Islands are biodiversity hotspots but are highly vulnerable to invasive species that threaten natural resources, food security, economies, cultural practices, and public health. In this article, we synthesize invasive species challenges on US and US-affiliated islands and develop informed recommendations to strengthen biosecurity and management strategies. We highlight three priority areas for federal action: social, economic, and capacity conditions; terrestrial and marine biosecurity; and control measures and long-term restoration. Our key findings emphasize the critical need for better prevention at ports of entry and stronger multiagency coordination, which would also reduce invasion risks to the continent and bolster US national security. Lessons from successful global island programs stress the importance of collaborative governance, community engagement, and innovation. Although they are grounded in the US context, our findings have global relevance for improving island resilience, protecting biodiversity, and enhancing socioeconomic and cultural stability.

Melophorus anderseni is a thermophilic ant species that nests near colonies of Iridomyrmex on which it conducts brood raids. We examined its colony founding behavior and foraging ecology to evaluate possible mechanisms that may facilitate interspecific nest raiding, as well as determine if it is a parasite or specialist predator. Specifically, we (1) examined colony establishment and survival, (2) patterns of worker activity (walking speed, foraging and raiding behavior), and (3) compared cuticular hydrocarbon profiles of M. anderseni and I. reburrus workers. Following nuptial flights, M. anderseni queens established colonies in clusters around I. reburrus colonies, with an average distance to the nearest Iridomyrmex nest of 133.1(± 8.9) cm (range 25 to 650 cm). The average number of M. anderseni queens per Iridomyrmex nest entrance was 8.4 (± 1.9), and the average distance to the nearest M. anderseni neighbor was 44.9 (± 5.3) cm (range 10 to 233 cm). Queen survival was lower in clusters that were farther from the nearest I. reburrus nest or to other M. anderseni queens. Iridomyrmex reburrus activity was negatively related to soil temperature, with no activity occurring above 50 °C. In contrast, M. anderseni activity was positively related to temperature with peak activity occurring just above 50 °C. Melophorus anderseni worker activity commenced when soil temperatures exceeded 37.4 °C, and activity increased until mid-day. Activity ceased in the afternoon at temperatures lower than that for activity commencement, on average at 36.7 °C. Activity of M. anderseni at I. reburrus nests followed that of activity at M. anderseni nests. Workers of M. anderseni had an average foraging duration of 63 s and a mean foraging distance of 249 cm. Of the 49 foragers followed, 42 (86

The monsoonal (seasonal) tropics of northern Australia is a global center of ant diversity but is unrecognized as such because the great majority of its species is undescribed. Here, we document undescribed diversity in the Meranoplus unicolor Forel complex, which is formally recognized as a single species occurring throughout central and northern Australia. We obtained 80 CO1 sequences from specimens collected from throughout the taxon's range, and from these we recognize 42 species, 33 from the monsoonal zone. None of the species appears to be M. unicolor. Most of the species have very limited distributions and many are represented by single collections; given that no specimens are available for most of central and northern Australia, the total number of species in the complex is likely to be in the order of twice as many as we have recognized. Our findings provide further evidence that the ant fauna of monsoonal Australia contains several thousand species, which is many more than current estimates for any other regional fauna.

This paper continues the documentation of remarkable levels of undescribed ant diversity in the Australian monsoonal (seasonal) tropics. It considers the Melophorus castaneus Heterick, Castalanelli & Shattuck species group, as considered here consisting of four described species: M. castaneus, M. clypeatus Heterick, Castalanelli & Shattuck, M. kuklos Heterick, Castalanelli & Shattuck, and M. teretinotus Heterick, Castalanelli & Shattuck. Based on an integration of morphological, genetic (CO1), and distributional information, we recognize 24 species among 79 sequenced specimens from the group in monsoonal Australia, only one of which (M. teretinotus) is described. Our species delimitations are strongly supported by species inference from the Poisson tree processes model. We provide images of all our recognized species, along with images of four additional monsoonal species from the group that were not sequenced. Of the 28 monsoonal species in total that we document, 20 occur in the Top End of the Northern Territory, and none of these are known from elsewhere. Most locations within the Top End remain unsampled, and so many more species can therefore be expected to occur in it, and much more so elsewhere in monsoonal Australia. The total number of monsoonal species within the M. castaneus group is therefore very likely well over 50, only one of which is described. Our findings provide further evidence that the ant fauna of monsoonal Australia numbers several thousand species, a number far higher than estimated for any other of the world's regional ant faunas.

