Exploiting Allee effects for managing biological invasions

Pest categorisation of Calepitrimerus baileyi

The EFSA Panel on Plant Health performed a pest categorisation of Bailey's rust mite, Calepitrimerus baileyi Keifer (Acariformes: Eriophyidae), following the commodity risk assessment of Malus domestica plants from Türkiye performed by EFSA, in which C. baileyi was identified as a pest of possible concern to the European Union. This mite is not listed in Annex II of Commission Implementing Regulation (EU) 2019/2072. The eriophyid is known to occur in Africa, America, Asia, Europe (Greece and Serbia) and Oceania on Malus spp., which is the only confirmed host genus for C. baileyi. Plants for planting of Malus spp. are the main potential pathway for entry into the EU. However, plants for planting of the genus Malus Mill. are considered as high-risk plants (EU 2018/2019) and therefore prohibited from entering the EU unless granted a country-specific derogation. This is the case for the import of Malus spp. plants for planting from Serbia ((EU) 2020/1361 corrected by 2022/1309). Therefore, this derogation could provide a plausible entry pathway for C. baileyi into the EU. Climatic conditions and the ample availability of the host, Malus spp., in the EU are conducive for establishment, as proven by the occurrence of C. baileyi in Greece. However, the species is not reported as having an impact in Greece, despite reports of damage outside the EU. Measures to prevent further entry and spread of C. baileyi in the EU are available. C. baileyi satisfies all the criteria that are within the remit of EFSA to assess for it to be regarded as a potential Union quarantine pest. However, uncertainties about the distribution of C. baileyi within the EU and its impact on apples in the EU are considered key and affect the confidence of conclusions for this categorisation.

Insect population dynamics under Wolbachia-induced cytoplasmic incompatibility: Puzzle more than buzz in Drosophila suzukii

In theory, the introduction of individuals infected with an incompatible strain of Wolbachia pipientis into a recipient host population should result in the symbiont invasion and reproductive failures caused by cytoplasmic incompatibility (CI). Modelling studies combining Wolbachia invasion and host population dynamics show that these two processes could interact to cause a transient population decline and, in some conditions, extinction. However, these effects could be sensitive to density dependence, with the Allee effect increasing the probability of extinction, and competition reducing the demographic impact of CI. We tested these predictions with laboratory experiments in the fruit fly Drosophila suzukii and the transinfected Wolbachia strain wTei. Surprisingly, the introduction of wTei into D. suzukii populations at carrying capacity did not result in the expected wTei invasion and transient population decline. In parallel, we found no Allee effect but strong negative density dependence. From these results, we propose that competition interacts in an antagonistic way with Wolbachia-induced cytoplasmic incompatibility on insect population dynamics. If future models and data support this hypothesis, pest management strategies using Wolbachia-induced CI should target populations with negligible competition but a potential Allee effect, for instance at the beginning of the reproductive season.

Factors affecting establishment and population growth of the invasive weed Ambrosia artemisiifolia

Ambrosia artemisiifolia is a highly invasive weed. Identifying the characteristics and the factors influencing its establishment and population growth may help to identify high invasion risk areas and facilitate monitoring and prevention efforts. Six typical habitats: river banks, forests, road margins, farmlands, grasslands, and wastelands, were selected from the main distribution areas of A. artemisiifolia in the Yili Valley, China. Six propagule quantities of A. artemisiifolia at 1, 5, 10, 20, 50, and 100 seeds m-2 were seeded by aggregation, and dispersion in an area without A. artemisiifolia. Using establishment probability models and Allee effect models, we determined the minimum number of seeds and plants required for the establishment and population growth of A. artemisiifolia, respectively. We also assessed the moisture threshold requirements for establishment and survival, and the influence of native species. The influence of propagule pressure on the establishment of A. artemisiifolia was significant. The minimum number of seeds required varied across habitats, with the lowest being 60 seeds m-2 for road margins and the highest being 398 seeds for forests. The minimum number of plants required for population growth in each habitat was 5 and the largest number was 43 in pasture. The aggregation distribution of A. artemisiifolia resulted in a higher establishment and survival rate. The minimum soil volumetric water content required for establishment was significantly higher than that required for survival. The presence of native dominant species significantly reduced the establishment and survival rate of A. artemisiifolia. A. artemisiifolia has significant habitat selectivity and is more likely to establish successfully in a habitat with aggregated seeding with sufficient water and few native species. Establishment requires many seeds but is less affected by the Allee effect after successful establishment, and only a few plants are needed to ensure reproductive success and population growth in the following year. Monitoring should be increased in high invasion risk habitats.

Noise-induced dynamics in a single species model with Allee effect driven by correlated colored noises

In this paper, a single species model with Allee effect driven by correlated colored noises is proposed and investigated. The stationary probability density of the model is obtained using the approximative Fokker-Planck equation, and its shape is discussed in detail. P-bifurcation and noise-induced bistability are explored, followed by the observation of noise-enhanced stability through mean first passage time analysis. Our findings demonstrate that: (i) noise can induce P-bifurcation, causing the structure of a stationary probability distribution to shift from unimodal to monotonic under positive correlation and switch from unimodal to bimodal under negative correlation; (ii) correlation time promotes population growth, leading to a higher probability of large population size and delaying the extinction process; (iii) noise-enhanced stability induced by multiplicative noise depends on both additive noise and correlation time, while it always exists for additive noise.

Could non-native species boost their chances of invasion success by socializing with natives?

Most invasions start with the introduction of a few individuals and the majority fail to establish and become invasive populations. A possible explanation for this is that some species are subject to Allee effects-disadvantages of low densities-and fail to perform vital activities due to the low availability of conspecifics. We propose that 'facilitation' from native individuals to non-natives through heterospecific sociability could enhance chances of the latter establishing in novel environments by helping them avoid Allee effects and even reducing the minimum number of non-native individuals necessary to achieve the density for a viable population (the Allee effect threshold). There is evidence from experiments carried out with freshwater fish, snails, lizards, mussels and bird that supports the idea of heterospecific sociability between native and non-native species as a process to promote invasion success. We propose that to understand invasion success in social non-native species we need to investigate how they integrate into the recipient community. Furthermore, to manage them, it may be necessary to reduce population density not just below the Allee effect threshold but also to understand how natives could help them shift the conspecific Allee effect threshold to their benefit. This article is part of the theme issue 'Mixed-species groups and aggregations: shaping ecological and behavioural patterns and processes'.

