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Pinus radiata (radiata pine or Monterey pine) is threatened in its native range in California and, at the same time, one of the most widely-planted tree species worldwide, especially in the southern hemisphere. It is affected by a wide range of plant-feeding insects both in its native range and in regions where it is planted as an introduced tree. In addition, there are many invasive insects that have colonised P. radiata, in some cases causing major damage. Here, our objectives were to provide a complete and up-to-date overview of all insect species recorded from P. radiata worldwide, to summarise where these insects are native and which countries or regions they have invaded, to categorise them according to their impacts as damaging species or as vectors of plant pathogens, and to examine border interceptions to determine whether pathways exist that would allow these species to enter and potentially invade additional regions. Our compilation of insects feeding on P. radiata provides a list of 649 species (and an additional 11 species identified at the genus level only). Coleoptera is the most represented order in the list (299 species), followed by Lepidoptera (224 species) and Hemiptera (65 species). We classified 28 species as high-impact, including 12 true bark beetles (Coleoptera: Curculionidae: Scolytinae), eight Lepidoptera, five other Coleoptera, two Hymenoptera and one Hemiptera. These species can cause substantial direct damage or act as vectors of highly-damaging plant pathogens. Other species cause only occasional damage, rarely requiring management (classified as 'low-medium impact') or they are generally benign ('negligible impact'). Hemiptera and Scolytinae have a high proportion of species established outside their native range. The Nearctic and Neotropic regions have been invaded by the most high-impact species, mainly by species native to Europe. Border interceptions of 185 species (29% of those on our list) were recorded during import inspections between 1995-2021, indicating considerable potential for further invasions. The findings of our study can be used to identify potential high-impact invaders and the pathways that may require more phytosanitary attention. Furthermore, our analyses provide useful insights into the insect-plant interactions resulting from the global distribution of a tree species and the native and non-native insects feeding on it. [ABSTRACT FROM AUTHOR]

Nonnative insects and pathogens pose major threats to forest ecosystems worldwide, greatly diminishing the ecosystem services trees provide. Given the high global diversity of arthropod and microbial species, their often unknown biological features or even identities, and their ease of accidental transport, there is an urgent need to better forecast the most likely species to cause damage. Several risk assessment approaches have been proposed or implemented to guide preventative measures. However, the underlying assumptions of each approach have rarely been explicitly identified or critically evaluated. We propose that evaluating the implicit assumptions, optimal usages, and advantages and limitations of each approach could help improve their combined utility. We consider four general categories: using prior pest status in native and previously invaded regions; evaluating statistical patterns of traits and gene sequences associated with a high impact; sentinel and other plantings to expose trees to insects and pathogens in native, nonnative, or experimental settings; and laboratory assays using detached plant parts or seedlings under controlled conditions. We evaluate how and under what conditions the assumptions of each approach are best met and propose methods for integrating multiple approaches to improve our forecasting ability and prevent losses from invasive pests. [ABSTRACT FROM AUTHOR]

Aim: Species introductions have reshaped island faunas for the last 200 years, often threatening native biodiversity. Approximately equal numbers of native and alien species currently co‐occur in the New Zealand avifauna, but they show distinct habitat use. Antagonistic interactions, habitat affinities and legacies of introduction history may concur to explain their segregation along habitat gradients. To investigate these processes, we explored how habitat, ecological traits and introduction history relate with the current composition of bird assemblages. Location: New Zealand Taxon: Birds Methods: We analysed 917 bird point counts spread along habitat and elevation gradients in the Canterbury region, South Island and related 10 ecological traits to landscape composition using a three‐table ordination method known as "RLQ analysis", accounting for spatial autocorrelation and phylogeny. We tested whether alien species' positions in the RLQ were related to proxies of introduction history. Results: Eighteen endemic, 11 native and 19 alien species were distributed along a gradient from forest to open‐habitat assemblages, in relation to foraging mode, nesting site and body size. A second gradient segregated species between native and exotic forests according to territoriality, sedentarity and diet. Traits accounted for the separation of native and alien bird species in forests, but not in open habitats. Phylogenetic signals emerged from the separation of native and alien species by forest type, and spatial structures suggested a landscape‐level, rather than regional or local determinism. These correlations were independent of introduction history, although open‐habitat assemblages tended to host alien species introduced later in time. Main conclusions: Habitat type and resource availability explain the spatial partitioning of New Zealand bird assemblages between native and alien species more consistently than competitive exclusion. We conclude that trait‐mediated ecological differences among species have likely played a predominant role in species' segregation among landscapes, while maintaining endemic bird assemblages in native forests. [ABSTRACT FROM AUTHOR]

