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.

Common tansy (Tanacetum vulgare L., Asteraceae), an herbaceous perennial native to Europe, was introduced into North America as a culinary and medicinal herb. Now widely naturalized in pastures, roadsides, waste places, and riparian areas across Canada and the northern USA, tansy is also spreading in forested areas. It contains several compounds toxic to humans and livestock if consumed, particularly α-thujone, and is listed as a noxious weed in several states and provinces. A biological control program for common tansy is being coordinated by a Canadian-US consortium led by the Alberta Invasive Plant Council and the Minnesota Department of Agriculture, with CABI Switzerland Centre identifying and testing potential agents for efficacy and host specificity. Collection efforts are focused on Eastern Europe (Russia and Ukraine) to maximize the climatic match with the infested areas in North America. Several potential agents are under study, the most promising agent at present being a stem-mining weevil, Microplontus millefolii (Schltz.). A root-feeding flea beetle, Longitarsus noricus Leonardi, also shows promise, and DNA barcoding is being used to separate this species from morphologically similar species that may emerge as contaminants in host-specificity tests. The leaf-feeding tortoise beetle Cassida stigmatica Suffr. is specific to Tanacetum but is able to complete development on the North American native T. bipinnatum ssp. huronense (Nutt.) Breitung; further evaluation of the risk to this species is needed. Life history studies on a stem-mining moth, Isophrictis striatella (Denis & Schiffermüller), suggest that it develops mainly in the previous year’s dead stems. This may reduce its potential impact as a biological control agent. The effects of chemical and genetic variation in tansy on the feeding and oviposition responses of insects are being studied, and molecular methods are also being used to evaluate the relationships between T. vulgare and other species.

Environmental factors determining the population density of the weevil Microplontus millefolii , a stem miner of the common tansy, Tanacetum vulgare , were investigated in the suburbs and environs of St. Petersburg, Russia. Larvae or empty mines of M. millefolii were found in 39 out of 43 inspected sites; in total, 620 out of 2283 T. vulgare stems were infested. The percentage of infested stems per site ranged from 0 up to almost 90%, the density of infestation (the mean number of larvae and empty mines per stem) ranged up to 2.3 with the mean of 0.51 for all inspected sites. The surrounding vegetation was the single environmental factor significantly correlated with the percentage of infested stems (30 and 20% in sites with domination of grasses and of forbs, correspondingly). The mechanisms of this dependence are not clear. Probably, the domination of grasses (that is a relatively advanced stage of the vegetation succession) is correlated with the longer period of time for accumulation of phytophagous insects associated with tansy. The analysis of data for individual stems (within-site distribution) showed that the mean number of the weevil larvae almost linearly increased with the diameter of the stem. The dependence on the host plant population density was also strong but not linear: both in dense patches (percent cover of more than 50%) and in sparse plants (percent cover of 1% and less) the density of infestation was higher than at a medium abundance of the host plant. In addition, in the patches with only a short time shadow from trees or tall herbs the density of infestation was higher than in those where the shadow stayed for longer or was absent at all. The mean density of T. vulgare infestation by M. millefolii was independent of the type of habitat (meadows, old fields, roadsides, ruderal sites), the size of the site, the average cover of T. vulgare , the total cover of green plants, the degree of anthropogenic disturbance, soil composition, and humidity. This ability to infest T. vulgare in very different habitats allows considering M. millefolii as a potentially effective agent for biological control of the common tansy in the invasion areas.

