition studies that include multiple levels of seed augmentation, and follow plants through to the adult stage, are critical to achieving this goal. Such data are also vital to understanding when biotic pressures, such as herbivory, influence plant abundance. In this study, we experimentally added seeds of a native thistle, Cirsium canescens, at four augmentation densities to plots at two long-term study sites and quantified densities of seedlings and reproductive adults over 9 years. Recruitment to both seedling and adult stages was strongly seed-limited at both sites; however, the relative strength of seed limitation decreased with plant age. Fitting alternative recruitment functions to our data indicated that post-dispersal mortality factors were important as well. Strong density-dependent mortality limited recruitment at one site, while density-independent limitation predominated at the other. Overall, our experimental seed addition demonstrates that the environment at these sites remains suitable for C. canescens survival to reproduction and that seed availability limits adult densities. The results thus provide support for the hypothesis that seed losses due to the invasive weevil, Rhinocyllus conicus, rather than shifting microsite conditions, are driving C. canescens population declines. Shifts in the importance of density-dependent recruitment limitation between sites highlights that alternate strategies may be necessary to recover plant populations at different locations.

The species belonging to the weevil genus Rhinocyllus are studied. A new species, Rhinocyllus alpinus sp. nov. living on the inflorescences of Cirsium alsophilum (Pollini) Soldano (Asteraceae), is described from the central Italian Alps. A new subgenus, Rhinolarinus subgen. nov., is created for this new species. The following new synonymy is proposed: Curculio inquilinus Gyllenhal, 1827 syn. nov. of Rhinocyllus conicus (Froelich, 1792). Lectotypes for Curculio inquilinus Gyllenhal, 1827, Rhinocyllus olivieri Gyllenhal, 1835 and Rhinocyllus oblongus Capiomont, 1873 are designated. Due to lack of type specimens and information subsequently to its description, Rhinocyllus turkestanicus Desbrochers des Loges, 1900 is considered as species incertae sedis. Keys to the subgenera and to the species of Rhinocyllus s. str. are provided and taxonomical differences are illustrated.Key words: Rhinocyllus, Rhinolarinus, new subgenus, new species, Cirsium, Italy

Rhinocyllus conicus (Frölich, 1792) Records. DON [Arzanov et al., 2016: 160; Yunakov et al., 2018: 403]; LUG [Yunakov et al., 2018: 403]. Localities. Donetsk Region. Volodarskoe Distr.: Kamennye mogily NR, 8.07.2001 (M. Sergeev), 3.06.2012 (V. Gramma). Shakhtersk Distr.: Donetskiy kryazh RLP, Saur-Mogila, 12.06.2002., Published as part of Arzanov, Yu. G., Martynov, V. V. & Nikulina, T. V., 2021, A contribution to the fauna of weevil beetles (Coleoptera: Curculionoidea) of the Central Donbass, pp. 5-44 in Caucasian Entomological Bulletin 17 (1) on page 40, DOI: 10.23885/181433262021171-544, http://zenodo.org/record/8145644, {"references":["Arzanov Yu. G., Martynov V. V., Nikulina T. V. 2016. The weevils of Lixinae subfamily (Coleoptera: Curculionidae) of Donbass. In: Okhrana, vosstanovlenie i izuchenie stepnykh ekosistem v XXI veke: Materialy Mezhdunarodnoy nauchno-prakticheskoy konferentsii, posvyashchennoy 90 - letiyu so dnya osnovaniya zapovednika \" Khomutovskaya step' \" [Conservation, restoration and research of steppe ecosystems in XXI century. Proceedings of the International Scientific and Practical Conference, dedicated to the 90 th Anniversary from the foundation of \" Khomutovskaya Steppe \" Nature Reserve (Donetsk, 24 - 26 August 2016)]. Donetsk: Noulig, Donetsk Branch: 150 - 162 (in Russian).","Yunakov N., Nazarenko V., Filimonov R., Volovnik S. 2018. A survey of the weevils of Ukraine (Coleoptera: Curculionoidea). Zootaxa. 4404 (1): 1 - 494. DOI: 10.11646 / zootaxa. 4404.1.1"]}

The weevil Rhinocyllus conicus Froelich was introduced in Georgia, USA as a biological control agent of musk thistle, Carduus nutans L. (Asteraceae) in 1991. Musk thistle populations and R. conicus infestations were monitored over 10 yr at four sites in central Georgia. Musk thistle populations declined substantially as R. conicus populations increased at all sites, but thistle infestations remained problematic at some sites. A laboratory cage study found that R. conicus would lay eggs on flower buds of yellow thistle, Cirsium horridulum Michaux, bull thistle Cirsium vulgare (Savi) Tenore, and blessed milkthistle, Silybum marianum (L.) Gaertner in no-choice and choice tests with and without Ca. nutans. Carduus nutans was preferred over the other thistle species, but the other thistle species were acceptable for oviposition by R. conicus. One or more mixed field infestations of musk thistle and yellow, bull, or blessed milkthistles were sampled for R. conicus infestation. Rhinocyllus conicus was n...

Musk thistle, Carduus nutans, is a major noxious weed throughout its non-native range. The flower head weevil, Rhinocyllus conicus, deemed likely to be a strong candidate for biocontrol based on laboratory tests, has proven variable in its efficacy, suggesting a possible influence of ecological context. To improve our understanding of the dynamics of this system, we examined how R. conicus responds to the spatial distribution of musk thistle individuals. We manipulated the size and density of host plant patches to determine their effect on weevil oviposition. Neither patch size nor plant density significantly affected the number of eggs laid by R. conicus. However, plant characteristics such as flower head size, as well as plant height and number of flower heads per plant, significantly influenced oviposition. Although larger thistle flower heads provide more sites for oviposition, there is also more seed production in these heads. Thus, while R. conicus oviposition is highest in larger flower heads, the surplus of seed offsets the effectiveness of biological control. This observation may in part explain the variable levels of control by this biological control agent and ascertains circumstances when augmentative management procedures may be needed.

