Negative impacts of invasive predators used as biological control agents against the pest snail Lissachatina fulica: the snail Euglandina ‘rosea’ and the flatworm Platydemus manokwari

The challenge of preventing extinctions: Lessons from managing threatened land snails on Norfolk Island

Norfolk Island, situated between Australia, New Zealand and New Caledonia, has a rich, narrowly endemic land snail fauna, which has suffered considerably from habitat loss and introduced predators. Eleven species (Stylommatophora, Microcystidae) are currently listed by the IUCN and/or Australia's EPBC Act 1999 as Endangered, Critically Endangered or Extinct. Based on targeted surveys undertaken since 2020, we re-assess the threat status of these taxa. For three species assessed to be at imminent risk of extinction, we report on the implementation of in-situ and ex-situ conservation actions and assess their effectiveness after a three-year period. We document current distributions and abundances of these species and describe experimental conservation methods, such as increased predator control, the erection of predator-proof exclosures, and the establishment of an ex-situ breeding population. We found that the relative abundance of one subspecies, Advena campbellii campbellii, was strongly correlated with monthly rainfalls. Trials of predator-proof exclosures that retain adults but allow juveniles to disperse indicated that snails can be successfully secured from predation. Increased efforts in predator control led to the killing of more rodents and chickens; however, the impact on the snail population is unclear. The ex-situ breeding population had high birth rates initially followed by high adult mortality. Adjustments in husbandry conditions reduced stress levels leading to sustainable birth rates and increased survivorship with the result of rapid population growth. We determined that the ovoviviparous A. campbellii campbellii matures at the age of 3-4 months and has a lifespan of 10-12 months in captivity. We conclude that focused predation studies are needed to determine the impact of introduced predators. The use of exclosures requires further refinement especially regarding feeding schedules. In-situ breeding requires significant time for establishment but can be implemented successfully. We assess three endemic species as Extinct, four as Critically Endangered and two as Vulnerable.

Invasion Potential of Ornamental Terrestrial Gastropods in Europe Based on Climate Matching

Invasive species are one of the main causes of biodiversity loss worldwide. Pet trade is a well-known pathway for the introduction of non-native species. Prevention is the most effective, least time-consuming, and least financially demanding way to protect biodiversity against the spreading of invasive species. The main part of prevention is the early detection of a potentially high-risk species, as well as the successful implementation of prevention strategies in legislation and practice. This study summarizes the pre-introduction screening of pet-traded terrestrial gastropod species and their potential occurrence in the EU territory. Based on the list of species traded in the Czech Republic, one of the most important global hubs of the pet trade, 51 species (49 snails and 2 slugs) were analysed. Due to a lack of certain native occurrence data, only 29 species (28 snails and 1 slug) from 10 families were modelled using MaxEnt software. Twenty species from seven families have potential occurrence in the EU territory. Based on MaxEnt modelling, we considered the following species to be high-risk candidates for the EU: Anguispira alternata, A. strongylodes, Laevicaulis alte, Megalobulismus oblongus, Rumina decollata, and R. saharica. Based on this estimation, we present considerations with which to further improve the risk assessment and recommend continuous monitoring of the pet trade market.

Distribution patterns of established alien land snail species in the Western Palaearctic Region

Established alien land snail species that were introduced into the Western Palaearctic Region from other regions and their spread in the Western Palaearctic are reviewed. Thirteen of the 22 species came from North America, three from Sub-Saharan Africa, two from the Australian region, three probably from the Oriental Region and one from South America. The establishment of outdoor populations of these species was usually first seen at the western or southern rims of the Western Palearctic. Within Europe, the alien species usually spread from south to north and from west to east. The latitudinal ranges of the alien species significantly increased with increasing time since the first record of introduction to the Western Palearctic. The latitudinal mid-points of the Western Palaearctic and native ranges of the species are significantly correlated when one outlier is omitted. There is a general trend of poleward shifts of the ranges of the species in the Western Palaearctic compared to their native ranges. There are three reasons for these shifts: (1) the northward expansion of some species in Western Europe facilitated by the oceanic climate, (2) the impediment to the colonisation of southern latitudes in the Western Palaearctic due to their aridity and (3) the establishment of tropical species in the Mediterranean and the Middle East. Most of the species are small, not carnivorous and unlikely to cause serious ecological or economic damage. In contrast, the recently introduced large veronicellid slugs from Sub-Saharan Africa and the giant African snail Lissachatina fulica could cause economic damage in irrigated agricultural areas or greenhouses in the Mediterranean and the Middle East.