We integrate morphological variation, CO1 distance and clustering, and geographic distribution to document unrecognized diversity within Meranoplus ‘berrimah’ and M. ‘snellingi’, members of the M. diversus group of specialist seed harvesters from Australia’s monsoonal (seasonal) tropics. This follows similar analyses of two other monsoonal ‘species’ of the group, M. ajax and M. unicolor, showing that both represent highly diverse complexes comprising an estimated 100 species each. We recognize eleven species among the 34 sequenced specimens attributable to M. berrimah and ten species among the 29 sequenced specimens attributable to M. snellingi. Images of all these species are provided. The M. berrimah complex has a far broader geographic range than was apparent when M. berrimah was originally described, occurring in the Kimberley region of Western Australia in addition to the Top End of the Northern Territory, whereas the M. snellingi complex appears to be restricted to the Top End. The limited geographic representation of our sequenced specimens suggests that many additional species occur in both complexes. We estimate that the M. snellingi complex contains 15–20 species in total, and that this number is considerably higher in the M. berrimah complex because of its broader distributional range. Our study provides further evidence that monsoonal Australia is a global centre of ant diversity, but it is not formally recognized as such because the great majority of its species is undescribed.

Ants are often referred to as "the little things that rule the world" because of the critical roles they play as ecosystem engineers and through trophic and non-trophic interactions. We describe an experimental test of the influence of ants on spiders and beetles in an Australian tropical savanna. We experimentally suppressed ant abundance through baiting in six plots, each matched with adjacent reference plots, across two sites (Territory Wildlife Park [TWP] and Tropical Ecosystem Research Centre [TERC]), and documented the impact on ground and arboreal spider and beetle communities. At the TWP site, ants were highly abundant and diverse, dominated by species of aggressive Iridomyrmex. Ant diversity was lower and Iridomyrmex low in abundance at the TERC site. At the TWP site, suppression treatment predominantly affected species of Iridomyrmex, reducing overall ant abundance on the ground by 52%-77%, but because few Iridomyrmex forgage arboreally, there was no change on vegetation. Suppression treatment had little effect on ant abundance on both the ground and vegetation at the TERC site. Despite marked ant suppression on the ground at TWP, we observed little response from either spiders or beetles after two years. Among spiders, the only response was a decrease (by 50%) in abundance of the ant-associated family Prodidomidae. One beetle family (Scarabaeidae) also declined after ant suppression but was a suspected nontarget casualty of baiting. No spider or beetle family showed the increase in abundance that we predicted. Curiously, an increase was shown by the spider family Clubionidae at TERC despite minimal ant suppression. At both sites, experimental treatment had little influence on spiders and beetles on vegetation, consistent with the lack of suppression of ants on plants. The general lack of effect of ant suppression implies that there is surprisingly limited regulation of arthropod communities by ants in our study system. This contrasts with findings from other ant manipulation experiments and is particularly surprising as ant abundance is so high in Australian savannas. While our experiment involved ant suppression rather than elimination, our results suggest that Australian savannas are resilient to large reductions of a ubiquitous faunal group.

It is becoming increasingly clear that the Australian monsoonal (seasonal) tropics is a global centre of ant diversity despite only a small proportion of species being described. Several monsoonal ‘species’ have recently been shown to be species groups or complexes containing dozens or even hundreds of species. Here we investigate species richness in samples attributable to Melophorus dicyrtos Heterick, Castalanelli and Shattuck, a recently described taxon occurring throughout monsoonal Australia. We obtained CO1 sequences from 74 specimens, and through integration of CO1 data with morphological variation and distributional information, we recognise 26 species from them. Images of all these are provided. All 26 putative species are supported by both Poisson tree processes (PTP) and Bayesian implementation of the PTP model analyses of CO1 divergence and clustering. Based on sample coverage and patterns of species turnover, we estimate that the total size of the M . dicyrtos complex is more than 50 species. Monsoonal Australia is not formally recognised as a region of high ant diversity, but this is an artefact of its hyperdiverse undescribed diversity. Our findings provide further evidence that monsoonal Australia harbours several thousand ant species, dwarfing that currently estimated for the Amazon basin where ant diversity is traditionally considered to be greatest.