Rhinocyllus conicus (Fr��lich) Curculio conicus Fr��lich, 1792 Rhinocyllus latirostris Latreille, 1804 Rhinocyllus schoenherri Capiomont, 1873 Records. CRI* ČER ČNG DON KHM KHE* KHR* KYI LUG LWI MYK* ODE* POL RIV* TER VIN ZAK ZAP [Nowicky 1864: 36; Łomnicki 1866: 7, 1886: 207; Cherkunov 1889: 43; Lukjanovitch 1928: 250; Penecke 1928: 358; Tveritina 1959: 183; Mazur & Kuśka 1994: 305; Kubisz et al. 1998: 270; Nazarenko et al. 2003: 53; Volovnik 1993: 586]. Distribution. Palaearctic (excluding north), Ethiopia; introduced to North America, South Africa, Australia and New Zealand ( G��ltekin & Fremuth 2013). Material examined. 102 specimens (ZIN, SIZK, KUMN, ZMUK, ZMUM, NSPU, IMC, SKC) from 10 provinces were studied. Crimea: 1 spec. (SKC) Koktebel near Feodosia, Konovalenko leg., 11.vi.2013; 1 spec. (ZIN) Simferopol Distr., Skelyaste (= Tav-Bodrak), Pavlovskyj leg., 16.vi.1911; 1 spec. (ZIN)) Bakhchisaray Distr., Mangup, L. Arnoldi, 6.vii.1937; 1spec. (ZIN) Kirovske Distr., Staryi Krym, Agarmish Mt., 23.vi.1906; 1spec. (ZIN) Feodosia; 1spec. (ZIN) Kertch, 12.v.1902; 1 spec. (ZMUM) Artek, Shavrov leg., vi.1910; 3 spec. (ZMUM) Feodosia, 10.v.1904; 1 spec. (SIZK) Yedi Quyu Distr., Kazantip Cape, S. V. Volovnik leg., 18.v.1983; 3 spec. (SIZK) Bilohirsk Distr., Bila Skelia, S. V. Volovnik, 18.v.1983; 1 spec. (IMC) Tarkhankut Peninsula, Olenivka, I. Maltsev leg., 22.iv.1952; 1 spec. (IMC) Yedi Quyu Distr., Marfovka, Sokova leg., 6.vi.1952; 1 spec. (IMC) Tarkhankut Peninsula, Chernushki, I. Maltsev leg., 27.iv.1952; 1 spec. (IMC) Simferopol Distr., Krasnolissya, I. Maltsev leg., 22.vi.1974; 1 spec. (IMC) source of Kara-Su River, I. Maltsev leg., 8.vii.1974; Donetsk Prov.: 1 spec. (ZIN) Slovyansk, Th. Lukjanovitsh, 28.vi.1924; 1 spec. (ZMUK) Novoazovsk Distr., Samsonove, Khomutovskyi Step Nature Reserve, on Carduus, Globova leg., 10.vii.1954; 1 spec. (SIZK) Telmanovo Distr., Granitne, S. V. Volovnik leg., 21.vi.1983; 2 spec. (SIZK) Lyman Distr., Zakitne, S. V. Volovnik leg., 2.vi.1983; Kharkiv Prov.: 1 spec. (KUMN) Bliznyuky Distr., Novopavlivka, A. Drogvalenko leg., 7.viii.1991; Velykyi Burluk Distr., Nesterivka, V. Gorbunov leg., 25.vi.1997; Kherson Prov.: 1 spec. (ZMUK) Velika Lepetikha Distr., woodland belt near Kakhovka reservoir, 28.vi.1965; 1 spec. (IMC) Bilozerski Distr., Daryivka, Rafalskyi leg., vii.1964; 1 spec. (IMC) Kherson 2.vii.1964; Mykolaiv Prov.: 1 spec. (photo observation, UkrBIN ID 51494) Mykolaiv Distr., observed by R. Stepoviy, 3.v.2017; Odesa Prov.: 2 spec. (ZIN) Odesa; 1 spec. (ZMUK) Bilyayivka Distr., Yasky, 30.v.1968; 1 spec. (IMC) Savran Distr., Polyanetskoye, I. Maltsev leg., 16.vi.1970; 1 spec. (IMC) Kotovsk [= Podilsk], I. Maltsev leg., 31.v.1965; 1 spec. (IMC) Khadzhibeysky Lyman, I. Maltsev leg., 19.v.1973; Rivne Prov.: 1 spec. (photo observation, UkrBIN ID 48361), Rivne Distr., Novostav, 50.758201, 25.954720, observed by V. Finchuk, 5.v.2017. Biology. Primary and secondary grasslands, tree plantations; abundant in ruderal habitats. Adults occur in IV��� IX. Oligophagous on Asteraceae (Zw��lfer & Preiss 1983; Zw��lfer & Harris 1984; Volovnik 1994a)., Published as part of Yunakov, Nikolai, Nazarenko, Vitalij, Filimonov, Rostislav & Volovnik, Semyon, 2018, A survey of the weevils of Ukraine (Coleoptera: Curculionoidea), pp. 1-494 in Zootaxa 4404 (1) on page 403, DOI: 10.11646/zootaxa.4404.1.1, http://zenodo.org/record/3766751, {"references":["Lomnicki, M. A. (1866) Przyczynek do fauny chrzaszczow galicyjskich. Uniwersytet Jagiellonski, Krakow, 9 pp.","Lomnicki, M. A. (1886) Chrzaszcze czyli Tegoskrzydle. (Coleoptera). IV. Zoologiczny Oddzial zwierzat bezkregowych. Dzial I. Muzeum imienia Dzieduszyckich we Lwowie. Muzeum imienia Dzieduszyckich, Lwow, xxxi + 308 pp.","Cherkunov, N. (1889) Spisok zhukov, vodiashchikhsia v Kieve i ego okrestnostiakh. Zapiski Kievskogo Obshchestva Estestvoispytatelei, 10, 147 - 204. [1888, in Russian]","Lukjanovitch, Th. K. (1928) Spisok Cleoninae Poltavskoy gubernii (Coleoptera, Curculionidae). Zbirnyk Poltavskogo derzhavnogo muzeiu, 1, 1 - 4. [in Russian]","Penecke, K. A. (1928) Die Curculioniden (Russelkafer) Fauna der Bucovina. Buletinul Facultatu de Stiinte, Cernauti, 2 (2), 329 - 362.","Tveritina, T. A. (1959) Dolgonosiki Zakarpatskoi oblasti. Nauchnye zapiski Uzhgorodskogo universiteta, 40, 181 - 187.","Mazur, M. & Kuska, A. (1994) Chrzaszcze Miodoborow (Zachodnia Ukraina). I. Ryjkowce (Coleoptera: Attelabidae, Apionidae, Curculionidae) - wyniki ekspedycji w latach 1993 - 1994. Polskie Pismo Entomologiczne, 63, 277 - 310.","Kubisz, D., Mazur, M., Pawlowski, J. (1998) Chrzaszcze Miodoborow (Zachodnia Ukraina). Czesc II. Aktualny stan poznania (Insecta, Coleoptera). Studia Osrodka Dokumentacji Fizjograficznej, 25, 217 - 293.","Gultekin, L. & Fremuth J. (2013). Tribe Lixini. In: Lobl, I. & Smetana, A. (Eds.), Catalogue of Palaearctic Coleoptera. Vol. 8. Brill, Leiden, pp. 456 - 472. https: // doi. org / 10.1163 / 9789004259164","Zwolfer, H. & Preiss, M. (1983) Host selection and oviposition behaviour in West? European ecotypes of Rhinocyllus conicus Froel. (Col., Curculionidae). Journal of Applied Entomology, 95 (1 - 5), 113 - 122. https: // doi. org / 10.1111 / j. 1439 - 0418.1983. tb 02620. x","Zwolfer, H. & Harris, P. (1984) Biology and host specificity of Rhinocyllus conicus (Froel.) (Col., Curculionidae), a successful agent for biocontrol of the thistle, Carduus nutans L. Journal of Applied Entomoljgy, 97, 36 - 62. https: // doi. org / 10.1111 / j. 1439 - 0418.1984. tb 03714. x","Volovnik, S. V. (1994 a) On the distribution and ecology of some species of Cleonine weevils (Coleoptera: Curculionidae) II. Genera Rhinocyllus Germ., Eustenopus Petri, and Lachnaeus Schonh. Entomologicheskoe Obozrenie, 1993, 72 (3), 586 - 590. [in Russian, translated in Entomological Review, 73 (2), 79 - 82]"]}

