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Biological invasions threaten biodiversity worldwide, especially on tropical Islands such as Reunion Island where the largest area of intact vegetation occurs within the Mascarene's archipelago. With the impetus of the local government, we initiated a partnership between scientists and managers to address the management of invasive alien plant species on the island. This study aims to map biodiversity priority areas and to prioritise alien plant clearing on the island. We first established a conceptual framework shared by all partners. We then combined all existing data on habitats, both threatened and endemic species, and the distribution of alien plant species using expert knowledge where necessary. We developed a decision-making process using Zonation, a conservation planning tool, to identify biodiversity conservation priorities. Conservation priority areas were selected with the aim of maximising biodiversity levels in areas slightly invaded. The criteria used to identify priority areas for the control of alien plant species included clearing costs, accessibility, and the history of previous management programmes. A total of 60,303 ha were identified as conservation priority areas, 30% of which are not considered to be invaded. Based on biodiversity and implementation issues, we identified plant clearing priority areas that highlighted invasion fronts. Priorities identified helped to spatially re-align existing clearing operations. This study, conducted jointly by managers, decision-makers and scientists has allowed the identification of priority areas concerning the control of alien plants and their implementation thereafter. The engagement of stakeholders at each relevant step of a conservation project is essential in guiding decision making, and the future implementation.

International audience; An increasing number of invasive fruit fly pests are colonizing new grounds. With this study, we aimed to uncover the invasion pathways of the oriental fruit fly, Bactrocera dorsalis into the islands of the Indian Ocean. By using genome-wide SNP data and a multipronged approach consisting of PCA, ancestry analysis, phylogenetic inference, and kinship networks, we were able to resolve two independent invasion pathways. A western invasion pathway involved the stepping-stone migration of B. dorsalis from the east African coast into the Comoros, along Mayotte and into Madagascar with a decreasing genetic diversity. The Mascarene islands (Reunion and Mauritius), on the contrary, were colonized directly from Asia and formed a distinct cluster. The low nucleotide diversity suggests that only a few genotypes invaded the Mascarenes. The presence of many long runs of homozygosity (ROH) in the introduced populations is indicative of population bottlenecks, with evidence of a more severe bottleneck for populations along the western migration pathway than on the Mascarene islands. More strict phytosanitary regulations are recommended in order to prevent the further spread of B. dorsalis.

Insects harbor a diversity of microbes that are known to affect their host's response to biotic and abiotic stressors. This is important in the context of climate change and human-caused habitat alterations, during which drastic changes are so rapid that organisms have little time to adapt. Symbionts often accompany invading species, and might play a role in the success or failure of insect invasions. Yet, few studies have examined the evolutionary dynamics and role of gut-associated symbionts at different stages of an insect invasion. We focus on the family Tephritidae (Diptera), which comprises many invasive pest species, and examine how gut-associated bacteria might influence their invasion process based on literature review. Based on our review, we first summarize the prevalence and diversity of gut-associated bacteria harbored by tephritid species. Next, we highlight how those gut communities may influence the fitness of invasive species during the colonization process. We conclude that gut-associated symbionts are highly flexible, and can respond rapidly to changes in biotic and abiotic factors and compensate for limited adaptive capacities of their hosts to counteract these stressors, through changes in the taxonomic composition or prevalence of the community. However, bacteria of Enterobacteriaceae are dominant as well as constitute constant and stable populations in fruit fly gut under different environmental stressors. Our review reveals that this family represents a key bacteria group in all studied tephritid species. This review indicates that knowledge on symbiont–insect interactions is crucial for understanding the success of insect invasion and it should be considered in risk analyses, impact modeling and optimizing invasive pest management.

1. Theory in ecology and evolution often relies on the analysis of invasion processes, and general approaches exist to understand the early stages of an invasion. However, predicting the long-term transformations of communities following an invasion remains a challenging endeavour. 2. We propose a general analytical method that uses both resident community and invader dynamical features to predict whether an invasion causes large long-term impacts on the invaded community. 3. This approach reveals a direction in which classic invasion analysis, based on initial invasion growth rate, can be extended. Indeed, we explain how the density dependence of invasion growth, if properly defined, synthetically encodes the long-term biotic transformations caused by an invasion, and therefore predicts its ultimate outcome. This approach further clarifies how the density dependence of the invasion growth rate is as much a property of the invading population as it is one of the invaded community. 4. Our theory applies to any stable community model, and directs us towards new questions that may enrich the toolset of invasion analysis, and suggests that indirect interactions and dynamical stability are key determinants of invasion outcomes. Funding Agencies|H2020 European Research Council [666971]; Agence Nationale de la RechercheFrench National Research Agency (ANR)European Commission [ANR-10-LABX-41]; VetenskapsradetSwedish Research Council [VR-2017-05245]; Irish Research CouncilIrish Research Council for Science, Engineering and Technology [IRCLA/2017/186]

Outbreaks of whitefly, Bemisia tabaci species in East and Central Africa, have become increasingly prevalent during the previous 25 years and are responsible for driving the spread of plant-virus diseases, such as cassava mosaic disease and cassava brown steak disease. Epidemics of these diseases have expanded their ranges over the same period, spreading from Uganda into other sub-Saharan African countries. It was hypothesised that a highly abundant ‘invader’ population of B. tabaci was responsible for spreading these diseases from Uganda to neighbouring countries and potentially hybridising with the resident cassava B. tabaci populations. Here, we test this hypothesis by investigating the molecular identities of the highly abundant cassava B. tabaci populations from their supposed origin in Uganda, to the northern, central, eastern and coastal regions of Tanzania. Partial mitochondrial cytochrome oxidase I (mtCOI) barcoding sequences and nuclear microsatellite markers were used to analyse the population genetic diversity and structure of 2734 B. tabaci collected from both countries and in different agroecological zones. The results revealed that: (i) the putative SSA1 species is structured according to countries, so differ between them. (ii) Restricted gene flow occurred between SSA1–SG3 and both other SSA1 subgroups (SG1 and SG2), even in sympatry, demonstrating strong barriers to hybridization between those genotypes. (iii) Not only B. tabaci SSA1-(SG1 and SG2) was found in highly abundant (outbreak) numbers, but B. tabaci SSA1-SG3 and the Indian Ocean (IO) species were also recorded in high numbers in several sites in Tanzania. (iv) The SSA1-(SG1 and SG2) species was distributed in both countries, but in Tanzania, the B. tabaci IO and SSA1–SG3 species predominated. These data confirm that multiple, local Tanzanian B. tabaci species produce highly abundant populations, independent of the spread of the putative invasive B. tabaci SSA1-(SG1 and SG2) populations.

