At the beginning of their establishment, alien species appear as a peculiar subject of the new habitat. Their further encroachment can lead to noxious effects on overall ecosystem services and native biodiversity. The moment they become invasive, a multi-level intervention is required to remove them. Therefore, after prevention, the identification of a new non-native species is the most important step in monitoring. Higher altitude areas are not resistant to negative anthropogenic influences, which are also reflected in the flora. The distribution patterns and abundance of non-native species have not been sufficiently studied in the mountain areas of Serbia and the Balkan Peninsula. The floristic survey of the Zlatibor Mountain and Nature Park (western Serbia) took place in the period 2020–2024. The species Cotoneaster bullatus Bois, from SW China, was recorded with 16 individuals in a semi-natural forest of Pinus nigra and P. sylvestris, right next to the motorway in the wider surroundings of the locality Partizanske vode. In 2024, an expansion of the population was observed up to 50 individuals with the appearance of shoots. Hollyberry cotoneaster is a new allochthonous taxon for the flora of Serbia and the Balkan Peninsula. The newly recorded Cotoneaster taxon is presented on the basis of its morphology, distribution, habitat preferences, ecology and population size. The only known population is most likely of subspontaneous origin and was established by ornithochory. The species does not yet represent an aggravating factor for native plant communities. However, there is a risk that the population of C. bullatus will spread to the surrounding natural forest habitats.

Cucurbita foetidissima is a native plant species found in the central and southwestern United States, as well as from northern to central Mexico. It is a perennial trailing vine, with large fleshy tap root (tuber) and one to many long prostrate and climbing stems. The aim of the present article is to report C. foetidissima for the first time for Bulgaria as a naturalised alien species and to provide some biosystematic, chorological and ecological data from the Bulgarian population. The species is found in the Thracian Lowland, in and near the town of Sadovo, and occupies a total area of about 3 ha. The chromosome number and genome size of the species are reported here for the first time based on Bulgarian accessions and they are in line with earlier data from the native distribution range of the taxon. Cucurbita foetidissima grows mainly in man-disturbed habitats. It blooms and fructifies abundantly and the fruits have numerous seeds. It is supposed to be dispersed mainly by debris and waste associated with human activities but other dispersal modes are also possible. The species easily forms dense overgrowths mainly on the earth’s surface, but also climbs on the surrounding plants, thus competing with them for sunlight, water, and nutrients. It also changes the structure and composition of plant communities. Thus, it can be inferred that C. foetidissima is locally invasive.

This study provides an update on the non-native succineid (amber snail) species established in the Hawaiian Islands, with a focus on resolving taxonomic ambiguities and expanding the understanding of their distributions and potential impacts. Surveys across the Hawaiian Archipelago, coupled with morphological and genetic data, identified three non-native succineid species currently established in Hawaiʻi : Succinea costaricana, S. luteola, and S. unicolor. Additionally, a fourth species, Novisuccinea lyrata, intercepted at quarantine facilities, has not yet become established in the islands. Using integrative taxonomy, including DNA sequencing, shell morphology, and comparison with type materials, this research clarifies the identities of these species, correcting prior misidentifications, particularly of S. unicolor, which was previously confused with S. tenella, a species yet to be recorded in Hawaiʻi. The study also reveals a new invasion of S. luteola and documents the range expansion of S. costaricana within Hawaiʻi. These findings have significant biosecurity implications, as accurate species identification is crucial for effective quarantine measures. Furthermore, the introduction of these snails to sensitive environments like the Hawaiian Islands presents a risk of unanticipated ecological consequences, such as the spread of zoonotic disease agents. This research highlights the critical role precise taxonomic knowledge plays in preventing economic losses from species misidentifications in international trade. The study further underscores the complexity of managing non-native species invasions, particularly in island ecosystems with limited native species resilience, and for understudied taxa like snails.

The ever-increasing transportation of people and goods across the globe has facilitated the introduction of organisms beyond their native range. The translocation and subsequent establishment of alien plants has led to the unintentional introduction and further spread of alien insects, with parasitoid wasps being deliberately introduced as biocontrol agents of injurious agricultural pests, or in many cases inadvertently introduced alongside their host plants or animals. Nevertheless, numerous alien invertebrates and plants are becoming integrated in natural ecological networks, with native parasitoids observed fulfilling their ecological cycles in association with alien hosts. Megastigmus transvaalensis (Hussey, 1956) (Hymenoptera: Megastigmidae), a phytophagous wasp native to South Africa, has managed to shift its host range to Neotropical pepper trees of the family Anacardiaceae, developing in their fruits. In the Mediterranean it develops in the fruits of the ornamental plants Schinus molle and S. terebinthifolia (Sapindales: Anacardiaceae). In this article, M. transvaalensis is recorded for the first time as a new alien species for Greece and Cyprus. Native parasitoids Sycophila sp., Eurytoma pistaciae Rondani, 1877 (Eurytomidae), and Eupelmus confusus Al Khatib, 2015 (Eupelmidae), were also reared from M. transvaalensis galls, with E. pistaciae being reported for the first time from the island of Cyprus. The taxonomic status of Sycophila sp. is briefly discussed.

