Biology and host specificity of Ceutorhynchus scrobicollis (Curculionidae; Coleoptera), a root-crown mining weevil proposed as biological control agent against Alliaria petiolata in North America

Ceutorhynchus scrobicollis is a root-crown mining weevil proposed for release as biological control agent of Alliaria petiolata (Brassicaceae, Thlaspideae), a European biennial herb, currently invading temperate North America. Using a combination of laboratory, common garden and fieldwork we studied biology, ecology and host range of C. scrobicollis, a univoltine species that oviposits and develops in A. petiolata rosettes in fall and spring. Individual C. scrobicollis can be long-lived (>2 years) and females show a second oviposition period. Weevils did not attack any of 31 test plant species outside the Brassicaceae. Within the Brassicaceae, five species allowed complete larval development under no-choice conditions. In subsequent choice tests, three of these five species (Nasturtium officinale, Peltaria alliacea and Thlaspi arvense; which are of European origin) were attacked. North American Rorippa sinuata was the only native species to be attacked by C. scrobicollis and only under no-choice conditions. Results of subsequent impact experiments showed that C. scrobicollis attack changed plant architecture but had no effect on overall plant vigour and reproductive output of R. sinuata, suggesting lack of impact on demography or population dynamics. A petition for field release of C. scrobicollis in North America has been submitted.     

Twenty‐five years after: post‐introduction association of Mecinus janthinus s.l. with invasive host toadflaxes Linaria vulgaris and Linaria dalmatica in North America

Linaria vulgaris, common or yellow toadflax, and Linaria dalmatica, Dalmatian toadflax (Plantaginaceae), are Eurasian perennial forbs invasive throughout temperate North America. These Linaria species have been the targets of classical biological control programmes in Canada and the USA since the 1960s. The first effective toadflax biological control agent, the stem‐mining weevil Mecinus janthinus (Coleoptera: Curculionidae) was introduced from Europe in the 1990s. This weevil has become established on L. dalmatica and L. vulgaris in both countries, although it has shown greater success in controlling the former toadflax species. Genetic and ecological studies of native range M. janthinus populations revealed that weevils previously identified as a single species in fact include two cryptic species, now recognised as M. janthinus, associated with yellow toadflax, and the recently confirmed species Mecinus janthiniformis, associated with Dalmatian toadflax. The results of a comprehensive study characterising haplotype identities, distributions and frequencies within M. janthinus s.l. native range source populations were compared to those populations currently established in the USA and Canada. The presence of both Mecinus species in North America was confirmed, and revealed with a few exceptions a high and consistent level of host fidelity throughout the adopted and native ranges. Genetic analysis based on mitochondrial cytochrome oxidase subunit II gene (mtCOII) defined the origin and records the subsequent North American establishment, by haplotype, of the European founder populations of M. janthinus (northern Switzerland and southern Germany) and M. janthiniformis (southern Macedonia), and provided population genetic indices for the studied populations. This analysis together with existing North American shipment receipt, release and rearing records elucidates probable redistribution routes and sources of both weevil species from initially released and established adopted range populations.     

Host specificity testing and suitability of the parasitoidMicroctonus hyperodae (Hym.: Braconidae,Euphorinae) as a biological control agent ofListronotus bonariensis (Col.: Curculionidae) in New Zealand

The behaviour of the parasitoidMicroctonus hyperodae Loan was studied under quarantine conditions to determine its likely host range in New Zealand. The species was imported from South America as a potential biological control agent of Argentine stem weevil,Listronotus bonariensis (Kuschel). The study involved systematic evaluation of the parasitoid's behaviour when exposed to 24 non-host weevil species; all but three of these were native to New Zealand. Of those tested, four were found to sustain someM. hyperodae development. However, further examination showed that in all but one species,Irenimus aequalis (Broun), parasitoid development was impeded, with up to 50% of the larvae becoming encapsulated. Overall, those weevil species that were attacked produced only 19% of the parasitoids derived fromL. bonariensis controls. As an adjunct to this quarantine study, a review of the habitats of the native weevil and target pest populations indicated that refugia would probably exist for native alpine species. I. aequalis was not considered to be threatened byM. hyperodae as this weevil has benefited from the advent of European agricultural systems to the extent that it is now recognised as a minor pest. In view of its relatively oligophagous behaviour, the parasitoid was recommended as suitable for release.      