International audience; Ambrosia trifida L. (giant ragweed, Asteraceae) is native to the North American continent and was introduced into Europe and Asia at the end of the 19th century. In its native range, this tall annual species is common in riparian and ruderal habitats and is also a major weed in annual cropping systems. For nearly a century, A. trifida has also been of great concern in the U.S. for its highly allergenic pollen, necessitating targeted control measures to reduce its impact on human populations. Based on the distribution of A. trifida in North America and in its introduced range, riparian systems in the rest of the world may be particularly at risk to invasion, with potential negative consequences for their biodiversity. Currently, A. trifida has invaded Asia more widely than Europe, likely due to the more favourable local conditions in Asia. Throughout its introduced range, A. trifida is host to a limited number of invertebrates and pathogens and only a few biological agents are available for its control. The main impacts of A. trifida at a global level are on crop yield and human health, resulting in significant socio-economic impacts. The success of A. trifida invasion in areas in which it has been introduced is still unclear, but climate change may increase climate suitability, increasing the potential for A. trifida to spread. While effective management in cultivated fields seems potentially possible, the development and control of A. trifida in natural riparian habitats is of great concern due to the difficulty of management in these areas.

International audience; The aim of our review was to examine the cases of Tephritidae invasions across island systems in order to determine whether they follow a hierarchical mode of invasion. We reviewed the literature on factors and mechanisms driving invasion sequences in Pacific and Southwest Indian Ocean islands and gathered every record of invasion by a polyphagous tephritid in island groups. From invasion date or period, we defined an invasion link when a new fruit fly established on an island where another polyphagous tephritid is already resident (that was indigenous or a previous invader). Across surveyed islands, we documented 67 invasion links, involving 24 tephritid species. All invasion links were directional, i.e., they involved a series of invasions by invaders that were closely related to a resident species but were increasingly more competitive. These sequential establishments of species are driven by interspecific competition between resident and exotic species but are also influenced by history, routes, and flows of commercial exchanges and the bridgehead effect. This information should be used to improve biosecurity measures. Interactions between trade flow, invasive routes, and the presence of invasive and resident species should be integrated into large-scale studies.

We developed a correlative model at high resolution for predicting the distribution of one of the main vectors of Crimean-Congo haemorrhagic fever virus (CCHFV), Hyalomma marginatum, in a recently colonised area, namely southern France. About 931 H. marginatum adult ticks were sampled on horses from 2016 to 2019 and 2021 in 14 southern French departments, which resulted in the first H. marginatum detection map on a large portion of the national territory. Such updated presence/absence data, as well as the mean number of H. marginatum per examined animal (mean parasitic load) as a proxy of tick abundance, were correlated to multiple parameters describing the climate and habitats characterising each collection site, as well as movements of horses as possible factors influencing tick exposure. In southern France, H. marginatum was likely detected in areas characterised by year-long warm temperatures and low precipitation, especially in summer and mostly concentrated in autumn, as well as moderate annual humidity, compared to other sampled areas. It confirms that even in newly invaded areas this tick remains exclusively Mediterranean and cannot expand outside this climatic range. Regarding the environment, a predominance of open natural habitats, such as sclerophyllous vegetated and sparsely vegetated areas, were also identified as a favourable factor, in opposition to urban or peri-urban and humid habitats, such as continuous urban areas and inland marshes, respectively, which were revealed to be unsuitable. Based on this model, we predicted the areas currently suitable for the establishment of the tick H. marginatum in the South of France, with relatively good accuracy using internal (AUC = 0.66) and external validation methods (AUC = 0.76 and 0.83). Concerning tick abundance, some correlative relationships were similar to the occurrence model, as well as the type of horse movements being highlighted as an important factor explaining mean parasitic load. However, the limitations of estimating and modelling H. marginatum abundance in a correlative model are discussed.

Most of the West African forests have disappeared or have been deeply fragmented. This deforestation dynamic is still ongoing under a strong demographic pressure, forests being mostly replaced by agricultural lands. On the other hand, some reforestation projects are also undertaken, in particular by planting non-native species like Cedrela odorata. To our knowledge, this study is the first to investigate the causes and consequences of Cedrela odorata spread in West African natural forests. We studied a 400ha area of natural forest where 100ha of permanent plots have been affected by a major fire in 1983. Within these permanent plots, 21,444 trees were mapped, botanically determined and their diameters at breast height were measured in 2018. Using a bayesian hierarchical framework, we modelled the causes of the spread of Cedrela odorata in the studied plots, and its consequences on aboveground biomass and tree community diversity. Regarding the causes, the occurrence of Cedrela odorata is significantly linked to the fire occurence 25 years ago, to the proximity of the forest edge and to the presence of hydromorphic soils. Regarding the consequences, Cedrela odorata invasion doesn't have any significant impact on the above-ground biomass but has a strong negative effect on the tree community diversity, as far as decreasing Simpson diversity in Hill numbers from 27 equivalent species in slightly invaded plots to 2 equivalent species in largely invaded plots. Our results highlight the long-lasting impacts of human disturbance (fire, Cedrela odorata introduction) on forest ecosystems and the need to use local species for ongoing reforestation plans in West African semi-deciduous forests.

Eucalyptus is one of the most planted tree genera across the world, but is heavily challenged by invasive insect pests originating from the native range of these trees. The rate of introduction of non-native Eucalyptus-feeding insects has increased globally, including in sub-Saharan Africa where Eucalyptus trees have an important socio-economic role. In this study, we mapped the distribution and examined the genetic diversity of non-native Eucalyptus insect pests in 14 countries across sub-Saharan Africa. We focused on five foliage-feeding insect pests of Eucalyptus which are known to be present in the region, namely the bluegum chalcid wasp, Leptocybe invasa; the redgum lerp psyllid, Glycaspis brimblecombei; the bronze bug, Thaumastocoris peregrinus; the Eucalyptus weevil, Gonipterus sp.n.2; and the Eucalyptus gall wasp, Ophelimus maskelli. Insect samples were collected through structured surveys and small-scale sampling which were both combined with published literature to determine the distribution of these insect pests. Genetic diversity of each of these insect pests was estimated/assessed based on mitochondrial cytochrome oxidase I (COI) or cytochrome b (Cyt b) sequence data. Except O. maskelli, which is a relatively recent arrival, the other insect pests were found broadly distributed across the sampled countries, with first reports in many countries. Analysis of genetic diversity confirmed a common origin of geographically distant populations for G. brimblecombei and O. maskelli, moderate diversity for T. peregrinus and Gonipterus sp.n.2 and at least two distinct lineages for L. invasa. Two divergent haplogroups of L. invasa, with overlapping geographic range were confirmed in Ghana, Malawi, Sierra Leone, South Africa and Zimbabwe. Compared to published literature, new haplotypes were detected for T. peregrinus, Gonipterus sp.n.2 and L. invasa, suggesting multiple introduction of those pests in the region. Results of this study will have implications for quarantine, management and future research of Eucalyptus insect pests in the region and beyond.