With regard to the recent discovery of the red imported fire ant in Sicily (Menchetti et al. 2023), Genovesi et al. highlight the delay in communicating the observation and call on the scientific communities, scientific journals, and local authorities to ensure that new invasive alien species records are immediately reported for enhancing action.

Analysis of environmental DNA (eDNA) enables indirect detection of species without the need to directly observe and sample them. For biosecurity and invasion biology, eDNA-based methods are useful to address biological invasions at all phases, from detecting arrivals to confirming eradication of past invasions. We conducted a systematic review of the literature and found that in biosecurity and invasion biology, eDNA has primarily been used to detect new incursions and monitor spread in marine and freshwater ecosystems, with much slower uptake in terrestrial ecosystems, reflecting a broader trend common to the usage of eDNA tools. In terrestrial ecosystems, eDNA research has mostly focussed on the use of eDNA metabarcoding to characterise biodiversity, rather than targeting biosecurity threats or non-native populations. We discuss how eDNA-based methods are being applied to terrestrial ecosystems for biosecurity and managing non-native populations at each phase of the invasion continuum: transport, introduction, establishment, and spread; across different management options: containment, control, and eradication; and for detecting the impact of non-native organisms. Finally, we address some of the current technical issues and caveats of eDNA-based methods, particularly for terrestrial ecosystems, and how these might be solved. As eDNA-based methods improve, they will play an increasingly important role in the early detection and adaptive management of biological invasions, and the implementation of effective biosecurity controls.

A partial mitochondrial DNA Cytochrome Oxidase subunit I (mtCOI) gene haplotype variant of the coconut rhinoceros beetle (CRB) Oryctes rhinoceros, classed as ‘CRB-G (clade I)’, has been the focus of much research since 2007, with reports of invasions into new Pacific Island locations (e.g., Guam, Hawaii, Solomons Islands). For numerous invasive species, inference of invasion biology via whole genome is superior to assessments via the partial mtCOI gene. Here, we explore CRB draft mitochondrial genomes (mitogenomes) from historical and recent collections, with assessment focused on individuals associated within the CRB-G (clade I) classification. We found that all Guam CRB individuals possessed the same mitogenome across all 13 protein-coding genes and differed from individuals collected elsewhere, including ‘non-Guam’ individuals designated as CRB-G (clade I) by partial mtCOI assessment. Two alternative ATP6 and COIII partial gene primer sets were developed to enable distinction between CRB individuals from Guam that classed within the CRB-G (clade I) haplotype grouping and CRB-G (Clade I) individuals collected elsewhere. Phylogenetic analyses based on concatenated ATP6–COIII genes showed that only Guam CRB-G (clade I) individuals clustered together, and therefore Guam was not the source of the CRB that invaded the other locations in the Pacific assessed in this study. The use of the mtCOI and/or mtCOIII genes for initial molecular diagnosis of CRB remained crucial, and assessment of more native CRB populations will further advance our ability to identify the provenance of CRB invasions being reported within the Pacific and elsewhere.

Workers of the red imported fire ant Solenopsis invicta are repeatedly claimed in the literature not to have ovaries. Here, we demonstrate that we cannot find a source publication that proves the statement, and we show how publications are erroneously citing this statement. To remedy this gap, we dissected 87 S. invicta workers over a range of worker sizes, and demonstrate that S. invicta workers do not have reproductive organs. To the best of our knowledge, this is the first time such a demonstration has been published in the scientific literature. We flag that the same issue of a lack of published evidence for the same statement likely exists for many other species and genera, precluding the ability for appropriate referencing of such details.