Evaluation of Cyphocleonus trisulcatus (Coleoptera: Curculionidae) as a potential biological control agent for Leucanthemum vulgare in North America

Leucanthemum vulgare, a perennial forb native to Eurasia, has become invasive in several other parts of the world. Since there is a lack of methods suitable for sustainable management of this plant across invaded landscapes, a biological control project has been initiated in North America and Australia. We evaluated the potential of the root-feeding weevil Cyphocleonus trisulcatus as a biological control agent for L. vulgare in North America by investigating its impact on L. vulgare and studying its larval host range under no-choice, multiple-choice cage and open-field conditions. Our impact experiment revealed that larval feeding by C. trisulcatus can severely damage and even kill plants. No-choice tests conducted with 41 non-target species showed that C. trisulcatus can develop on five closely related species. In a multiple-choice cage test established with three of these species, the medicinal plant Matricaria chamomilla and the native North American M. occidentalis were also attacked, but to a lower degree than L. vulgare. An open-field test conducted with four varieties of the ornamental Shasta daisy (Leucanthemum × superbum and L. × maximum) revealed similar attack on Shasta daisy as on L. vulgare. Due to the popularity of Shasta daisies, we suggest that C. trisulcatus, despite its potential to suppress L. vulgare populations, is not a suitable biological control agent for North America. However, C. trisulcatus may still be a potential biological control agent for L. vulgare in regions where Shasta daisy is less popular, such as Australia. Further host-range tests with species native to Australia as well as with additional species important for the horticultural industry in Australia are currently under way.     

Effects of Rhinoncomimus latipes on the growth and reproduction of Persicaria perfoliata,an invasive plant in North America

Native to Asia, mile-a-minute Persicaria perfoliata, is an invasive weed in North America, and the weevil Rhinoncomimus latipes is a host-specific insect agent which occurs widely in China. We conducted a common garden experiment to compare P. perfoliata plant responses of native and invasive populations to herbivory by the weevils from different origins. We found weevils from Hunan, Hubei and Heilongjiang Provinces had strong, moderate and weak ability to suppress host plant, respectively. Weevils from Hunan and Hubei Provinces had stronger impact on the growth of both native and invasive plant populations than the weevil from Heilongjiang Province. The losses in seed output of invasive plants were also significantly greater than natives in the weevil treatments. Our results suggested that the weevil population from Hunan Province may be the most suitable for the control of mile-a-minute, while the population from Heilongjiang Province may be the least suitable due to climate matching.     

Insect herbivores associated with the introduced weed Bidens frondosa L. (Asteraceae) in Korea,and their potential role as augmentative biological control agents

The annual herb Bidens frondosa L., native to North America, is an invasive weed. Currently no information is available on the insect herbivores associated with this weed in Korea. A survey was carried out at two‐weekly intervals from May to October 2008 at two sites, and the incidence and abundance of various insect herbivores studied. A total nine species of insects was recorded and among them the defoliating caterpillar Hadjina chinensis (Wallengren) (Lepidoptera) was the only species known to have host plants restricted to genus Bidens. Further host specificity studies are required to evaluate the potential of this insect as a candidate for augmentative biological control agent for B. frondosa in Korea. All other insect species are either polyphagous or known crop pests.     

Biogeographical comparison of the arthropod herbivore communities associated with Lepidium draba in its native, expanded and introduced ranges

Aim To examine the composition and structure of the arthropod community on the invasive weed Lepidium draba in its native, expanded and introduced ranges, in order to elucidate the lack of a biotic constraint that may facilitate invasion. Location Europe and western North America. Methods Identical sampling protocols were used to collect data from a total of 35 populations of L. draba in its native (Eastern European), expanded (Western European) and introduced (western US) ranges. A bootstrapping analysis was used to compare herbivore richness, diversity and evenness among the regions. Core species groups (monophages, oligophages and polyphages) on the plant were defined and their abundances and host utilization patterns described. Results Species richness was greatest in the native range, while species diversity and evenness were similar in the native and expanded range, but significantly greater than in the introduced range of L. draba. Specialist herbivore abundance was greater in the native and expanded compared with the introduced range. Oligophagous Brassicaceae‐feeders were equally abundant in all three ranges, and polyphagous herbivore abundance was significantly greater in the introduced range. Overall herbivore abundance was greater in the introduced range. Host utilization was more complete in the two European ranges due to monophagous herbivores that do not exist in the introduced range. Root feeders and gall formers were completely absent from the introduced range, which was dominated by generalist sap‐sucking herbivores. However, one indigenous stem‐mining weevil, Ceutorhynchus americanus, occurred on L. draba in the introduced range. Main conclusions This is, to our knowledge, the first study documenting greater herbivore abundance on an invasive weed in its introduced, compared with its native, range. However, greater abundance does not necessarily translate to greater impact. We argue that, despite the greater total herbivore abundance in the introduced range, differences in the herbivore community structure (specialist vs. generalist herbivory) may contribute to the invasion success of L. draba in the western USA.     