The fall armyworm, Spodoptera frugiperda (J.E. Smith) is native to the Americas and a major pest of corn and several other crops of economic importance. The species has characteristics that make it of particular concern as an invasive pest, including broad host range, long-distance migration behavior, and a propensity for field-evolved pesticide resistance. The discovery of fall armyworm in western Africa in 2016 was followed by what was apparently a remarkably rapid spread throughout sub-Saharan Africa by 2018, causing economic damage estimated in the tens of billions USD and threatening the food security of the continent. Understanding the history of the fall armyworm invasion of Africa and the genetic composition of the African populations is critical to assessing the risk posed to different crop types, the development of effective mitigation strategies, and to make Africa less vulnerable to future invasions of migratory moth pests. This paper tested and expanded on previous studies by combining data from 22 sub-Saharan nations during the period from 2016 to 2019. The results support initial descriptions of the fall armyworm invasion, including the near absence of the strain that prefers rice, millet, and pasture grasses, while providing additional evidence that the magnitude and extent of FAW natural migration on the continent is more limited than expected. The results also show that a second entry of fall armyworm likely occurred in western Africa from a source different than that of the original introduction. These findings indicate that western Africa continues to be at high risk of future introductions of FAW, which could complicate mitigation efforts.

Understanding the major mechanisms that allow an alien species to become invasive is crucial for limiting the impact of such species, and individual immunity seems to be a crucial trait for their large range colonization when introduced to a new area. Indeed, a high resistance to pathogens and parasites could favour the establishment and proliferation of an alien species in a newly colonized region. A striking example of recent successful invasion is represented by the Asian hornet, Vespa velutina nigrithorax, which has invaded Western Europe threatening bees and beekeeping activities. Investigating the biology of this species is fundamental to understand how V. velutina nigrithorax has become invasive in Europe and this knowledge could be crucial for limiting its impact. Here, by performing bacterial challenge bioassays, we compare the immune competence of different castes and sex of a population of the invasive Asian hornet, V. velutina nigrithorax, and of the native European hornet, V. crabro. Our results demonstrate that the two species differ in their immunocompetence with respect to caste: a higher level of immunocompetence was found in the reproductive females of the Asian hornet which were resistant to bacterial challenge when compared to workers and males of both species and to reproductive females of the native European hornet. The high pathogen resistance in reproductive females of the Asian hornet, might therefore represent a key factor contributing to the ecological success and spread of this invader.

Simple Summary Hornets of the genus Vespa and honey bees are the main characters of a coevolutionary arms race that is made evident by the conspicuous number of reciprocal adaptations evolved by both predator and prey. Through this ancient process predatory hornets and honey bees seem to have reached a fragile balance, which is lost when alien hornet species are accidentally introduced into new geographic areas. This is the case of Asian hornet species, such as Vespa velutina and Vespa mandarinia, which have invaded Europe and North America in recent decades, with a heavy impact on Western honey bees and commercial beekeeping. Here, we provide a comprehensive review of the existing studies that have investigated the interactions between hornets and honey bees throughout the world, highlighting the complexity of the specialized strategies adopted by Asian honey bees and their sympatric predators and the relative lack of coevolution and effective defenses of Western honey bees against invasive hornets. Abstract Hornets and honey bees have a long history of coevolution resulting in a plethora of captivating adaptations and counteradaptations between predator and prey. From simple physiological mechanisms to complex behavioral strategies, some Vespa hornets have specialized in hunting honey bees, while the latter have put in place effective defenses to counteract their attack. Both hornets and honey bees have evolved the ability to detect the odors and the pheromones emitted by the other to locate the prey or to spot foraging predators. Hornets often rely on their bigger size, heavily armored body and destructive attacks, while honey bees differentiated collective defense responses finely coordinated to deter or kill the hornet menace. However, when new species of hornets and honey bees come into contact, the absence of coevolution can have a heavy impact on the defenseless bees. The evolutionary arms race between hornets and honey bees provides not only compelling examples of adaptations and counteradaptations between predator and prey, but could also represent a starting point for the development of effective and sustainable strategies to protect honey bees and beekeeping activities and to control invasive alien species of hornets.

International audience; The largest area of intact vegetation in the Mascarene's archipelago is found on Reunion Island, but the remaining natural areas are under threats. Biological invasions are one of the main threats to biodiversity loss on this island and globally worldwide. This study aimed to quantify invasion degree by alien plants species in Reunion Island. This work was possible thanks to a large partnership between researchers and managers. All existing spatial data on invasion pattern were combined and completed by expert knowledge to develop the first 250 x 250 m map of invasion degree at the island scale. To fill the gaps where no field survey data or expert knowledge was available, we used a Random Forest model using nine climatic, landscape and anthropogenic variables. This model also provides a preliminary assessment of drivers of invasion at Reunion Island. Results showed that 85% of the extant native vegetation was invaded in different proportions; 38% are slightly invaded, 26% moderately invaded and 22% very heavily invaded. Despite the high levels of invasion in some places, more than 50% of the extant vegetation is not invaded or slightly invaded. Most of the invaded areas are located in the lowland and in the leeward coast although alien plants invade all types of vegetation from the coast to the top of the island. These results highlight a clear increase in the distribution of alien species over time. This study constitutes a key first step for about the ongoing prioritisation of management interventions on Reunion Island.

International audience; Aims. Invasive species, which recently expanded, may help understand how climatic niche can shift at the time scale of the current global change. Here, we address the climatic niche shift of an invasive shrub (common gorse, Ulex europaeus) at the world and regional scales to assess how it could contribute to increasing invasibility. Methods. Based on a 28,187 occurrences database, we used a combination of 9 species distribution models (SDM) to assess regional climatic niche from both the native range (Western Europe) and the introduced range in different parts of the world (North-West America, South America, North Europe, Australia and New Zealand). Important Findings. Despite being restricted to annual mean temperature between 4 and 22 °C, as well as annual precipitation higher than 300 mm / yr, the range of bioclimatic conditions suitable for gorse was very large. Based on a native vs introduced SDM comparison, we highlighted a niche expansion in North-West America, South America and to a lesser degree in Australia, while a niche displacement was assessed in North Europe. These niche changes induced an increase in potential occupied areas by gorse by 49, 111, 202 and 283% in Australia, North Europe, North-West America and South America, respectively. On the contrary, we found no evidence of niche change in New Zealand, which presents similar climatic condition to the native environment (Western Europe). This study highlights how niche expansion and displacement of gorse might increase invasibility at regional scale. The change in gorse niche toward new climatic conditions may result from adaptive plasticity or genetic evolution and may explain why it has such a high level of invasibility. Taking into account the possibility of a niche shift is crucial to improve invasive plants management and control.; Objectifs : Les espèces envahissantes peuvent aider à comprendre comment la niche climatique peut évoluer à une échelle temporelle de l'ordre de celle du changement global en cours. La prise en compte de cette possibilité d'un changement de niche est cruciale pour améliorer la gestion et le contrôle des plantes envahissantes. Ici, nous abordons le changement de niche climatique d'un arbuste envahissant (l'ajonc Ulex europaeus) à l'échelle mondiale et régionale.Méthodes : Sur la base d'une base de données de 28 187 occurrences, nous avons utilisé une combinaison de 9 modèles de distribution d'espèces (SDM) pour évaluer la niche climatique régionale de la zone native native (Europe occidentale) et des zones introduites (Amérique du Nord-Ouest, Amérique du Sud, Europe du Nord, Australie et Nouvelle-Zélande).Principaux résultats : La gamme des conditions bioclimatiques adaptées aux ajoncs est très large, bien qu'elle soit limitée par une température annuelle moyenne comprise entre 4 et 22 °C, et des précipitations annuelles supérieures à 300 mm an. Nous avons mis en évidence plusieurs changemenbts de niche : une expansion de niche en Amérique du Nord-Ouest, en Amérique du Sud et dans une moindre mesure en Australie, un déplacement de niche en Europe du Nord. Ces changements de niche ont entraîné une augmentation de 49, 111, 202 et 283 % des zones potentiellement colonisables par l'ajonc en Australie, Europe du Nord, Amérique du Nord et Amérique du Sud, respectivement. Nous n'avons trouvé aucun indice de changement de niche en Nouvelle-Zélande, pays qui présente des conditions climatiques similaires à celles de la zone native. Le changement de niche des ajoncs vers de nouvelles conditions climatiques peut résulter de la plasticité adaptative ou de l'évolution génétique de l'espèce, et contribue à expliquer pourquoi elle est si invasive.