We report biosecurity interceptions of Oryctes rhinoceros in Australia, New Zealand, Guam, United States, and other jurisdictions to provide the first such published assessment for this highly invasive species. Between 2003 and July 2023 New Zealand found O. rhinoceros 13 times. Between 2002 and July 2023 Australia found Oryctes rhinoceros 14 times. Since 2017 inspections in Guam detected individuals twice. Between 2003 and 2014, beetles were found eight times at ports in the United States. No credible interceptions were made in the European Union. Four other intercepts were reported from two other jurisdictions. There were very little commonalities among the intercept data. All but one detection were of adults, and of the 14 adults that were sexed, eight were female and six were male. From the Australian data, which included month of detection, there was no seasonality associated with detections. Detections were associated with a broad array of commodities or situations. Oryctes rhinoceros appears to be a generalist passenger, being accidentally transported by a wide variety of means at any time. This finding indicates that there is little possibility of focusing on any specific commodity, packaging, vessel, or season to detect accidental transport of this species. Instead, biosecurity vigilance is required on all goods and vessels arriving at, or leaving, destinations.

Australia’s monsoonal (seasonal) tropics are a global centre of ant diversity, but are largely unrecognised as such because the vast majority of its species are undescribed. Here we document another case of undescribed hyper-diversity within a taxon that is formally recognised as a single, widespread species, Meranoplus ajax Forel. We recognise 50 species among 125 specimens of M. ‘ajax’ that we CO1-barcoded, integrating CO1 clustering and divergence, morphological differentiation and geographic distribution. A large proportion (44%) of these species are represented by single records, indicating that very many additional species are yet to be collected in this extremely remote and sparsely populated region. Sampling has been concentrated in the Northern Territory, where 27 of the 50 species occur. If diversity in Western Australia and Queensland were similar to that in the Northern Territory, as appears likely, then the M. ajax complex would comprise >100 species. In 2000, when Australia’s monsoonal ant fauna was estimated to contain 1500 species, Meranoplus ajax was considered to represent a single species. Our previous analyses of a range of other taxa have shown that their diversity has been similarly under-appreciated in this estimate. Our findings suggest that the total number of ant species in monsoonal Australia is several thousand, which would make the region by far the world’s richest known.

The Argentine ant, Linepithema humile, is one of the world's worst invasive species, with established populations in at least 40 countries on six continents.In this review, we synthesise the vast literature on this species in four areas, concentrating on its introduction to natural systems.The first section reviews its distribution, habitat preferences, and the factors promoting its invasion success.Second, we review current knowledge of its ecological impacts on invertebrates, vertebrates and ecosystem functions.The third section deals with behaviour and genetics, particularly traits promoting invasiveness.Finally, we address applied issues, emphasising the quantification of the economic costs and eradication strategies associated with L. humile invasion.Despite tremendous research efforts, especially over the past 40 years, numerous knowledge gaps remain in the understanding of the distribution, ecology, impacts, management, and economic costs of this species.We conclude by highlighting the most critical gaps and propose a research agenda to tackle the future challenges in the study of L. humile biology.

The inaugural Pacific Ecological Security Conference (PESC) was held in October 2022, bringing together over 100 island leaders, policy-makers, natural resource managers and global and regional invasive species experts to prioritise the critical issue of invasive species in the Pacific Islands Region. Participants confirmed that invasive species are a major threat to building and maintaining climate resilience and adaptability of Pacific Island ecosystems, as well as food security, biodiversity, sustainable livelihoods and the protection of cultural resources and way of life. Three region-wide strategic action plans were developed to guide interventions focused on the topics of invasive ants, coconut rhinoceros beetle and the use of biological control as a pest and weed management tool. These plans were the major outcome of the PESC and, when implemented, will result in coordinated activities that take a “whole-of-Pacific” approach to invasive species biosecurity and management. Here, we briefly describe the background, planning and engagement process for the three plans, summarise any country- and territory-level data obtained through the process and detail what is planned to occur over the next few years. In addition to the adoption and implementation of the strategies as a result of this inaugural PESC, we anticipate that the PESC will become the premier regional conference aimed at reducing the entry and impacts of invasive species to improve sustainability of environments and peoples of the Pacific.

