Score-based decision-support tools are increasingly used to identify potentially invasive non-native species as part of the risk screening (initial risk identification) component of non-native species risk analysis. Amongst these tools are the Weed Risk Assessment (WRA) and its derivatives, e.g. the Aquatic Species Invasiveness Screening Kit (AS-ISK), which have been extensively used on a large variety of terrestrial and aquatic plants and of aquatic animals worldwide. In this paper, a correction is made to the previous guidance on the use of two separate thresholds to risk-rank species, i.e. one for current climate conditions (basic risk assessment: BRA threshold) and one for future climate conditions (BRA + climate change assessment: BRA+CCA threshold). Re-evaluation of this practice reveals that, to avoid the incorrect risk-ranking of species, only the BRA threshold should be used in all future applications of WRA-type toolkits that include a separate set of climate-change questions – at present, this involves the AS-ISK and the newly released Terrestrial Animal Species Invasiveness Screening Kit (TAS-ISK). As a result of this revised guidance, all published studies containing AS-ISK applications to date are reviewed here, and where approrpiate corrected risk ranks are provided for species that were risk-ranked using a BRA+CCA threshold. Corrections are also made whenever applicable to published errors or incorrect risk ranks based on the BRA threshold in the AS-ISK applications reviewed.

Invasive marine species are well documented but options to manage them are limited. At Palmyra Atoll National Wildlife Refuge (Central North Pacific), native invasive corallimorpharians, Rhodactis howesii, have smothered live native corals since 2007. Laboratory and field trials were conducted evaluating two control methods to remove R. howesii overgrowing the benthos at Palmyra Atoll (Palmyra): 1) paste mixed with chlorine, citric acid, or sodium hydroxide (NaOH), and 2) hot water. Paste mixed with NaOH had the most efficacious kill in mesocosm trials and resulted in > 90% kill over a 98 m² area three days after treatment. Hot water at 82°C was most effective in mesocosms; in the field hot water was less effective than paste but still resulted in a kill of ca. 75% over 100 m² three days after treatment. Costs of paste and heat (excluding capital equipment and costs of regulatory approval should this method be deployed large scale) were $70/m² and $59/m² respectively. Invasive R. howesii currently occupy ca 5,800,000 m² of reef at Palmyra with ca. 276,000 m² comprising heavily infested areas. Several potential management strategies are discussed based on costs of treatment, area covered, and the biology of the invasion. The methods described here expand the set of tools available to manage invasive species in complex marine habitats.

The introduction of non-native fish poses a major threat to aquatic fauna in freshwater ecosystems around the world, often as a consequence of increased predation pressure, which results in adverse environmental and socioeconomic effects. In this study, we present a survey of publicly available information on the occurrence of pirarucu (Arapaima spp.) throughout Brazil, with an emphasis on the status of native and non-native populations, and discuss the implications for the conservation of aquatic biodiversity and the urgent need for strict control and monitoring of pirarucu breeding programs, especially in regions where it is non-native. We believe that researchers and public policy makers/managers should collaborate in managing introductions of non-native fish, and develop regulations, scientific research, risk assessments, and environmental education with this end in mind.

Invasions of exotic herbivores often result in considerable damage to vegetation. Slugs are one of the herbivores that pose a high risk of altering vegetation when introduced to new sites. The large invasive slug, Limax maximus, was recently introduced into Japan. We examined its feeding behavior to assess potential effects on vegetation at introduced sites. We conducted two complementary experiments: feeding trials and DNA meta-barcoding analyses. In the feeding trials, we provided L. maximus with 23 test plants and calculated Acceptability Index (AI) values to evaluate palatability. Limax maximus clearly favored specific plants; average AI was highest for Brassica oleracea, followed by Lactuca indica, and Sambucus racemosa. DNA meta-barcoding analyses identified plants from six families in the feces of wild individuals. According to the generalized linear mixed model analyses, the plants that L. maximus preferred to eat were crops, herbaceous plants, and plants with glabrous leaves. Because native slugs and land snails do not show these preferences, L. maximus may exert herbivory pressure on native and agricultural plants that is different from that exerted by native molluscan communities. Our work demonstrated that combining multiple methods helps to estimate the potential risk of exotic herbivory in natural ecosystems. Additional research should examine how L. maximus influences forest vegetation structure and crop productivity in areas where it is introduced.

