Exotic Slugs Research Articles

Invasion of the exotic slug, Laevicaulis haroldi Dundee, 1980 in Sunderban Biosphere Reserve, India

Invasion of the exotic slug, Laevicaulis haroldi Dundee, 1980 in Sunderban Biosphere Reserve, India

Post-dispersal seed predation in the hedgerows of agroecosystems in southern Chile

Agricultural ecosystems host a large variety of organisms that can contribute to weed control through seed consumption. However, seed consumption rates in the agroecosystems of southern Chile are virtually unknown. We experimentally evaluate oat seed consumption by birds, rodents and invertebrates, in hedgerows dominated by trees, shrubs and grasses. Seed biomass consumed was not affected by the dominant vegetation present in the hedgerows, but did vary according to the seed consuming animal group. The principal seed consumers were rodents, followed by invertebrates and birds, the latter only appearing to be significant in shrub-dominated habitats. In addition, we observed the exotic slug Deroceras reticulatum consuming seeds in 62% of the experimental stations. Additional studies addressing the spatial-temporal dynamics of interactions between granivores and weed seeds are required to confirm the potential controlling and regulating function of rodents on weeds in the agricultural ecosystems of southern Chile.

Multiple introduction events and artificial long-distance dispersal of the exotic slug Ambigolimax valentianus in Japan

ABSTRACT The three-band garden slug Ambigolimax valentianus, native to the Iberian Peninsula, is an exotic species distributed worldwide and was introduced to Japan into the 1950s. For control of this slug, it is necessary to elucidate its introduction sources and dispersal patterns since the introduction event occurred. However, knowledge about this slug in Japan remains poor. Thus, we attempted to estimate the origin and dispersal patterns of this slug using genetic approaches. We investigated the genetic diversity of the mitochondrial cytochrome c oxidase subunit I gene across 11 populations of A. valentianus in three prefectures in central Japan. Ten haplotypes were found in the Japanese populations, five of which were haplotypes found in foreign individuals. The same haplotypes were found in all three prefectures, whereas the average haplotype diversity was high across all populations. Significant genetic differentiation was detected among 22 of 55 population pairs, but there was no isolation by distance. These molecular results suggest that multiple introductions to Japan may have occurred in the past such that the founder effect in the early stage of introduction was diluted. Furthermore, long-distance dispersal of A. valentianus would have occurred after introduction into Japan because of human activities rather than natural dispersal.

Can native plantings encourage native and beneficial invertebrates on Canterbury dairy farms?

ABSTRACTFarming intensification negatively effects native habitat and associated biodiversity in New Zealand. Planting native species around field margins has been proposed as a means of restoring biodiversity within this highly modified landscape. To test this hypothesis, we collected invertebrates on a dairy farm at Lincoln, Canterbury, in three habitat types: native plantings in field corners, native plantings along a double fence line, and pasture. Invertebrates were collected from pitfall traps, yellow pan traps, wooden discs and leaf litter samples were collected from the sites over summer. Assemblages of spiders, flying insects, slugs and litter mites in the planted areas had distinct compositions compared with those found in adjacent pasture. Species richness of native spiders was increased in the planted areas compared with adjacent pasture, as was the abundance of ecosystem service providers, such as honeybees, parasitoid wasps and hoverflies. Exotic slugs were significantly more abundant under discs in pasture than in planted areas. However, not all native or beneficial invertebrates responded positively to the planted areas. Further research is required to examine whether these results are repeatable at other locations, if invertebrate assemblages at this location develop further over time, and to evaluate whether any perceived benefits of these service providers can be quantified in terms of meaningful endpoints such as reduced pest levels and/or increases in yield.

Slugs (of Florida) (Gastropoda: Pulmonata)

Florida has a depauparate slug fauna, having only three native species which belong to three different families. Eleven species of exotic slugs have been intercepted by USDA and DPI quarantine inspectors, but only one is known to be established. This document is EENY-087 (originally published as DPI Entomology Circulars No. 197 and 261), one of a series of Featured Creatures from the Entomology and Nematology Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Published: June 1999. Revised: April 2004.

First Records of Four Exotic Slugs in Argentina

This paper reports for the fi rst time the occurrence of four exotic terrestrial slug species in Argentina: Lehmannia valentiana (Ferussac, 1823) (Limacidae), Deroceras invadens Reise et al. 2011 (Agriolimacidae), Arion intermedius Normand, 1852 (Arionidae) and Meghimatium pictum (Stolyczka, 1873) (Philomycidae). The study is based on specimens deposited in museums in Argentina. Both the morphologic characteristics and the mitochondrial cytochrome oxidase I gene sequences were used to identify the exotic species. Phylogenetic analyses were also carried out in order to explore the location of their origins. Lehmannia valentiana had the oldest records and has been widely distributed in Argentina. Deroceras invadens and A. intermedius were found to be restricted to the southern portion of the country. Meghimatium pictum was recorded in the northwest and northeast Argentina, and the DNA sequences analyzed from this species were more closely related to specimens from the west of the Strait of Taiwan. A determination of the origin of the other species was impossible because either the sequences analyzed grouped with samples from different geographical origins or only few sequences were available for comparison. In view of the invasive potential of these slug species, the present work provides new and potentially useful DNA sequence data obtained from morphologically-confi rmed specimens. Information provided from these analyses should assist in making a rapid identifi cation of these exotic slugs by nonspecialists and governmental authorities who are responsible for managing and controlling the presence of exotic species.