Optimizing the use of suppression zones for containment of invasive species

Despite efforts to prevent their establishment, many invasive species continue to spread and threaten food production, human health, and natural biodiversity. Slowing the spread of established species is often a preferred strategy; however, it is also expensive and necessitates treatment over large areas. Therefore, it is critical to examine how to distribute management efforts over space cost-effectively. Here we consider a continuous-space bioeconomic model and we develop a novel algorithm to find the most cost-effective allocation of treatment efforts throughout a landscape. We show that the optimal strategy often comprises eradication in the yet-uninvaded area, and under certain conditions, it also comprises maintaining a "suppression zone," an area between the invaded and the uninvaded areas, where treatment reduces the invading population but without eliminating it. We examine how the optimal strategy depends on the demographic characteristics of the species and reveal general criteria for deciding when a suppression zone is cost effective.

The establishment of plants following long-distance dispersal

Long-distance dispersal (LDD) beyond the range of a species is an important driver of ecological and evolutionary patterns, but insufficient attention has been given to postdispersal establishment. In this review, we summarize current knowledge of the post-LDD establishment phase in plant colonization, identify six key determinants of establishment success, develop a general quantitative framework for post-LDD establishment, and address the major challenges and opportunities in future research. These include improving detection and understanding of LDD using novel approaches, investigating mechanisms determining post-LDD establishment success using mechanistic modeling and inference, and comparison of establishment between past and present. By addressing current knowledge gaps, we aim to further our understanding of how LDD affects plant distributions, and the long-term consequences of LDD events.

Pest categorisation of Eotetranychus sexmaculatus

The EFSA Panel on Plant Health performed a pest categorisation of Eotetranychus sexmaculatus (Acari: Tetranychidae), the six-spotted spider mite, for the EU. The mite is native to North America and has spread to Asia and Oceania. It is not known to occur in the EU. The species is not listed in Annex II of Commission Implementing Regulation (EU) 2019/2072. E. sexmaculatus feeds on more than 50 hosts in 20 botanical families and can be a serious pest of important crops in the EU such as citrus (Citrus spp.), avocado (Persea americana), grapevine (Vitis spp.) and ornamentals such as Ficus spp. and Rosa spp. In California and New Zealand, the mite can breed continuously on evergreen hosts such as avocados and citrus, growing slowly during the winter and faster during the summer. Dry weather conditions hamper its development. Plants for planting, fruit, cut branches and cut flowers provide potential pathways for entry into the EU. Some host plants for planting are prohibited from entering the EU while others require a phytosanitary certificate, as do cut branches and cut flowers. In the warmer parts of southern EU Member States, climatic conditions and host plant availability are conducive for establishment and spread. The introduction of E. sexmaculatus is expected to have an economic impact in the EU through the reduction in yield, quality and commercial value of citrus and avocado production. Additional damage on other host plants, including ornamentals, under EU environmental conditions and cropping practices cannot be ruled out. Phytosanitary measures are available to reduce the likelihood of entry and spread. E. sexmaculatus satisfies with no key uncertainties the criteria that are within the remit of EFSA to assess for it to be regarded as a potential Union quarantine pest.

Of clockwork and catastrophes: advances in spatiotemporal dynamics of forest Lepidoptera

We applied a systematic global literature survey from the last 2.5 years on spatiotemporal population dynamics - broadly defined - of Lepidopteran forest pests. Articles were summarized according to domain-specific (planetary ecology - remote sensing, evolutionary ecology - genetics and genomics, and theoretical ecology - modeling) contributions to contemporary investigation of the above theme. 'Model systems' dominating our literature survey were native Choristoneura fumiferana and invasive Lymantria dispar. These systems represent opposing ends of a more general equilibrium-disequilibrium gradient, with implications for less-studied taxa. The dynamics of Lepidopteran systems defy simple modeling approaches. Technologies and insights emerging from 'slower' science domains are informing more complex theory, including predictions of spread, impacts, or both posed by more recent invasions and the disrupting effects of climate change.

Pest categorisation of Nipaecoccus viridis

The EFSA Panel on Plant Health performed a pest categorisation of Nipaecoccus viridis (Hemiptera: Sternorrhyncha: Pseudococcidae), the spherical scale, for the EU. It is of Asian origin and occurs widely in southern Asia, Africa and tropical Australia. It has been introduced to a few countries in the Americas. In the Mediterranean basin it is found in Algeria, Egypt, Israel, Syria and Turkey, where it is limited to the Marmara region. It has not been reported within the EU. It is not listed in Annex II of Commission Implementing Regulation (EU) 2019/2072. It reproduces sexually, has three generations each year in citrus orchards in South Africa, and all stages can overwinter. First instar nymphs may move to neighbouring plants by crawling or be passively dispersed by wind or hitchhiking on clothing, equipment or animals. It is highly polyphagous, feeding on plants in 115 genera and 46 families. It is an important pest of citrus (Citrus spp.), cotton (Gossypium spp.), mango (Mangifera indica), avocado (Persea americana) and stored potatoes (Solanum tuberosum). It also feeds on a wide range of other fruit (apple Malus domestica, olive Olea europea, pear Pyrus communis and grape Vitis vinifera) and vegetable crops (tomato Solanum lycopersicum), and ornamental plants (roses, Rosa spp.) that are widely grown in the EU. Plants for planting, fruits, vegetables, and cut flowers are the main potential pathways for entry of N. viridis into the EU. Climatic conditions and availability of host plants in southern parts of the EU where there are few days of frost each year would likely allow this species to successfully establish and spread. Reductions in yield and quality of cultivated hosts including avocado, citrus, cotton and mango is anticipated if establishment occurs. Phytosanitary measures are available to reduce the likelihood of entry and spread. N. viridis meets the criteria that are within the remit of EFSA to assess for this species to be regarded as a potential Union quarantine pest.

Pest risk assessment of Amyelois transitella for the European Union

Following a request from the European Commission, the EFSA Panel on Plant Health performed a pest risk assessment of Amyelois transitella (Lepidoptera: Pyralidae), the navel orangeworm, for the EU. The quantitative assessment considered two scenarios: (i) current practices and (ii) a requirement for chilled transport. The assessment focused on pathways of introduction, climatic conditions and cultivation of hosts allowing establishment, spread and impact. A. transitella is a common pest of almonds, pistachios and walnuts in California, which is the main source for these nuts imported into the EU. Based on size of the trade and infestation at origin, importation of walnuts and almonds from the USA was identified as the most important pathways for entry of A. transitella. Using expert knowledge elicitation (EKE) and pathway modelling, a median estimate of 2,630 infested nuts is expected to enter the EU each year over the next 5 years (90% certainty range (CR) from 338 to 26,000 infested nuts per year). However, due to estimated small likelihoods of transfer to a host, mating upon transfer and survival of founder populations, the number of populations that establish was estimated to be 0.000698 year-1 (median, 90% CR: 0.0000126-0.0364 year-1). Accordingly, the expected period between founding events is 1,430 years (median, 90% CR: 27.5-79,400 year). The likelihood of entry resulting in establishment is therefore considered very small. However, this estimate has high uncertainty, mainly concerning the processes of transfer of the insect to hosts and the establishment of founder populations by those that successfully transfer. Climate matching and CLIMEX modelling indicate that conditions are most suitable for establishment in the southern EU, especially around the Mediterranean basin. The median rate of natural spread was estimated to be 5.6 km/year (median, 90% CR 0.8-19.3 km/year), after an initial lag period of 3.1 year (mean, 90% CR 1.7-6.2 year) following the establishment of a founder population. If A. transitella did establish, estimated median yield losses in nuts were estimated to be in the order of 1-2% depending on the nut species and production system. A scenario requiring imports of nuts to be transported under chilled conditions was shown to provide potential to further reduce the likelihood of entry.