1. A demographic Allee effect refers to increasing per capita population growth with increasing abundance. It arises from component Allee effects, which exist when some component of individual fitness has a positive relationship with density. Newly arrived populations tend to be small, and their establishment success is influenced by various factors, including demographic Allee effects. Identifying mechanisms driving the Allee effect is of relevance for understanding establishment failure, developing strategies for improving biological control and conservation, and for managing biological invasions. 2. We utilised an invasive plant biocontrol agent, Neolema ogloblini, as model to study Allee effects experienced by invading populations. We investigated mating failure and predator satiation as two component Allee effects that could potentially drive a demographic Allee effect in N. ogloblini populations. 3. We released unmated adults onto isolated host patches using five release sizes and evaluated the mating status of females after 3 weeks in the field. The probability of being mated increased as number of males recovered increased, suggesting the presence of a mating‐failure component Allee effect in very small populations of N. ogloblini. Exclosures were used to evaluate survival of immatures of N. ogloblini developing in small group sizes, either in the presence or absence of generalist predators. Results revealed high levels of predation, but a positive relationship between larval survival and group size in the presence of generalist predators could not be verified. 4. Our study identified relevant life‐history traits contributing to establishment failure in N. ogloblini and demonstrates the value of biocontrol agents as models to study mechanisms of species invasion. [ABSTRACT FROM AUTHOR]

Although most populations of non‐native species arriving in new environments fail to establish, mechanisms behind failed biological invasions are still poorly understood.Propagule pressure has been found to be a dominant driver of establishment success, underpinned by processes such as stochasticity and Allee effects. While studies have revealed the presence of a component Allee effect in field populations, empirical support for demographic Allee effects has been limited.We used the leaf‐feeding beetle Neolema ogloblini, a biological control agent against the plant Tradescantiafluminensis, as a proxy invasive species to experimentally study the process of establishment. We investigated how the initial size of the population released affects the probability of establishment and population growth in the first season after introduction at isolated sites in New Zealand.The probability of establishment was found to increase with numbers of individuals released. A significant quadratic relationship was found between population size released and per capita population growth rate; that is per capita population growth rate initially increased as population size released increased but decreased at higher population levels.These results support the presence of a demographic Allee effect. However, as the influence of stochasticity (environmental and demographic) could not be completely separated from that of a demographic Allee effect, we conclude that extinction probability in the experimental populations of N. ogloblini was influenced by both a demographic Allee effect and stochasticity.Our study demonstrates and supports the concept that experimental biocontrol agent releases can be used for testing hypotheses regarding invasion biology. [ABSTRACT FROM AUTHOR]

Predicting how increasing rates of global trade will result in new establishments of potentially damaging invasive species is a question of critical importance to the development of national and international policies aimed at minimizing future invasions. Centuries of historical movement and establishment of invading species may have depleted the supply of species available for future invasions, and it has been suggested that the problem of invasions will diminish as a result of this. However, the extent to which source pool depletion affects future invasions remains unclear., Here we describe a mechanistic model that captures the simultaneous effects of depletion of source species pools along with increases in pathway rates (e.g. imports) to predict future numbers of new invasions. We assume that the distribution of species abundance within invasion pathways is positively skewed, which is modelled using a log-normal distribution. Given their high propagule pressure, the most abundant species are likely to invade first, while the many rare species are likely to invade only under high pathway volumes. We apply this model to the case study of bark beetle, Scolytinae, invasions in the USA., Source species pools in Europe and Asia (225 and 655 species of Scolytinae, respectively) are much larger than numbers that have historically established (16 and 32). Parameterization of the model indicates a highly skewed species abundance distribution in the pathway and this is confirmed by species frequencies in port inspection records, thus explaining why only a small fraction of species has historically invaded., Forecasts from the model indicate that with increasing rates of imports, more species from these regions are likely to invade in the future despite the depletion of the most abundant species from source species pools. Previous statistical models tend to underestimate future establishments in the presence of increasing import rates due to their failure to account for key underlying mechanisms., Policy implications. The mechanistic model developed here is widely applicable for predicting future invasions of all taxa and provides insights into how increases in rates of imports counteract the species pool depletion effect, resulting in the continued establishment of new species. [ABSTRACT FROM AUTHOR]