Herbarium specimens reveal a historical shift in phylogeographic structure of common ragweed during native range disturbance

Invasive plants provide ample opportunity to study evolutionary shifts that occur after introduction to novel environments. However, although genetic characters pre‐dating introduction can be important determinants of later success, large‐scale investigations of historical genetic structure have not been feasible. Common ragweed (Ambrosia artemisiifolia L.) is an invasive weed native to North America that is known for its allergenic pollen. Palynological records from sediment cores indicate that this species was uncommon before European colonization of North America, and ragweed populations expanded rapidly as settlers deforested the landscape on a massive scale, later becoming an aggressive invasive with populations established globally. Towards a direct comparison of genetic structure now and during intense anthropogenic disturbance of the late 19th century, we sampled 45 natural populations of common ragweed across its native range as well as historical herbarium specimens collected up to 140 years ago. Bayesian clustering analyses of 453 modern and 473 historical samples genotyped at three chloroplast spacer regions and six nuclear microsatellite loci reveal that historical ragweed's spatial genetic structure mirrors both the palaeo‐record of Ambrosia pollen deposition and the historical pattern of agricultural density across the landscape. Furthermore, for unknown reasons, this spatial genetic pattern has changed substantially in the intervening years. Following on previous work relating morphology and genetic expression between plants collected from eastern North America and Western Europe, we speculate that the cluster associated with humans’ rapid transformation of the landscape is a likely source of these aggressive invasive populations.     

Preadaptation and post‐introduction evolution facilitate the invasion of Phragmites australis in North America

Compared with non‐invasive species, invasive plant species may benefit from certain advantageous traits, for example, higher photosynthesis capacity and resource/energy‐use efficiency. These traits can be preadapted prior to introduction, but can also be acquired through evolution following introduction to the new range. Disentangling the origins of these advantageous traits is a fundamental and emerging question in invasion ecology. We conducted a multiple comparative experiment under identical environmental condition with the invasive haplotype M lineage of the wetland grass Phragmites australis and compared the ecophysiological traits of this invasive haplotype M in North America with those of the European ancestor and the conspecific North American native haplotype E lineage, P. australis ssp. americanus. The invasive haplotype M differed significantly from the native North American conspecific haplotype E in several ecophysiological and morphological traits, and the European haplotype M had a more efficient photosynthetic apparatus than the native North American P. australis ssp. americanus. Within the haplotype M lineage, the introduced North American P. australis exhibited different biomass allocation patterns and resource/energy‐use strategies compared to its European ancestor group. A discriminant analysis of principal components separated the haplotype M and the haplotype E lineages completely along the first canonical axis, highly related to photosynthetic gas‐exchange parameters, photosynthetic energy‐use efficiency and payback time. The second canonical axis, highly related to photosynthetic nitrogen use efficiency and construction costs, significantly separated the introduced P. australis in North America from its European ancestor. Synthesis. We conclude that the European P. australis lineage was preadapted to be invasive prior to its introduction, and that the invasion in North America is further stimulated by rapid post‐introduction evolution in several advantageous traits. The multicomparison approach used in this study could be an effective approach for distinguishing preadaptation and post‐introduction evolution of invasive species. Further research is needed to link the observed changes in invasive traits to the genetic variation and the interaction with the environment.     

Assessing the biological control of yellow starthistle (Centaurea solstitialis L): prospective analysis of the impact of the rosette weevil (Ceratapion basicorne (Illiger))

相似文献   

Integration of Biological Control and Native Seeding to Restore Invaded Plant Communities