Paratenic hosts of Angiostrongylus cantonensis and their relation to human neuroangiostrongyliasis globally

The nematode parasite Angiostrongylus cantonensis (rat lungworm) has a complex life cycle involving rats (definitive hosts) and gastropods (intermediate hosts), as well as various paratenic hosts. Humans become infected and develop rat lungworm disease (neuroangiostrongyliasis) when they consume intermediate or paratenic hosts containing the infective parasite larvae. This study synthesizes knowledge of paratenic hosts of A. cantonensis and investigates their role in causing human neuroangiostrongyliasis worldwide. A literature review was conducted by searching PubMed, JSTOR and Scopus, pooling additional information from sources accumulated over many years by RHC, and snowball searching. The review identified 138 relevant articles published between 1962 and 2022. Freshwater prawns/shrimp, crayfish, crabs, flatworms, fish, sea snakes, frogs, toads, newts, lizards, centipedes, cattle, pigs and snails were reported to act as paratenic hosts in various regions including South and Southeast Asia, Pacific islands, the USA and the Caribbean, as well as experimentally. Human cases of neuroangiostrongyliasis have been reported from the 1960s onwards, linked, sometimes speculatively, to consumption of freshwater prawns/shrimp, crabs, flatworms, fish, frogs, toads, lizards and centipedes. The potential of paratenic hosts to cause neuroangiostrongyliasis depends on whether they are eaten, how frequently they are consumed, the preparation method, including whether eaten raw or undercooked, and whether they are consumed intentionally or accidentally. It also depends on infection prevalence in the host populations and probably on how high the parasite load is in the consumed hosts. To prevent human infections, it is crucial to interrupt the transmission of rat lungworm to humans, from both intermediate hosts and frequently consumed paratenic hosts, by adhering to safe food preparation protocols. Educating the general public and the medical community about this largely neglected tropical/subtropical disease is key.

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Neuroangiostrongyliasis, an emerging parasitic disease of humans and wildlife.

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Caused by the nematode Angiostrongylus cantonensis (rat lungworm).

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Infection primarily via ingestion of stage 3 larvae of the parasite.

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People eat raw intermediate or paratenic hosts infected with stage 3 larvae.

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Comprehensive review of paratenic hosts’ role in neuroangiostrongyliasis globally.

Environmental Stressors and Pathology of Marine Molluscs

Mollusca is one of the most species-rich phylum of the Animal Kingdom, comprising a wide range of both terrestrial and aquatic organisms [...]

Dietary effects on fitness in captive-reared Hawaiian tree snails

The native terrestrial snail fauna of the Hawaiian Islands faces numerous threats that have led to severe range reductions, population declines, and extinction of species. With the continued declines of many wild populations, a crucial component of preserving Hawaiian terrestrial snail biodiversity is through captive rearing programs, like that implemented by the Hawai‘i Department of Land and Natural Resources Snail Extinction Prevention Program. Rare and endangered tree snails in the family Achatinellidae, which feed on epiphytic microbial communities, are maintained in captivity with a diet that includes native vegetation brought in from nearby forests, as well as a cultured fungus originally isolated from native host trees. Recent mortality events in lab populations have been attributed to wild-gathered vegetation. These events have increased interest in developing a completely manufactured or cultured diet that would eliminate the need for exposure to wild-gathered plants. This study compared survival and egg production in Auriculella diaphana provided with lab-cultured fungus, and those provided with wild vegetation. We compared the number of eggs laid and number of deaths among three treatments: (1) wild collected vegetation only; (2) wild vegetation supplemented with laboratory-cultured fungus; and (3) laboratory cultured fungus only. Mortality did not significantly differ among treatments, but the number of eggs laid was significantly higher in snails provided wild vegetation and cultured fungus (F = 24.998; P < 0.001), compared with those provided with only wild vegetation (t = 1.88, P = 0.032) or only cultured fungus (t = 4.530, P = 0.004). Our results suggest: (1) the existing strain of cultured fungus alone is not sufficient to maintain captive-reared snail populations; (2) the additional energy or calcium provided by the cultured fungus appears to enhance egg reproduction in captive-reared populations; (3) the presence or absence of live vegetation influences snail behavior, including aestivation and egg laying. These results highlight the importance of ongoing research to culture additional species of fungi at a rate that could support captive-reared populations, as the diversity of fungi present in wild epiphytic microbial communities may be important for snail reproductive health.