When a non-native species succeeds in establishing in a new habitat, one of the possible responses is to attempt its eradication. In the present study, we analysed European eradication programmes against nonnative pests and pathogens of woody plants (PPWP) from 1945 to date. Our main goal was to identify which factors affect the success of an eradication programme, reinforcing guidelines for future eradication of PPWP. Data on eradication campaigns were obtained from online databases, scientific and grey literature, and Plant Protection Organizations' reports. Factors influencing eradication success for both arthropods and pathogens were analysed with LASSO regression and decision tree learning. A total of 848 cases officially declared as eradication attempts were documented in our database (8-fold higher than previous reports). Both the number of programmes and their rate of success increased sharply over the last two decades. Only less than 10% of the non-native organisms affecting woody plants were targeted for attempted eradication despite the high economic and ecological impacts caused by some species for which no efforts were undertaken. Almost one-third of the officially declared cases of eradication concerned organisms that were still restricted to the material with which they were introduced. For these cases the success rate was 100%. The success rate of established species was only 50% for arthropods and 61% for pathogens. The spatial extent of the outbreak was the factor that most affected the outcome of eradication campaigns. The eradication success decreased abruptly above 100 ha for arthropods and 10 ha for pathogens. Additionally, other variables were shown to influence the outcome of eradication programmes, in particular the type of environment, with the highest eradication success rate found in nurseries and glasshouses, with successful outcomes increasing if quarantine measures were applied and when monitoring included asymptomatic plants. Particular species traits may reduce eradication success: parthenogenetic arthropods, saprotrophic pathogens, wind dispersal, the possibility to remain asymptomatic indefinitely, and the existence of resting spores or stages. In conclusion, small affected areas, quick response, and efficient implementation of quarantine restrictions, together with particular species traits, may allow a high probability of eradication success. Preparedness at the country and European level would allow a larger number of target species to be included in future eradication programmes. [ABSTRACT FROM AUTHOR]

Biological invasions resulting from international trade can cause major environmental and economic impacts. Propagule pressure is perhaps the most important factor influencing establishment, although actual arrival rates of species are rarely recorded. Furthermore, the pool of potential invaders includes many species that vary in their arrival rate and establishment potential. Therefore, we stress that it is essential to consider the size and composition of species pools arriving from source regions when estimating probabilities of establishment and effects of pathway infestation rates. To address this, we developed a novel framework and modeling approach to enable prediction of future establishments in relation to changes in arrival rate across entire species pools. We utilized 13 828 border interception records from the United States and New Zealand for 444 true bark beetle (Scolytinae) and longhorned beetle (Cerambycidae) species detected between 1949 and 2008 as proxies for arrival rates to model the relationship between arrival and establishment rates. Nonlinearity in this relationship implies that measures intended to reduce the unintended transport of potential invaders (such as phytosanitary treatments) must be highly effective in order to substantially reduce the rate of future invasions, particularly if trade volumes continue to increase. [ABSTRACT FROM AUTHOR]

Biological invasions can cause major ecological and economic impacts. During the early stages of invasions, eradication is desirable but tactics are lacking that are both effective and have minimal non-target effects. Mating disruption, which may meet these criteria, was initially chosen to respond to the incursion of light brown apple moth, Epiphyas postvittana (LBAM; Lepidoptera: Tortricidae), in California. The large size and limited accessibility of the infested area favored aerial application. Moth sex pheromone formulations for potential use in California or elsewhere were tested in a pine forest in New Zealand where LBAM is abundant. Formulations were applied by helicopter at a target rate of 40 g pheromone per ha. Trap catch before and after application was used to assess the efficacy and longevity of formulations, in comparison with plots treated with ground-applied pheromone dispensers and untreated control plots. Traps placed at different heights showed LBAM was abundant in the upper canopy of tall trees, which complicates control attempts. A wax formulation and polyethylene dispensers were most effective and provided trap shut-down near ground level for 10 weeks. Only the wax formulation was effective in the upper canopy. As the pheromone blend contained a behavioral antagonist for LBAM, 'false trail following' could be ruled out as a mechanism explaining trap shutdown. Therefore, 'sensory impairment' and 'masking of females' are the main modes of operation. Mating disruption enhances Allee effects which contribute to negative growth of small populations and, therefore, it is highly suitable for area-wide control and eradication of biological invaders. [ABSTRACT FROM AUTHOR]

The economic and environmental threats posed by non-native forest insects are ever increasing with the continuing globalization of trade and travel; thus, the need for mitigation through effective biosecurity is greater than ever. However, despite decades of research and implementation of preborder, border, and postborder preventative measures, insect invasions continue to occur, with no evidence of saturation, and are even predicted to accelerate. In this article, we review biosecurity measures used to mitigate the arrival, establishment, spread, and impacts of non-native forest insects and possible impediments to the successful implementation of these measures. Biosecurity successes are likely under-recognized because they are difficult to detect and quantify, whereas failures are more evident in the continued establishment of additional non-native species. There are limitations in existing biosecurity systems at global and country scales (for example, inspecting all imports is impossible, no phytosanitary measures are perfect, knownunknowns cannot be regulated against, and noncompliance is an ongoing problem). Biosecurity should be a shared responsibility across countries, governments, stakeholders, and individuals. [ABSTRACT FROM AUTHOR]