Disturbed natural areas frequently experience invasion by introduced plant species that can reduce native biodiversity. Biological control can suppress these introduced species, but without restoration another introduced species can invade. Integration of biological control with concurrent revegetation can both aid in weed reduction via interspecific plant competition and establish a restored native plant community. This 3‐year study investigated an integrated approach to controlling the introduced annual Mile‐a‐minute weed (Persicaria perfoliata [L.] H. Gross [Polygonaceae]) using the biocontrol weevil Rhinoncomimus latipes Korotyaev (Coleoptera: Curculionidae) and restoration planting using a native seed mix. A fully factorial design tested weevils and seeding, separately and together, using insecticide to eliminate weevils. The weevils together with the native seed mix reduced P. perfoliata percent cover in 2009 and 2010, and peak seed cluster production in 2010, compared to the insecticide ? no seed control treatment. Persicaria perfoliata final dry biomass was reduced by 75% in 2010 and by 57% in 2011 in the weevils plus seed treatment compared to the control, with weevils having the greatest effect in 2010 and the seed treatment having the greatest impact in 2011. Results suggest an additive effect of biocontrol and seeding in suppressing P. perfoliata. Seeded treatments also developed the highest native plant species richness and diversity, comprised of spontaneous recolonization in addition to species from the seed mix. Results support the use of integrated management of this invasive weed, with suppression through biological control and native revegetation together helping prevent reinvasion while restoring native plant biodiversity.     

Evidence for multiple introductions of Centaurea stoebe micranthos (spotted knapweed,Asteraceae) to North America

Invasive species’ success may depend strongly on the genetic resources they maintain through the invasion process. We ask how many introductions have occurred in the North American weed Centaurea stoebe micranthos (Asteraceae), and explore whether genetic diversity and population structure have changed as a result of introduction. We surveyed individuals from 15 European native range sites and 11 North American introduced range sites at six polymorphic microsatellite loci. No significant difference existed in the total number of alleles or in the number of private alleles found in each range. Shannon–Weaver diversity of phenotype frequencies was also not significantly different between the ranges, while expected heterozygosity was significantly higher in the invasive range. Population structure was similar between the native range and the invasive range, and isolation by distance was not significant in either range. Traditional assignment methods did not allocate any North American individuals to the sampled European populations, while Bayesian assignment methods grouped individuals into nine genetic clusters, with three of them shared between North America and Europe. Invasive individuals tended to have genetically admixed profiles, while natives tended to assign more strongly to a single cluster. Many North American individuals share assignment with Romania and Bulgaria, suggesting two separate invasions that have undergone gene flow in North America. Samples from three other invasive range sites were genetically distinct, possibly representing three other unique introductions. Multiple introductions and the maintenance of high genetic diversity through the introduction process may be partially responsible for the invasive success of C. stoebe micranthos.     

Herbivory below ground and biological weed control: life history of a root-boring weevil on purple loosestrife

The life history of the root-boring weevil Hylobius transversovittatus was studied in north and central Europe. The weevil develops on Lythrum salicaria, a perennial marshland plant that has become a problem weed in North America. It was found in all habitats of its host plant with the exception of permanently flooded sites. It also attacked L. salicaria in an early successional stage, devastating large parts of the storage tissue. The beetle was found in two-thirds of the field populations examined with a mean attack rate of 76.3%. Larvae developed according to a 1- or 2-year generation cycle depending on the time of oviposition. Adult beetles developing within 1 year emerged between July and October, whereas beetles with a 2-year larval period emerged within 3 weeks in July and August. Adults were long-lived and could hibernate several times. Beetles of the new generation mated right on the spot and some oviposited prior to overwintering. Hibernated females had an oviposition period from May to early September and produced 3–4 eggs/day during the peak oviposition period. Specific mortality factors were scarce. Dispersal flights ensure the regular occurrence of H. transversovittatus in scattered L. salicaria populations. The severe impact of the weevil is expected to reduce the competitive ability of its host plant after introduction into North America.     

Impact of the belowground herbivore and potential biological control agent, Ceutorhynchus scrobicollis, on Alliaria petiolata performance

We studied the influence of the root-crown weevil Ceutorhynchus scrobicollis on its host plant Alliaria petiolata, a European biennial herb that is currently invading much of temperate North America. Varying timing of attack and herbivore densities in a common garden allowed to assess seasonality of plant response, density-dependence of impact, and the effect of intraspecific competition on C. scrobicollis recruitment (number of F₁ generation adults emerged). Data collected in the common garden were compared with data collected at field sites. C. scrobicollis is a common weevil in Europe, frequently attaining high attack levels on its host plant. In the common garden, weevil attack decreased plant survival by up to 43%, reduced plant height by 54%, increased the number of shoots by up to four–fold and delayed seed ripening, but had no significant negative effect on seed production. Plants infested in spring allocated less biomass to aboveground plant parts, and remained smaller than plants attacked in autumn, indicating that the latter were able to partly compensate for weevil attack. Increasing weevil density rarely had an effect on A. petiolata performance, and did not increase F₁ recruitment, suggesting strong intraspecific competition. At field sites, C. scrobicollis attack is spread over a long time period, which probably alleviates intraspecific competition. In summary, attack by the root-crown feeding weevil, C. scrobicollis, can substantially reduce growth and survival of A. petiolata. If introduced as a biological control agent into North America, C. scrobicollis is likely to decrease the fitness and competitive superiority of A. petiolata.     