We document unrecognised diversity within the Tetramorium spininode Bolton group of the Australian monsoonal tropics, which has a single described species. At the time of its description, T. spininode was known from just two collections, but there have since been hundreds of collections from throughout monsoonal Australia. We document morphological and genetic (CO1) variation within the group’s fauna of the Northern Territory (NT), in the centre of its range, where collection intensity has been highest. We recognise 20 species among 124 CO1-sequenced specimens, and 32 species in total from the NT. A key to these species is provided. The most intensively sampled regions within the NT are the mesic (>1000 mm mean annual rainfall) Top End in the far north (with 14 species) and the semi-arid (500–900 mm) Sturt Plateau region to its south (13 species). Only one species is known from both regions. Given such high regional turnover and highly patchy sampling, we estimate that at least 40 species of the T. spininode group occur in the NT. Similar diversity appears to occur in Western Australia, especially in the Kimberley region, but less in Queensland. Our findings suggest that the total number of species in the T. spininode group is likely to be around 100. Our study provides further evidence that monsoonal Australia is an unrecognised global centre of ant diversity.

Melophorus hirsutipes Heterick, Castanelli & Shattuck is a recently described taxon that was presented as occurring throughout most of mainland Australia and showing highly variable morphology. One highly variable character is sculpture, which is smooth and shiny in the type specimen but conspicuously scabrid and even rugulose in other forms. The scabrid and rugulose forms occur primarily in the monsoonal (seasonal) tropics of the northern third of the continent, a region that has recently been shown to be a global centre of ant diversity, but largely unrecognized as such because the great majority of species are undescribed. Here, we provide an integrated morphological, genetic (CO1) and distributional analysis of diversity within the scabrid and rugulose forms of M. 'hirsutipes'. We recognize 16 species among the 56 scabrid/rugulose specimens sequenced, along with four shiny or shagreenate species that are embedded within them. We conclude that Melophorus 'hirsutipes' is a highly diverse group of at least 30 species given the very patchy geographical coverage of sequenced specimens. Our findings provide further evidence that the total number of species in monsoonal Australia is likely in the several thousands, which would make it the world's richest known region for ant species.

We present three studies assessing the efficacy and non-target impacts of multiple unregistered forms of hydrogel ant baits, as well as some co-use with the granular bait Antoff, that were experimentally used targeting Argentine ant, Linepithema humile, and yellow crazy ant, Anoplolepis gracilipes, within natural/semi-natural environments in Australia.The three studies varied greatly in design and treatment regimens, and were each conducted to address real-time learning needs while attempting to understand how best to use these experimental baits within the spatial, temporal and logistic limitations of three eradication programs.All studies involved broadscale applications of numerous forms of the baits, with greatly varying treatment regimens, coupled with before-after sampling of ant communities, as well as other soil invertebrates in one study.All studies found the baits were highly efficacious against both species, more so for A. gracilipes than L. humile.Eradication is considered to have been achieved for A. gracilipes in one treatment area with a triple treatment regimen, but not using different treatment regimens in other areas.Six treatments conducted approximately one week apart did not eradicate L. humile.Few nontarget impacts were found, predominantly occurring only when sampling was conducted within days of a treatment, or at the end of six treatments of a high application rate.Instead, non-target species richness and composition were most often more affected by spatial location or sample time than treatment.Any treatment effects were non-persistent after 6-18 months.Hydrogel baits are likely to have significant roles to play for ant management and eradication.

Here we report the establishment in Hawai`i of a trap-jaw ant, Odontomachus ruginodis, a species well known for its potent sting. In June 2017, a farmer on the island of Kaua`i reported "bites" from large ants and supplied a specimen to the U.S. Fish and Wildlife Service for identification. Additional specimens were found in 2019 and 2020 in multiple locations up to 5 kilometres away from the initial detection. Multiple morphological identifications were made and combined with CO1 genetic assessment confirmed the species to be Odontomachus ruginodis, which had not been recorded prior from Hawai`i. We argue that greater biosecurity protocols are needed in Hawai'i to prevent further incursions, especially the introduction of the red imported fire ant, Solenopsis invicta.