Plusieurs études et des observations de terrain ont confirmé que les renouées asiatiques sont sensibles à la compétition pour la lumière. C’est en partant de ce constat que différentes techniques de génie végétal ont été mises au point pour contrôler le développement des renouées et restaurer une communauté végétale diversifiée dans les zones envahies. Pour augmenter leur taux de succès, ces méthodes alternatives doivent cependant être associées parfois à des prétraitements et obligatoirement à des mesures d’accompagnement.

International audience; The land flatworm Platydemus manokwari (Platyhelminthes, Geoplanidae) is recorded from the islands of Guadeloupe, Martinique, and Saint Martin in the Caribbean arc. Photographs and records were obtained mainly from citizen science and ranged from the end of 2018 to February 2021; several specimens were deposited in the collections of the Muséum National d'Histoire Naturelle in Paris, France. Thirty records were from Guadeloupe, but only one from Martinique and from Saint Martin, respectively. The COI sequences of 3 specimens from Guadeloupe show that they belong to the World haplotype also found in many countries. We also report P. manokwari from Fort Myers, Florida, USA, with molecular characterization, which was also the World haplotype. This is the first published record of P. manokwari for Guadeloupe, Martinique and Saint Martin and the second for islands in the Caribbean, after Puerto Rico.; Le Plathelminthe terrestre Platydemus manokwari (Plathelminthes, Geoplanidae) est signalé dans les îles de Guadeloupe, Martinique et Saint Martin dans l'arc caraïbe. Les photographies et les documents ont été obtenus principalement grâce aux sciences participatives et datent de la fin de 2018 à février 2021; plusieurs spécimens ont été déposés dans les collections du Muséum National d'Histoire Naturelle à Paris, France. Trente signalements provenaient de Guadeloupe, mais un seul a été reçu respectivement de Martinique et de Saint Martin. Les séquences COI de 3 spécimens de Guadeloupe montrent qu'ils appartiennent à l'haplotype mondial également présent dans de nombreux pays. Nous rapportons également P. manokwari de Fort Myers, Floride, USA, avec sa caractérisation moléculaire, qui était également l'haplotype mondial. Il s'agit du premier signalement de P. manokwari publié pour la Guadeloupe, la Martinique et Saint Martin et le deuxième pour les îles des Caraïbes, après Porto Rico.

Les invasions biologiques menacent la conservation de la biodiversité mondiale, notamment en milieu insulaire comme La Réunion où se trouve les plus grandes reliques de végétation naturelle de l'archipel des Mascareignes. Sous l'impulsion du département de La Réunion, un partenariat a été initié réunissant gestionnaires, décideurs et scientifiques afin de mieux coordonner la lutte contre les espèces végétales envahissantes sur le territoire. Cette thèse, qui s'inscrit dans ce partenariat, a pour objectif principal d'améliorer les connaissances quant à l'état de conservation des milieux naturels afin de prioriser spatialement les actions de lutte contre les plantes exotiques. La thèse comporte trois axes de recherche : 1) la quantification du degré d'invasion à une échelle régionale comme outil d'aide à la décision ; 2) la quantification du degré d'invasion à une échelle locale comme outil d'aide à la gestion ; et 3) la priorisation spatiale des actions de lutte à partir de critères biologiques et opérationnels. Elle se termine sur une réflexion de l'approche transdisciplinaire utilisée à l'interface entre science et gestion. Le degré d'invasion des milieux naturels a été quantifié à deux échelles différentes : régionale (La Réunion) et locale (massifs de Mare Longue et du Volcan). La quantification du degré d'invasion à l'échelle régionale a sollicité en plus des données d'inventaire obtenues grâce au large effort partenarial mis en place ; l'intervention d'experts et le recours à la modélisation. Ainsi les résultats ont montré que 85% de la végétation indigène était envahie dans des proportions différentes, notons que plus de 50% de la végétation reste tout de même peu à pas envahie. A l'échelle locale, un protocole terrain a été mis en place permettant de quantifier le degré d'invasion des trois strates structurantes de l'habitat ; à savoir les strates herbacées, arbustives et arborées. Au travers d'analyses de cluster et de krigeage, une nouvelle cartographie du degré d'invasion à une échelle plus fine (25 x 25 m) a pu être réalisée sur les massifs étudiés. Les résultats ont montré une strate herbacée particulièrement envahie. En parallèle, les enjeux de conservation en termes de biodiversité ainsi que les priorités de gestion des plantes exotiques ont pu être cartographiés à l'échelle de l'ile. Au travers d'une vingtaine d'ateliers de travail avec l'ensemble des partenaires, nous avons pu co-développer une approche partagée par tous. De par l'utilisation de Zonation, un logiciel d'aide à la décision ainsi qu'en respectant les concepts clés de la planification de la conservation, l'approche mise en place a bénéficiée des apports de la science. L'inclusion de critères opérationnels, tels que l'accessibilité de la zone ou l'historique des chantiers, a constitué un important apport de la gestion. Ainsi, 60 303 ha ont été identifié comme enjeux de conservation et des priorités de gestion des plantes exotiques à l'échelle de l'île ont pu être définies, mettant en avant la gestion des fronts d'invasion.

Invasive fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), is a species native to the Americas which has spread to Africa in 2016. This insect has been reported in Benin as a major pest of maize causing important economic losses and putting at risk food and nutritional security. This study evaluated the damage caused by this pest to maize in different cropping system and management practices. It also assessed predatory ants presence and diversity and their potential in controlling FAW. Results showed that 50% of farmers grow maize in a mixed cropping systems in association with sorghum, cassava and cowpea and also used biopesticides. FAW larval population and damage in maize fields varied accros villages. Surprinsingly FAW larval population was higher in maize field sprayed with insecticides than untreated field. Seven species of predatory ants were recorded in maize field. Ants' population was higher in untreated field (1043 ants per hectare) than treated field (806 ants per hectare). In the laboratory, ants species exhibits great predatory potential. Further studies are needed to discuss uses of ants in FAW management in Benin.