Rhamnus cathartica (common buckthorn) is a shrub (or small tree) of Eurasian origin, which has become invasive in North America. Internal feeders and sap suckers were prioritized for biological control from over 30 specialized insects identified from the target plant in its native European range. Five leaf‐feeding moths were also considered for further investigations. Field observations and preliminary host range tests with the stem‐boring beetle Oberea pedemontana , the root‐boring moth Synanthedon stomoxiformis , the shoot‐tip‐boring moth Sorhagenia janiszewskae and the leaf‐feeding moths Ancylis apicella , A. unculana , Triphosa dubitata , Philereme transversata and P. vetulata confirmed that all of these species were lacking host specificity in no‐choice conditions. Choice oviposition tests carried out with most of the prioritized species to assess their ecological host range yielded unreliable results. Three psyllids, Trichochermes walkeri , Cacopsylla rhamnicolla and Trioza rhamni are promising in terms of host specificity, but are infected with the plant disease ‘ Candidatus Phytoplasma rhamni’. Fruit‐ or seed‐feeding insects may present the best potential for biological control of buckthorn in directly reducing seed set and thus seedling establishment. However, it was not possible to obtain adult fruiting trees of native North American Rhamnus species for testing. It is concluded that there are no promising arthropod agents based on what is known to date. Pathogens could offer new opportunities for biological control of R. cathartica in North America.

G erber E, S chaffner U, G assmann A, H inz HL, S eier M & M üller‐ S chärer H (2011). Prospects for biological control of Ambrosia artemisiifolia in Europe: learning from the past. Weed Research 51 , 559–573. Summary The recent invasion by Ambrosia artemisiifolia (common ragweed) has, like no other plant, raised the awareness of invasive plants in Europe. The main concerns regarding this plant are that it produces a large amount of highly allergenic pollen that causes high rates of sensitisation among humans, but also A. artemisiifolia is increasingly becoming a major weed in agriculture. Recently, chemical and mechanical control methods have been developed and partially implemented in Europe, but sustainable control strategies to mitigate its spread into areas not yet invaded and to reduce its abundance in badly infested areas are lacking. One management tool, not yet implemented in Europe but successfully applied in Australia, is biological control. Almost all natural enemies that have colonised A. artemisiifolia in Europe are polyphagous and cause little damage, rendering them unsuitable for a system management approach. Two fungal pathogens have been reported to adversely impact A. artemisiifolia in the introduced range, but their biology makes them unsuitable for mass production and application as a mycoherbicide. In the native range of A. artemisiifolia , on the other hand, a number of herbivores and pathogens associated with this plant have a very narrow host range and reduce pollen and seed production, the stage most sensitive for long‐term population management of this winter annual. We discuss and propose a prioritisation of these biological control candidates for a classical or inundative biological control approach against A. artemisiifolia in Europe, capitalising on past experiences from North America, Asia and Australia.

Classical biological control of insect pests and weeds may lead to potential conflicts, where insect pests are closely related to weed biological control agents. Such a conflict may occur in the classical biological control of the cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham) in North America, which belongs to the same subfamily, Ceutorhynchinae, as a number of agents introduced or proposed for introduction against non-indigenous invasive weed species. We propose a step-by-step procedure to select non-target species and thereby to develop a non-target species test list for screening candidate entomophagous biological control agents of a herbivore pest insect in a way that would simultaneously evaluate non-target potential on weed biological control agents and other non-target species. Using these recommendations, we developed a non-target test list for host specificity evaluations in the area of origin (Europe) and the area of introduction (North America) for cabbage seedpod weevil parasitoids. Scientifically based predictions on expected host-parasitoid interactions and ecological information about the ecological host range in the area of origin can help avoid conflicts, while still allowing the introduction of safe and effective agents against both insect pests and weeds.