Early detection of dreissenid mussels (Dreissena polymorpha and D. rostriformis bugensis) is crucial to mitigating the economic and environmental impacts of an infestation. Plankton tow sampling is a common method used for early detection of dreissenid mussels, but little is known about the sampling intensity required for a high probability of early detection using the method. We used implicit dynamic occupancy models to estimate plankton tow detection probabilities of dreissenid mussels from a long-term data set containing plankton tow samples collected across central and western United States. We fit models using a) the entire data set, including water bodies with unknown occupancy status in addition to heavily infested water bodies, b) a data subset that included water bodies with paired water temperature data, and c) a data subset that included water bodies with lower dreissenid densities. For the entire data set, we found that estimated detection probabilities varied by water body size and ranged from approximately 0.10 to 0.86. For the water temperature subset, we observed the same pattern between detection probability and water body size as we did for the full data but additionally found that the estimated detection probabilities were much higher when water temperatures were above 12 °C. For the lower dreissenid density subset, we found that the estimated probability of detecting dreissenid mussels with a single aggregated plankton tow sample was near zero. Given these estimates, we conclude that the number of aggregated plankton tow samples taken per water body in the data is far fewer than the number needed to ensure a high probability of detecting dreissenid mussels, especially if they are at low densities. We summarize the analyses with a discussion of plankton tow sampling protocol changes needed to improve estimates of dreissenid detection probabilities.

Monitoring invasive species is required, but ground field-based assessment is often impractical, time-consuming and expensive. In the present paper, we compare standard ground and drone mapping methods to estimate the distribution and abundances of Helianthus tuberosus and Solidago canadensis across a 1.9 km long river bank area in Croatia. We describe beneficial factors and limitations researchers should consider for planning aerial drone surveys. The criteria used include time, precision, cost, and other indicators of the value of each method based on its long term potential. We utilised the Mavic 2 Enterprise Dual model of a drone equipped with an M2ED Visual Camera. Among tested drone modes, the best was the video recording mode at a height of 15 m and speed of 1.2 m/sec, for which we developed a protocol. Obtained data can be useful in adding information on vegetation distribution but also contribute to an effective management plan for invasive species.

The giant African land snail (Lissachatina fulica) is a major pest that damages agricultural products and the environment, along with raising public health concerns. Although various methods have been applied to control these invasive snails, they have various limitations. The use of plant extracts is an alternative control method that is environmentally friendly and can reduce the use of harmful chemicals. This study was established to evaluate the molluscicidal effects of soapberry crude extract and to develop a molluscicide from it to control the giant African land snail. The soapberry (Sapindus rarak) crude extract exerted molluscicidal effects against L. fulica within 4 h. Soapberry concentration of 30% caused snail mortality of nearly 90% in 72 h. This plant extract exerted potential repellent and molluscicidal effects in the laboratory and semi-field experiments, while having no observable toxic effects on the vegetable Brassica rapa L. Thus, S. rarak crude extract at this concentration is suitable for snail control in vegetable plots.