Revisiting implementation of multiple natural enemies in pest management

A major goal of biological control is the reduction and/or eradication of pests using various natural enemies, in particular, via deliberate infection of the target species by parasites. To enhance the biological control, a promising strategy seems to implement a multi-enemy assemblage rather than a single control agent. Although a large body of theoretical studies exists on co-infections in epidemiology and ecology, there is still a big gap in modelling outcomes of multi-enemy biological control. Here we theoretically investigate how the efficiency of biological control of a pest depends on the number of natural enemies used. We implement a combination of eco-epidemiological modelling and the Adaptive Dynamics game theory framework. We found that a progressive addition of parasite species increases the evolutionarily stable virulence of each parasite, and thus enhances the mortality of the target pest. However, using multiple enemies may have only a marginal effect on the success of biological control, or can even be counter-productive when the number of enemies is excessive. We found the possibility of evolutionary suicide, where one or several parasite species go extinct over the course of evolution. Finally, we demonstrate an interesting scenario of coexistence of multiple parasites at the edge of extinction.

Confirming the broadscale eradication success of nutria (Myocastor coypus) from the Delmarva Peninsula, USA

Nutria (Myocastor coypus) were introduced to the eastern shore of Chesapeake Bay, USA in the 1940s. They reached peak densities in the late 1990s, causing massive wetland loss. Beginning in 2002, a systematic plan to eradicate nutria from the 1.7M ha Delmarva Peninsula was implemented. Since that time the nutria population has been effectively reduced, and no nutria have been detected since May 2015. A lack of detection does not equate with complete absence. We address the following three questions. (1) What is the expected probability of nutria eradication from the Delmarva Peninsula as of the end of 2020? (2) If the probability of eradication is below the management target of 0.95, how much more surveillance is required? (3) How sensitive is the estimated probability of eradication to varying levels of public surveillance and modelled population growth rates? These questions were addressed by employing a stochastic spatially-explicit surveillance model that uses data in which no nutria were detected to quantify the probability of complete absence (PoA) over the entire Delmarva Peninsula. We applied an analytical framework that decomposes the spatial risk of survivors and data into management zones, and took advantage of low-cost public reporting of nutria sightings. Active surveillance by the eradication program included detector dog and tracker surveys, shoreline surveys, detection with ground and water platforms (with hair snares), and camera traps. Results showed that the PoA increased with time and surveillance from a beginning PoA in May 2015 of  0.01 to a mean of 0.75 at the end of 2020. This indicates that the PoA on the Delmarva was well below the target threshold of 0.95 for declaring eradication success. However, given continued surveillance without detection, a PoA of 0.95 would be achieved by June 2022. This analysis provides an objective mechanism to align the expectations of policy makers, managers and the public on when eradication of nutria from the entire Delmarva Peninsula should be declared successful.

Pest categorisation of Amathynetoides nitidiventris

The EFSA Panel on Plant Health performed the pest categorisation of the ulluco weevil, Amathynetoides nitidiventris (Hustache), for the EU territory. This species is not included in EU Commission Implementing Regulation 2019/2072. However, its only substantiated host, ulluco (Ullucus tuberosus), is included in Annex I of Regulation EU 2018/2019 as a high risk plant prohibited from entering the EU, pending risk assessment. In its native Andean region, A. nitidiventris is univoltine, with a lifecycle highly synchronised with the phenology of its host, reproduction and development take place during the development of tubers. Oviposition occurs in the soil. Larvae feed by tunnelling into the tubers, which most of them abandon to pupate in the soil. A minority pupates in the tubers. Because adult A. nitidiventris are often found in other crops due to crop rotations and crop associations, this species has been mistakenly identified as a pest of other crops. In principle soil and tubers of ulluco could provide a pathway for A. nitidiventris into the EU. However, the soil pathway is closed and ulluco tubers are regulated as high risk plants. There are no EU records of interception. Should this weevil enter the EU, the rarity of its host, which is not known to be cultivated in EU MSs, would hamper establishment, spread, and impact. As a consequence, A. nitidiventris does not satisfy all the criteria that are within the remit of EFSA to assess for it to be regarded as a potential Union quarantine pest. The criteria that are not met are the potential for establishment, spread, and economic or environmental consequences in the EU.

Pest categorisation of Oligonychus perseae

The EFSA Panel on Plant Health performed a pest categorisation of Oligonychus perseae (Acari: Prostigmata: Tetranychidae), the persea mite, for the EU. O. perseae is a tropical species that originated in Mesoamerica and has now spread and established in California, Florida, Hawaii, Morocco, southern Europe and Israel. Within the EU, it is established in Italy, Portugal and Spain. O. perseae is not listed in Commission Implementing Regulation (EU) 2019/2072. It is polyphagous, feeding on plants in 20 genera in 17 families. It is most frequently reported on avocado (Persea americana), where it is considered a key pest. No evidence was found indicating damage to other crops. O. perseae live on leaves and do not attack the fruit. Populations usually grow exponentially at the beginning of summer and decline at the end of this season. High population densities can cause severe defoliation, resulting in downgrading of fruit through sunburn. However, this type of damage is common only if trees additionally suffer from water stress. The lack of additional avocado pests in the EU, which facilitates the production of organic avocados, is jeopardised by the occurrence of this mite, as it may require pesticide applications. This is why O. perseae is considered an important pest of avocados in Spain, where more than 80% of EU avocado production occurs. Natural dispersal is restricted to neighbouring trees. However, human‐assisted movement can result in long‐distance spread. Plants for planting provide potential pathways for further entry and spread, including O. perseae‐free EU MS where avocados are grown (i.e. Cyprus, France, Greece). Climatic conditions and availability of host plants in southern EU countries are conducive for establishment. Phytosanitary measures are available to reduce the likelihood of further entry and spread. O. perseae satisfies with no key uncertainties the criteria that are within the remit of EFSA to assess for it to be regarded as a potential Union quarantine pest.

