Identifying eradication units in an invasive mammalian pest species

Eradication of invasive species is an important component for species conservation and ecosystem restoration. Success of eradications is dependent on knowledge of population connectivity in order to determine reinvasion pathways, and hence populations requiring simultaneous eradication (eradication units). The common brushtail possum (Trichosurus vulpecula) was introduced into New Zealand from Australia and Tasmania, and now occupies a wide range of habitats across the majority of New Zealand. Possums are one of the most destructive invaders within New Zealand, with extensive control operations occurring throughout the country. Understanding the population connectivity of possums on mainland New Zealand (North and South Islands) will enhance the success of planned eradications. We examined the genetic population structure of invasive possums to identify gene flow, thus reinvasion pathways, between seven populations around Dunedin and on the Otago Peninsula where eradication of possums is occurring. Genetic variation at 12 microsatellite loci was comparable between all sampled populations and exhibited a significant isolation by distance pattern. Bayesian clustering methods supported the existence of two population clusters, indicating the presence of a reinvasion pathway onto the Otago Peninsula from urban areas at the Southern end of the Peninsula. To avoid recolonisation, all possums on the Otago Peninsula should be eradicated simultaneously, with the implementation and ongoing maintenance and monitoring of an urban buffer zone. We recommend pre-eradication genetic analyses be adopted by all pest managers to define appropriate eradication units, thereby maximising eradication success and avoiding costly failures.     

Risk management to prioritise the eradication of new and emerging invasive non-native species

Robust tools are needed to prioritise the management of invasive non-native species (INNS). Risk assessment is commonly used to prioritise INNS, but fails to take into account the feasibility of management. Risk management provides a structured evaluation of management options, but has received little attention to date. We present a risk management scheme to assess the feasibility of eradicating INNS that can be used, in conjunction with existing risk assessment schemes, to support prioritisation. The Non-Native Risk Management scheme (NNRM) can be applied to any predefined area and any taxa. It uses semi-quantitative response and confidence scores to assess seven key criteria: Effectiveness, Practicality, Cost, Impact, Acceptability, Window of opportunity and Likelihood of re-invasion. Scores are elicited using expert judgement, supported by available evidence, and consensus-building methods. We applied the NNRM to forty-one INNS that threaten Great Britain (GB). Thirty-three experts provided scores, with overall feasibility of eradication assessed as ‘very high’ (8 species), ‘high’ (6), ‘medium’ (8), ‘low’ (10) and ‘very low’ (9). The feasibility of eradicating terrestrial species was higher than aquatic species. Lotic freshwater and marine species scored particularly low. Combining risk management and existing risk assessment scores identified six established species as priorities for eradication. A further six species that are not yet established were identified as priorities for eradication on arrival as part of contingency planning. The NNRM is one of the first INNS risk management schemes that can be used with existing risk assessments to prioritise INNS eradication in any area.     

Adaptive management for eradication of exotic species

The problems of controlling exotic species have been acknowledged as serious threats to an indigenous ecosystem as well as to society. In response to these threats, various management programs of exotic species have been proposed for supporting eradication in many regions. Although eradication is regarded as the first-best solution, such attempts have been unsuccessful in reality due to mainly two factors: (1) stock-dependent catchability, and (2) uncertainties. This article demonstrates when to aim at eradication through addressing an optimal adaptive management strategy in the framework of a bio-economic model with the aforementioned factors. The study sets out that the sensitivity of catchability in response to a change in the existing stock determines whether or not aiming at eradication is justified. The results also show that process uncertainty associated with stock growth significantly affects the timing of removal actions for eradication, and an increase in the degree of uncertainty could help achieve eradication in a cost–effective manner if we optimally adapt our removal actions to the uncertainty.     