Biological control can be an effective conservation strategy to manage invasive species when other conventional methods cannot be implemented. Estimating the benefits of biological control for the conservation of native biodiversity remains a challenging task. Following the introduction of a defoliating sawfly, Cibdela janthina, for biological control of invasive giant bramble, Rubus alceifolius, on Reunion Island (Mascarene Archipelago), we monitored the consequent change in R. alceifolius cover as well as species richness and cover of non-native species and native species within a set of patches along an altitudinal gradient in the National Park of Reunion Island. There was an increase in native species richness and cover together with a decrease in R. alceifolius cover, showing that biological control positively impacted the native plant communities. The effectiveness of C. janthina was influenced by the altitudinal range, the surface area of the patches and the location of each patch, i.e forest edge or forest matrix. We discuss the extent to which the use of biological control within an integrated approach can optimize benefits for biodiversity conservation in the short to medium term by selecting complementary and standardised protocols.

Ce rapport est disponible dans : BioRxiv. This article has been peer-reviewed and recommended by Peer Community in Evolutionary Biology; Experiments comparing native to introduced populations or distinct introduced populations to each other show that phenotypic evolution is common and often involves a suit of interacting phenotypic traits. We define such sets of traits that evolve in concert and contribute to the success of invasive populations as an ‘invasion syndrome’. The invasive Harlequin ladybird Harmonia axyridis displays such an invasion syndrome with, for instance, females from invasive populations being larger and heavier than individuals from native populations, allocating more resources to reproduction, and spreading reproduction over a longer lifespan. Invasion syndromes could emerge due to selection acting jointly and directly on a multitude of traits, or due to selection on one or a few key traits that drive correlated indirect responses in other traits. Here, we investigated the degree to which the H. axyridis invasion syndrome would emerge in response to artificial selection on either female body mass or on age at first reproduction, two traits involved in their invasion syndrome. To further explore the interaction between environmental context and evolutionary change in molding the phenotypic response, we phenotyped the individuals from the selection experiments in two environments, one with abundant food resources and one with limited resources. The two artificial selection experiments show that the number of traits showing a correlated response depends upon the trait undergoing direct selection. Artificial selection on female body mass resulted in few correlated responses and hence poorly reproduced the invasion syndrome. In contrast, artificial selection on age at first reproduction resulted in more widespread phenotypic changes, which nevertheless corresponded only partly to the invasion syndrome. The artificial selection experiments also revealed a large impact of diet on the traits, with effects dependent on the trait considered and the selection regime. Overall, our results indicate that direct selection on multiple traits was likely necessary in the evolution of the H. axyridis invasion syndrome. Furthermore, they show the strength of using artificial selection to identify the traits that are correlated in different selective contexts, which represents a crucial first step in understanding the evolution of complex phenotypic patterns, including invasion syndromes.

En raison de la destruction des reliques de forêt tropicale indigène aux Comores, il est très urgent de définir les priorités de conservation en particulier à La Grande Comore qui porte encore des larges zones de forêt tropicale en moyenne altitude. Comme dans la majorité des îles volcaniques, les forêts de l'archipel des Comores sont aussi exposées aux effets de changement globaux, en particulier les invasions biologiques. Or les données de base sur les espèces exotiques envahissantes et les niveaux d'invasion dans les différents habitats dans cet archipel sont très disparates. Dans cette étude, à l'échelle l'île de La Grande Comore nous proposons de répondre aux questions suivantes : (i) quelles sont les plantes les plus invasives en terme de recouvrement et de fréquence ? (ii) quel est le niveau d'invasion mesuré en terme de recouvrement par les espèces exotiques à l'échelle habitat et comment varie-t-il au sein des types d'habitats ? Les effets du gradient d'altitude et de l'occupation du sol à l'échelle transect et section influencent-ils le niveau d'invasion au sein des habitats ? Cette étude a été réalisée sur les plantes ligneuses exotiques. Les inventaires ont été conduits dans les forêts de basse et de moyenne altitude (entre 24 et 1100 m d'altitude), dans 44 transects de 150 - 300 m de longueur et de 8 - 10 m de largeur, dans lesquels tous les individus supérieurs à 1 m de hauteur ont été répertoriés. Les plantes exotiques dominantes au sein des forêts natives et perturbées sont Psidium cattleyanum, Clidemia hirta et Rubus rosifolius. La forêt de basse altitude (100 - 700 m) est quasiment remplacée par des peuplements d'espèces exotiques d'intérêt agronomique (Cocos nucifera, Mangifera indica, Syzygium aromaticum, etc). Les forêts de moyenne altitude (700 - 1100 m) à dominance des genres Nuxia, Ocotea, Tambourissa et Weinmannia sont généralement non envahies au sein de leurs canopées et très peu envahies en sous-bois. Ces résultats constituent un premier cas d'évaluation du degrés d'invasion des habitats à l'échelle de l'île. En améliorant les connaissances sur les menaces liées aux invasions par les plantes dans la région, ce travail apporte une contribution à l'amélioration des connaissances pour la gestion et la conservation des écosystèmes indigènes de l'archipel des Comores.

Thousands of plant species have been introduced, intentionally and accidentally, to South Africa from many parts of the world. Alien plants are now conspicuous features of many South African landscapes and hundreds of species have naturalised (i.e. reproduce regularly without human intervention), many of which are also invasive (i.e. have spread over long distances). There is no comprehensive inventory of alien, naturalised, and invasive plants for South Africa, but 327 plant taxa, most of which are invasive, are listed in national legislation. We collated records of 759 plant taxa in 126 families and 418 genera that have naturalised in natural and semi-natural ecosystems. Over half of these naturalised taxa are trees or shrubs, just under a tenth are in the families Fabaceae (73 taxa) and Asteraceae (64); genera with the most species are Eucalyptus, Acacia, and Opuntia. The southern African Plant Invaders Atlas (SAPIA) provides the best data for assessing the extent of invasions at the national scale. SAPIA data show that naturalised plants occur in 83% of quarter-degree grid cells in the country. While SAPIA data highlight general distribution patterns (high alien plant species richness in areas with high native plant species richness and around the main human settlements), an accurate, repeatable method for estimating the area invaded by plants is lacking. Introductions and dissemination of alien plants over more than three centuries, and invasions over at least 120 years (and especially in the last 50 years) have shaped the distribution of alien plants in South Africa. Distribution patterns of naturalised and invasive plants define four ecologically-meaningful clusters or “alien plant species assemblage zones”, each with signature alien plant taxa for which trait-environment interactions can be postulated as strong determinants of success. Some widespread invasive taxa occur in high frequencies across multiple zones; these taxa occur mainly in riparian zones and other azonal habitats, or depend on human-mediated disturbance, which weakens or overcomes the factors that determine specificity to any biogeographical region.