Status of an ongoing biological control program for the invasive vine, <Emphasis Type="Italic">Persicaria perfoliata</Emphasis> in eastern North America

Mile-a-minute weed, Persicaria perfoliata (L.) H. Gross (Polygonaceae), an aggressive annual vine native to Asia, has invaded forest edges, light gaps, open fields, and riparian borders in eastern North America. It was accidentally introduced into Pennsylvania in the 1930s and has since expanded its range north to Massachusetts, south to North Carolina, and west to Ohio. A biological control program was initiated in 1996, and in 2004, a permit was issued for release of Rhinoncomimus latipes Korotyaev (Coleoptera: Curculionidae), a host-specific weevil initially collected in China. Since 2004, the biology of the weevil in its introduced range has been studied, along with its impact on P. perfoliata, which can be substantial. Weevils have been released in ten states through 2010, and populations have increased considerably at many sites. Although P. perfoliata continues to expand its North American range, natural and human-assisted dispersal of R. latipes is reducing its negative effects. Here we review and assess the current status of the biological control program.     

Introduced or glacial relict? Phylogeography of the cryptogenic tunicate Molgula manhattensis (Ascidiacea,Pleurogona)

Aim The tunicate Molgula manhattensis has a disjunct amphi‐Atlantic distribution and a recent history of world‐wide introductions. Its distribution could be the result of regional extinctions followed by post‐glacial recolonization, or anthropogenic dispersal. To determine whether the North Atlantic distribution of M. manhattensis is natural or human‐mediated, we analysed mtDNA cytochrome c oxidase subunit I (COI) sequence variation in individuals from cryptogenic and introduced ranges. Location North Atlantic Europe and America; Black Sea; San Francisco Bay; Osaka Bay. Methods Nuclear 18S rDNA sequences were used to resolve phylogenetic relationships and mtDNA COI sequences for phylogeographic analyses. Results Phylogenetic analyses confirmed that M. manhattensis and M. socialis, which are frequently confused, are distinct species. MtDNA haplotype diversity was nearly three times higher with deeper relationships among haplotypes on the North‐east American coast than in Europe. Diversity declined from south to north in America but not in Europe. In areas of known introductions (Black Sea, Japan, San Francisco Bay), M. manhattensis showed variable levels of haplotype diversity. Medium‐to‐high‐frequency haplotypes originating from the North‐west Atlantic were present in two locations of known introductions, but not in Europe. Private haplotypes were found on both sides of the Atlantic and in introduced populations. The mismatch distribution for the North‐east Atlantic coast indicates a recent expansion. Main conclusions Molgula manhattensis is native in North‐east America. However, whether it was introduced or is native to Europe remains equivocal. Additional sampling might or might not reveal the presence of putative private European haplotypes in America. The low European diversity may be explained by low effective population size and a recent expansion, or by low propagule pressure of anthropogenic introduction. Absence of medium‐to‐high‐frequency American haplotypes in Europe may be the result of exclusive transport from southern ports, or long‐term residence. These arguments are ambiguous, and M. manhattensis remains cryptogenic in Europe.     

Effects of a nematode Meloidogyne incognita and its interaction with above‐ground herbivory on an invasive wetland plant,alligator weed (Alternanthera philoxeroides)

Invasive plants may be attacked both above ground and below ground. Few studies have, however, investigated the simultaneous effects of above‐ground and below‐ground herbivory. In the present study, we report the effects of beetle herbivory and nematode infection on alligator weed, Alternanthera philoxeroides, an invasive plant in China. We found that the root‐knot nematode Meloidogyne incognita widely occurred on the plant in south China. To examine its effect on the plant in conjunction with above‐ground herbivory, we conducted a field common garden experiment with a local insect defoliator, Cassida piperata. We also included the native congener Alternanthera sessilis in our experiments for a comparison of the response of invasive and native species. We found no significant effects on plant biomass of the nematode infection in conjunction with the above‐ground herbivory. Further chemical analysis, however, showed that the water‐soluble carbohydrate content in roots of A. philoxeroides was significantly increased in plants attacked by both the nematode and the herbivore compared with the water‐soluble carbohydrate content in plants attacked by only the nematode or herbivore alone. We found no such change in the native congener A. sessilis. Together these results may suggest that A. philoxeroides tolerates joint above‐ground and below‐ground damage by allocating more resources to below‐ground material.     