Ecology Letters (2010) 13: 506–515 The translocation of species beyond their native range is a major threat to biodiversity. Invasions by tree-feeding insects attacking native trees and the colonization of introduced trees by native insects result in new insect–tree relationships. To date there is uncertainty about the key factors that influence the outcome of these novel interactions. We report the results of a meta-analysis of 346 pairwise comparisons of forest insect fitness on novel and ancient host tree species from 31 publications. Host specificity of insects and phylogenetic relatedness between ancient and novel host trees emerged as key factors influencing insect fitness. Overall, fitness was significantly lower on novel host species than on ancient hosts. However, in some cases, fitness increased on novel hosts, mainly in polyphagous insects or when close relatives of ancient host trees were colonized. Our synthesis enables greatly improved impact prediction and risk assessment of biological invasions. [ABSTRACT FROM AUTHOR]

Aim: Invasions of non‐native insects can have substantial impacts on agriculture, forestry, human health and biodiversity with considerable economic and environmental consequences. To understand the causes of these invasions, it is important to quantify the relative influence of principal drivers such as international imports and climatic effects. Location: North America, Chile, Europe, Australia, New Zealand and Japan. Time Period: 1881–2020. Methods: To evaluate the relative contributions of various factors in explaining global variation in numbers of non‐native insect establishments in different world regions, we conducted two multivariate regression analyses to quantify temporal changes in family‐level composition and native ranges of established non‐native species in several world regions. Results: There were temporal changes in the family‐level composition of non‐native species assemblages. Prior to 1900, invasions were dominated by scale insects, subsequently shifting to a more diverse set of species, except in North America, which had relatively small compositional change over time compared to other regions. Spatial and temporal variation in the composition of established species was associated with differences in the origin of imports and climatic factors, each explaining 26.3% and 27.4% of the total variation, respectively. The analysis of native ranges of non‐native species indicated that there was no consistent temporal variation across all regions. Established species in New Zealand were predominantly native to Australasia and species in North America and Chile were mainly from Europe. Non‐native species in Europe mainly originated from the Nearctic region while those in Japan and Australia generally originated from multiple regions. Climatic factors in the destination regions had a primary effect (66.3%) on variation in the native range of established species, although imports also had substantial effects (45.4%). Main Conclusions: Geographical variation in climate and imports act together as drivers of establishment success for non‐native insects in all six regions. [ABSTRACT FROM AUTHOR]

Two Asian longhorn beetles, Anoplophora glabripennis and Anoplophora chinensis, are among the most serious alien invasive species attacking forest and urban trees, both in North America and Europe. Major efforts have been put into preventing further entry and establishment of the two species as well as promoting their successful eradication. Here, we review these efforts, their progress and outcome, and scientific advancements in monitoring and control methods. The combined international activities and harmonizing legislative changes in detection and eradication methods have proven worthwhile, with more than 45% of eradication programmes successful in the last 12 years. Some countries were able to completely eradicate all populations and others managed to reduce the area affected. Although the costs of the eradication programmes can be very high, the benefits outweigh inaction. Attempts to eradicate A. chinensis have been more challenging in comparison with those targeting A. glabripennis. For both species, efforts are hampered by the ongoing arrival of new beetles, both from their native regions in Asia and from other invaded regions via bridgehead effects. The methods used for eradication have not changed much during the last decade, and host removal is still the method most commonly used. On the other hand, detection methods have diversified during the last decade with advances in semiochemical research and use of detection dogs. The next decade will determine if eradications continue to be successful, particularly in the case of A. chinensis, which has been targeted in some countries for containment instead of eradication. [ABSTRACT FROM AUTHOR]

Human impacts such as habitat loss, climate change and biological invasions are radically altering biodiversity, with greater effects projected into the future. Evidence suggests human impacts may differ substantially between terrestrial and freshwater ecosystems, but the reasons for these differences are poorly understood. We propose an integrative approach to explain these differences by linking impacts to four fundamental processes that structure communities: dispersal, speciation, species‐level selection and ecological drift. Our goal is to provide process‐based insights into why human impacts, and responses to impacts, may differ across ecosystem types using a mechanistic, eco‐evolutionary comparative framework. To enable these insights, we review and synthesise (i) how the four processes influence diversity and dynamics in terrestrial versus freshwater communities, specifically whether the relative importance of each process differs among ecosystems, and (ii) the pathways by which human impacts can produce divergent responses across ecosystems, due to differences in the strength of processes among ecosystems we identify. Finally, we highlight research gaps and next steps, and discuss how this approach can provide new insights for conservation. By focusing on the processes that shape diversity in communities, we aim to mechanistically link human impacts to ongoing and future changes in ecosystems. [ABSTRACT FROM AUTHOR]