Western Flower Thrips (WFT, Frankliniella occidentalis (Pergande, 1895)), is one of the major pests of crops worldwide. WFT was first detected in Australia in 1993 and is now present in all Australian states. Previous genetic studies detected two distinct WFT genetic lineages outside Australia known as the “lupin” strain and the “greenhouse” strain. Until now the genetic diversity and presence of different WFT genetic lineages in Australia was unknown. During recent thrips surveys of ornamental plant nurseries in Victoria, Australia, two WFT genetic lineages were detected, based on comparative analysis of the mitochondrial cytochrome oxidase I (COI), internal transcribed spacer 2 (ITS2) and the nuclear 28S rRNA genes. These two Victorian WFT genetic lineages appear to be identical morphologically and have no genetic differences in the ITS2 and 28S rRNA genes sequences but have a significant COI genetic difference (up to 4.63%). Our study confirms the presence of the “greenhouse” lineage in Victoria, which was found on a range of plant species at several locations and describes the first detection of a unique lineage that was only observed on Lotus berthelotii Masf. (Fabaceae), named hereafter “Aus_Lotus_COI”, at one location. Both lineages were found to co-exist on L. berthelotii, with the “greenhouse” lineage more abundant (9/12 specimens) than “Aus_Lotus_COI” (3/12 specimens) collected from this host at the time of survey (March–June 2021).

The Japanese beetle, Popillia japonica Newman (Coleoptera, Scarabaeoidea), listed by the European Commission as one of the 20 priority plant pests, is reported for the first time in Slovenia. In the summer of 2024, eight beetles were found in funnel traps at two motorway service stations in central Slovenia: Lukovica South and Barje South. Visual inspections in the surrounding area revealed no infestation or damage to susceptible host plants. In addition to morphological identification, we confirmed the presence of P. japonica through molecular barcoding using the cytochrome c oxidase I (COI) gene. Based on its distribution in neighbouring northern Italy, the nearby outbreak and the isolated findings near the Slovenian border as well as the heavy freight traffic between northern Italy and Slovenia, a passive transport of P. japonica as a hitchhiker is very likely.

In the past two decades, several alien insect species have been introduced to Europe. One of these is the chrysomelid beetle Ophraella communa, a promising biocontrol agent against its host plant, Ambrosia artemisiifolia. Ambrosia artemisiifolia produces highly allergenic pollen that causes significant health issues, leading to substantial healthcare costs. Since its first recorded occurrence in Italy and Switzerland in 2013, O. communa has been rapidly spreading across Europe. In 2023 and 2024, we monitored 27 populations of A. artemisiifolia in various habitats in northeastern Slovenia and one population across the border in Austria. We recorded the presence of O. communa, its developmental stages, herbivory damage, and associated fauna. Ambrosia artemisiifolia population sizes ranged from a single plant to entire fields with over 100 individuals. We confirmed the presence of O. communa in 89% of the monitored Slovenian populations as well as in the Austrian site. Ophraella communa was observed in Radkersburg, Austria, on July 31, 2024, with a single adult specimen found in a large A. artemisiifolia population growing in a pumpkin field. One week later, eggs were detected, and by the end of August, all developmental stages of O. communa were present. Despite this, the herbivory rate remained relatively low in all monitored populations. The accompanying fauna of A. artemisiifolia in agricultural fields included several specimens of Corythucha arcuata. In an urban environment, at a ruderal parking lot in Maribor, we observed one adult Cicadella viridis on an A. artemisiifolia stem and a final instar of Zicrona caerulea preying on a larva of O. communa. This research provides valuable insights into the dynamics of invasive species and their rapid range expansion.

As international trade and travel increase around the world, invasive species detections and incursions are increasing in frequency. Here we document the first detection and incursion within Australia by the Polyphagous shot-hole borer (PSHB), Euwallacea fornicatus (Eichhoff, 1868) (Coleoptera: Curculionidae: Scolytinae), an ambrosia beetle, and two of the associated fungal species; Fusarium sp. [AF18], and Graphium euwallaceae. All three exotic species were detected in a confined region within Perth, Western Australia, and represent a co-invasion. This multispecies incursion into one of the world’s most remote cities highlights the rapid increase in biological invasions globally and the pressures that urban, agricultural, and native environments face from invasive species.