Pest categorisation of Sirex nitobei

The EFSA Panel on Plant Health performed a pest categorisation of Sirex nitobei (Hymenoptera: Siricidae), the nitobe horntail, for the territory of the EU. S. nitobei is not listed in Annex II of Commission Implementing Regulation (EU) 2019/2072 but was identified as a potential regulated pest in a commodity risk assessment of Pinus thunbergii artificially dwarfed plants from Japan. This species is present in Japan (except Hokkaidō), the Republic of Korea and 13 Chinese provinces. S. nitobei attacks several Pinus species and has been reported less frequently on Abies firma and Larix spp., including L. leptolepis. The females oviposit into the sapwood. Eggs are deposited together with a phytotoxic mucus and a symbiotic fungus, Amylostereum areolatum or A. chailletii. The combined action of the venom and the fungus results in the death of the host trees. The fungus degrades the lignocellulosic components of the wood, and the larvae feed on the liquid fraction of the digested residues left by the fungus. All immature stages live in the hosts sapwood. The lifecycle of the pest lasts 1 year. S. nitobei can travel with conifer wood, wood packaging material or plants for planting, but these pathways from third countries are closed by prohibition. However, a derogation exists for artificially dwarfed Japanese black pine (Pinus thunbergii) from Japan, which therefore provides a potential pathway. Climatic conditions in several EU member states and host plant availability in those areas are conducive for establishment. The introduction of S. nitobei is potentially damaging for pines. Phytosanitary measures are available to reduce the likelihood of entry and further spread, and there is a potential for biological control. S. nitobei satisfies all the criteria that are within the remit of EFSA to assess for it to be regarded as a potential Union quarantine pest.

Pest categorisation of Bagrada hilaris

The EFSA Panel on Plant Health performed a pest categorisation of Bagrada hilaris (Hemiptera: Pentatomidae) for the EU territory. B. hilaris, known as the bagrada bug or painted bug, is a polyphagous pest feeding on at least 25 plant families including several economically important brassica crops such as broccoli, cabbage and cauliflower. Other economically important hosts suffering impacts include beans (Fabaceae), wheat and maize (Poaceae). Young plants are particularly vulnerable to adults and nymphs feeding on tender leaves and growing points, which can cause yield losses. B. hilaris occurs in Africa and Asia and has spread to North America (USA and Mexico) and South America (Chile) where there are multiple generations per year. It is not widely distributed in the EU but has been established in Malta and on the Italian island of Pantelleria, south west of Sicily, since the 1970s where it is an economically important pest of capers. The reasons why it has not spread further within southern Europe are unknown. B. hilaris is not a regulated pest in the EU. It could further enter and spread within the EU via the import and movement of host plants or as a hitchhiking species forming aggregations in conveyances and amongst non‐plant traded goods. Host availability and climate suitability suggest that, in addition to Malta and Pantelleria, southern areas of the EU around the Mediterranean would also be suitable for B. hilaris establishment. The introduction of B. hilaris to other Mediterranean areas of the EU would likely cause impacts in a range of crops, particularly brassicas. Measures to prevent entry and spread are available. B. hilaris satisfies all of the criteria that are within the remit of EFSA to assess for it to be regarded as a potential Union quarantine pest.

Pest categorisation of Thecodiplosis japonensis

The EFSA Panel on Plant Health performed a pest categorisation of Thecodiplosis japonensis (Diptera: Cecidomyiidae) for the EU territory. This species is not included in the EU Commission Implementing Regulation 2019/2072. T. japonensis Uchida & Inouye is a well-defined species, native to a large part of Japan, which was introduced to the Republic of Korea and eastern China: Fujian and Shandong. It attacks Pinus densiflora, P. thunbergii and P. luchuensis in Japan; P. densiflora and P. thunbergii in Korea; and P. massoniana in China, and has been observed to attack other two-needle pine species, including species present in the EU. The pest is univoltine and the adults emerge between May and August. The adults live only for 1 day. Each female oviposits in batches on developing needles. The neonate larvae crawl to the base of the needle fascicle and create a gall in which they feed gregariously by sap sucking. The third-instar larvae leave the galls in November, overwinter in a cocoon in the soil and pupate at the end of the winter. Degree day models have been developed to predict adult emergence. Survival of overwintering stages is poor below 15°C and above 30°C. The pest can be detected by its symptoms (stunted or dead needles, galls at the base of infected needle fascicles), and identified using morphological characters or the mitochondrial COI gene. T. japonensis is one of the major forest pests in the Republic of Korea, where 1.7 million trees were cut to control it in 2014-2015. It flies uneasily (a few hundred metres) but can be transported in galls on Pinus plants for planting, including artificially dwarfed plants, or with cut branches. Climate matching and host tree distribution suggest that T. japonensis would be able to establish and have an impact in the EU territory. T. japonensis satisfies all the criteria that are within the remit of EFSA to assess for it to be regarded as a potential Union quarantine pest.

Pest categorisation of Arboridia kakogawana

The EFSA Panel on Plant Health performed a pest categorisation of the Japanese grape leafhopper, Arboridia kakogawana (Matsumura, 1932) (Hemiptera: Cicadellidae), for the EU territory. This species is not included in the EU Commission Implementing Regulation 2019/2072. Adults of A. kakogawana overwinter in broad-leaved and mixed forests and move to vineyards in the spring where there may be up to four generations, before adults move back to forests during late summer-early autumn to overwinter, possibly under diapause. A. kakogawana has a restricted host range (Vitis spp. and Parthenocissus quinquefolia). It is native to Eastern Asia, from where it moved westwards reaching southern Russia in 1999, and subsequently Ukraine, Romania, Bulgaria and Serbia in 2020. A. kakogawana develops on the abaxial side of the leaves causing chlorotic spots that reduce grape quality. Plants for planting of Vitis L. are banned from entering the EU except from Switzerland, where A. kakogawana is not known to occur. Therefore, this can be considered as a closed entry pathway. However, other plants for planting including the host P. quinquefolia and many broad-leaved trees where overwintering takes place, as well as isolated bark and wood with bark provide potential pathways which are partly regulated but remain open. There are no EU records of interception. Additional introductions and further spread of A. kakogawana into/within the EU, coupled with the ample availability of grapevines and the climatic conditions would most probably allow successful establishment in most EU member states. Should this happen, economic impact in table and wine grapes is anticipated. A. kakogawana satisfies all the criteria that are within the remit of EFSA to assess for it to be regarded as a potential Union quarantine pest (UQP).

Using Chemical Ecology to Enhance Weed Biological Control

Simple Summary

Signaling chemicals produced by one organism that bring about a behavioral response in a recipient organism are known as semiochemicals, with pheromones being a well-known example. Semiochemicals have been widely used to monitor and control insect pests in agricultural and forestry settings, but they have not been widely used in weed biological control. Here, we list the few examples of semiochemical use in the practice of classical weed biological control, where a natural enemy (biocontrol agent) from the native range of the plant is introduced into the new invaded range. Uses of semiochemicals include monitoring of biocontrol agents (sex pheromones), keeping biocontrol agents together long enough for them to become well established (aggregation pheromones) and repelling agents from areas where they may be unwanted (host or non-host plant volatile organic deterrents). We make the case that given the vast potential of biological control in suppressing invasive plants it is well worth developing and utilizing semiochemicals to enhance biocontrol programs.