Although many non‐native species arrive in novel environments, only a fraction successfully establish. A crucial factor affecting the colonization process of invading species is propagule pressure. The positive association between propagule pressure and colonization probability is driven both by stochastic dynamics and the 'Allee effect'. Although the role of Allee effects in invading populations is theoretically compelling, they are difficult to quantify in the field because the earliest phases of biological invasions are typically not observed.We conducted parallel studies using two species of bark beetles, Hylurgus ligniperda in New Zealand and Ips pini in North America, to (i) assess the role of propagule pressure on colonization success, (ii) empirically test for Allee effects and (iii) estimate Allee thresholds. We evaluated each of these factors by experimentally testing the effect of propagule pressure (numbers released) on simulated tree colonization success in two different settings: (1) field conditions where beetles could disperse freely and (2) enclosed cages where dispersal loss was prevented.Colonization success was positively associated with numbers released (i.e. propagule pressure) for both species, though colonization occurred at lower numbers for H. ligniperda than for I. pini. A demographic Allee effect was only detected in H. ligniperda and the Allee threshold was smaller when beetles were released 1 m from host billets than when they were released 10 m away. Greater colonization success at lower release densities may explain the invasion success of H. ligniperda worldwide. Higher release densities required for successful colonization may explain why I. pini is a poor establisher.Synthesis and applications. Our results linking invasion failure to small founding population densities generally support the theoretical literature on the role of propagule pressure and Allee effects in biological invasions. Agencies such as the International Plant Protection Committee (IPPC) setting phytosanitary measures such as the International Standards for Phytosanitary Measures No. 15 (ISPM 15) should consider using the colonization thresholds estimated here to limit numbers of colonizing individuals below invasion thresholds. Additionally, agencies conducting trapping efforts at ports‐of‐entry should be aware of these thresholds and widely report when trapping numbers exceed these thresholds. [ABSTRACT FROM AUTHOR]

Aim: Biological invasions are a major threat to biodiversity in aquatic and terrestrial habitats. Insects represent an important group of species in freshwater and terrestrial habitats, and they constitute a large proportion of non‐native species. However, while many non‐native insects are known from terrestrial ecosystems, they appear to be less represented in freshwater habitats. Comparisons between freshwater and terrestrial habitats of invader richness relative to native species richness are scarce, which hinders syntheses of invasion processes. Here, we used data from three regions on different continents to determine whether non‐native insects are indeed under‐represented in freshwater compared with terrestrial assemblages. Location: Europe, North America, New Zealand. Methods: We compiled a comprehensive inventory of native and non‐native insect species established in freshwater and terrestrial habitats of the three study regions. We then contrasted the richness of non‐native and native species among freshwater and terrestrial insects for all insect orders in each region. Using binomial regression, we analysed the proportions of non‐native species in freshwater and terrestrial habitats. Marine insect species were excluded from our analysis, and insects in low‐salinity brackish water were considered as freshwater insects. Results: In most insect orders living in freshwater, non‐native species were under‐represented, while they were over‐represented in a number of terrestrial orders. This pattern occurred in purely aquatic orders and in orders with both freshwater and terrestrial species. Overall, the proportion of non‐native species was significantly lower in freshwater than in terrestrial species. Main conclusions: Despite the numerical and ecological importance of insects among all non‐native species, non‐native insect species are surprisingly rare in freshwater habitats. This is consistent across the three investigated regions. We review hypotheses concerning species traits and invasion pathways that are most likely to explain these patterns. Our findings contribute to a growing appreciation of drivers and impacts of biological invasions. [ABSTRACT FROM AUTHOR]

Aim: Lepidoptera is a highly diverse, predominantly herbivorous insect order, with species transported to outside their native range largely facilitated by the global trade of plants and plant‐based goods. Analogous to island disharmony, we examine invasion disharmony, where species filtering during invasions increases systematic compositional differences between native and non‐native species assemblages, and test whether some families are more successful at establishing in non‐native regions than others. Location: Hawaii, North America, Galapagos, Europe, South Africa, South Korea, Japan, Nansei Islands, Ogasawara Islands, Australia, New Zealand. Taxon: Lepidoptera. Methods: We compared numbers of non‐native, unintentionally introduced Lepidoptera species with the land area of 11 regions worldwide. Differences among native and non‐native assemblages in the distribution of species among families were investigated using ordination analysis. We tested whether invasion disharmony is explained by propagule pressure (proxied by species richness in border interceptions) and if families were associated with specific trade commodities. Results: In total, 741 non‐native Lepidoptera species, accounting for 0.47% of the global diversity of lepidopterans, are established in at least one of the 11 regions. Crambidae, Pyralidae, Tineidae and Gracillariidae were particularly successful invaders, whereas the two most species‐rich families, Erebidae and Geometridae, were under‐represented among non‐native Lepidoptera. Much of the variation in species numbers in the native, and less so in the non‐native assemblages could be attributed to land area. Although native assemblages were similar among nearby regions, non‐native assemblages were not, suggesting geography had little effect on invasion disharmony. Comparison of established with intercepted species revealed that macromoth families were generally under‐represented in establishments, whereas several micromoth families were under‐represented in interceptions. This discrepancy may relate to greater detectability of larger species or high propagule pressure via associations with specific invasion pathways. Main conclusions Invasion disharmony in Lepidoptera appears to be driven by processes unrelated to the success of native assemblages. While native assemblages developed through long‐term evolutionary radiation, the composition of non‐native assemblages is driven by differential invasion pathways and traits affecting the establishment of founder populations that vary among families. [ABSTRACT FROM AUTHOR]