While most alien species fail to establish, some invade native communities and become widespread. Our understanding of invasion success is derived mainly from pairwise interactions between aliens and natives, while interactions among more than two species remain largely unexplored. Here, we experimentally tested whether and how a third plant species, either native or alien, affected the competitive outcomes between alien and native plants through its soil legacy. We first conditioned soil with one of ten species (six natives and four aliens) or without plants. We then grew on these 11 soils five aliens and five natives without competition, or with intra- or interspecific competition. We found that aliens were not more competitive than natives when grown on soil conditioned by other natives or on non-conditioned soil. However, aliens were more competitive than natives on soil conditioned by other aliens (that is, invasional meltdown). Soil conditioning did not change competitive outcomes by affecting the strength of competition between later plants. Instead, soil conditioned by aliens pushed competitive outcomes towards later aliens by affecting the growth of aliens less negatively than that of natives. Microbiome analysis verified this finding, as we showed that the soil-legacy effects of a species on later species were less negative when their fungal endophyte communities were less similar, and that fungal endophyte communities were less similar between two aliens than between aliens and natives. Our study reveals invasional meltdown in multispecies communities and identifies soil microorganisms as a driver of the invasion success of alien plants. published

The sugarcane aphid (SCA), Melanaphis Sacchari (Zehntner) (Hemiptera: Aphididae), has been considered an invasive pest of sugarcane in the continental United States since 1977. Then, in 2013, SCA abruptly became a serious pest of U.S. sorghum and is now a sorghum pest in 22 states across the continental United States. Changes in insect-associated microbial community composition are known to influence host-plant range in aphids. In this study, we assessed whether changes in microbiota composition may explain the SCA outbreak in U.S. sorghum. We characterized the SCA bacterial microbiota on sugarcane and grain sorghum in four U.S. states, using a metabarcoding approach. In addition, we used taxon-specific polymerase chain reaction (PCR) primers to screen for bacteria commonly reported in aphid species. As anticipated, all SCA harbored the primary aphid endosymbiont Buchnera aphidicola, an obligate mutualistic bacterial symbiont. Interestingly, none of the secondary symbionts, facultative bacteria typically associated with aphids (e.g., Arsenophonus, Hamiltonella, Regiella) were present in either the metabarcoding data or PCR screens (with the exception of Rickettsiella and Serratia, which were detected by metabarcoding at low abundances

BACKGROUND: Global and intensive use of insecticides has led to the emergence and rapid evolution of resistance in the major pest Bemisia tabaci (Gennadius). In La Reunion, an island of the South West Indian Ocean, three whitefly species coexist, two of which are predominant, the indigenous Indian Ocean (IO) and the invasive Middle East Asia Minor 1 (MEAM1) species. To assess the resistance level of both of these species to acetamiprid and pymetrozine, whitefly populations were sampled at 15 collection sites located all over the island in agroecosystems and natural areas, and tested using leaf‐dip bioassays. We also investigated the potential cost of resistance to acetamiprid by measuring six fitness‐related traits for MEAM1 populations that displayed different resistance levels. RESULTS: IO was mainly found in natural areas and was susceptible to both acetamiprid and pymetrozine. MEAM1 populations displayed evidence of high resistance to pymetrozine, whereas resistance to acetamiprid was more variable. No fitness‐related costs were associated with this resistance in MEAM1 populations. CONCLUSION: This is the first assessment of the susceptibility to insecticides for B. tabaci IO species. For the time being, no resistance to the tested insecticides has evolved in this species despite (i) its presence in agroecosystems and their surroundings, and (ii) its close proximity to, and possible hybridization with, the MEAM1 species. In contrast, with continuous selection pressure of insecticide treatments and in the absence of fitness cost to resistance, the invasive exotic species MEAM1 will continue to threaten agriculture in La Reunion. © 2019 Society of Chemical Industry.

Renouées envahissantes – Avant-propos

Globalisation has resulted in the movement of organisms outside their natural range, often with negative ecological and economic consequences. As cities are hubs of anthropogenic activities, with both highly transformed and disturbed environments, these areas are often the first point of entry for alien species. We compiled a global database of cities with more than one million inhabitants that data had on alien species occurrence. We then identified the most prominent pathways of introduction and vectors of spread of alien species in these cities. Most species were intentionally introduced to cities and were released or escaped from confinement. The majority of alien species then spread within cities through natural means (primarily unaided dispersal). Pathway prominence varied across the taxonomic groups of alien species: the most prominent pathway for plants and vertebrates was the escape pathway; for invertebrates the stowaway and contaminant pathways were most likely to facilitate introductions. For some organisms, pathway prominence varied with the geographical and climatic characteristics of the city. The characteristics of the cities also influenced the prominence of vectors of spread for alien species. Preventing the natural spread of alien species within cities, and into adjacent natural environments will be, at best, difficult. To prevent invasions, both the intentional and unintentional introduction of potentially harmful alien species to cities must be prevented. The pathways of introduction and vectors of spread identified here should be prioritised for management.

Modern food systems facilitate rapid dispersal of pests and pathogens through multiple pathways. The complexity of spread dynamics and data inadequacy make it challenging to model the phenomenon and also to prepare for emerging invasions. We present a generic framework to study the spatio-temporal spread of invasive species as a multi-scale propagation process over a time-varying network accounting for climate, biology, seasonal production, trade and demographic information. Machine learning techniques are used in a novel manner to capture model variability and analyse parameter sensitivity. We applied the framework to understand the spread of a devastating pest of tomato, Tuta absoluta , in South and Southeast Asia, a region at the frontier of its current range. Analysis with respect to historical invasion records suggests that even with modest self-mediated spread capabilities, the pest can quickly expand its range through domestic city-to-city vegetable trade. Our models forecast that within 5–7 years, Tuta absoluta will invade all major vegetable growing areas of mainland Southeast Asia assuming unmitigated spread. Monitoring high-consumption areas can help in early detection, and targeted interventions at major production areas can effectively reduce the rate of spread.

Parasitic plants have major impacts on host fitness. In the case of species of the holoparasitic Cuscuta genus, these impacts were shown to be particularly strong in some invasive alien plants, which has raised interest in the underlying mechanism. We hypothesized that Cuscuta parasitization may exert strong influence in shaping the diversity patterns in the host rhizosphere microbiome and that this may vary between native (coevolved) and alien (non-coevolved) plants. Here, we report on a field study exploring the effect of parasitization by Cuscuta australis on the rhizosphere microbiota (16S and ITS rDNA) of four plant species sharing and three plant species not sharing the parasite's native range. Despite a predominant role of the host species in shaping the rhizosphere microbiota, the role of host origin and of parasitization still appeared important in structuring microbial communities and their associated functions. Bacterial communities were more strongly influenced than fungi by the native range of the host plant, while fungi were slightly more affected than bacteria by parasitization. About 7% of bacterial phylotypes and 11% of fungal phylotypes were sensitive to Cuscuta parasitization. Parasitization also reduced the abundance of arbuscular mycorrhizal fungi by ca. 18% and of several genes related to plant growth promoting functions (e.g., nitrogen metabolism and quorum sensing). Both fungi and bacteria differentially responded to host parasitization depending on host origin, and the extent of these shifts suggests that they may have more dramatic consequences for alien than for native plants. published

Global identification and monitoring programs for invasive species aim to reduce imminent impacts to biodiversity, ecosystem services, agriculture, and human health. This study employs a 658 base pair fragment of the cytochrome c oxidase subunit I (COI) gene to identify and categorize clades of the banded grove snail (Cepaea nemoralis (Linnaeus, 1758)) from native (European) and introduced (North American) ranges using a maximum-likelihood phylogeny and haplotype networks. This work corroborates the existence of eight clades within C. nemoralis and further identified three clades that were common to both Europe and North America (A, D, O). Clades A and D were found in eastern Canada, Ontario (Canada), and British Columbia (Canada), whereas clade O was restricted to Ontario, possibly introduced from Poland or central Europe. Haplotype networks suggest clade A was introduced from northern Europe, whereas clade D was introduced from western and central Europe. Networks contained many private haplotypes and a lack of haplotype sharing, suggesting strong genetic structure in this system, possibly resulting from reduced dispersal in this species. This study describes the contemporary distribution of C. nemoralis in Canada and demonstrates the efficacy of DNA barcoding for monitoring the spread of invasive species, warranting its widespread adoption in management policies.

