Occurrence of the invasive Spanish slug in gardens: can a citizen science approach help deciphering underlying factors?

Plant volatiles mediated the orientation preference of slugs to different plant species

BACKGROUND

Slugs mechanically damage plant leaves, resulting in significant economic losses. However, there are limited cost-efficient strategies available in slug management. By studying how slugs utilize plant volatiles to locate host plants, we can gain insights into the design of attractants and repellents.

RESULTS

Bioassay results suggest slugs (Agriolimax agrestis) prefer to orientate to lettuce (Lactuca sativa), cabbage (Brassica oleracea L.), and young tobacco seedlings, compared with old tobacco seedlings. We analyzed the volatomics of lettuce, cabbage, young and old tobacco seedlings. 2-(2-butoxyethoxy)-ethanol acetate (2EA) had high abundance while nonanal, decanal, and β-cylocitral had relatively low content in volatiles. Old tobacco seedlings released significantly more hexanal but fewer 1,4-dihydro-4-oxopyridazine (DO). In olfactory tests, hexanal, nonanal, decanal, and β-cylocitral showed strong repellency to slugs, while DO at a dose of 500 ng/μL and 2EA at a dose of 1% were attractive to slugs. The two alkanes, hexadecane and heptadecane, had no effect on slug orientating to host plants. DO and 2EA can thus alleviate the repellency of hexanal, nonanal, decanal and β-cylocitral.

CONCLUSION

The high emission of hexanal in old tobacco seedlings helps repel slugs, while 2EA and DO attract slugs to lettuce and cabbage. These findings suggest that these chemicals can be utilized in the design of repellents and attractants, and contribute to constructing a push-pull system for slug control. © 2023 Society of Chemical Industry.

Species identification of introduced veronicellid slugs in Japan

Reliable identification of species is important for protecting native ecosystems against the invasion of non-native species. DNA barcoding using molecular markers, such as the mitochondrial cytochrome oxidase subunit 1 (COI) gene, helps researchers distinguish species. In this study, we focused on introduced veronicellid slugs in the Ryukyu Islands and some greenhouses on mainland Japan. Some veronicellids are medium-to-high risk pest species for humans. Identifying veronicellid species by their external morphology is difficult and unreliable because there is substantial overlap between intraspecific variation and interspecific differentiation. Therefore, internal morphologies such as male genitalia have been the primary traits used to distinguish veronicellids. To identify introduced veronicellid slugs in Japan to the species level, we used morphological assessment of male genitalia and DNA barcoding of the standard COI gene fragment. We also conducted species-delimitation analyses based on the genetic data. The results showed that five evolutionarily significant units, corresponding to four nominal species inhabit the Ryukyu Islands, of which two species were also found in the greenhouses of mainland Japan, including the first record of Sarasinula plebeia in Japan. The presence of non-native slug species could increase the transmission of parasites in Japan.

Reducing the Application Rate of Molluscicide Pellets for the Invasive Spanish Slug, Arion vulgaris

Simple Summary

Arion vulgaris has become a major invasive pest slug in Europe, causing extensive damage to many crops. To control this pest, the use of chemical molluscicides remains the most important. However, despite the proved efficacy, they still have detrimental environmental effects. We performed two double-replicated laboratory studies testing molluscicide pellets with metaldehyde (3% and 5%) and iron phosphate (1%) and found the reluctance of slugs to eat a full lethal dose regardless of whether the poison is stronger or weaker. As a consequence, slugs remain alive and only reduce their herbivory by half; the remaining granules or their parts are the main source of toxic effects of molluscicides in the environment. Moreover, a higher metaldehyde content of the pellets does not lead to lower herbivory. The results showed that a new application of molluscicides could be useful; the application rate should be decreased according to the ability of slugs to eat a certain amount of molluscicide pellets.

Abstract

Arion vulgaris are mostly controlled using chemical molluscicide products, and the detrimental environmental effects of these molluscicides can be reduced by decreasing the number of pellets applied per unit area. The objective of this study was to compare three slug control methods during two double-replicated seven-day laboratory experiments, in which slugs could choose the number of pellets with metaldehyde (3% or 5%) or iron phosphate (1%) and different types of food: leafy plants (lettuce), root vegetables (carrot), a cereal-based diet (oatmeal), or an animal-based diet (dry cat food). Slugs were irrigated and allowed to recover. We found a reluctance of slugs to eat big amounts of pellets and, therefore, to reach a full lethal dose, which resulted in low mortality (the rate was only 2.1%), regardless of whether the poison was stronger or weaker. Herbivory of slugs was in some cases reduced by half, but no treatments resulted in slugs to stop eating. Pellets with 3% metaldehyde were significantly more acceptable than pellets with 5% metaldehyde (uneaten pellets were left). The results showed that the new application of molluscicides could be useful; the application rate should be decreased according to the slugs number and ability of slugs to eat a certain amount of molluscicide pellets.