Eradication is the deliberate elimination of a species from an area. Given that international quarantine measures can never be 100% effective, surveillance for newly arrived populations of nonnative species coupled with their eradication represents an important strategy for excluding potentially damaging insect species. Historically, eradication efforts have not always been successful and have sometimes been met with public opposition. But new developments in our understanding of the dynamics of low-density populations, the availability of highly effective treatment tactics, and bioeconomic analyses of eradication strategies offer new opportunities for developing more effective surveillance and eradication programs. A key component that connects these new developments is the harnessing of Allee effects, which naturally promote localized species extinction. Here we review these developments and suggest how research might enhance eradication strategies. [ABSTRACT FROM AUTHOR]

Aim: The biotic resistance hypothesis posits that greater native species richness limits invasions of exotic species. However, negative native‐exotic richness relationships (NERRs) may reverse with increasing spatial scale, seemingly refuting the hypothesis. Here, we explore the effects of species competitive interactions, environmental factors, habitat heterogeneity and vertical vegetation tiers on the NERRs across spatial scales in native forests. Location: New Zealand. Methods: We combined vegetation, land cover and climate data to predict exotic richness from native richness at different vertical tiers (ground to canopy), land cover, plant competition (tree basal area, native ground cover), mean annual temperature and total rainfall. We considered four spatial scales, from single 20 × 20 m plots on an 8‐km grid to groups of plots across grids up to 128 km. Habitat heterogeneity was measured using the variance of climatic conditions among plots within a group. Results: A negative native tree‐exotic richness relationship (NTERR) was observed at plot level but reversed with increasing spatial scale. Species competitive interactions showed a negative relationship with exotic richness at small/intermediate scales (≤32 km). Rainfall and temperature heterogeneity contributed to the positive NTERR at the largest scale. Adjacent exotic grassland cover had a positive relationship with exotic richness across all scales but did not prevent the NTERR from reversing. Main conclusions: Our analysis shows the importance of considering vegetation structure and adjacent land covers, along with spatial heterogeneity and climatic factors, when testing the biotic resistance hypothesis in forest ecosystems. There is a clear indication that biotic resistance is primarily driven by native trees in the overstorey, probably by limiting resources available to ground tier plants. The results support the notion that the NERR is driven by competitive interspecific interactions at small spatial scales and by habitat heterogeneity at larger scales. [ABSTRACT FROM AUTHOR]

Aim: The concept of "island disharmony" has been widely applied to describe the systematic over‐ and under‐representation of taxa on islands compared to mainland regions. Here, we explore an extension of that concept to biological invasions. We compare biogeographical patterns in native and non‐native beetle (Coleoptera) assemblages from around the world to test whether beetle invasions represent a random sample of species or whether some families are more prone to invade than others. Location: Global. Methods: Numbers of non‐native beetle species established in ten regions worldwide were compared with the land area of each region. The distribution of species among families was compared with the distribution among families for all species native to the same region and with the distribution among families for the global pool of all known beetle species. Ordination analysis was used to characterize differences among native and non‐native assemblages based upon the distribution of species among families. Results: We report a total of 1,967 non‐native beetle species across all ten regions, and a classic log–log relationship between numbers of species per region and land area though relationships are generally stronger for native assemblages. Some families (e.g., Dermestidae and Bostrichidae) are over‐represented and others (e.g., Carabidae, Scarabaeidae and Buprestidae) are under‐represented in non‐native assemblages. The distribution of species among families is generally similar among native assemblages with greatest similarities among nearby regions. In contrast, non‐native species assemblages are more similar to each other than to native species assemblages. Main conclusions: Certain families are over‐represented, and others are under‐represented in non‐native beetle assemblages compared to native assemblages, indicating "invasion disharmony" in the global representation of beetle families. Similarities in composition among non‐native assemblages may reflect unobserved associations with invasion pathways and life‐history traits that shape invasion success of different insect groups. [ABSTRACT FROM AUTHOR]