Analysis of the Trojan Y-Chromosome eradication strategy for an invasive species

The Trojan Y-Chromosome (TYC) strategy, an autocidal genetic biocontrol method, has been proposed to eliminate invasive alien species. In this work, we analyze the dynamical system model of the TYC strategy, with the aim of studying the viability of the TYC eradication and control strategy of an invasive species. In particular, because the constant introduction of sex-reversed trojan females for all time is not possible in practice, there arises the question: What happens if this injection is stopped after some time? Can the invasive species recover? To answer that question, we perform a rigorous bifurcation analysis and study the basin of attraction of the recovery state and the extinction state in both the full model and a certain reduced model. In particular, we find a theoretical condition for the eradication strategy to work. Additionally, the consideration of an Allee effect and the possibility of a Turing instability are also studied in this work. Our results show that: (1) with the inclusion of an Allee effect, the number of the invasive females is not required to be very low when the introduction of the sex-reversed trojan females is stopped, and the remaining Trojan Y-Chromosome population is sufficient to induce extinction of the invasive females; (2) incorporating diffusive spatial spread does not produce a Turing instability, which would have suggested that the TYC eradication strategy might be only partially effective, leaving a patchy distribution of the invasive species.     

Optimal surveillance and eradication of invasive species in heterogeneous landscapes

Cost-effective surveillance strategies are needed for efficient responses to biological invasions and must account for the trade-offs between surveillance effort and management costs. Less surveillance may allow greater population growth and spread prior to detection, thereby increasing the costs of damages and control. In addition, surveillance strategies are usually applied in environments under continual invasion pressure where the number, size and location of established populations are unknown prior to detection. We develop a novel modeling framework that accounts for these features of the decision and invasion environment and determines the long term sampling effort that minimises the total expected costs of new invasions. The optimal solution depends on population establishment and growth rates, sample sensitivity, and sample, eradication, and damage costs. We demonstrate how to optimise surveillance systems under budgetary constraints and find that accounting for spatial heterogeneity in sampling costs and establishment rates can greatly reduce management costs.     

Evaluation of machine learning methods for predicting eradication of aquatic invasive species

In the work, we evaluate the performance of machine learning approaches for predicting successful eradication of aquatic invasive species (AIS) and assess the extent to which eradication of an invasive species depends on the certain specified ecological features of the target ecosystem and/or features that characterize the planned intervention. We studied the outcomes of 143 planned attempts for eradicating AIS, where each attempt was described by ecological and eradication-strategy-related features of the target ecosystem. We considered several machine learning approaches to determine whether one could produce a classifier that accurately predicts weather an invasive species will be eradicated. To assess each learner’s performance, we examined its tenfold cross-validated prediction accuracy as well as the false positive rate, the F-measure, and the Area Under the ROC Curve. We also used Kaplan–Meier survival analysis to determine which features are relevant to predicting the time required for each eradication program. Across the five typical machine learning approaches, our analysis suggests that learners trained by the decision tree work well, and have the best performance. In particular, by examining the trained decision tree model, we found that if an occupied area was not large and/or containments of AIS dispersal were employed, the eradication of AIS was likely to be successful. We also trained decision tree models over only the ecological features and found that their performances were comparable with that of models trained using all features. As our trained decision tree models are accurate, decision makers can use them to estimate the result of the proposed actions before they commit to which specific strategy should be applied.     

Pheromone trapping models for insect pest control

Pheromones have recently been suggested for use in insect pest control. We formulate a discrete version of a model with virgin females (or female equivalent of pheromone) in traps, and explore conditions under which this mechanism can eradicate the pest. Our model is density independent, thus when eradication is not possible, the pest increases without bound, in reality density dependent effects limit population growth. Successive refinements incorporating various features, show that delayed mating together with monogamy has a strong influence on the outcome, whereas other aspects of mating behaviour are relatively unimportant. All our models show that when males are in excess control is impossible but when some virgins are left unmated each day the outcome depends on the parameters. As the birth rate or survivorship increase, control by this method becomes more difficult.     