Biotic and abiotic factors can have a profound influence on the occurrence, species composition, structure, distribution, relative abundance, and dynamics of plant species and their associated natural enemies. Elucidation of some of the more relevant habitat characteristics for a pestiferous plant or phytophage species in its place of origin may enable better prediction of its rates of colonization and spread should it accidentally be introduced into new areas. A similar analysis of the habitat requisites for the associated natural enemies of the plant/phytophage should enable the development of predictive models that identify habitat factors conducive to the establishment and impact on the particular plant or phytophage species. In this study, habitat associations were characterized for four different Euphorbia species and their associated flea beetle species in the Aphthona complex from 17 field sites in Europe, representing xeric, mesic, and hydric habitats. Micro- and macronutrient analyses were conducted on soil and spurge foliage and roots; physical properties of the soil were analyzed; plant cover of grasses, forbs (a broad-leaved herbaceous plant), and Euphorbia species (and total plant productivity) were estimated at each of the sites, and relative abundance counts were made for each of the flea beetle species at each of the 17 sites during spring, early summer, and mid-summer 1991. Spurge species included Euphorbia cyparissias, E. lucida, E. seguieriana, and E. virgata. Flea beetles species included Aphthona cyparissiae, A. czwalinae, A. lacertosa, A. nigriscutis, A. pygmaea, A. venustula, and A. violacea. Ordination models generated for the spurge species suggested that E. virgata and E. lucida were associated with higher levels of soil matric potential, clay, organic matter, Ca, Fe, K, Mg, N, P, Zn (soil layer B), and plant productivity. In contrast, E. cyparissias and E. seguieriana were associated with relatively lower levels of plant productivity and higher levels of sand, CaCO3, and Zn (soil layer A). Ordination models developed for the Aphthona species suggested that A. czwalinae and A. lacertosa were associated with sites containing higher levels of clay and plant productivity and higher levels of Mn in the Euphorbia roots; A. violacea was associated with sites with intermediate levels of sand, clay, and plant productivity, in addition to spurge roots with higher levels of Cu, Fe, K, N, P, and Zn. A. nigriscutis was associated with sandier soils with lower levels of plant productivity and higher levels of Ca, K, and N in the Euphorbia roots. A. cyparissiae, A. pygmaea, and A.venustula were associated with moderately sandy soils with relatively lower levels of plant productivity and Euphorbia species with higher levels of Ca and N in the roots. The ordination models generated from this study provide the diagnostic framework for the identification of appropriate habitats and key site requisites that might be conducive to the establishment and impact of the Aphthona species on leafy spurge in North America.

Renewed debate over the risk of non-target effects in biological control reflects, in part, the recent quantification of direct and indirect ecological effects of the flowerhead weevil, Rhinocyllus conicus Frol., in North America. To help resolve the issue, we review the published data for R. conicus from both Europe and North America: pre-release (1961-1968), post-release (1969-1985) and more recent (1986-1999). Our aim was to determine the extent to which host range expansion on to native North American species, and the associated ecological effects, were predicted or predictable. Our overall conclusion is that more was known than is generally realized, Yet more information would have been required to complete the initial assessment of ecological consequences. Three important points emerge. First, the potential effect of R. conicus on native North American species was not a major element of the testing programme. Second, the host range expansion observed is consistent with the pre-release and early post-release data, and so was predictable, if not predicted. The pre- and early post-release data showed that R. conicus could feed and develop on multiple Cirsium species, including two North American species. Third, we found that tile studies needed to quantify the likely magnitude of feeding by R. conicus on North American Cirsium species, and thus the ecological consequences of that feeding, were not done. Instead, inferential arguments were used to suggest that any feeding by R. conicus on North American species would not be substantial. We conclude that there were sufficient data, which suggested that North American Cirsium species would be acceptable host species, to have warranted further testing to define and quantify the potential ecological side-effects of introducing P, conicus to North America. Contemporary concerns should now mandate such tests.

The description of the ten Chamaesphecia species associated with Euphorbia in eastern and south-eastern Europe is based on external adult morphology, male and female genitalia, and the structure of the egg chorion. These species can be divided into two groups according to the shape of the setae of the dorso-basal part of the valvae in the male genitalia. Most Chamaesphecia species are associated with one species of host-plant and all are closely tied to one habitat type. The host-plant and the structure of the egg chorion are fundamental characteristics for the determination of a few species, and very helpful for the others. All species bore into the main root of their host-plant and overwinter as larvae. With the exception of two species which have an annual or biennial life cycle, all species are univoltine. The larvae of three of the eight Chamaesphecia spp. investigated feed and develop in the roots of North American leafy spurge, Euphorbia esula sensu late. Of these, the best candidate for the biological control of leafy spurge is C. crassicornis, because the larvae have a similar survival rate on the target weed and the European host-plant, E. virgata.