Invasions by non‐native pests and diseases represent serious threats to biodiversity, agriculture and human health. Under current border arrival rates associated with international trade not all such invasions can be prevented, so early detection and eradication (forced extinction) are important strategies for preventing establishment and long‐term impacts. Removal of host plants has historically been a common tool used alone and in concert with other tools for eradication of plant pests but there is little scientific theory specific to the management of invasive species to guide the application of this eradication strategy.We drew upon extensive conservation biology literature documenting the effect of habitat destruction or fragmentation driving extinction. We applied a previously developed spatially explicit model of gypsy moth, Lymantria dispar, spatial dynamics to explore how fragmentation affects population persistence. This model accounts for a component Allee effect driven by mate‐finding failure that interacts with dispersal.We observed a nonlinear dependency of population persistence on the fraction of habitat cover and the level of habitat fragmentation. Simulation of active habitat fragmentation via the removal of habitat in swaths of varying widths or the application of pesticide in varying swaths showed that removal of hosts or pesticide application in narrow swaths (i.e. 40 m wide) caused the greatest probabilities of extinction. Generally, habitat removal was more effective than one‐off pesticide treatments at causing extinction.Synthesis and applications. Spatially explicit modelling of Allee dynamics in invading gypsy moth populations showed that host removal can be an effective method to eradicate invasive plant‐feeding insects especially when habitat fragmentation is applied at a desirable level. Furthermore, this can be used as an alternative to, or in conjunction with, pesticide treatments, to provide more options for carrying out eradications and to increase the probability of eradication success. [ABSTRACT FROM AUTHOR]

The brown marmorated stink bug, Halyomorpha halys, is an agricultural and urban pest that has become widely established as an invasive species of major concern in the USA and throughout Europe. The insect forms large aggregations before entering diapause, and it is often these aggregations that are found by biosecurity officials conducting inspections of internationally shipped freight. Here, we aimed to gain insights into the potential volatile emissions, mobility, and mortality rates of the insects after undergoing a ship voyage across the equator (i.e. from northern hemisphere winter to southern hemisphere summer). Experiments were performed to simulate the effects on aggregations of diapausing H. halys of two variables associated with trans-Pacific voyages, i.e. ship and container movement and temperature changes within containers. Thus, H. halys aggregations were exposed to simulated shipping movement, using a 6-axis VS-6577G-B Denso robot arm, and emission of defence volatiles was measured repeatedly during the "voyage." We also simulated temperature changes as they occur during a 26-day voyage from Baltimore, northeast USA, to Auckland, New Zealand, and assessed the effects on the mortality and mobility of the bugs. Aggregations that experienced movement were not found to be any more likely to release volatiles than stationary aggregations and neither did the movement affect bug mobility. Temperature changes had a significant effect on mobility. However, towards the end of the temperature simulation, most H. halys had died, probably from a lack of food and moisture. These findings are highly relevant for border biosecurity risk assessment and pathway risk management. [ABSTRACT FROM AUTHOR]

International trade and movement of people are largely responsible for increasing numbers of non-native insect introductions to new environments. For forest insects, trade in live plants and transport of wood packaging material (WPM) are considered the most important pathways facilitating long-distance invasions. These two pathways as well as trade in firewood, logs, and processed wood are commonly associated with insect infestations, while "hitchhiking" insects can be moved on cargo, in the conveyances used for transport (e.g., containers, ships), or associated with international movement of passengers and mail. Once established in a new country, insects can spread domestically through all of the above pathways. Considerable national and international efforts have been made in recent years to reduce the risk of international movement of plant pests. International Standards for Phytosanitary Measures (ISPMs) No. 15 (WPM), 36 (plants for planting), and 39 (wood) are examples of phytosanitary standards that have been adopted by the International Plant Protection Convention to reduce risks of invasions of forest pests. The implementation of ISPMs by exporting countries is expected to reduce the arrival rate and establishments of new forest pests. However, many challenges remain to reduce pest transportation through international trade, given the ever-increasing volume of traded goods, variations in quarantine procedures between countries, and rapid changes in distribution networks. It is therefore likely that many more human-assisted invasions of forest insects will take place. New geographic expansions by natural modes are also made possible due to changes in host distribution and/or climate. [ABSTRACT FROM AUTHOR]