Stochastic models for the Trojan Y-Chromosome eradication strategy of an invasive species

The Trojan Y-Chromosome (TYC) strategy, an autocidal genetic biocontrol method, has been proposed to eliminate invasive alien species. In this work, we develop a Markov jump process model for this strategy, and we verify that there is a positive probability for wild-type females going extinct within a finite time. Moreover, when sex-reversed Trojan females are introduced at a constant population size, we formulate a stochastic differential equation (SDE) model as an approximation to the proposed Markov jump process model. Using the SDE model, we investigate the probability distribution and expectation of the extinction time of wild-type females by solving Kolmogorov equations associated with these statistics. The results indicate how the probability distribution and expectation of the extinction time are shaped by the initial conditions and the model parameters.     

外来入侵种——苹果绵蚜在中国的适生区预测

苹果绵蚜Eriosoma lanigerum(Hausmann)是我国重要的检疫性害虫,主要为害苹果、海棠等苹果属(Malus Mill.)植物。目前,该种害虫已在我国一些苹果主产区迅速扩散,并给我国的苹果产业造成了较为严重的经济损失。为了对其进行有效监控,控制其蔓延,制定合理的防治策略,本研究利用GARP和MAXENT两种生态位模型,结合其寄主地理分布,预测苹果绵蚜在我国的潜在地理分布区。研究结果表明:GARP和MAXENT预测结果相似,但前者预测面积比后者广泛。苹果绵蚜在我国的最适适生区主要分布在东北(辽宁南部)、华北(河北东、南部、北京、天津和山西南部)、华东(山东大部)、华中(河南北部)和西北(陕西中部)。另外,河北南部、山东和河南南部、甘肃东部、四川中南部、陕西大部、云南与西藏的零星地区是苹果绵蚜的中度适生区;黑龙江、吉林、新疆等20个省份(市、自治区)的全境是苹果绵蚜低度适生区或不适生区。此外,刀切法(Jackknifetest)检验结果表明,1月份平均最高温是影响苹果绵蚜分布最重要的环境变量。最后,提出几点管理苹果绵蚜的方法和防治策略,避免该种害虫传播或入侵到其它苹果产区。     

Landscape diversity slows the spread of an invasive forest pest species

According to the associational resistance hypothesis, diverse habitats provide better resistance to biological invasions than monocultures. Host‐plant abundance has been shown to affect the range expansion of invasive pests, but the effect of landscape diversity (i.e. density of host/non‐host patches and diversity of forest habitat patches) on invasions remains largely untested. We used boundary displacement models and boosted regression tree analyses to investigate the effects of landscape diversity on the invasion of Corsica by the maritime pine bast scale Matsucoccus feytaudi over an 18‐yr period. Taking the passive wind dispersal of the scale into account, we showed that open habitats and connectivity between host patches accelerated spread by up to 13%, whereas landscapes with high tree diversity and a high density of non‐host trees decreased scale spread by up to 14%. We suggest a new mechanism for such associational resistance to pest invasion at the landscape level, which we term ‘the pitfall effect’.     

Economics of invasive species policy and management

This article examines the use of economic analysis to inform bioinvasion management, with particular focus on forest resources. Economics is key for understanding invasion processes, impacts, and decision-making. Biological invasions are driven by and affect economic activities at multiple scales and stages of an invasion. Bioeconomic modeling seeks to inform how resources can be optimally allocated across invasion management activities—including prevention, surveillance programs for early detection and management, and controlling invasion populations and spread—to minimize the long-term costs and damages. Economic analysis facilitates understanding of decisions by public and private decision-makers, gaps between these, and the design of policies to achieve socially desirable outcomes. Private decision-makers may undercontrol invasions relative to socially optimal levels, because they generally account for their own costs and benefits of control but less often for broader ecosystem impacts or future spread across the landscape. Economic analysis considers approaches for increasing private invasion management and evaluates feedbacks between ecological and economic systems that can affect policy outcomes. Future research should continue evaluation and design of control strategies across the biosecurity continuum and across species to enhance cost-effectiveness, better incorporate uncertainty into policy design, increase focus on incentives and behavioral tools to influence private behaviors that affect invasion spread, and incorporate invasive species consideration within broader systems-focused science. In addition, challenges in valuing biodiversity and ecosystem service impacts and the costs and effectiveness of control measures are key data gaps. Greater collaboration between decision-makers and researchers will facilitate development and communication of usable economic research.     

