Abstract

The recruitment life stage, including germination and early seedling establishment, is the most vulnerable life stage of plants and has cascading effects on plant performance at later life stages. However, surprisingly little is known on the eco-evolutionary processes that determine the success of biological invasions at this life stage. We performed germination experiments with and without simulated drought stress and monitored early seedling growth in diploid and tetraploid Centaurea stoebe. . While diploids are the major cytotype in the native European range, only tetraploids became invasive in North America. Thus, C. stoebe is an excellent model species to simultaneously study both, pre-adaptive differences in the native range (diploids vs. tetraploids) and post-introduction evolution in the non-native range (native tetraploids vs. non-native tetraploids). To account for broad spatial-environmental variation within cytotypes and ranges, we germinated 23,928 seeds from 208 widely distributed populations. Tetraploids germinated better than diploids. Within tetraploids, invasive populations outperformed native populations in germination. However, these differences were not evident under simulated drought stress. Seedlings of invasive tetraploids had a higher biomass and developed the first true leaf earlier than those from the native range, while the native cytotypes did not differ in these early seedling traits. Our results suggest that a combination of pre-adaptation related to superior performance of polyploids (greater and faster germination) and post-introduction evolution towards higher performance in the invasive range (greater and faster germination, greater and faster accumulation of seedling biomass) may have contributed to the invasion success of tetraploid C. stoebe in North America.

Abstract

Assessing global variation in phenotypic traits and linking that variation to colonization and range expansion is notably rare in invasion biology. Here, we studied variation in seed size in Centaurea solstitialis, a weed with worldwide distribution. Additionally, we explored how seed size variation affects seedling survival of C. solstitialis under favorable precipitation conditions in Anatolia, an ancestral region, and unfavorable precipitation conditions in Argentina, a non-native region. To that end, we conducted seed collections following dispersal pathways of C. solstitialis in ancestral, expanded, and non-native ranges. Locally, collections followed elevation gradients. Also, we performed a greenhouse experiment with C. solstitialis populations varying in seed size and water additions simulating precipitation patterns in Anatolia and Argentina. Seeds from ancestral populations at low elevation were smaller than those from the rest of study populations. Also, seed size in populations at high elevation in the expanded range, the main source of non-native populations, was similar to that in all, but one non-native population, where seeds exhibited further increase. Increments in seed size thus track range expansion in C. solstitialis. Locally, seed size increased with elevation in all three ranges, suggesting convergent responses to that gradient. Seedlings from larger seeds displayed greater survival than those from smaller seeds only under Argentinean conditions. Consequently, populations with large seeds may have been instrumental for colonizing that non-native region. Our findings suggest that ancient and recent dispersal of large-seeded populations contribute to explain the reported global pattern of seed size divergence and worldwide distribution of C. solstitialis.

Abstract

Lepidiumdraba (Brassicaceae) is a major concern for agriculture and biodiversity in the western United States. As current control methods do not provide long-term, sustainable solutions, research has been conducted to find biological control agents. Ceutorhynchusassimilis is one of the currently investigated candidates. Known as oligophagous in the literature, a specialist clade of this root-galling weevil exists in southern Europe. This raised the question of its ability to survive in colder climates in the target range. We investigated the phenology of C.assimilis in the field in southern France (specialist clade) and Romania (generalist clade) and measured various temperature-dependent parameters in the laboratory. In both ranges, weevils were univoltine. Oviposition in autumn started later in France compared to Romania, while mature larvae exited galls (to pupate in the soil) earlier the following year. On average, 25% and 32% of galls from France and Romania were completely below the soil surface, respectively, and this appeared to depend on soil substrate. Weevils transported from France to Romania were able to develop, but at a much lower rate than Romanian weevils. Mortality of overwintering larvae of both clades increased with decreasing temperature and exposure time. At -5 degrees C, lethal times Lt(50) and Lt(95) were 15 and 42days for the specialist clade and 26 and 72days for the generalist clade. A higher proportion of third instar larvae compared to first and second instar larvae survived. Pupation time at different temperatures did not differ between weevils from France or Romania. A climate match model (comparing winter temperatures) indicated that the specialist clade of C.assimilis from France has the potential to establish in some parts of the target range (e.g. Washington, Oregon, California). However, temperature extremes and winters without snow cover will likely limit its establishment unless rapid adaptive evolution takes place.