Biological invasions are a major threat to biological diversity, agriculture, and human health. To predict and prevent new invasions, it is crucial to develop a better understanding of the drivers of the invasion process. The analysis of 4,533 border interception events revealed that at least 51 different alien ant species were intercepted at US ports over a period of 70 years (1914-1984), and 45 alien species were intercepted entering New Zealand over a period of 68 years (1955-2013). Most of the interceptions did not originate from species' native ranges but instead came from invaded areas. In the United States, 75.7% of the interceptions came from a country where the intercepted ant species had been previously introduced. In New Zealand, this value was even higher, at 87.8%. There was an overrepresentation of interceptions from nearby locations (Latin America for species intercepted in the United States and Oceania for species intercepted in New Zealand). The probability of a species' successful establishment in both the United States and New Zealand was positively related to the number of interceptions of the species in these countries. Moreover, species that have spread to more continents are also more likely to be intercepted and to make secondary introductions. This creates a positive feedback loop between the introduction and establishment stages of the invasion process, in which initial establishments promote secondary introductions. Overall, these results reveal that secondary introductions act as a critical driver of increasing global rates of invasions. [ABSTRACT FROM AUTHOR]

Our ability to predict the identity of future invasive alien species is largely based upon knowledge of prior invasion history. Emerging alien species–those never encountered as aliens before–therefore pose a significant challenge to biosecurity interventions worldwide. Understanding their temporal trends, origins, and the drivers of their spread is pivotal to improving prevention and risk assessment tools. Here, we use a database of 45,984 first records of 16,019 established alien species to investigate the temporal dynamics of occurrences of emerging alien species worldwide. Even after many centuries of invasions the rate of emergence of new alien species is still high: One-quarter of first records during 2000-2005 were of species that had not been previously recorded anywhere as alien, though with large variation across taxa. Model results show that the high proportion of emerging alien species cannot be solely explained by increases in well-known drivers such as the amount of imported commodities from historically important source regions. Instead, these dynamics reflect the incorporation of new regions into the pool of potential alien species, likely as a consequence of expanding trade networks and environmental change. This process compensates for the depletion of the historically important source species pool through successive invasions. We estimate that 1-16% of all species on Earth, depending on the taxonomic group, qualify as potential alien species. These results suggest that there remains a high proportion of emerging alien species we have yet to encounter, with future impacts that are difficult to predict. [ABSTRACT FROM AUTHOR]

1. Dispersal and host detection are behaviours promoting the spread of invading populations in a landscape matrix. In fragmented landscapes, the spatial arrangement of habitat structure affects the dispersal success of organisms. 2. The aim of the present study was to determine the long distance dispersal capabilities of two non-native pine bark beetles ( Hylurgus ligniperda and Hylastes ater) in a modified and fragmented landscape with non-native pine trees. The role of pine density in relation to the abundance of dispersing beetles was also investigated. 3. This study took place in the Southern Alps, New Zealand. A network of insect panel traps was installed in remote valleys at known distances from pine resources (plantations or windbreaks). Beetle abundance was compared with spatially weighted estimates of nearby pine plantations and pine windbreaks. 4. Both beetles were found ≥25 km from the nearest host patch, indicating strong dispersal and host detection capabilities. Small pine patches appear to serve as stepping stones, promoting spread through the landscape. Hylurgus ligniperda (F.) abundance had a strong inverse association with pine plantations and windbreaks, whereas H. ater abundance was not correlated with distance to pine plantations but positively correlated with distance to pine windbreaks, probably reflecting differences in biology and niche preferences. Host availability and dispersed beetle abundance are the proposed limiting factors impeding the spread of these beetles. 5. These mechanistic insights into the spread and persistence of H. ater and H. ligniperda in a fragmented landscape provide ecologists and land managers with a better understanding of factors leading to successful invasion events, particularly in relation to the importance of long-distance dispersal ability and the distribution and size of host patches. [ABSTRACT FROM AUTHOR]

Untangling the relative influences of environmental filtering and biotic interactions on species coexistence at various spatial scales is a long-held issue in community ecology. Separating these processes is especially important to understand the influences of introduced exotic species on the composition of native communities. For this aim, we investigated coexistence patterns in New Zealand exotic and native birds along multiple-scale habitat gradients. We built a Bayesian hierarchical model, contrasting the abundance variations of 10 native and 11 exotic species in 501 point counts spread along landscape and local-scale gradients of forest structure and composition. Although native and exotic species both occurred in a wide range of habitats, they were separated by landscape-level variables. Exotic species were most abundant in exotic conifer plantations embedded in farmland matrices, while native birds predominated in areas dominated by continuous native forest. In exotic plantation forests, and to a lesser extent in native forests, locally co-occurring exotic and native species were segregated along a gradient of vegetation height. These results support the prediction that exotic and native bird species are segregated along gradients related to anthropogenic disturbance and habitat availability. In addition, native and exotic species overlapped little in a multivariate functional space based on 10 life history traits associated with habitat selection. Hence, habitat segregation patterns were probably mediated more by environmental filtering processes than by competition at landscape and local scales. [ABSTRACT FROM AUTHOR]