Co-Occurrence of Domestic Dogs and Gastropod Molluscs in Public Dog-Walking Spaces and Implications for Infection with Angiostrongylus vasorum: A Preliminary Study

Simple Summary

Angiostrongylus vasorum is a serious parasitic disease increasing in range and prevalence in Europe. The parasite passes through land slugs and snails before it can infect dogs but contact between dogs and these intermediate hosts is not well studied. We surveyed dogs and slugs/snails in parks and on streets in an urban A. vasorum hotspot area in southern England, United Kingdom, with the aim of determining the conditions under which they overlap. We counted 1672 slugs/snails and 763 dogs across seven sites. We found that habitat types in which the hosts were present differed, with dogs occurring 15× more often on hard surfaces (e.g., concrete) than woodland/scrub, but also occurring on natural grassland. Large numbers of slugs/snails were present 5.82× more often in woodland/scrub and natural grassland than on hard surfaces. Slug and snail species at risk of a greater likelihood of infection with A. vasorum were present 65.12× more often in woodland/scrub and 62.17× more often in amenity grassland than other habitats. The results suggest that contact between dogs and slugs/snails is most likely in amenity and natural grassland but that infection risk with A. vasorum is greatest in amenity grassland and woodland/scrub.

Abstract

Angiostrongylusvasorum is a helminth parasite of domestic dogs that is increasing in range and prevalence. Its lifecycle requires terrestrial gastropod mollusc (“gastropod”) intermediate hosts, but research is lacking regarding contact risk in situ. We studied co-occurrence between dogs and gastropods in dog-walking spaces in an A. vasorum hotspot in southern England, United Kingdom, with the aim of quantifying environmental and spatio-temporal overlap. We surveyed 390 quadrats and 180 point-counts along 3 km transects at seven sites, yielding 1672 gastropod and 763 dog observations. Common gastropods comprised Arion, Cornu, Monacha, Deroceras, Tandonia, Cochlicella, and Trochulus species. Habitat was the most important factor structuring both gastropod and dog presence and abundance. Likelihood ratio comparisons from conditional probability trees revealed that dogs were 15× more likely to be present on hardstanding surfaces than other habitats but were also present on natural and amenity grassland. Presence of gastropod species associated with high A. vasorum prevalence was 65.12× more likely in woodland/scrub and 62.17× more likely in amenity grassland than other habitats. For gastropods overall, high abundance was 5.82× more likely in woodland/scrub and natural grassland. The findings suggest co-occurrence is highest in amenity and natural grassland, but infection risk is greatest in amenity grassland and woodland/scrub.

Microbes to-go: slugs as source for Caenorhabditis elegans microbiota acquisition

Research on the Caenorhabditis elegans microbiota only recently started, with little known about how C. elegans acquires its microbiota. Slugs live in the same habitat as C. elegans and are known vectors for the worm. Hence, we wondered how the passage through a slug affects the C. elegans gut microbiota and whether worms can acquire bacteria from the slug. Using fluorescently labelled microbiota and 16S rRNA gene amplicon sequencing, we evaluated microbiota persistence and acquisition in C. elegans after slug passage. We compared C. elegans gut microbiomes isolated from wild-caught slugs to the microbiomes of worms after experimental slug passage to compare similarities and differences in microbiome composition. We found that microbiota persists in C. elegans while passing the slug gut and that worms simultaneously acquire additional bacteria species from the slug. Although the amplicon sequencing variant (ASV) richness of worms from the experiment did not exceed the richness of worms that naturally occur in slugs, we found a high number of shared ASVs indicating the importance of commonly associated microbiota. We demonstrate that C. elegans can take advantage of its passage through the slug by acquiring new potential microbiota without losing its native microbiota.

Terrestrial Slugs in Neotropical Agroecosystems

Slugs can be important agricultural pests in tropical regions. They are also intermediate hosts of parasitic nematodes, such as Angiostrongylus costaricensis and A. cantonensis, which can cause abdominal and cerebral angiostrongyliasis in humans. Management of slugs in conventional agriculture has relied heavily in the use of pellets containing metaldehyde. In this article, we review cases of slug problems and their management in neotropical agroecosystems.

Experimental indications of gardeners' anecdotes that snails interfere with invasive slugs

The invasive Spanish slug (Arion vulgaris) is an important pest species in agriculture and horticulture in Europe. In the last decades it has spread across the continent where it outcompetes native slug and snail species, thus posing a threat for biodiversity. A popular anecdote suggests to promote Roman snails (Helix pomatia) in gardens because they are able to control A. vulgaris. We examined a potential interrelationship between these two species using a mesocosm experiment with lettuce plants. ¹³C-¹⁵N stable isotope labelling of lettuce allowed us to investigate interactions between Helix and Arion on weight gain/loss and herbivory. Additionally, we wanted to know whether different watering regimes (daily vs. every 3rd day watering of weekly amount) and earthworms alter these interactions. Egg predation of Helix on Arion eggs was further tested in a food-choice experiment. Arion showed a five times higher herbivory per body mass than Helix in a single-species setting. However, in mesocosms containing both species percentage of herbivory per body mass was significantly lower than in Arion-only mesocosms, especially when watered every three days. Overall isotope uptake via eaten lettuce was unaffected by the presence of the other species. Only very little predation (three out of 200 eggs) of Helix on Arion eggs was observed. Our results provide no evidence for a clear dismissal or confirmation of the popular gardener’s anecdote that Helix snails have a negative effect on Arion abundance or herbivory.