Abstract

Lepidium draba (Brassicaceae) is a clonal herb, originating from Eurasia, which is invasive in North America. A classical biological control project was initiated in 2001, and the gall-forming weevil Ceutorhynchus cardariae was prioritized as a candidate agent. We studied its biology and field host range between 2003 and 2014 in the laboratory and a common garden in Switzerland and in the field in Romania. Ceutorhynchus cardariae is a univoltine to bivoltine species. In Switzerland, oviposition usually started at the beginning of March and can occur at temperatures as low as 2.5 degrees C. Galls are formed on stems, leaf stalks and midribs of L.draba rosettes and bolting plants. Gall size increased with an increasing number of larvae per gall. The three larval instars feed inside the galls and leave the plant to pupate in the soil once mature. In Switzerland, development from egg to adult took about 12weeks in spring. Adults emerged from May to July. After a brief feeding period, adults aestivate. From late summer, feeding recommenced and females may oviposit, forming a partial second generation. Eggs and all larval instars can be found in galls throughout winter. The rate of larval ectoparasitism reached 78%, while endoparasitism was low with a maximum of 2.3%. Lepidium draba populations differed in their suitability for development (number of C.cardariae produced), indicating that effectiveness of C.cardariae - in case released - may be variable. In the field, we observed that gall formation by C.cardariae can severely stunt or even kill shoots. Investigations on the field host range of C.cardariae indicated that only the closely related Lepidium campestre may act as an alternative host for the weevil in Europe. Host-specificity tests are underway to determine its environmental safety before field release in North America is being considered.

Abstract

We determined the host range of the parasitoid Trichomalus perfectus (Walker), a candidate for classical biological control of cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham), an important pest of canola in Canada. Studies were conducted in Europe and in North America. In laboratory experiments, the levels of parasitism (acceptance) of Ceutorhynchus turbatus Schultze, C. cardariae Korotyaev, C. omissus Fall and C. querceti (Gyllenhal) by T. perfectus were not significantly different than of the target host C. obstrictus. Although C. typhae (Herbst), C. pallidactylus (Marsham), C. americanus Buchanan, C. neglectus Blatchely and Ceutorhynchus sp. nr. nodipennis were parasitised by T. perfectus, the levels of parasitism were significantly lower on these species than on C. obstrictus. Ceutorhynchus peyerimhoffi Hustache, C. erysimi (Fabricius), C. alliariae H. Brisout, C. roberti Gyllenhal, Mogulones borraginis (Fabricius), Mononychus vulpeculus (Fabricius) and the leaf-mining fly Scaptomyza flava (Fallen) were not attacked. Ecological host range surveys in Europe corroborated the prediction that T. perfectus would attack C. cardariae at similar rates to C. obstrictus. In North America, the recent discovery of T. perfectus in a C. omissus population suggests that laboratory findings predicting that C. omissus is a preferred host may be the case in the field. We found that T. perfectus attacks larvae of some Ceutorhynchus spp. feeding on Brassicaceae and does not attack species outside of that host range. Thus, the parasitoid can be defined as narrowly oligophagous. These results demonstrate the value of ecological host range studies in the area of origin to validate hypotheses generated through laboratory host range experiments.