Leafy spurge (Euphorbia esula) is an herbaceous perennial of European origin that was accidentally introduced into North America where it has become a serious weed in pastures and rangelands. Five species of root-feeding chrysomelid beetles in the genusAphthonahave been released in North America for the biological control of leafy spurge. They originate from central and eastern Europe and occur in different habitats. The brown species,Aphthona cyparissiae, Aphthona flava,andAphthona nigriscutis,occur predominantly in open dry habitats, and the black species,Aphthona czwalinaiandAphthona lacertosa,prefer moister habitats. All five species are univoltine and overwinter as larvae. The host range of these fiveAphthonaspecies is restricted to species in the subgenusEsula.

Abstract: Studies on the life history and host specificity of the root‐feeding chrysomelid Aphthona venustula were made to determine the suitability of this insect as a classical biological control agent for leafy spurge (Euphorbia esula) in North America. The adults of A. venustula emerge in summer, and are in reproductive diapause until the following spring when the main adult feeding and oviposition activity occurs. A. venustula prefers mesic shaded and transitional areas but can survive on formerly forested land. The experimental adult feeding range of the beetle is restricted to species in genus Euphorbia, while the larval feeding range is restricted to species in subgenus Esula. Within its habitat in Europe, the beetle discriminates between species in subgenus Esula.

During field surveys made in Europe nearly 40 specialized insect species were found and considered as potential biological control agents of leafy spurge and cypress spurge (Euphorbia esula and Euphorbia cyparissias). More insect species were found on the most common and the geographically most widespread spurge species and on those occurring in a wide range of habitat types. The insect families most frequently associated with perennial spurges in Europe are the chrysomelids, sesiids, cecidomyids, and anthomyiids. Although the areas surveyed include only the most western parts of the leafy spurge and cypress spurge distribution in the Palearctic, all food niches and habitats of the target weeds were found to be occupied by herbivorous insects. The history of the search for biological control agents of leafy and cypress spurges in Europe is briefly reviewed. The selection of candidate agents during the past 30 years is discussed, and the 22 insect species which have been screened so far are briefly considered. It is concluded that suitable agents were found outside optimal survey areas with regard to ecoclimatic and host-plant matching.

The biology and host specificity of Oxicesta geographica F. from Romania, Hungary, and Southwestern Russia were studied to evaluate the potential of this moth as a new biological control agent of leafy spurge, Euphorbia esula L., ''complex'' in North America. This oligophagous, multivoltine tent caterpillar is common on perennial spurges in southeastern Europe and Asia Minor and prefers dry, open sites. Results of no-choice feeding tests with first instars on 93 plant species and biotypes, distributed in 33 families, show that O. geographica completed its life cycle mainly on plants of Euphorbia, subgenus Esula, and occasionally fed and developed on species in other subgenera of the genus. Studies of late instars did not show any important extensions of the host range.

Leafy spurge (Euphorbia esula (s.1.)) is an herbaceous perennial and serious weed of Eurasian origin that has been accidentally introduced into North America. The two European root-boring mothsChamaesphecia hungarica andCh. astatiformis are univoltine and overwinter as mature larvae. Both species have a lower survival rate on leafy spurge than on their field hosts, and thus are not optimal candidates for the biological control of leafy spurge. However, the rate of larval development and larval growth on the target weed and on the two field hosts is nearly the same. The experimental host range of both species is restricted to a few species in the subgenusEsula within the genusEuphorbia. The two species occupy different habitats in the steppe biome and are targeted for similar leafy spurge habitats in North America.