We examined the presence of the exotic weevil Rhinocyllus conicus Froelich on native thistles at high elevations in the Rocky Mountains of Colorado. We tested whether the distribution of R. conicus was related to elevation by performing 2 separate studies. First, transects along an elevation gradient were sampled in Rocky Mountain National Park and presence/absence of R. conicus was scored to infer relationships between environmental variables and weevil occurrence. Second, an experiment was conducted on Niwot Ridge to determine whether weevils were able to complete their reproductive cycle and overwinter at an elevation where they do not currently exist. Results of a logistic regression indicated that R. conicus presence was negatively correlated with elevation. In addition, weevils successfully reproduced at tree line, but climatic limitations suppressed their ongoing presence at this site. The ability of the weevils to utilize native thistles at tree line was unknown prior to this experiment, ...

Cirsium ownbeyi is a habitat-specific, endemic, polycarpic thistle in northwest Colorado, northeast Utah, and southwest Wyoming. In 1998, seven C. ownbeyi populations, which ranged from 4 to >30,000 plants, were known from Wyoming. The population genetics of C. ownbeyi and the threat posed by an exotic flower head–feeding weevil, Rhinocyllus conicus, in Wyoming are unknown. Between 2014 and 2016, we visited Wyoming C. ownbeyi populations to determine (1) changes in population sizes since 1998, (2) extent of R. conicus use, and (3) amount and distribution of genetic variation within and between populations. We quantified densities of plants within populations by life stage, population spatial extents, and, for 10 plants per population, proportion of flower heads with R. conicus ovipositions. Data at 6 simple sequence repeat loci were also collected. Three C. ownbeyi populations were

Use of the weevil, Rhinocyllus conicus Froelich, for classical biological control of Carduus species in Argentina has not been controversial, as it has been in Canada and the United States, because there are no native thistle species in the South American release areas. In this study, 30 years after its first field release in Argentina, the Pampas region was surveyed to confirm the establishment of R. conicus , covering the original release sites and most of the overall area of distribution of its host thistles, Carduus species. Sites ( n = 121) were systematically selected and natural populations of thistles were examined to confirm the presence of the weevil. Twenty four sites with R. conicus were selected to record the weevil’s prevalence on Carduus thoermeri Weinman and Carduus acanthoides L. Additional opportunistic surveys were conducted in other regions of Argentina and Uruguay, more distant from the original release sites. Rhinocyllus conicus was found at 81% of the original release sites and at 69% of the total sites surveyed, an area of approximately 370.000 km 2 . On average, 92% of the examined heads had damage in areas where the weevil was present, showing its high prevalence. A pilot study showed that the oviposition period of the weevils lasted 119 days and seed production of C. acanthoides was reduced by 15.5%. These results encourage the implementation of an integrated management of thistles in Argentina, and maybe in other parts of South America.