Biological Control of Pest Non-Marine Molluscs: A Pacific Perspective on Risks to Non-Target Organisms

Simple Summary

As malacologists long concerned with conservation of molluscs, we present empirical evidence supporting the proposition that biological control of nonmarine mollusc pests has generally not been demonstrated to be safe and effective, which are the basic measures of success. Yet claims of success often accompany contemporary biological control programs, although without rigorous evaluations. Failed molluscan biocontrol programs include well known classical control efforts that continue to devastate native biodiversity, especially on Pacific islands, as well as more contemporary programs that claim to be safer, with minimal non-target impacts. We do not condemn all biological control programs as ineffective, unsafe, and poorly evaluated, but emphasize the need for programs targeting non-marine molluscs to incorporate the lessons learned from past failures, and to do a better job of defining and measuring success both pre- and post-release of biocontrol agents. Most importantly, we call for the biocontrol community not to rely on entomologists with backgrounds in use of host-specific agents, who yet promote generalist parasites/predators for mollusc control, but to engage more actively with those knowledgeable in molluscan biology, particularly conservation. In doing so, maybe some programs targeting molluscan pests can become safe and effective.

Abstract

Classic biological control of pest non-marine molluscs has a long history of disastrous outcomes, and despite claims to the contrary, few advances have been made to ensure that contemporary biocontrol efforts targeting molluscs are safe and effective. For more than half a century, malacologists have warned of the dangers in applying practices developed in the field of insect biological control, where biocontrol agents are often highly host-specific, to the use of generalist predators and parasites against non-marine mollusc pests. Unfortunately, many of the lessons that should have been learned from these failed biocontrol programs have not been rigorously applied to contemporary efforts. Here, we briefly review the failures of past non-marine mollusc biocontrol efforts in the Pacific islands and their adverse environmental impacts that continue to reverberate across ecosystems. We highlight the fact that none of these past programs has ever been demonstrated to be effective against targeted species, and at least two (the snails Euglandina spp. and the flatworm Platydemus manokwari) are implicated in the extinction of hundreds of snail species endemic to Pacific islands. We also highlight other recent efforts, including the proposed use of sarcophagid flies and nematodes in the genus Phasmarhabditis, that clearly illustrate the false claims that past bad practices are not being repeated. We are not making the claim that biocontrol programs can never be safe and effective. Instead, we hope that in highlighting the need for robust controls, clear and measurable definitions of success, and a broader understanding of ecosystem level interactions within a rigorous scientific framework are all necessary before claims of success can be made by biocontrol advocates. Without such amendments to contemporary biocontrol programs, it will be impossible to avoid repeating the failures of non-marine mollusc biocontrol programs to date.

The tree snail on Rota Island, Northern Mariana Islands, long identified as Partula gibba (Partulidae), is a different species

Tree snails in the family Partulidae are widespread across the tropical Pacific, with endemic species occurring on most high islands. Partulid species have faced catastrophic range reductions and extinctions due primarily to introduced predators. Consequently, most extant species are threatened with imminent extinction. The U.S. administered Mariana Islands, consisting of Guam in the South and the Commonwealth of the Northern Mariana Islands (CNMI) in the north, historically harbored six endemic partulid species, half of which are thought to be extinct. While conducting a phylogenetic assessment of Partulagibba, an extant tree-snail with a range spanning at least seven islands within the archipelago, it was discovered that what has been identified as P.gibba on the island of Rota is a misidentified cryptic species. Here we use molecular phylogenetics, shell morphometrics and reproductive anatomy to describe it as a new species, Partulalutaensissp. nov.. Because the new species has suffered population declines and has a restricted range, consisting solely of the small island of Rota, we highlight the urgent need for conservation measures.