Abstract

Abstract

The natural history of introduced species is often unclear due to a lack of historical records. Even when historical information is readily available, important factors of the invasions such as genetic bottlenecks, hybridization, historical relationships among populations and adaptive changes are left unknown. In this study, we developed a set of nuclear, simple sequence repeat markers and used these to characterize the genetic diversity and population structure among native (Eurasian) and non-native (North and South American) populations of Centaurea solstitialis L., (yellow starthistle). We used these data to test hypotheses about the invasion pathways of the species that were based on historical and geographical records, and we make inferences about historical relationships among populations and demographic processes following invasion. We confirm that the center of diversity and the native range of the species is likely the eastern Mediterranean region in the vicinity of Turkey. From this region, the species likely proceeded to colonize other parts of Europe and Asia via a slow, stepwise range expansion. Spanish populations were the primary source of seed to invade South America via human-mediated events, as was evident from historical records, but populations from the eastern Mediterranean region were also important. North American populations were largely derived from South America, but had secondary contributors. We suggest that the introduction history of non-native populations from disparate parts of the native range have allowed not just one, but multiple opportunities first in South America then again in North America for the creation of novel genotypes via intraspecific hybridization. We propose that multiple intraspecific hybridization events may have created especially potent conditions for the selection of a noxious invader, and may explain differences in genetic patterns among North and South America populations, inferred differences in demographic processes, as well as morphological differences previously reported from common garden experiments.

Abstract

Abstract

In the apple plantations, codling moth (Cydia pomonella L.) is one of the most important pests in Romania, which causes large and constant damages, far above the economic threshold of damage, frequently being about 25-50%, and sometimes even larger. The main aim of this study was the control of codling moth in accordance with the special evolution of its biology and ecology related to local biotope conditions. The purpose of this paper was to underline the dynamics of species evolution of Cydia pomonella L., due to the application of some practical and technical measures meant to improve integrated control system. Latest researches regarding control of codling moth, have revealed some changes in pest biology and also the efficacy of new generation of active substances. During the period 2009-2011, at S. C. D. P. (Station for Research and Development of Fruit-Growing), Iasi, there have been developed experimentations regarding the control of codling moth within the program of integrated control of pathogens and pests from apple orchards by using plant protection active substances which were recently introduced in the phytosanitary treatments. The biological cycle of the species Cydia pomonella L. in the weather conditions of Iasi County, presented two generations/year, a complete generation and a second incomplete one. During the three years of study, the codling moth has recorded three curves of the flight during the vegetative season (two for the first generation and one for the second generation) and with respect to control, this was realized with plant protection substances of latest generation which recorded a very good efficiency. By using these active substances it aimed to improve fruit quality and environmental protection.

Abstract

Differences in morphological or ecological traits expressed by exotic species between their native and non-native ranges are often interpreted as evidence for adaptation to new conditions in the non-native ranges. In turn this adaptation is often hypothesized to contribute to the successful invasion of these species. There is good evidence for rapid evolution by many exotic invasives, but the extent to which these evolutionary changes actually drive invasiveness is unclear. One approach to resolving the relationship between adaptive responses and successful invasion is to compare traits between populations from the native and non-native ranges for both exotic invaders and congeners that are exotic but not invasive. We compared a suite of morphological traits that are commonly tested in the literature in the context of invasion for three very closely related species of Centaurea, all of which are sympatric in the same native and non-native ranges in Europe and North America. Of these, C. solstitialis is highly invasive whereas C. calcitrapa and C. sulphurea are not. For all three species, plants from non-native populations showed similar shifts in key traits that have been identified in other studies as important putative adaptive responses to post-introduction invasion. For example, for all three species plants from populations in non-native ranges were (i) larger and (ii) produced seeds that germinated at higher rates. In fact, the non-invasive C. calcitrapa showed the strongest trait shift between ranges. Centaurea solstitialis was the only species for which plants from the non-native range increased allocation to defensive spines, and allocated proportionally less resources to reproduction, patterns contrary to what would be predicted by theory and other empirical studies to enhance invasion. Our results suggest caution when interpreting the commonly observed increase in size and reproductive capacity as factors that cause exotics to become invaders.