Carduus nutans es una planta anual, nace a fines de marzo y forma la roseta durante el invierno, desarrolla el tallo florífero a principios de primavera y florece a mediados y fines de la misma. EEA Bordenave Fil: Vigna, Mario Raúl. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Bordenave; Argentina Fil: Carretto Nocolo, Luis Miguel. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Bordenave; Argentina

Consumer communities are being re-arranged through unprecedented rates of human-mediated invasions and extinctions. Such changes in consumer diversity potentially alter community function and impact on resource populations. Although insect herbivore invasions are increasingly common, the infl uence of such species additions on native resident herbivore guilds, along with their individual and combined eff ects on native plant resources, are rarely investigated. Here, we used site-to-site and plant-to-plant variation in herbivore composition to examine how the addition of an invasive exotic weevil, Rhinocyllus conicus , combines with a guild of native fl oral herbivores (tephritid fl ies, pyralid moths) to infl uence two key components of herbivore community function – aggregate herbivore densities and cumulative levels of seed destruction – on a native thistle, Cirsium canescens. Invasion of a site by R. conicus more than doubled aggregate herbivore density, resulting in increased levels of seed destruction and a halving of seed production by the native thistle. Further, herbivore function was signifi cantly higher on individual plants attacked by R. conicus , compared to plants attacked only by native herbivores. Insect densities and levels of seed destruction on plants attacked by multiple herbivore taxa never exceeded those observed for plants attacked by R. conicus alone, suggesting that increases in herbivore community function with invasion resulted from the inclusion of a functionally dominant insect rather than any complementarity eff ects. Some evidence for interference between insects emerged, with a trend towards reduced moth and weevil densities in two and three taxon mixtures compared with plants attacked by each taxon alone. However, density compensation was limited so that, overall, the addition of a novel herbivore to the fl oral guild was associated with a signifi cant increase in herbivore community function and impact on seed production. Th e results suggest that invasion of a functionally dominant herbivore into an unsaturated recipient community can augment function within a resource guild.

Mechanisms underlying invasive species impacts remain incompletely understood. We tested the hypothesis that priority resource access by an invasive biocontrol weevil, Rhinocyllus conicus, intensifies and alters the outcome of competition with native floral herbivores over flower head resources of the non-target, native host plant Cirsium canescens, specifically with the predominant, synchronous tephritid fly Paracantha culta. Four main results emerged. First, we documented strong, asymmetric competition, with R. conicus out-competing P. culta. Second, weevil priority access to floral resources accelerated competitive suppression of P. culta. Evidence for competitive suppression with increased weevil priority included decreases in both the numbers and the total biomass of native flies, plus decreases in individual P. culta fly mass and, so, potential fitness. Third, we found evidence for three concurrent mechanisms underlying the competitive suppression of P. culta by R. conicus. Prior use of a flower head by R. conicus interfered with P. culta pre-oviposition behavior. Once oviposition occurred, the weevil also reduced fly post-oviposition performance. Preemptive resource exploitation occurred, shown by the significant effect of flower head size on the total number of insects developing and in the magnitude of R. conicus effects on P. culta. Interference also occurred, shown by a spatial shift of surviving P. culta individuals away from the preferred receptacle resources as R. conicus priority increased. Finally, fourth, using an individual-based model (IBM), we found that the competitive interactions documented have the potential for imposing demographic consequences, causing a reduction in P. culta population sizes. Thus, priority resource access by an invasive insect increased competitive impact on the predominant native insect in the invaded floral guild. This study also provides the first experimental evidence for non-target effects of a weed biological control agent on an associated native insect herbivore.

Cirsium arvense (L.) Scop. is a perennial herb indigenous to Eurasia that is now present throughout temperate regions of the world where it is considered one of the worst weeds of pastoral and agricultural systems. Classical biological control has been attempted in both North America (NA) and New Zealand (NZ). However, nearly 50 years after the first agent releases there are no indications of successful control. We review the status of the five agents deliberately released for control of C. arvense in NA and NZ, plus the species unintentionally introduced, and the occurrence of insects native to NA on C. arvense. We retrospectively evaluate C. arvense as a target weed, critique the agents selected for release, and contrast the different situations in NA and NZ. In retrospect, we see justification for the agents released in NA, but it is evident that these agents would not meet the more stringent host specificity requirements necessary to be released today. The failure of the program in NA is attributed to compromised safety, and lack of impact. Non-target impacts by one of the released agents, Rhinocyllus conicus, have raised safety concerns for native thistle plants. The other released agents either failed to establish, or if established, had no impact on the weed. In contrast, the situation in NZ is quite different because there are no related native thistles (Cardueae), and thus little chance of non-target impacts. Thus far, failure in NZ is attributed to lack of effectiveness due to non-establishment, or no impact, of released agents. In the past, the same agents that were released in NA were subsequently released in NZ, without considering whether or not these were the best choices. Thus, the past failure in NZ might be due to the previous lack of a NZ-specific approach to biocontrol of thistles in general and C. arvense in particular. A new approach taking into consideration the absence of native Cardueae has resulted in the release of agents more likely to be effective, and has potentially set NZ on track towards successful biological control of C. arvense, and other thistles.