Abstract

In agricultural systems, chemical ecology and the use of semiochemicals have become critical components of integrated pest management. The categories of semiochemicals that have been used include sex pheromones, aggregation pheromones, and plant volatile compounds used as attractants as well as repellents. In contrast, semiochemicals are rarely utilized for management of insects used in weed biological control. Here, we advocate for the benefit of chemical ecology principles in the implementation of weed biocontrol by describing successful utilization of semiochemicals for release, monitoring and manipulation of weed biocontrol agent populations. The potential for more widespread adoption and successful implementation of semiochemicals justifies multidisciplinary collaborations and increased research on how semiochemicals and chemical ecology can enhance weed biocontrol programs.

Pest categorisation of Phlyctinus callosus

The EFSA Panel on Plant Health performed a pest categorisation of Phlyctinus callosus (Coleoptera: Curculionidae) for the EU territory. This species is not included in EU Commission Implementing Regulation 2019/2072. P. callosus is a polyphagous pest native to South Africa which has spread to Australia and New Zealand, Reunion and St Helena. Immature development takes place in the soil where larvae feed on the roots of a variety of plants including grasses, root vegetables and herbaceous plants; adults are noted as significant pests of apples, nectarines and grapes, feeding on foliage and the surface of fruit causing scarring. Soft fruits such as strawberries and blueberries can also be damaged by adult feeding. P. callosus has been intercepted in Europe on apples and peaches from South Africa. Table grapes could also provide a pathway for entry to the EU. Rooted plants for planting could also provide a potential pathway. Hosts are grown widely across the EU in areas with climates comparable to those in parts of South Africa, New Zealand and Australia where the pest is established suggesting that conditions in the EU are suitable for the establishment of P. callosus. If introduced into the EU, natural spread would be limited because adults cannot fly and must disperse by walking. However, the movement of host plants for planting within the EU could spread juvenile stages much faster and adults could spread with fruits. The prohibition of soil or growing media from third countries should prevent the entry of P. callosus larvae and pupae. Other phytosanitary measures are available to inhibit the entry of P. callosus. P. callosus satisfies the criteria that are within the remit of EFSA to assess for it to be regarded as a potential Union quarantine pest.

Pest categorisation of Phenacoccus solenopsis

The EFSA Panel on Plant Health performed a pest categorisation of Phenacoccus solenopsis (Hemiptera: Pseudococcidae) for the European Union (EU) territory. This species is not included in EU Commission Implementing Regulation 2019/2072. P. solenopsis is native to North America and has spread to all continents except Antarctica. It has recently been reported from Cyprus, Greece and Italy. This mealybug is a polyphagous pest, feeding on about 300 plant species. It usually feeds on aerial plant parts, especially new growth, but also occurs on roots, and is often associated with ants. It is an economically important pest of ornamentals, such as hibiscus and lantana, glasshouse vegetable crops, mainly bell pepper, tomato and eggplant, and field crops, such as cotton. Large populations cause die-back and reduction in yield. Adult and immature P. solenopsis could enter the EU with imported fresh fruit, vegetables and cut flowers, although the main pathway of introduction is likely to be plants for planting. Host availability and climate suitability indicate that most of the EU would be suitable for establishment. The main natural dispersal stage is the first instar, which crawls over the plant or may be dispersed further by wind and animals. All stages may be transported over longer distances in trade. Phytosanitary measures are available and should prevent further introductions and slow the spread within the EU. P. solenopsis is under official control in Cyprus and has recently been reported in Greece and Italy. Assuming that these reports reflect a limited distribution, and P. solenopsis shortly comes under official control, it would satisfy all the criteria that are within the remit of EFSA to assess for it to be regarded as a potential Union quarantine pest.

Managing propagule pressure to prevent invasive species establishments: propagule size, number, and risk-release curve

There is considerable evidence that keeping propagule pressure low can drastically reduce establishment probability of potential invasive species. Yet, most management plans and research efforts fail to explicitly acknowledge all three of the components of propagule pressure: size, number, and the risk-release relationship. It is unclear how failing to specify one or more of these components can influence the efficacy of management plans in preventing invasive species establishment. Furthermore, even if all components are acknowledged and quantified, there currently is no mathematical tool available to calculate the levels of propagule pressure that ensure attainment of a predetermined, and system-specific, target establishment probability. Here, we quantify the resulting uncertainty in establishment probability when one or more components of propagule pressure is unknown by using parameter uncertainty analysis on realistic values of propagule pressure. In addition, to aid in the development of management plans that explicitly set propagule pressure limits, we develop a propagule-pressure sensitivity analysis that we use to determine the required reduction in levels for propagule size and number (representative of management actions) to maintain a target establishment probability. We show that the precision of establishment estimates is highly dependent on knowledge of all three propagule pressure components, where the possible range of values for establishment probability can vary by over 50% without full specification. In addition, our sensitivity analysis showed that propagule size and number can be altered independently or in conjunction to lower establishment probability below a target level. Importantly, our sensitivity analysis was able to specifically quantify how much reduction in a propagule pressure component(s) is needed to reach a given target establishment probability. Our findings suggest that quantifying the three components of propagule pressure should be a priority for invasive species prevention moving forward. Furthermore, our sensitivity analysis tool can serve to guide the development of new invasive species management plans in a transparent and quantitative manner. Together with information on the costs associated with approaches to reducing propagule pressure, our tool can be used to identify the most cost-effective approach to prevent invasive species establishments.

Pest categorisation of Elasmopalpus lignosellus

The European Commission requested the EFSA Panel on Plant Health to conduct a pest categorisation of Elasmopalpus lignosellus (Zeller) (Leipidoptera: Pyralidae) for the territory of the EU following interceptions of the organism within the EU and its addition to the EPPO Alert List. E. lignosellus feeds on over 70 species; hosts include cereals, especially maize, legumes, brassicas and a range of grasses. Seedlings of ornamental and forest trees can also be hosts. E. lignosellus is established in tropical and subtropical areas of North, Central and South America. Eggs are usually laid in the soil or on the lower stem of hosts. Larvae develop in the soil and feed on roots and stems causing stunting and yield losses. Plants for planting, rooted with growing media, or with stems cut close to the soil, and fresh vegetables harvested with stems, such as asparagus and cabbage, provide pathways for entry. Population development is favoured by dry and hot conditions (27-33°C). Adults fly and can be carried in air currents. Adults are recorded from temperate areas within the Americas contributing some uncertainty regarding the limits of its establishment potential in the EU. Although cultivated and wild hosts are distributed across the EU, impacts are likely to be confined to production areas on sandy soils around the coastal Mediterranean during hot dry years. Phytosanitary measures are available to inhibit the entry of E. lignosellus. E. lignosellus satisfies the criteria that are within the remit of EFSA to assess for it to be regarded as a potential Union quarantine pest.