Ready, Set, Go: Community Science Field Campaign Reveals Habitat Preferences of Nonnative Asian Earthworms in an Urban Landscape

Asian pheretimoid earthworms of the genera Amynthas and Metaphire (jumping worms) are leading a new wave of coinvasion into Northeastern and Midwestern states, with potential consequences for native organisms and ecosystem processes. However, little is known about their distribution, abundance, and habitat preferences in urban landscapes—areas that will likely influence their range expansion via human-driven spread. We led a participatory field campaign to assess jumping worm distribution and abundance in Madison, Wisconsin, in the United States. By compressing 250 person-hours of sampling effort into a single day, we quantified the presence and abundance of three jumping worm species across different land-cover types (forest, grassland, open space, and residential lawns and gardens), finding that urban green spaces differed in invasibility. We show that community science can be powerful for researching invasive species while engaging the public in conservation. This approach was particularly effective in the present study, where broad spatial sampling was required within a short temporal window.

Control of the number of field slugs Deroceras agreste L. in the plantations of garden strawberry

Slugs cause serious harm to nurseries and young plantations of fruit and berry crops in the Krasnodar region. On garden strawberries, the most common species is the field slug Deroceras agreste L., whose larvae damage ripe fruits and leaves, as well as contaminate them with their secretions and mucus, which leads to a decrease in the quality of seedlings and contributes to damage by secondary pests. In modern protection systems, the most commonly used pest control systems are molluscicides containing methaldehyde. The aim of our research was to assess the biological effectiveness of the molluscicides Sliznyakoff, G (60 g/kg methaldehyde) and Slizneed, G (60 g/kg methaldehyde) in controlling the abundance of field slugs in strawberry agrocenoses on the Clery variety. It was found that with an average number of phytophage larvae in the control variant (12.5-16.0 individuals / 10 m2), a single use of molluscicides causes 95.3 % mortality of D. agreste L. on the 7th day.

Occurrence of canine and feline lungworms in Arion vulgaris in a park of Vienna: First report of autochthonous Angiostrongylus vasorum, Aelurostrongylus abstrusus and Troglostrongylus brevior in Austria

So far, neither the feline lungworms Aelurostrongylus abstrusus and Troglostrongylus brevior nor the canine lungworm Angiostrongylus vasorum was reported in wildlife or intermediate hosts from Austria. The slug Arion vulgaris represents an invasive species in Europe and serves as intermediate host for several lungworm species. This study aimed to analyse the occurrence of metastrongyloid lungworm larvae in slugs in Vienna, Austria. Therefore, 193 A. vulgaris were collected in the central Prater park in summer 2016. Specimens were artificially digested, analysed microscopically for lungworm larvae, and species were confirmed via PCR and sequencing. Out of 193, five slugs were positive to lungworms (2.6%), one for A. vasorum, two for A. abstrusus (genotypes A and B) and one for T. brevior, and one slug had a mixed infection of A. abstrusus and T. brevior larvae. The current study is the first evidence on the endemicity of these metastrongyloid lungworm species in Austria.

Efficacy of chemical and biological slug control measures in response to watering and earthworms

The Spanish Slug (Arion vulgaris, formerly known as Arion lusitanicus) is an invasive agricultural and horticultural pest species that causes great damages all over Europe. Numerous options to control this slug are on the market; among the most commonly used are slug pellets containing the active ingredients metaldehyde or iron-III-phosphate and the application of parasitic nematodes (Phasmarhabditis hermaphrodita). These control measures potentially also affect non-target organisms like earthworms (Lumbricidae), which themselves can directly and/or indirectly alter a plant’s susceptibility against slug herbivory. Also, the efficacy of slug control treatments is expected to be influenced by watering. In a greenhouse experiment we investigated the influence of daily watering vs. every third day watering on slug control efficacy and potential interactions with earthworms. We found significant interactions between watering and slug control efficacy. Slug herbivory and biomass decreased after application of slug pellets; metaldehyde was more effective under less frequent watering while iron-III-phosphate was unaffected by watering. Parasitic nematodes had no effect on slug herbivory and biomass production. Earthworm activity was reduced with less frequent watering but did not interact with slug control. We conclude that watering patterns should be considered when choosing slug control measures.