Classical weed biocontrol has long been criticised, worldwide, for a lack of post-release long-term monitoring. This paper reports on a rare opportunity to follow up, three agents and 35 years later, a biocontrol programme against nodding thistle (Carduus nutans) in New Zealand. In New Zealand, the establishment of all three agents has been reported previously, but impacts have only been assessed for the receptacle weevil (Rhinocyllus conicus). This paper reports on the abundance of the nodding thistle crown weevil (Trichosirocalus horridus), and on the abundance, phenology and impact of the seed predators, R. conicus and Urophora solstitialis, in Canterbury, based on field surveys and, for the seed predators, also from a cultivated population. Trichosirocalus horridus was abundant at all field sites and on rosettes of all sizes. Seed destruction per larva by R. conicus (34 seeds per larva) was similar to previous estimates, but U. solstitialis achieved rates (21 seeds per larva) three times high...

Nontarget feeding of Rhinocyllus conicus Fröelich and Trichosirocalus horridus (Panzer) on native North American thistles in the genus Cirsium has been documented. Some species of these native thistles have shown greater infestation levels of R. conicus in populations that are in close proximity to the target plant species, Carduus nutans L. In 2005 a study was initiated to identify areas of potential nontarget feeding by R. conicus and T. horridus on thistle species by predicting habitats of two known introduced hosts [C. nutans and Cirsium vulgare (Savi) Tenore] and two native species [Cirsium carolinianum (Walter) Fernald and Schubert and C. discolor (Muhlenberg ex Willdenow) Sprengel] using Mahalanobis distance (D(2)). Cumulative frequency graphs showed that the D(2) models for all four plant species effectively identified site conditions that contribute to the presence of the respective species. Poisson regression showed an association between D(2) values and plant counts at field-test sites for C. nutans and C. carolinianum. However, negative binomial regression detected no association between D(2) values and plant counts for C. discolor or C. vulgare. Chi-square analysis indicated associations between both weevil species and sites where C. vulgare and Carduus nutans were found, but not between the weevil and native thistle species. Habitats of C. nutans and Cirsium carolinianum overlapped in ≈12% of the study area. Data-based habitat models may provide a powerful tool for land managers and scientists to monitor native plant populations for nontarget feeding by introduced biological control agents.

The release of non-native insects to control noxious weeds is commonly used to combat invasions without disturbing the environment through chemical or mechanical methods. However, introduced biological control agents can have unintended effects. This study was initiated to evaluate potential non-target effects of the flowerhead weevil, Rhinocyllus conicus Frolich, on Cirsium ownbeyi S.L. Welsh, a rare, native and short-lived perennial thistle in northwestern Colorado, northeastern Utah, and southwestern Wyoming. C. ownbeyi represents one of 22 known native hosts on which this introduced weevil has naturalized. The study population remained stable over the eight years of the study despite floral damage by the biocontrol beetle. The growth rate ( λ ) from a count-based population viability analysis of the population was 1.03; however, large inter-year variation indicates this rare species is still vulnerable to local extirpation. The biocontrol weevil consistently damaged the developing seeds over the course of the study independent of changes in overall population size and variation in the number of flowering individuals. The target species, Carduus nutans L. (musk thistle) is generally absent near the study plots, which may limit the population levels of R. conicus that can be sustained in this area. Although R. conicus utilizes C. ownbeyi as a host plant, the late flowering period of this native thistle and the small size of the flower heads may limit the demographic impact of R. conicus on C. ownbeyi .