This study was undertaken to test the hypothesis about the allelopathic activity of the alien (invasive) tree species Acer negundo in Eurasia compare with native tree species. Research of allelopathic effects of invasive plants is important for its management because of their influence on native communities. Two experiments in Petri dishes were conducted. The effect of water extracts from leaves on the seed germination of herbaceous plants was assessed. Leaves were collected in the summer and autumn season in areas invaded by A. negundo in Yekaterinburg, Russian Federation. Four treatments (invasive A. negundo and native tree species Sorbus aucuparia, Prunus padus, and Salix caprea) were tested on seeds of three recipient plant species (Festuca rubra, Sinapis alba, and Trifolium repens). We found that water extracts from A. negundo leaves weakly inhibit seed germination compared to distilled water. However, the inhibitory effect of A. negundo was no greater than effects of extracts from leaves of native P. padus and S. caprea. Seed germination was most strongly inhibited with extracts from a native shrub S. aucuparia, and the delay in comparison with distilled water was 1–2 days. Therefore, in Petri dishes water extracts from leaves of A. negundo do not inhibit seed germination of test plants more than native tree species. Our data do not support a hypothesis that allelopathy can explain the ability of A. negundo to influence native communities.

A rapid response action carried out against the invasion of water hyacinth (Eichhornia crassipes) in the Guadalquivir River branch in Seville (Southern Spain) is described and analyzed. Removal was implemented and coordinated by the regional environmental Council, National security forces and public companies. Immediately after its detection, the distribution and abundance of water hyacinth, and the possible origin of introduction were assessed as the basis for selecting a feasible removal method. Plants were scattered across 110 ha and a perimeter of 8.4 km. A total biomass of 1,931 kg (fresh weight) was removed between May and December 2021 by combining manual removal from water using inflatable boats, floating booms, wetsuits and fishing waders, as well as removal from the shore. In total, the action cost ca. €22,500. Most biomass (83%) was removed during the initial control phase (one month). However, most of the efforts and costs (83%) were made in the following seven months, especially for monitoring and follow-up treatments. Rapid response avoided the growth, blooming and spread that could be expected in summer, coinciding with the optimal growing conditions. Moreover, rapid response reduced ca. 50 times the biomass and control costs with respect to a delayed action (i.e., after summer). Despite the fact that monitoring required a higher effort and cost than the initial control phase, it altogether represented a great cost saving as the invasion was kept at bay. The coordination between the regional Council, National security forces and public companies has taken advantage of the specific strengths of each one of them, achieving the shortest possible response time.

Toxic baits are a potential control mechanism for nuisance carps, but rotenone-based baits for grass carp Ctenopharyngodon idella have been ineffective. Failures have been attributed to the palatability of rotenone because innocuous training pellets are readily consumed prior to provision of piscicide baits. Several studies suggest antimycin A, a common alternative piscicide, typically applied directly to water, may be suitable as an ingested bait. The oral toxicity of antimycin A is not well described. We evaluated the oral toxicity of antimycin A in two carriers (ethanol and corn oil) on grass carp and black carp Mylopharyngodon piceus, administered via gavage. Doses ranged from 1–16 mg/kg. Lethal dose estimates for 50% of treated fish (LD50) were calculated, and the observed treatment levels resulting in complete mortality are reported at 24- and 96-hours post-treatment. Ethanol was a more effective carrier than corn oil with lower LD50 estimates and observed treatment levels with complete mortality. Antimycin A in corn oil produced only partial mortality of black carp even 96 hours from treatment and at the highest dose administered. Results document ingested doses required for mortality of grass carp and black carp that may be used for future development of species-selective antimycin A baits.