The invasive species Melanoides tuberculata was detected in culture ponds for shrimp (Penaeus vannamei) and the Pacific fat sleeper fish (Dormitator latifrons) in Manabí, Ecuador, through morphological and molecular identification using the COI gene. This finding confirms the presence of the Malayan snail in the Amazon-Andes ecoregion, evidencing its wide distribution in South America and its genetic relationship with populations from Iran and the United States, suggesting a recent invasion event in the continent. This is the first report of the species in culture ponds of the shrimp P. vannamei and fish D. latifrons, representing a new habitat and a potential negative factor for aquaculture activities. It is necessary to expand sampling efforts to other regions and conduct genetic analyses to identify lineages with a higher potential for transmitting parasitic infections. This information is crucial for developing early warning systems and effective management strategies. Further studies are needed to assess the potential risks of M. tuberculata in aquaculture systems, such as its ability to transmit parasites to farmed organisms and its possible impacts on human health.

The gold / Asian clam (Bivalvia: Cyrenidae) Corbicula fluminea was first detected in the North Island of Aotearoa New Zealand in May 2023. C. fluminea which is native to eastern Asia, was detected in the Waikato River, the longest river in Aotearoa New Zealand, which drains Lake Taupō, Australasia’s largest lake. Subsequently, in March 2024, another “gold clam” species, Corbicula australis, native to Australia, was detected in a man-made lagoon, immediately adjacent to the Waikato River. The population structures of both species, with adults and juveniles present in large numbers, indicate both had been present for several years before first detection. A delimiting survey of C. fluminea in the Waikato indicated that the riverine population was significantly more widespread than the initial detection site, unlike C. australis which still appears restricted to the lagoon. Despite this, C. fluminea has not been detected within Lake Taupō or outside the Waikato catchment. Future plans involve a management strategy targeting containment within the Waikato catchment, along with continued long-term surveillance efforts. The documented worldwide impacts of C. fluminea as an “ecosystem-engineer”, its ability to thrive in a broad variety of environmental conditions, high reproductive potential and the apparently vacant niche ready to be exploited (with few resident competitors or predators), all indicate it could have the greatest impact of any known freshwater animal invader in Aotearoa New Zealand so far. The long-term impacts of C. fluminea in Aotearoa New Zealand will ultimately be determined by how effective management efforts, involving both government and non-governmental entities, are at restricting its distribution and protecting native ecosystems from new incursions.

One of the major challenges faced by protected areas is the introduction and subsequent spread of invasive non-native species, which must be effectively managed to ensure protected area function. In protected freshwaters, fish invasions are a substantial threat through impact mechanisms such as predation and hybridisation. Xiphophorus helleri, a freshwater species native to northern Mexico and Central America, was introduced globally through the aquarium trade and has become established in various non–native habitats. The distribution of swordtail fish Xiphophorus helleri in the Lowveld National Botanical Garden (LNBG) and the nearby Crocodile River system was assessed by investigating its growth, mortality rate, population structure, and diet composition. This study provides new insights, revealing that swordtail fish, which had not been previously recorded in the Crocodile River system, are now present in this area. Sampling conducted in October 2023 and March 2024 revealed significant population of X. helleri in a LNBG pond and in the nearby Crocodile River downstream of the pond, accounting for 91.7% of the total fish caught. We found that X. helleri exhibited rapid growth and competitive superiority, likely contributing to its dominance over native species. Mortality rates were found to be low, suggesting that X. helleri is well-suited to the environmental conditions of the LNBG and Crocodile River systems. This spread indicates that the species’ distribution was influenced by local hydrology, particularly the occasional flooding of the pond into the Crocodile River. The findings highlight the threat posed by X. helleri, which can potentially outcompete native species, underscoring the need for effective management strategies to control the spread of X. helleri and mitigate its ecological impacts.

Amur minnow, Rhynchocypris lagowskii (Dybowski, 1869), is a small omnivore cyprinid and native from Lena River in the north to the Yangtze River in the south. In August 2022, we first caught this species in Duobu Reservoir in the Niyang River, a tributary of middle reaches Yarlung Tsangpo River in Xizang, China. Thereafter, more and more individuals (adults and juveniles) of this species were caught in the middle reaches of Yarlung Tsangpo River. The annual variation of gonosomatic index and body length distribution of two years fully confirmed that the species has successfully established populations and dispersed in the Yalung Tsangpo River. This study documents one of the fastest freshwater fish successful invasions recorded in China, as evidenced by the establishment of large wild populations and rapid range expansion within just one year of initial introduction. The rapid range expand of Amur minnow in the Yarlung Tsangpo River is primarily attributable to multiple human-mediated introduction events (religious release) at various locations. As an omnivore and cold-adapted cyprinid with similar diet of native, Amur minnow has potential significant impact to native fishes and biodiversity.