The weevil species Rhinocyllus conicus has been widely and successfully used for biocontrol of Carduus nutans and related thistles. An analysis of the taxonomic position of R. conicus shows that it belongs to a tribe where many taxa have developed close associations with Cardueae host plants. Within the genus Rhinocyllus, R. conicus, which predominates on C. nutans, is geographically the main species and the other Rhinocyllus spp. occupy restricted distributions on the southern fringe of the R. conicus range. The life history of R. conicus is summarized. An account of the natural control factors of the eggs, larvae, pupae and adults of R. conicus in Europe and North America and on the effect of R. conicus on C. nutans is given. Field records of a 20-year survey show that the basic host range of R. conicus is restricted to the closely related Cardueae genera Carduus, Cirsium and Silybum. Within this overall range, C. nutans is the most important host, but many local or regionally distributed populations of R. conicus have developed preferences for species such as Carduus pycnocephalus, Silybum marianum, Cirsium vulgare or C. arvense. The results of various types of screening tests are summarized to demonstrate the specificity of R. conicus. It is shown that the host specificity in the field depends primarily on adult feeding on the host plant, as this determines oogenesis and the oviposition behaviour. Only with access to plants which elicit adult feeding is the female able to produce the protective cap which covers the egg. This is a prerequisite for the successful establishment of the young larva within the flower heads, although it does not necessarily result in establishment on non-preferred hosts. Zusammenfassung Biologie und Wirtsspezifitat von Rhinocyllus conicus (Froel.) (Col., Curculionidae), einem erfolgreich zur biologischen Bekampfung von Carduus nutans L. eingesetzten Russelkafer Der Russelkafer Rhinocyllus conicus ist in Nordamerika und Neuseeland in vielen Gebieten erfolgreich zur biologischen Bekampfung von Carduus nutans und verwandten Distelarten eingesetzt worden. Eine Analyse der systematischen Stellung von R. conicus zeigt, das die Art zu einer Tribus gehort, in der viele Taxa eine enge Bindung an Cardueae-Wirtspflanzen entwickelt haben. Innerhalb der Gattung Rhinocyllus ist R. conicus, eine primar mit Carduus nutans assoziierte Art, in geographischer Hinsicht eine „zentrale Art”, wahrend die ubrigen Rhinocyllus-Arten kleine Teilareale am sudlichen Rand des R. conicus-Areals besetzen. Es wird ein Uberblick uber die Biologie von R. conicus und uber die Mortalitatsfaktoren der in Europa und Nordamerika an C. nutans lebenden Populationen gegeben. Zwanzigjahrige Felduntersuchungen in Europa zeigen, das das Grundwirtspflanzenspektrum von R. conicus die nahe miteinander verwandten Cardueae-Gattungen Carduus, Cirsium und Silybum umfast. Innerhalb dieses Grundspektrums ist C. nutans die wichtigste Wirtspflanze. Lokal oder regional hat R. conicus aber auch Praferenzen fur Cirsium vulgare, C. arvense, Carduus pycnocephalus und Silybum marianum entwickelt. Die verschiedenen, mit R. conicus im Labor und im Versuchsgarten durchgefuhren Futterwahl-, Eiablage- und Frastests werden in ihren wichtigsten Ergebnissen geschildert, sie veranschaulichen den hohen Grad an Wirtsspezifitat von R. conicus. Es konnte experimentell gezeigt werden, das unter Freilandbedingungen die Wirtsspezifitat in erster Linie von der Futterpflanzenwahl der Imagines abhangt, da diese die Oogenese und das hoch spezialisierte Eiablageverhalten entscheidend beeinflust. Nur solche Weibchen, die Zugang zu den richtigen Futterpflanzen der Carduus-Cirsium-Silybum-Gruppe haben, sind in der Lage, die fur das Uberleben der Junglarven notwendige Eischutzhulle zu bilden. Bei einzelnen R. conicus-Rassen wird das Wirtspflanzenspektrum weiterhin durch das larvale Frasverhalten eingeschrankt. Die Bedeutung von R. conicus fur die Entwicklung von Carduus-Populationen wird anhand zweier Beispiele aus Saskatchewan, Kanada, geschildert.

Rhinocyllus conicus Froel., a weevil species successfully used in the biocontrol of introduced Carduus spp. in North America, shows in western Europe a marked ecotypic variation in host preference. Local or regional host specialization is developed within the limits of the genera Carduus, Cirsium and Silyhum. Data on the distribution of Rh. conicus ecotypes associated with Carduus nutans, Carduus pycnocephalus, Silyhum marianum, Cirsium arvense, and Cirsium vulgare are given. While under field conditions the west-French Rh. conicus ecotype associated with Cirsium vulgare shows a 90–100 % preference of this species over Carduus nutans, eggs are deposited in about the same rate on both hosts under laboratory conditions. An analysis of egg numbers/flower head and head size shows that under field conditions (Rh. conicus populations from Silyhum) and in laboratory experiments (Rh. conicus populations from Cirsium vulgare) there is a highly significant correlation between these variables. The role of “resource predictability” with regard to the marked preference of the west-French Rh. conicus populations for Cirsium vulgare and the possibilities of this ecotype for biocontrol of Cirsium vulgare in oversea areas are discussed. Zusammenfassung Wirtswahl und Eiablageverhalten bei der westeuropaischen Rasse von Rhinocyllus conicus Froel. (Col., Curculionidae) Der in Nordamerika bei der biologischen Bekampfung von eingeschleppten Distelpopulationen (Carduus spp.) erfolgreich angesiedelte Russelkafer Rhinocyllus conicus Froel. tritt in Westeuropa in einer Reihe von Rassen mit unterschiedlicher Wirtspraferenz und ausgesprochener “regionaler Stenophagie” auf. Die Differenzierung der Wirtswahl lokaler und regionaler Rh. corners-Rassen liegt innerhalb des experimentell nachweisbaren “Gesamt-Wirtspflanzen-Spektrums”, das die nahe verwandten Gattungen Carduus, Cirsium und Silybum umfast. Es werden Angaben uber die Verbreitung von Rh. conicus-Rassen, die auf Carduus nutans, Carduus pycnocephalus, Silybum marianum, Cirsium arvense und Cirsium vulgare spezialisiert sind, gemacht. Dabei wird besonders auf die westfranzosische Rasse eingegangen, die unter Freilandbedingungen Cirsium vulgare zu 90–100% gegenuber Carduus nutans bevorzugt, wahrend sie beim Eiablageversuch mit Blutenkopfen im Labor beide Distelarten im gleichen Grad befallt. Die Bedeutung dieser Rasse als Ausgangsmaterial fur die biologische Bekampfung der weltweit verschleppten und teilweise sehr aggressiven Speerdistel wird erortert. Statistische Analysen zeigen, das sowohl bei der Silybum-Rasse wie auch bei der Cirsium vulgare-Rasse von Rh. conicus die Eiablage der Grose des jeweiligen Blutenkopfs angepast werden kann. Zusammen mit der auserordentlich breiten Streuung der Eiablage uber 80–100 % der im Juni verfugbaren Blutenkopfe ist dieses Verhalten fur die hohe Leistungsfahigkeit von Rh. conicus mitverantwortlich.