Asian knotweeds are invasive alien species that, due to their colonization capacity, rapid growth and dense foliage, have a significant impact on transport infrastructure. In addition to ecological and landscape issues, they involve safety requirements and require more extensive and complex management of the rights-of-way concerned. The spatial dynamics of knotweeds during the colonization of an area is still poorly understood. Many biotic and abiotic factors interfere with this dynamic. The management and maintenance methods of green dependencies also seem to play a role, either negatively by contributing to the dispersion of knotweeds, or positively by limiting their spatial development. Each type of infrastructure (road, rail or waterborne) has its own specificities and management constraints that influence the development of knotweeds.; Les renouées asiatiques sont des espèces exotiques envahissantes qui, du fait de leur capacité de colonisation, de leur croissance rapide et de la densité de leur feuillage, ont un impact marqué sur les infrastructures de transport. Au-delà des enjeux écologiques et paysagers, elles engagent notamment des impératifs de sécurité et nécessitent une gestion plus importante et plus complexe des emprises concernées. La dynamique spatiale des renouées lors de la colonisation d'un secteur est encore mal connue. De nombreux facteurs biotiques et abiotiques interfèrent dans cette dynamique. Les modes de gestion et d'entretien des dépendances vertes semblent également jouer un rôle, soit négatif en participant à la dispersion des renouées, soit positif en limitant leur développement spatial. Chaque type d'infrastructure (routière, ferroviaires ou navigables) possède ses propres spécificités et contraintes de gestion qui influent sur le développement des renouées.

Based on the competitive effects of native plants, bioengineering technics aim both at controlling the development of Asian knotweeds and at restoring a diverse plant community in invaded areas. These methods are appealing to more and more managers. This article deals with such methods mobilizing herbaceous or ligneous species, associated sometimes with pre-treatments but always with accompanying measures. After a synthesis on the ecological mechanisms involved, some technics specifically used to manage Asian knotweeds are described with a focus on riparian habitats. Finally the conclusion raises the question of the importance to share experiences in order to progress in the implementation of bioengineering methods to control knotweeds.; Basées sur l'utilisation des effets compétitifs des végétaux indigènes, les techniques de génie écologique visent à la fois le contrôle du développement des renouées asiatiques et la restauration d'une communauté végétale diversifiée dans les zones envahies. Ces méthodes alternatives intéressent de plus en plus de gestionnaires. Cet article s'intéresse ici à ces techniques, mobilisant des ligneux comme des herbacées, parfois associées à des prétraitements, mais obligatoirement à des mesures d'accompagnement. Après une synthèse des mécanismes écologiques sur lesquels elles reposent, une description de différentes méthodes est proposée, appliquées au cas des renouées asiatiques avec un focus particulier sur les milieux rivulaires. Enfin, la conclusion insiste sur la nécessité de partager et mutualiser les expériences afin de mieux comprendre les déterminants des succès et des échecs et avancer faire une meilleure mise en oeuvre de ces méthodes prometteuses.

International audience; Chez les renouées asiatiques (complexe Reynoutria), l’eau des rivières est un des principaux vecteurs naturels de dispersion des propagules sexuées (akènes ailés) et végétatives (fragments de tiges et de rhizomes). Les auteurs de cet article ont étudié la flottaison et la viabilité de ces trois types de propagules en conditions expérimentales pour différentes taches de renouées. De leurs études, il en ressort une grande variabilité entre les taches pour un grand nombre de traits impliqués dans la dispersion par le cours d’eau et la colonisation des berges.

Will the models soon help managers optimize their field intervention strategies to curb the Asian knotweed invasion? This is the challenge that Irstea researchers are taking up by proposing a new modelling tool that will eventually make it possible to describe the growth dynamics of a knotweed massif subjected to different mowing frequencies.; Les modèles permettront-ils prochainement d'aider les gestionnaires à optimiser leurs stratégies d'intervention sur le terrain pour freiner l'invasion par les renouées asiatiques ? C'est le pari que font les chercheurs d'Irstea en proposant un nouvel outil de modélisation qui permettra à terme de décrire la dynamique de croissance d'un massif de renouées soumis à différentes fréquences de fauche.

[Departement_IRSTEA]Territoires; International audience; Asian knotweeds are part of our landscapes. Introduced in France at the end of the XIXth century, they are now considered among the most threatening species for biodiversity worldwide. This article mobilizes ecologists, geographers, historians and managers in the aim to introduce what we know about these alien invasive species for this special issue. Their ecology is described as well as the history of their invasion, from the first introduction to the change in perception that came with their expansion out of gardens. This article also deals with their numerous impacts and their legal regulation in the French context. Management practices are also described and questioned in the light of a change in paradigm that could help to better take a fresh look at their management.; Les renouées asiatiques font partie de nos paysages. Introduites en France à la fin du dix-neuvième siècle, elles sont classées au niveau mondial parmi les espèces exotiques envahissantes les plus menaçantes pour la biodiversité. Cet article, mobilisant écologues, géographes, historiens et gestionnaires, vise à introduire les éléments de connaissance sur ces espèces, sujet de ce numéro spécial et objet de nombreuses recherches et essais de gestion en France, en Europe et dans le monde. Leur écologie est décrite et l'historique de leur introduction abordée, depuis la première importation jusqu'au changement de perception qui a accompagné leur développement incontrôlé en dehors des jardins. Cet article aborde leurs nombreux impacts et fait aussi le point sur la réglementation les concernant au niveau français. Les différentes pratiques de gestion sont également présentées, puis questionnées en conclusion, à la lumière d'un changement de paradigme qui peut apparaître nécessaire à la meilleure gestion de ce « problème ».

Foreword; Avant-propos

Dans l'expression "plantes invasives", le mot même d'invasif témoigne du mauvais accueil qu'elles peuvent recevoir. Pourtant, le regard sur ces étrangères évolue et elles finissent bien souvent par trouver leur place

Marnotte Pascal,Le Bourgeois Thomas. Porophyllum ruderale (Jacq.) Cass.. In: Le Journal de botanique, n°87, 2019. pp. 123-125.