Gambusia holbrooki is one of the most problematic invasive species globally, but its presence has yet to be confirmed in some regions. This is the case of the particularly conservation-sensitive freshwater insular ecosystems of Madeira Archipelago in Macaronesia. Freshwater ecosystems on the two main islands were inspected based on previous unconfirmed observations of mosquitofish. Specimens were found in three artificial ponds in Madeira Island and in one stream of Porto Santo Island. The morphology and mitochondrial DNA of the collected specimens confirmed their identification as G. holbrooki, confirming its presence on this archipelago for the first time. However, previous records suggest that the species may have inhabited Madeira Island for decades. Also, the high number of individuals detected in Porto Santo suggests an established population on this island. The apparent population size in Porto Santo may make an eradication action extremely challenging. Nonetheless, this may still be achievable on Madeira Island, which is extensively covered by inland waters. Proactive measures are essential to prevent further spread and mitigate potential biodiversity loss in freshwater ecosystems of this archipelago. Measures must be adapted to account for the current mosquitofish distribution and the reduced carrying capacity of Madeira’s freshwater ecosystems. It is also important to consider that these ecosystems serve as habitat for an endangered native fish species and several endemic macroinvertebrates. Ultimately, it is essential to develop a monitoring plan to avoid introductions into adjacent natural areas and towards other insular ecosystems.

Pseudorasbora parva, a small cyprinid from Asia, is considered the Europe’s most invasive fish. Typically introduced accidentally through fish stocking, its high habitat plasticity and early maturity enhance its invasiveness. In addition to competition, it asymptomatically transmits pathogens that harm native fish populations. First recorded on the Iberian Peninsula in 2001, it was found in a small intermittent river in the Guadiana River basin by 2010, an international river flowing from Spain to Portugal. Despite eradication efforts in Spain, the species’ expansion underscores the need for coordinated management between countries to address biological invasions. The recent detection in Portugal, near the Alqueva dam, raises conservation concerns, particularly for endemic species.

The Ponto-Caspian and broader Eurasian region have contributed numerous aquatic invaders to North America, including the infamous zebra mussel (Dreissena polymorpha Pallas, 1771) among many other invertebrates. Contrary to the regular invasion of Eurasian species, few records exist of cnidarians invading freshwater systems. Enter: the often-overlooked colonial benthic cnidarian, Cordylophora caspia (Pallas, 1771). The freshwater hydroid has spread to various parts of the United States including the Great Lakes and Mississippi drainage, with a single observation in 1922 in Benson Creek, Kentucky, a distant tributary of the lower Ohio River. During ichthyoplankton trawls of the Ohio River and tributaries in 2023 and 2024, we collected fragments of hydroid colonies in the bycatch of 38 trawls over 233 river kilometers. Use of DNA barcoding (genes) confirmed two 2023 samples as C. caspia. Briefly, we performed PCR reactions at the 16S and 28S regions to amplify DNA and used Sanger sequencing to produce nucleotide sequences. BLAST queries of these sequences in NCBI GenBank and a maximum-likelihood phylogenetic tree support sample identification as C. caspia. The remaining samples from 2024 closely resembled the genetically identified fragments from 2023. We obtained these samples at multiple points along the mainstem Ohio River, and near the mouths of the Guyandotte, Kanawha, and Scioto Rivers. The presence of C. caspia in the Ohio River and its tributaries could result in competition with native planktivores and sessile organisms and may have both positive and negative influences on other non-native species. A strong potential also exists for negative economic impacts, including biofouling of power plant intakes and water treatment facilities. We recommend future research efforts consider (1) assessment of its current distribution, (2) evaluation of ecological and economic vulnerabilities, and (3) development of effective means to manage this non-native species.

The non-indigenous syllid polychaete Myrianida pachycera (Augener, 1913), originally described from Australia, is reported for the first time in the Mediterranean Sea, based on individuals sampled in port environments in the Tyrrhenian and Ionian Sea. The identity of the specimens was investigated through morphological identification and DNA barcoding of two individuals, resulting in COI sequences with almost 100% identity with an individual from California. Myrianida pachycera must be considered non-indigenous for the Mediterranean Sea. The distribution of this species seems to be relatively wide in the basin, but its detection has possibly been hindered by the loss of the majority of the diagnostic characters following fixation. Conversely, due to their striking live colour pattern, live individuals might be successfully tracked via citizen science.