Acoustic deterrents are currently being considered for deployment at strategic bottlenecks, such as lock and dams of major rivers, to deter upstream movement of invasive carp. Previous studies have demonstrated that bighead and silver carp (Hypophthalmichthys nobilis and H. molitrix, respectively) display negative phonotaxis to playbacks of broadband sound recordings produced from a 100 hp outboard boat motor. However, there is concern that acoustic deterrents may impact the movement of non-target native fishes in the Upper Mississippi River. We evaluated the potential impacts of a broadband underwater acoustic deterrent on native ostariophysans [bigmouth buffalo (Ictiobus cyprinellus), channel catfish (Ictalurus punctatus) and fathead minnow (Pimephales promelas)], invasive ostariophysans [bighead carp, common carp (Cyprinus carpio), grass carp (Ctenopharyngodon idella) and silver carp], and native non-ostariophysans [(American eel (Anguilla rostrata), gizzard shad (Dorosoma cepedianum), hybrid striped bass (M. saxatilis × M. chrysops), lake sturgeon (Acipenser fulvescens) and paddlefish (Polyodon spathula)]. Fish were exposed to playback of the broadband sound (60–10000 Hz), and their behavior was evaluated. Bighead carp showed a strong negative phonotaxis response to the stimulus [12.3 ± 7.5 (SD) mean consecutive reactions], silver carp and grass carp showed moderate responses (4.5 ± 5.2 and 3.8 ± 3.5 reactions), and common carp displayed low responses (1.3 ± 1.9 reactions). Of the native fish, bigmouth buffalo (2.1 ± 2.9 reactions) and hybrid striped bass (0.3 ± 0.5 reactions) were the only species to demonstrate observable response to the acoustic stimulus. Based on this small-scale behavioral screening, acoustic deterrents should have minimal impact on native species; however, larger pond and field trials are necessary to confirm this finding.

Chemical sterilisation is a way to control populations of invasive exotic species. To investigate the potential to control populations of invasive American bullfrog (Lithobates catesbeianus), 26 adult male individuals were caught and injected with a dose of 0, 12.5, 25, 50, 100 mg/kg bisazir in order to induce DNA fragmentation in sperm cells and subsequent induce sterility. The results indicate that injecting 50 mg/kg bisazir causes significant fragmentation in the sperm of Lithobates catesbeianus. Before using chemicals in situ their potential risk for the environment should be documented. As a first step the inherent ecotoxic properties of bisazir were evaluated in both acute and chronic aquatic tests: microtox (Aliivibrio fischeri), microalga (Raphidocelis subcapitata), duckweed (Lemna minor), waterflea (Daphnia magna). The no effect concentration (NOEC) was 1 mg/l for Daphnia reproduction. Based on these results the predicted no effect concentration (PNEC) value was 20 µg/l. These results show the inherent ecotoxic properties of the compound and raise questions on the safe applicability in aquatic habitats.

Agricultural communities and crop production are negatively impacted by invasive species, with the effects of pathogenic fungi, parasitic insects and weedy plants being well studied. Mammals and birds are also recognized as impacting crops, but reptiles, such as non-native green iguanas (Iguana iguana), are typically not considered agricultural pests. Research on non-native green iguanas has largely focused on the lizard’s interactions with native species with little attention given to its impact in the agricultural landscape. We conducted semi-structured interviews with farmers from 20 farms in Puerto Rico to explore the effect of the invasive green iguana on the production of crops and how farmers manage impacts, if any. A total of 34 of 55 crop species reported by farmers were negatively affected by the green iguana. We found that green iguanas were absent from 20% of farms, did not consume crops in 10% of the farms and caused negative impacts in 70% of the remaining farms. Negative impacts included crop loss and infrastructural damage, which had behavioral, emotional, and economic effects on farmers. Specific outcomes of these effects were revenue loss, refurbishing costs, changes in crop selection, management costs and emotional stress. Farmers considered management strategies as mitigation measures that needed to be constant to produce any positive effects on crop yield. They reported use of mesh fencing, hunting, and domestic animals as attempts to reduce negative effects of green iguanas on crop production. Recognition of this species as an agricultural pest is warranted in Puerto Rico and perhaps elsewhere in its introduced range. Agricultural extension agents should consider providing guidance on strategies to reduce negative impacts of green iguanas including cultivating less susceptible crops when possible.