One of the most recent research areas in the field of management of invasive species deals with the capacity of plants to produce some growth or development inhibiting compounds. This article describes the different issues, French research projects and methodological challenges raised by this approach.; Une des pistes de recherche les plus récentes concernant la gestion des espèces végétales invasives porte sur les capacités des plantes à produire des composés chimiques inhibant la croissance ou le développement d'autres végétaux. Cet article décrit les enjeux, quelques recherches menées en France et les défis posés par cette démarche.

Les renouées affectionnent les espaces remaniés par l’Homme et notamment les voies de transport (routes, voies ferrées, voies navigables). Leur colonisation présente alors un risque vis-à-vis de la sécurité de ces infrastructures et nécessite une gestion plus importante et plus complexe. Après avoir fait le point des différents impacts liés à la colonisation des renouées le long des voies de transport, cet article illustre comment les modes de gestion et d’entretien des emprises colonisées peuvent limiter ou favoriser la dynamique spatiale des renouées.

Asian knotweeds (Reynoutria spp.) have been a concern and fascination for many botanists and managers for a long time. Now one of the most problematic species complexes on the planet, knotweeds have spatial and temporal dynamics with subtleties of great heuristic and practical importance. This review paper proposes to provide a portrait of the processes and factors underlying knotweed invasions from the regional scale of young plant establishment to the regional scale. Like most other invasive plants, knotweed invasion dynamics consist of a hierarchy of processes occurring at interlocking scales. On the other hand, what differs from many other plants and is often ignored or underestimated is that knotweeds are clonal plants. It therefore appears that knotweeds probably have a much wider ecological niche than is commonly accepted. While their seeds generally have difficulty producing new individuals in the wild, knotweed fragments appear to have the potential to invade most temperate terrestrial habitats if they are given time to do so.; Les renouées asiatiques (Reynoutria spp.) préoccupent et fascinent nombre de botanistes et de gestionnaires depuis bien longtemps. Devenues l'un des complexes d'espèces les plus problématiques de la planète, les renouées présentent des dynamiques spatiales et temporelles présentant des subtilités ayant une grande importance heuristique et pratique. Cet article de synthèse propose de dresser le portrait des processus et des facteurs qui sous-tendent les invasions des renouées de l'échelle de l'établissement des jeunes plantes à l'échelle régionale. Comme la plupart des autres plantes invasives, les dynamiques d'invasion des renouées consistent en une hiérarchie de processus se produisant à des échelles emboitées les unes dans les autres. En revanche, ce qui diffère de nombreuses autres plantes et qui est souvent ignoré ou sous-estimé, c'est que les renouées sont des plantes clonales. Il apparait donc que les renouées possèdent sans doute une niche écologique bien plus large que ce qui est couramment admis. En effet, si leurs graines ont généralement du mal à produire de nouveaux individus dans la nature, les fragments de renouées semblent potentiellement capables de provoquer l'invasion de la plupart des habitats terrestres tempérés, si on leur laisse le temps de le faire.

Confrontée au manque de filière de traitement de gros volumes de matériaux infestés par des rhizomes de renouée du Japon, la Compagnie nationale du Rhône a développé une technique très efficace pour neutraliser immédiatement les terres infestées. Les matériaux alluviaux, triés puis broyés finement, peuvent être remis au cours d’eau, valorisés comme substrat de plantation ou évacués dans des installations de stockage de déchets inertes.

Resume S’installant et colonisant des biotopes tres divers, bordures de rivieres et d’infrastructures lineaires, friches, etc., les renouees asiatiques peuvent concerner de nombreux gestionnaires publics et proprietaires prives. Or, trouver des moyens efficaces pour controler leur developpement relevent encore aujourd’hui du defi. Cependant, comme l’illustre cet article, en deux decennies, les competences et l’expertise sur le terrain progressent ainsi que les echanges entre la recherche et la gestion, l’ensemble contribuant a faire evoluer les reflexions et les pratiques.

International audience; Une des pistes de recherche les plus récentes concernant la gestion des espèces végétalesinvasives porte sur les capacités des plantes à produire des composés chimiques inhibantla croissance ou le développement d’autres végétaux. Cet article décrit les enjeux,quelques recherches menées en France et les défis posés par cette démarche.

Description of the subject. Vegetation of high conservation value can establish in quarries, during or after exploitation. Alien plants could hamper this process and cause additional rehabilitation costs. However, the situation of plant invasion in quarries is largely unknown.Objectives. We aimed to assess alien plant invasion in active and abandoned quarries, and to identify the most invaded quarry sectors. Method. We surveyed 6,692 plots in 31 quarries in Belgium and recorded occurrence, density and cover of the 65 listed alien invasive plants in Belgium. Results. Fourteen species were recorded and 25 quarries contained at least one species. The two most occurring species, Buddleja davidii Franch. and Senecio inaequidens DC., were more widespread in quarries in activity. All sectors of the quarries were affected by alien plant invasion.Conclusions. Alien plant invasion in limestone quarries is highly variable, but significant. Considering the ecological potential of quarry sites, this issue should be better tackled., Plantes exotiques envahissantes dans les carrières calcaires de Belgique Description du sujet. Une végétation de haute valeur conservatoire peut s’établir dans les carrières, pendant ou après l’exploitation. Les plantes exotiques peuvent empêcher ce processus et représenter des couts supplémentaires lors de la réhabilitation. La situation concernant les invasions végétales en carrières est largement méconnue. Objectifs. L’objectif était de quantifier les invasions végétales en carrières calcaires (en activité ou non) et d’identifier les secteurs des carrières les plus envahis. Méthode. Nous avons échantillonné 6 692 placettes dans 31 carrières en Belgique et noté l’occurrence, la densité et le recouvrement des 65 espèces exotiques envahissantes listées au niveau belge. Résultats. Quatorze espèces ont été observées et 25 carrières contenaient au moins une espèce. Les deux espèces les plus fréquentes, Buddleja davidii Franch. et Senecio inaequidens DC., étaient plus répandues dans les carrières en activité. Tous les secteurs étaient concernés par les invasions. Conclusions. La problématique des plantes exotiques envahissantes dans les carrières calcaires est très variable, mais significative. Vu le potentiel écologique de ces sites, celle-ci devrait être mieux prise en compte.

Plant control with covering can be an effective method to limit the expansion of invasive species (e.g. Knotweed). Numerous experiments have been led last years and new geotextile fabrics appeared in trade. In the case of Asian knotweed, this covering technics must stop the development of the plant. The paper gives the main conditions of use and recommendations especially on covering materials, ground preparation methods and installation monitoring. We also consider the interest of these techniques regarding its cost and efficacy.; Le bâchage peut permettre de contrôler l'expansion des espèces invasives, en particulier des renouées asiatiques, en témoignent de nombreux retours d'expériences et la mise sur le marché de nouvelles bâches dédiées à cet objectif. Mais l'efficacité de cette technique tient beaucoup à des modalités d'utilisation particulières qui doivent tenir compte des capacités de développement notamment souterrain des renouées. L'article donne les principales préconisations à suivre, aussi bien sur le choix du matériau et la préparation du sol, que les modalités d'installation et le suivi. Il donne également des éléments sur le cadre et le contexte d'utilisation de cette technique, au regard de son cout et de son efficacité.