The European sea lemon nudibranch Archidoris pseudoargus was introduced by shipping to the Northwest Atlantic Ocean sometime prior to 2017, the year it was discovered in the Gulf of Maine, USA and in Nova Scotia, Canada. In 2023, it was discovered in Long Island Sound, a large estuary of national significance south of the Gulf of Maine. The native lemon drop nudibranch Doriopsilla pharpa, originating in waters south of New England from Maryland to Florida, was first detected in the Sound subtidally in 2019. The two species, both well-known sponge predators, are not known to co-occur as of mid-2025. Sponge population declines in the Gulf of Maine have already been linked to A. pseudoargus predation and other bioinvasions, especially non-native colonial ascidians which compete with sponges for space. Here, we report the first discoveries of these nudibranch species in Long Island Sound and consider their potential for deleterious effects on the benthic communities of southern New England.

The giant freshwater prawn (Macrobrachium rosenbergii de Man, 1879) is a commercially important farmed species globally, it’s also considered invasive in some regions. In East Africa, it has not been exploited since occurrence in the region was disputed following FAO documentation in the 1960s. A combination of methodologies including focus group discussions and experimental fishing were used to assess the occurrence of the species in two major coastal rivers (Sabaki and Tana). Fishing for giant freshwater prawns was reported to be high during the rainy season. The catch rate of giant freshwater prawns was recorded as 8–15 individuals per pair of fishers (2–3 fishers) working together per day. Most fishers (69%) fished for more than 5 days a week. Salinity in the two river estuaries was influenced by distance from the river mouth (decreased with distance from river mouth) and tidal fluctuations (increased with rising tide and decreased with receding tide). More female M. rosenbergii were caught during experimental fishing than males. Morphometric characteristics of individual giant freshwater prawns caught were; upper rostrum teeth (12–15 for males; 11–15 for females), lower rostrum teeth (10–14 for males and 9–14 for females), rostrum spines and length of chelipeds (males 15–46 cm, females 9–21 cm). The recorded characteristics aligned with the specification provided by de Man thus confirming the presence of M. rosenbergii in the two coastal river systems and highlighting the need for research to assess distribution along the coastal river systems. The male prawns were observed to have a high individual weight (227.3 g) compared to females (104.6 g). Occurrence of adult giant freshwater prawn mainly females (some berried) is an indication of the significance of salinity (brackish water) in breeding of the species. Overall, the larger size of the prawns (104.6–227.3 g) suggests significant potential for contributing to food and nutrition security therefore its viability for aquaculture development.

The invasive crab species Hemigrapsus takanoi commonly known as the brush-clawed shore crab, has rapidly spread across European coastal regions and has now been found in the largest Danish fjord system, the Limfjorden. A detailed taxonomic review of H. takanoi and other potentially invasive and morphologically similar species, including H. penicillatus and H. sanguineus, confirms with high certainty that it is indeed H. takanoi that has been established in the Limfjord (Danish: Limfjorden). This identification was further supported by molecular barcoding data from selected specimens using the mitochondrial CO1 gene. Adult females carrying eggs indicate that the species is breeding in the inlet and most likely is present in breeding populations throughout the entire fjord. Two adult specimens of Hemigrapsus sanguineus were also found at the collection site; however, since neither of them were egg carrying females, it cannot be confirmed whether they were part of a breeding population. Additionally, we explore the reasons behind the late arrival of H. takanoi and H. sanguineus in the Limfjord compared to other nearby coastal areas in Denmark and southern Sweden. Based on the result of the present study and other observations from the Limfjorden, we introduce the concept of “Invasive Homesteading”, which describes scenarios where invasive species, native to the same geographical region, collectively establish themselves in new environments. Our findings confirm a breeding population of H. takanoi and the presence of H. sanguineus in the Limfjord and emphasize the need for continued monitoring and assessment of invasive species dynamics in this ecologically and economically significant region.

A sub-adult individual of Acanthurus xanthopterus Valenciennes, 1835 was caught from the shallow waters off the southeastern coast of Sicily, Italy, in autumn 2024. The subsequent taxonomic species identification was carried out through integrated morphological and molecular analyses. The species is recorded for the first time from Italian waters. This record, that comes just three years after its first collection from Egyptian Mediterranean waters, seems to indicate a rapid westward expansion of this tropical Indo-Pacific acanthurid from the east to the central Mediterranean Sea, although additional (and independent) introduction events could be contemplated, due to the current scarcity of distribution data for the species.