Recent outbreaks of Zika, chikungunya and dengue fever worldwide highlight the importance of understanding the spread of pathogen-carrying mosquitoes. Citizen or community science initiatives can contribute towards early warning rapid response systems and complement at spatial and temporal scales traditional mosquito surveillance which often relies on limited resources. Herein, we provide information regarding a first attempt of involving citizens in mosquito monitoring on the island of Cyprus. During the 2018–2019 season, an island wide network of citizen scientists was formed as part of The Three Mosquiteers initiative and the Mosquitoes Without Borders project that aims at educating and engaging citizens of all ages regarding mosquitoes. The new network was named Aedes Watch Out and it aims to provide information on island wide mosquito presence overcoming jurisdictional barriers and cost constraints. Aedes Watch Out aims to serve as an early warning information source about the non-native Asian tiger mosquito (Aedes albopictus) arrival to Cyprus, complementing current capacities and any work that the authorities undertake. The initial outcomes of the project demonstrate that even a small number of dedicated citizen scientists can generate important information and greatly facilitate experts in entomology and public health.

To advance national efforts for the detection and biosurveillance of aquatic invasive species (AIS), we employed a community consensus process to enable the incorporation of environmental DNA (eDNA) detection data into the U.S. Geological Survey’s (USGS) Nonindigenous Aquatic Species (NAS) database (https://nas.er.usgs.gov/eDNA/). Our goal was to identify minimum standards and best practices for the verification of eDNA data by working closely with AIS eDNA community practitioners and natural resource managers across government, private and academic sectors. To better inform management decisions, verified AIS eDNA data will be displayed on a separate mapping layer alongside visual sighting data with the inclusion of additional information on the eDNA methods employed to collect and produce the data. To allow for eDNA data display, we produced consensus derived online documents including a submission application and data submission template and are developing a guidance document for detailing the eDNA data submission process. We also developed a communication plan including a mechanism for reporting detections to appropriate managers for consideration prior to display. The products of these efforts are an application and data submission process that will be used in the new environmental DNA data layer on the Nonindigenous Aquatic Species (NAS) database. Herein, we detail how we engaged the eDNA community for consensus of our standards, share lessons learned from the process, and describe the benefits of such an approach at instilling confidence among the research and decision-maker community.

Verbesina encelioides (Cav.) Benth. & Hook. Fil ex Gray (Asteraceae) is a perennial herb species belonging to the family Asteraceae. The plant is an aggressive obligate outbreeder weed that has invaded vast expanses of pastures, orchards, and forest areas in tropical and subtropical regions. The purpose of this study was to determine the suitability of current and potential future habitats for V. encelioides, an invasive weed in South Africa, using species distribution modelling techniques with the sdm package in R. The result of the ensemble model, based on current climatic conditions, highlights that Verbesina encelioides has a high probability of occurrence in all nine provinces of South Africa, across all the projected future scenarios, namely, 2030, 2050, 2070 and 2090. Area values ranged from 810,612.09 km² in 2070, an increase of 4.23% over the current projection, to 663,356.44 km² in 2090, a decrease of 14.7% from the current projection. The outcome of these predictions showed that V. encelioides would benefit from the predicted climate change in South Africa. The findings could be used as a warning to implement early detection and a rapid response, or for developing one.

A fundamental consideration in aquatic invasive species risk management is the distribution of invasive taxa relative to the risk assessment area. However, sampling the distribution of aquatic invasive species (AIS) is costly and time consuming, especially when they are rare or clustered. While random sampling removes bias in most estimates, it could lead to many zeroes in the response variable if the target species is not evenly distributed. We surveyed the distribution of Tubifex tubifex, the obligate secondary host of Myxobolus cerebralis, an invasive parasite that causes whirling disease in salmonids. We used intensive grid and random sampling in a lake and two river systems but collected many samples with zero T. tubifex. Zero-altered models identified a single source of zero T. tubifex counts in each dataset and improved model validation compared to Poisson or negative binomial models. While T. tubifex counts were not predictable using the covariates we measured, the binomial processes identified zero odds of a T. tubifex occurrence at lake sites with water depths > 2 m and stream sites with channel slopes > 3%. These covariates could be used to stratify the landscape for future sampling, which would save survey time and resources and likely reduce uncertainty in parameter estimates. Model-based sample stratification could address some of the challenges with AIS surveys when species are at low abundance or are clustered.