The occurrence of the biological control weevil Rhinocyllus conicus is documented for the first time on the non-target thistle species, Cirsium hillii, in Wisconsin. Rhinocyllus conicus was released locally twice in Wisconsin before studies showed non-target compatibility with the rare C. hillii and the federally threatened C. pitcheri. These previously unpublished studies from the Wisconsin Department of Agriculture, Consumer, and Trade Protection prevented further releases of R. concnicus in Wisconsin during the early 1980s. Despite only localized releases, data from state collection records indicate that R. conicus has spread at least 80 miles from the initial release location. While R. conicus's effects on other non-target Cirsium species are well documented, the lack of information on the biology of C. hillii precludes understanding the effects of R. conicus on this species' conservation.

Theory predicts that damage by a shared herbivore to a secondary host plant species may either be higher or lower in the vicinity of a preferred host plant species. To evaluate the importance of ecological factors, such as host plant proximity and density, in determining the direction and strength of such herbivore-mediated indirect effects, we quantified oviposition by the exotic weevil Rhinocyllus conicus on the native wavyleaf thistle Cirsium undulatum in midgrass prairie on loam soils in the upper Great Plains, USA. Over three years (2001-2003), the number of eggs laid by R. conicus on C. undulatum always decreased significantly with distance (0-220 m) from a musk thistle (Carduus nutans L.) patch. Neither the level of R. conicus oviposition on C. undulatum nor the strength of the distance effect was predicted by local musk thistle patch density or by local C. undulatum density (

Summary 1 It is widely accepted that combining several control options into integrated pest management strategies is the most effective way to provide long-term suppression of pest populations. However, full factorial field trials of all single and integrated control options for a pest species would be prohibitively expensive and time consuming. Methods to allow triage of the huge array of management options would be of great value in streamlining the decision-making process. 2 We present a seasonally structured, individual-based model, specifically designed to compare and rank detailed management strategies for a noxious pasture weed. The model structure is determined in part by the demographic data available, and in part by the management options under consideration. The case study is for nodding thistle Carduus nutans in Australia. Eight years of demographic data, for more than 8000 mapped plants, were used to parameterize the model, which is age-, size- and density-dependent and incorporates individual variation. Management options for this plant include three biocontrol agents, as well as conventional herbicide and grazing management strategies, which can be used alone or in a variety of combinations. Data on management impacts were drawn from multiple studies. 3 The model predicts that the root-crown weevil Trichosirocalus mortadelo will more effectively suppress weed populations than either of the two flowerhead-feeding insect agents Urophora solstitialis and Rhinocyllus conicus. Crash grazing (up to four times the regular grazing pressure) in any single season, or when most effectively applied across spring and summer, is less effective than T. mortadelo, while combinations of crash grazing and biocontrol agents strongly decrease weed population persistence. However, lethal herbicide is the best single strategy, while spring spray–grazing (a combination of non-lethal herbicide and grazing) is the best integrated weed management strategy. 4 Synthesis and applications. The model is structured by, and serves to integrate, available information on demography and management from multiple sources. The subset of strategies that performed well forms the focus for fewer, more thorough, field trials. The decision-making approach illustrated here is also applicable to any species and any array of management options.

We monitored populations of Canada thistle biocontrol agents Cassida rubiginosa, Ceu- torhynchus litura, Larinus (= Hadroplantus) planus, Urophora cardui, Orellia (= Terellia) ruficauda, and Rhinocyllus conicus on Canada thistle (Cirsium arvense) at two national wildlife refuges in South Dakota from 1999 through 2003. C. litura, U. cardui, O. ruficauda, and R. conicus were present on both refuges. Agent populations were low except for C. litura, which was present in up to 90% of stems in some plots. C. litura infestation did not reduce thistle flowering, stem length, or over-winter survival. There was no change in thistle stem numbers over the study period and no difference in stem numbers in areas of high C. litura populations compared to areas of low C. litura populations. Our results suggest that insect biological control agents are inadequate for reduction of Canada thistle in southern South Dakota.

Nodding thistle receptacle weevil Rhinocyllus conicus and gallfly Urophora solstitialis attack the capitula of nodding thistle Carduus nutans L. Between 31 October and 15 December 2003, the phenology of both R. conicus and U. solstitialis was studied at a dryland site in Canterbury. Adult R. conicus were more numerous than U. solstitialis on capitula throughout the experiment. Larvae of R. conicus were fi rst found on 11 November (15% of capitula infested) and peaked on 2 December with 53% of capitula infested. Only 3% of capitula were infested by U. solstitialis. Adult R. conicus or U. solstitialis emerged from 79% of the selected primary and secondary capitula. The majority of infested capitula (81%) contained only R. conicus, 2% contained only U. solstitialis while 17% contained both insect species. Parasitism of R. conicus by the braconid parasitoid Microctonus aethiopoides was low and occurred when most weevil eggs had been laid.

Invasive species have the potential to alter trade-offs leading to selection in the populations they invade. Here we quantify the demographic and selective effects of herbivory by native insects and the introduced floral feeder Rhinocyllus conicus on Platte thistle (Cirsium canescens), a sparse monocarpic thistle endemic to North America. Rhin- ocyllus first invaded the Platte thistle population in 1993. Since then, its numbers have increased exponentially, while the Platte thistle population size has decreased. Data from 11 years were analyzed to determine how demographic rates varied with plant size and damage by native insects and Rhinocyllus. Individual growth, survival, flowering proba- bility, and seed set were all size dependent. Damage to vegetative structures did not influence demographic rates; damage to flower heads did because Platte thistle is seed limited. These analyses were used to parameterize a series of integral projection models (IPMs) that investigated the effects of floral herbivory on the population growth rate l, equilibrium population size, and the evolutionary stable (ES) flowering strategy. The IPMs showed that native insects have significant impact on the equilibrium population size and l, but not the ES flowering strategy, because they use the flowers of different-sized plants indiscrimi- nately. In contrast, Rhinocyllus has the potential to drive Platte thistle extinct. Rhinocyllus preferentially fed and oviposited on the flowers of larger plants and therefore selected for a reduction in flowering size. However, as the thistle population went into decline, this pattern reversed. Thus, selection imposed by an invader may be complex and will reflect behavioral interactions between herbivore and host, as well as demographic changes in the host population.