Imported Hyalomma ticks in the Netherlands 2018-2020

BACKGROUND

Ticks of the genus Hyalomma, which are vectors for several tick-borne diseases, are occasionally found in areas outside their endemic range including northern parts of Europe. The objective of this study was to analyse adult Hyalomma ticks that were recently found in the Netherlands.

METHODS

Hyalomma ticks were morphologically identified. Cluster analysis, based upon sequence data (cox1 barcoding) for molecular identification, and pathogen detection were performed. Additionally, a cross-sectional survey of horses was conducted to actively search for Hyalomma ticks in summer 2019. Analysis of temperature was done to assess the possibility of (i) introduced engorged nymphs moulting to adults and (ii) establishment of populations in the Netherlands.

RESULTS

Seventeen adult Hyalomma ticks (one in 2018, eleven in 2019, five in 2020) were found by citizens and reported. Fifteen ticks were detected on horses and two on humans. Twelve were identified as H. marginatum, one as H. rufipes and four, of which only photographic images were available, as Hyalomma sp. No Crimean-Congo haemorrhagic fever virus or Babesia/Theileria parasites were detected. One adult tick tested positive for Rickettsia aeschlimannii. In the cross-sectional horse survey, no Hyalomma ticks were found. Analysis of temperatures showed that engorged nymphs arriving on migratory birds in spring were able to moult to adults in 2019 and 2020, and that cumulative daily temperatures in the Netherlands were lower than in areas with established H. marginatum populations.

CONCLUSIONS

Our results show that Hyalomma ticks are regularly introduced in the Netherlands as nymphs. Under the Dutch weather conditions, these nymphs are able to develop to the adult stage, which can be sighted by vigilant citizens. Only one human pathogen, Rickettsia aeschlimannii, was found in one of the ticks. The risk of introduction of tick-borne diseases via Hyalomma ticks on migratory birds is considered to be low. Establishment of permanent Hyalomma populations is considered unlikely under the current Dutch climatic conditions.

Treatment-induced evolutionary dynamics in nonmetastatic locally advanced rectal adenocarcinoma

Multi-modal treatment of non-metastatic locally advanced rectal adenocarcinoma (LARC) includes chemotherapy, radiation, and life-altering surgery. Although highly effective for local cancer control, metastatic failure remains significant and drives rectal cancer-related mortality. A consistent observation of this tri-modality treatment paradigm is that histologic response of the primary tumor to neoadjuvant treatment(s), which varies across patients, predicts overall oncologic outcome. In this chapter, we will examine this treatment response heterogeneity in the context of evolutionary dynamics. We hypothesize that improved understanding of eco-evolutionary pressures rendering small cancer cell populations vulnerable to extinction may influence treatment strategies and improve patient outcomes. Applying effective treatment(s) to cancer populations causes a "race to extinction." We explore principles of eco-evolutionary extinction in the context of these small cancer cell populations, evaluating how treatment(s) aim to eradicate the cancer populations to ultimately result in cure. In this chapter, we provide an evolutionary rationale for limiting continuous treatment(s) with the same agent or combination of agents to avoid selection of resistant cancer subpopulation phenotypes, allowing "evolutionary rescue." We draw upon evidence from nature demonstrating species extinction rarely occurring as a single event phenomenon, but rather a series of events in the slide to extinction. We posit that eradicating small cancer populations, similar to small populations in natural extinctions, will usually require a sequence of different external perturbations that produce negative, synergistic dynamics termed the "extinction vortex." By exploiting these unique extinction vulnerabilities of small cancer populations, the optimal therapeutic sequences may be informed by evolution-informed strategies for patients with LARC.

Con- and Heterospecific Shoaling Makes Invasive Guppies More Risk Taking

Invasive species are one of the greatest threats to biodiversity. Behavioral traits are recognized as key to promote individual’s survival in changing conditions. For social species being part of a group is key to carry out vital activities. Heterospecific social environments could provide exotic species with the opportunity to join groups and gain the advantages of being part of a larger population. Short latency to exit a refuge is a behavioral response that could be linked to invasion success as it increases the chances of individuals to locate food sources and other resources in novel environments. The guppy (Poecilia reticulata), a successful invader, has been found to take advantage of the presence of native species to reduce its refuge emergence latency and acquire information. The research was carried out in Mexico, we investigated the effect of heterospecific social contexts that include natives and other invasive viviparous fishes on guppies’ refuge emergence latency. We found that guppies’ emergence latency was shorter when accompanied by another guppy than when alone. Their latency was also shorter when with other invaders and when with native goodeids, but with one of the invaders (Pseudoxiphophorus bimaculatus) and with goodeids (Skiffia bilineata) latency reduction was not as high as when with conspecifics or with the invader Poecilia gracilis. Our experiment supports both the idea that already established invaders could provide benefits to new ones, and that native species also provide benefits but less than invaders. Increasing our knowledge about conspecific and heterospecific social interactions that could make an exotic species become invasive is key to assess the invasion risk of a community.

The allelopathy of horseweed with different invasion degrees in three provinces along the Yangtze River in China

The effect of allelopathy from invasive alien plants (IAPs) on native species is one of the main factors for their adaptation and diffusion. IAPs can have different degrees of invasion under natural succession and are distributed in numerous regions. Seed germination and seedling growth (SGe-SGr) play a crucial role in population recruitment. Thus, it is critical to illustrate the differences in the allelopathy caused by an IAP with different degrees of invasion in numerous regions on SGe-SGr of native species to describe the primary force behind their adaptation and diffusion. This study assessed the allelopathy of the notorious IAP horseweed (Conyza canadensis (L.) Cronq.) on SGe-SGr of the native lettuce species (Lactuca sativa L.) under different degrees of invasion (light degree of invasion and heavy degree of invasion) in three provinces (Jiangsu, Anhui, and Hubei) along the Yangtze River in China. The allelopathy of horseweed leaf extract on lettuce SGe-SGr remarkably increased with the increased degree of invasion, which may be due to the buildup of allelochemicals generated by horseweed with a heavy degree of invasion compared with a light degree of invasion. A high concentration of horseweed leaf extract resulted in noticeably stronger allelopathy on lettuce SGe-SGr compared to the extract with a low concentration. There are noticeable differences in the allelopathy of the extract of horseweed leaves from different provinces on lettuce SGe-SGr with the following order i.e. Jiangsu > Hubei > Anhui. This may be due to the high latitudes for the three sampling sites in Jiangsu compared with the latitudes for the collection sites in Hubei and Anhui. There are certain differences in the environments among the three provinces. Thus, the allelopathy of horseweed on SGe-SGr of lettuce may have a greater negative impact in Jiangsu compared to the other two provinces.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-021-00962-y.