Host Specificity of the Argentine Root-Boring Weevil, Heilipodus ventralis (Coleoptera: Curculionidae), a Potential Biocontrol Agent for Snakeweeds (Gutierrezia: Asteraceae) in Western North American Rangelands—U.S. Quarantine Tests

Native snakeweeds, especially Gutierrezia sarothrae (Pursh) Britton and Rusby and Gutierrezia microcephala (DC.) A. Gray, are among the most widespread and damaging weeds of rangelands in the western United States and northern Mexico. The genus long ago spread to southern South America, where further speciation occurred. We have found several species of insects in Argentina that damage other species of snakeweeds there and are possible candidates for biological control in North America. The first of these, the root-boring weevil, Heilipodus ventralis (Hustache), was tested in Argentina and then sent to the USDA-ARS Insect Quarantine Facility at Temple, Texas, for host specificity testing on North American plants. We tested H. ventralis on 40 species of the family Asteraceae, in 19 tests of five types, using 686 adults and 365 larvae. Host specificity increased from adult feeding, to ovipositional selection, to larval development. At Temple, adults fed mostly on 6 species of the closely related genera Grindelia, Gutierrezia, and Gymnosperma, but with substantial feeding on four other genera of the two preferred subtribes Solidagininae and Machaerantherinae and on Baccharis in the tribe Baccharidinae, with lesser feeding on the subtribe Asterinae, all in the tribe Astereae, and on 1 species in the tribe Anthemideae. Females oviposited primarily on the same 6 species but very little on plants outside the 2 preferred subtribes. Larvae developed only on 9 of the 29 U.S. plant species tested, 6 within the two preferred subtribes and on Brickellia and Aster in other tribes. Only 5 species of three genera appear to be potential true hosts of H. ventralis in North America, on which all stages of the life cycle, adult feeding, oviposition, and larval development, can take place; these are Gymnosperma glutinosum (Spreng.) Less., Gutierrezia grandis Blake, Gut. microcephala, Gut. sarothrae, and Grindelia lanceolata Nutt. None of these genera contain species of economic or notable ecological value; the few rare species appear to be protected by habitat isolation from attack by H. ventralis. H. ventralis, therefore, appears sufficiently host specific for field release in North America. This is the first introduced biocontrol agent to be approved for release in a continental area to control a native weed.     

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

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

Field and laboratory studies to determine the suitability of Cissoanthonomus tuberculipennis (Coleoptera: Curculionidae) for release against Cardiospermum grandiflorum (Sapindaceae) in South Africa

Cardiospermum grandiflorum is an invasive creeper that was targeted for biological control in South Africa in 2003. To determine ecological host range of its natural enemies, surveys were conducted on C. grandiflorum and 11 other Sapindaceae at 40 sites in the weed's native range (Argentina). These surveys indicated that the seed-feeding weevil Cissoanthonomus tuberculipennis was restricted to C. grandiflorum, and that it was among the common natural enemies, occurring at most sites where C. grandiflorum was recorded. Open-field tests were conducted under natural conditions in Argentina to determine the host preference of C. tuberculipennis and other natural enemies of C. grandiflorum among three Cardiospermum species. These tests revealed that C. tuberculipennis and the bug Gargaphia sp. were restricted to C. grandiflorum though the latter subsequently developed on non-target Cardiospermum species in the laboratory. C. tuberculipennis was found to be highly damaging, destroying up to 44% of the seeds per plant in Argentina. In all the host-specificity tests, including no-choice, paired-choice and multi-choice tests, C. tuberculipennis only fed and developed on C. grandiflorum. Failure of C. tuberculipennis to feed and develop on all congeners of C. grandiflorum shows that the weevil is highly host-specific to the target weed. Results of host-specificity tests, open field tests and long-term monitoring of C. tuberculipennis populations demonstrate that the weevil poses no threat to non-target plant species, and therefore safe for release against C. grandiflorum in South Africa. Permission to release C. tuberculipennis in South Africa has been granted by the relevant regulatory authorities.