Controversy exists over estimation of ecological risk in biological control. At present, the risk to the rare, federally listed Pitcher's thistle (Cirsium pitcheri )i nNorth America from Rhinocyllus conicus ,a biological control weevil now feeding on many native thistles, is unknown. We hypothesized that quantification of host specificity and potential phenological overlap between insect and plant would improve assessment of the magnitude of risk. In laboratory host specificity tests, we found no significant difference in R. conicus feeding or oviposition preference between the rare C. pitcheri and the targeted exotic weed (Carduus nutans )o rbetween C. pitcheri and Platte thistle (C. canescens), a closely related native North American species known to be affected by R. conicus .I na garden environment, R. conicus spontaneously found, oviposited, and developed completely on C. pitcheri .T aller plants with more flower heads were significantly more vulnerable, suggesting that the greatest impact is likely to be on individuals that generally contribute the most to recruitment and population persistence. For eight sites in two national parks over three years, the calculated period of expected R. conicus activity overlapped 99% and 78% of the flower heads initiated by C. pitcheri in the southern and the northern park, respectively. A de- mographic model suggests that population growth rate ( )o fC. pitcheri will decrease from 0.9897 to 0.8686, while time to halve the population will decrease from 66.9 to 4.9 years, under the conservative assumption that oviposition by R. conicus on C. pitcheri will occur at the same rate as on the related C. canescens. Calculated decreases in and t0.5 are larger if the rate of oviposition actually observed in the laboratory tests is used. These results indicate that the weevil poses a serious quantitative, demographic risk to the threatened C. pitcheri. The study supports the suggestion that ecological data can be used to improve the quantification of risk to native nontarget plant populations within the potential physiological host range of a biological control insect.

Mathematical modeling is an important tool with which managers can understand, and hence plan to control, invasive species. A matrix model for the invasive musk thistle, derived from demographic studies in New Zealand, is used to conduct a retrospective analysis of the relative merits of three biological control agents released to control this species: Rhinocyllus conicus, Urophora solstitialis, and Trichosirocalus horridus. The analysis of musk thistle illustrates the utility of modeling approaches in management and demonstrates how model-derived information could shift the focus of future management efforts. By placing management in an adaptive framework, where active learning is used to improve management decisions, existing management strategies can be further improved to cope in situations where optimal control methods may depend on local conditions. Nomenclature: Musk thistle, Carduus nutans L. #3 CRUNU. Additional index words: Adaptive management, biological control, nodding thistle, optim...

Landscape change has great, yet infrequently measured, potential to influence the susceptibility of natural systems to invasive species impacts. We quantified attack by an invasive biological control weevil (Rhinocyllus conicus) on native thistles in relation to two types of landscape change: agricultural intensification and invasion by an exotic thistle, Carduus nutans, the original target of biological control. Weevil egg load was measured on native thistles in three landscape types: (1) agriculture dominated, (2) grassland dominated with exotic thistles, and, (3) grassland dominated without exotic thistles. We found no difference in egg load on native thistles within grassland landscapes without exotic thistles vs. within agricultural landscapes, suggesting that agricultural intensification per se does not influence levels of weevil attack. However, attack on the native Cirsium undulatum increased significantly (three- to fivefold) with increasing exotic thistle density. Within-patch exotic thistle density explained >50% of the variation in both the intensity and frequency of weevil attack. Since R. conicus feeding dramatically reduces seed production, exotic thistles likely exert a negative indirect effect on native thistles. This study provides some of the first empirical evidence that invasion by an exotic plant can increase attack of native plants by shared insect herbivores.

Field experiments were conducted in Northeast Kansas under conditions of limited plant competition to evaluate the individual and combined impact of the imported weevils Rhinocyllus conicus Froelich and Trichosirocalus horridus (Panzer) on the introduced weed, musk thistle (Carduus nutans L.). No effects on seed production occurred when low larval densities of T. horridus (

Field experiments were conducted to determine whether early vegetative feeding by Trichosirocalus horridus alters musk thistle ( Carduus nutans ) as a resource for the later-arriving Rhinocyllus conicus . Results showed that thistles with high larval densities of T. horridus (66 per plant) produced more and shorter flower stems, significantly fewer flower heads, and delayed flowering by 1 week when compared to uninfested thistles. Also, colonization and oviposition on flower heads by adult R. conicus were as much as three and five times lower, respectively, on thistles heavily infested with T. horridus than on uninfested thistles. As a result, 63% fewer R. conicus adults developed from T. horridus -infested thistles. Musk thistles that were infested with lower densities of T. horridus larvae ( R. conicus to T. horridus -infested and uninfested plants. In a greenhouse experiment, the mortality rate of R. conicus was higher on musk thistles that were heavily infested by T. horridus , implying a change in musk thistle quality. However, this effect was apparent only at low R. conicus larval densities. T. horridus can indirectly and negatively affect R. conicus through a variety of mechanisms, but only when densities of T. horridus are high. This finding may have important implications for the continued redistribution of both weevils, which were imported for the classical biological control of musk thistle, a noxious weed in pastures and rangeland.