Public support for invasive alien species eradication programs: insights from the Netherlands

Over the last few decades, the number of invasive alien species (IAS) has increased worldwide. IAS can have negative impacts on biodiversity, human health, and the economy. For a number of reasons, IAS policies and management schemes that have been implemented have not been sufficient to tackle the problem. In this article, we focus on IAS eradication and a main obstacle to eradication, namely a lack of public support. By analyzing three specific cases of IAS eradication in the Netherlands (Indian house crow; Pallas's squirrel; and American bullfrog), we show how factors initially affecting public support for eradication interact with each other and influence the effectiveness of the measures that IAS eradication managers implement in order to achieve support for their eradication programs. Our analysis provides a better understanding of the manipulability of factors affecting public support. Finally, it reveals concrete measures that IAS managers can implement in order to gain public support. A lesson for IAS eradication managers is that they can effectively aim for support for eradication, even if low public support for eradication is to be expected in first instance. In addition, this article provides insight into practical measures that IAS eradication managers can implement.     

Evaluation system for management measures of invasive alien species

The introduction and spread of invasive alien species is a serious threat to ecosystem structures, functions and services worldwide. At enormous cost and effort, attempts are being made to stop and reduce the ongoing appearance of alien species in ecosystems to protect the regional and native biodiversity. Still, management of invasive alien species in particular is often not successful. One reason is a lack of robust toolkits for the management of these species. Guidance on measures which are efficient and effective and which have no negative impact on the environment and human health is urgently needed for decision-making. As a result of an expert workshop, we present a set of three evaluation criteria: effectiveness, ecological impact, and impact on human health. These criteria allow an evaluation of management measures for the prevention, eradication, control and utilisation/disposal of invasive alien species for nature conservation purposes. We applied this evaluation system for 168 invasive and potentially invasive alien species of five taxonomic groups (fungi, non-vascular plants, vascular plants, invertebrates and vertebrates) involving 3619 different management measures. The evaluation of management measures and resulting recommendations for their application are a necessary basis for appropriate, ecologically necessary and professionally sound management. This new approach provides an essential framework for future decisions on management measures, for example in accordance with the provisions of the new Regulation (EU) No 1143/2014 of the European Parliament and of the Council of 22 October 2014 on the prevention and management of the introduction and spread of invasive alien species.     

使用冷冻方法防治昆虫标本虫害

皮蠹幼虫对昆虫标本的蛀蚀是我国北方地区标本保藏时需要注意的首要问题。经12次的试验观察表明,花斑皮蠹幼虫TrogodermavariabileBallion在冰柜中放置位置不同其冷冻致死率亦不相同置于冰柜表层的,死亡率介于0～50%;上层的死亡率为95%～100%;中上层及中层死亡率达100%。放置在表层及上层的皮蠹幼虫,在经2d以上的冷冻处理后部分个体出现复活。因此,对那些原先放置上层及表层的标本,第1次冷冻结束后,间隔数天应再进行第2次冷冻,以提高和巩固冷冻杀虫效果。经3年的实践证明,采用冷冻方法治理皮蠹幼虫为害效果明显,可以推广普及。     

Controlling sympatric pest mammal populations in New Zealand with self-resetting,toxicant-free traps: a promising tool for invasive species management

The control of invasive mammals is a key challenge for conservation biologists and management practitioners, particularly in locations with a high risk of re-invasion. Here, we tested whether sympatric populations of invasive mammal species could be suppressed simultaneously using self-resetting traps and toxicant-free baits. We used binomial GLM models to examine whether an intermittent pattern of trap checks could be used to predict kill rates under conditions of heavy scavenging. We also estimated the financial costs associated with deployment and maintenance of the multi-kill traps over 10 years, compared with those of aerial and ground-based poisoning methods. Trapping reduced the activity of all target species at the study site to ≤10 % within 9 months. Our results show that self-resetting traps are a promising tool for controlling multiple species of pest mammals on an island with a high potential for re-invasion.