Qualitative analysis of a diffusive predator–prey model with Allee and fear effects

In this study, we consider a diffusive predator–prey model with multiple Allee effects induced by fear factors. We investigate the existence, boundedness and permanence of the solution of the system. We also discuss the existence and non-existence of non-constant solutions. We derive sufficient conditions for spatially homogeneous (non-homogenous) Hopf bifurcation and steady state bifurcation. Theoretical and numerical simulations show that strong Allee effect and fear effect have great effect on the dynamics of system.

Density dependence and the spread of invasive big-headed ants (Pheidole megacephala) in an East African savanna

Supercolonial ants are among the largest cooperative units in nature, attaining extremely high densities. How these densities feed back into their population growth rates and how abundance and extrinsic factors interact to affect their population dynamics remain open questions. We studied how local worker abundance and extrinsic factors (rain, tree density) affect population growth rate and spread in the invasive big-headed ant, which is disrupting a keystone mutualism between acacia trees and native ants in parts of East Africa. We measured temporal changes in big-headed ant (BHA) abundance and rates of spread over 20 months along eight transects, extending from areas behind the front with high BHA abundances to areas at the invasion front with low BHA abundances. We used models that account for negative density dependence and incorporated extrinsic factors to determine what variables best explain variation in local population growth rates. Population growth rates declined with abundance, however, the strength of density dependence decreased with abundance. We suggest that weaker density dependence at higher ant abundances may be due to the beneficial effect of cooperative behavior that partially counteracts resource limitation. Rainfall and tree density had minor effects on ant population dynamics. BHA spread near 50 m/year, more than previous studies reported and comparable to rates of spread of other supercolonial ants. Although we did not detect declines in abundance in areas invaded a long time ago (> 10 years), continued monitoring of abundance at invaded sites may help to better understand the widespread collapse of many invasive ants.

Physical contact, volatiles, and acoustic signals contribute to monogamy in an invasive aggregating bark beetle

The behavioral strategies and mechanisms by which some insects maintain monogamous mating systems are not well understood. We investigated the mating system of the bark beetle Dendroctonus valens, and identified several contributing mechanisms. Field and laboratory observations suggest the adults commonly form permanent bonds during host colonization. Moreover, it showed mated females that remained paired with males produced more offspring than mated females that were alone in galleries. In bioassays, a second female commonly entered a gallery constructed by a prior female. Videos show she commonly reached the location of the first female, but they did not engage in actual fighting. Rather, the second female typically departs to form her own gallery. Acoustic signaling likewise does not appear to influence female-female encounters, based on controlled muting experiments. Instead, the intruder appears to perceive the resident's presence by physical contact. Both acoustic signals and volatiles released by females during gallery constructing were shown to attract males. After a male joined a female in a gallery, the male-produced aggressive sounds, which were shown by playback to deter other males from entering the gallery. Unlike female-female interactions, resident males use their head and rear to push intruders out of galleries. Additionally, volatiles released by males during feeding repelled intruding males, discouraging them from entering the gallery. Males also construct plugs that block the entrance, which may prevent subsequent males and predators from entering the gallery. Thus, D. valens has evolved multifaceted mechanisms contributing to single pairings that confer benefits to both sexes.

Combining multiple tactics over time for cost-effective eradication of invading insect populations

Because of the profound ecological and economic impacts of many non-native insect species, early detection and eradication of newly founded, isolated populations is a high priority for preventing damages. Though successful eradication is often challenging, the effectiveness of several treatment methods/tactics is enhanced by the existence of Allee dynamics in target populations. Historically, successful eradication has often relied on the application of two or more tactics. Here, we examine how to combine three treatment tactics in the most cost-effective manner, either simultaneously or sequentially in a multiple-annum process. We show that each tactic is most efficient across a specific range of population densities. Furthermore, we show that certain tactics inhibit the efficiency of other tactics and should therefore not be used simultaneously; but since each tactic is effective at specific densities, different combinations of tactics should be applied sequentially through time when a multiple-annum eradication programme is needed.

The Epidemiological Framework for Biological Invasions (EFBI): an interdisciplinary foundation for the assessment of biosecurity threats

Emerging microparasite (e.g. viruses, bacteria, protozoa and fungi) epidemics and the introduction of non-native pests and weeds are major biosecurity threats worldwide. The likelihood of these threats is often estimated from probabilities of their entry, establishment, spread and ease of prevention. If ecosystems are considered equivalent to hosts, then compartment disease models should provide a useful framework for understanding the processes that underpin non-native species invasions. To enable greater cross-fertilisation between these two disciplines, the Epidemiological Framework for Biological Invasions (EFBI) is developed that classifies ecosystems in relation to their invasion status: Susceptible, Exposed, Infectious and Resistant. These states are linked by transitions relating to transmission, latency and recovery. This viewpoint differs markedly from the species-centric approaches often applied to non-native species. It allows generalisations from epidemiology, such as the force of infection, the basic reproductive ratio R0, super-spreaders, herd immunity, cordon sanitaire and ring vaccination, to be discussed in the novel context of non-native species and helps identify important gaps in the study of biological invasions. The EFBI approach highlights several limitations inherent in current approaches to the study of biological invasions including: (i) the variance in non-native abundance across ecosystems is rarely reported; (ii) field data rarely (if ever) distinguish source from sink ecosystems; (iii) estimates of the susceptibility of ecosystems to invasion seldom account for differences in exposure to non-native species; and (iv) assessments of ecosystem susceptibility often confuse the processes that underpin patterns of spread within -and between- ecosystems. Using the invasion of lakes as a model, the EFBI approach is shown to present a new biosecurity perspective that takes account of ecosystem status and complements demographic models to deliver clearer insights into the dynamics of biological invasions at the landscape scale. It will help to identify whether management of the susceptibility of ecosystems, of the number of vectors, or of the diversity of pathways (for movement between ecosystems) is the best way of limiting or reversing the population growth of a non-native species. The framework can be adapted to incorporate increasing levels of complexity and realism and to provide insights into how to monitor, map and manage biological invasions more effectively.

The effect of cross-boundary management on the trajectory to commonness in biological invasions

The number of alien species introduced and undergoing range expansion in novel environments is steadily increasing, with important consequences for native ecosystems. The efficacy of management planning and decision making to limit such invasions can be improved by understanding how interventions will impact the population dynamics of recently introduced species. To do so, here we expand on a typological framework that enables the classification of populations over time into 10 categories of commonness, and apply it to a spatially discrete metapopulation with heterogeneous abundance across spatial units (patches). We use this framework to assess the effect of cross-boundary management on the capacity of a metapopulation with different demographic and dispersal characteristics, including time lags in population growth, to become common. We demonstrate this framework by simulating a simple theoretical metapopulation model capable of exploring a range of environments, species characteristics, and management actions. Management can vary in the efficacy of propagule interception between patches, and in the synchronisation of the implementation of these measures across patches (i.e. if management is implemented simultaneously across patches). Simulations show that poor interception efficacy that only modestly reduces the number of propagules entering a given spatial unit cannot be compensated for by strong management synchronisation between spatial units. Management synchronisation will nonetheless result in a reduction in rates of spread once a critical threshold of interception efficacy has been met. Finally, time lags in population growth that may result in delayed spread are an important aspect to be considered in management as they can amplify the efficacy of management. Our results demonstrate how a typological framework of categories of commonness can be used to provide practical insights for the management of biological invasions.

Spotlight on the invasion of a carabid beetle on an oceanic island over a 105-year period

The flightless beetle Merizodus soledadinus, native to the Falkland Islands and southern South America, was introduced to the sub-Antarctic Kerguelen Islands in the early Twentieth Century. Using available literature data, in addition to collecting more than 2000 new survey (presence/absence) records of M. soledadinus over the 1991-2018 period, we confirmed the best estimate of the introduction date of M. soledadinus to the archipelago, and tracked subsequent changes in its abundance and geographical distribution. The range expansion of this flightless insect was initially slow, but has accelerated over the past 2 decades, in parallel with increased local abundance. Human activities may have facilitated further local colonization by M. soledadinus, which is now widespread in the eastern part of the archipelago. This predatory insect is a major threat to the native invertebrate fauna, in particular to the endemic wingless flies Anatalanta aptera and Calycopteryx moseleyi which can be locally eliminated by the beetle. Our distribution data also suggest an accelerating role of climate change in the range expansion of M. soledadinus, with populations now thriving in low altitude habitats. Considering that no control measures, let alone eradication, are practicable, it is essential to limit any further local range expansion of this aggressively invasive insect through human assistance. This study confirms the crucial importance of long term biosurveillance for the detection and monitoring of non-native species and the timely implementation of control measures.

Can a barrier zone stop invasion of a population?

We consider an integro-difference model to study the effect of a stationary barrier zone on invasion of a population with a strong Allee effect. It is assumed that inside the barrier zone a certain proportion of the population is killed. A Laplace dispersal kernel is used in the model. We provide a formula for the critical width [Formula: see text] of barrier zone. We show that when a barrier zone is set at the front of a population, if the width of barrier zone is bigger than [Formula: see text] then the barrier zone can stop the population invasion, and if the width of barrier zone is less than [Formula: see text] then the population crosses the barrier zone and eventually occupies the entire space. The results are proven by establishing the existence and attractivity of three types of equilibrium solutions. The mathematical proofs involve phase plane analysis and comparison.

The mixed silicon and cadmium synergistically impact the allelopathy of Solidago canadensis L. on native plant species Lactuca sativa L

Several invasive alien plants (IAP) can trigger evidently allelopathy on the seed germination and seedling growth (SgSg) of native plant species (NPS). The getting worse condition with heavy metal pollution (e.g., cadmium) can significantly impact SgSg of plant species. Silicon can offset the adverse effects of environmental pressure on the growth and development of plant species. Thus, it is important to evaluate the influences of silicon on the allelopathy of IAP on SgSg of NPS under cadmium stress to better understand the mechanism driving the successful colonization of IAP. This study focuses on the allelopathy of the infamous IAP Solidago canadensis L. (Canada goldenrod; by using leaf extracts) on SgSg of NPS Lactuca sativa L. under the separated and mixed silicon and cadmium addition. S. canadensis triggers notably allelopathy on SgSg of L. sativa and gradually upsurges with increasing leaf extract concentration. Thus, the growth performance of NPS will be gradually reduced with an increasing degree of S. canadensis invasion. Cadmium evidently declines SgSg of L. sativa due to the broken balance of plant species for nutrient absorption. The mixed S. canadensis leaf extracts and cadmium synergistically impact seed germination of L. sativa but antagonistically affect seedling growth of L. sativa. The mixed silicon and cadmium intensify the allelopathy of S. canadensis on SgSg of L. sativa probably due to the increased effective content of cadmium in plant roots under silicon addition. Thus, the mixed silicon and cadmium will be advantageous to the following invasion process of IAP largely via the depressed SgSg of NPS.

Eradicating the large white butterfly from New Zealand eliminates a threat to endemic Brassicaceae

In May 2010 the large white butterfly, Pieris brassicae L. (Lepidoptera: Pieridae), was discovered to have established in New Zealand. It is a Palearctic species that-due to its wide host plant range within the Brassicaceae-was regarded as a risk to New Zealand's native brassicas. New Zealand has 83 native species of Brassicaceae including 81 that are endemic, and many are threatened by both habitat loss and herbivory by other organisms. Initially a program was implemented to slow its spread, then an eradication attempt commenced in November 2012. The P. brassicae population was distributed over an area of approximately 100 km2 primarily in urban residential gardens. The eradication attempt involved promoting public engagement and reports of sightings, including offering a bounty for a two week period, systematically searching gardens for P. brassicae and its host plants, removing host plants, ground-based spraying of insecticide to kill eggs and larvae, searching for pupae, capturing adults with nets, and augmenting natural enemy populations. The attempt was supported by research that helped to progressively refine the eradication strategy and evaluate its performance. The last New Zealand detection of P. brassicae occurred on 16 December 2014, the eradication program ceased on 4 June 2016 and P. brassicae was officially declared eradicated from New Zealand on 22 November 2016, 6.5 years after it was first detected and 4 years after the eradication attempt commenced. This is the first species of butterfly ever to have been eradicated worldwide.

Meta-modeling on detailed geography for accurate prediction of invasive alien species dispersal

Invasive species are recognized as a significant threat to biodiversity. The mathematical modeling of their spatio-temporal dynamics can provide significant help to environmental managers in devising suitable control strategies. Several mathematical approaches have been proposed in recent decades to efficiently model the dispersal of invasive species. Relying on the assumption that the dispersal of an individual is random, but the density of individuals at the scale of the population can be considered smooth, reaction-diffusion models are a good trade-off between model complexity and flexibility for use in different situations. In this paper we present a continuous reaction-diffusion model coupled with arbitrary Polynomial Chaos (aPC) to assess the impact of uncertainties in the model parameters. We show how the finite elements framework is well-suited to handle important landscape heterogeneities as elevation and the complex geometries associated with the boundaries of an actual geographical region. We demonstrate the main capabilities of the proposed coupled model by assessing the uncertainties in the invasion of an alien species invading the Basque Country region in Northern Spain.