How slug herbivory of juvenile hybrid willows alters chemistry, growth and subsequent susceptibility to diverse plant enemies

Background and AimsSelective feeding by herbivores, especially at the seedling or juvenile phase, has the potential to change plant traits and ultimately the susceptibility of surviving plants to other enemies. Moreover, since hybridization is important to speciation and can lead to introgression of traits between plant species, differential feeding (herbivore-induced mortality) can influence the expression of resistance traits of hybrids and ultimately determine the consequences of hybridization. While it would be expected that herbivore-induced mortality would lead to greater resistance, there may be trade-offs whereby resistance to one herbivore increases susceptibility to others. The hypothesis was tested that the exotic slug, Arion subfuscus, causes non-random survival of hybrid willows and alters plant: (1) susceptibility to slugs; (2) secondary and nutritional chemistry, and growth; and (3) susceptibility to other phytophages.MethodsTwo populations of plants, control and selected, were created by placing trays of juvenile willows in the field and allowing slugs access to only some. When ≤10 individuals/tray remained (approx. 85 % mortality), ‘selected’ and undamaged ‘control’ trays were returned to a common area. Traits of these populations were then examined in year 1 and in subsequent years.Key ResultsThe selected population was less palatable to slugs. Surprisingly, foliar concentrations of putative defence traits (phenolic glycosides and tannins) did not differ between treatments, but the selected population had higher foliar nitrogen and protein, lower carbon to nitrogen ratio and greater above-ground biomass, indicating that vigorously growing plants were inherently more resistant to slugs. Interestingly, selected plants were more susceptible to three phytophages: an indigenous pathogen (Melampsora epitea), a native herbivorous beetle (Chrysomela knabi) and an exotic willow leaf beetle (Plagiodera versicolora).ConclusionsThis exotic slug changed the population structure of F2 hybrid willows in unanticipated ways. Defence expression remained unchanged, while nutritional and growth traits changed. These changes caused plants to be more susceptible to other plant enemies. Other exotic herbivore species are anticipated to have similar direct and indirect effects on native plant populations.

Exotic Slugs Pose a Previously Unrecognized Threat to the Herbaceous Layer in a Midwestern Woodland

Developing effective restoration strategies requires first identifying the underlying factors limiting native plant recovery. The slug Deroceras reticulatum is an important herbivore in Europe, a global agricultural pest, and is introduced and abundant throughout eastern North America, but little information is available on the effect of this exotic herbivore on the forest herbaceous layer. Here, we test the palatability of 12 forest herbs to the introduced slug D. reticulatum and use field surveys to determine the degree to which slugs are damaging plants in the field. In laboratory feeding trials, slugs readily consumed most plants, but avoided the grass Elymus virginicus, the invasive forb Alliaria petiolata (garlic mustard), and thicker leaved plants. In the field, we documented significant slug damage, with close to 50% or more of plant leaves damaged by slugs on five of the six native species tested. Slug damage in the field was predicted by laboratory‐determined acceptability, but was significantly greater on short‐statured rosette species than on erect plants for a given acceptability value. Our results identify introduced slugs as an important, but overlooked obstacle to forest herb restoration and potential drivers of larger scale understory compositional change. The relaxed herbivore pressure on A. petiolata, relative to native competitors, suggests that invasive plant removal alone may not result in the recovery of native flora. Rather, restoration of unpalatable native species should accompany invasive plant control in slug invaded areas. Erect forbs, thick‐leaved plants, and graminoids should have the greatest success where introduced slugs are abundant.

Molecular identification of the exotic slug Arion subfuscus sensu stricto (Gastropoda: Pulmonata) in California, with comments on the source location of introduced populations

Arion subfuscus sensu lato (s. l.) refers to a cryptic slug species complex that is native to Europe and which, from there, has been introduced into the northeastern U.S. The species complex was detected in California for the first time in 2005 and recently 12 specimens were collected during statewide surveys. The genital morphology of these specimens suggested that only A. subfuscus sensu stricto (s. s.) was present and partial sequences of mitochondrial 16S rDNA (443 bp) showed that they all belonged to a single haplotype of the mitochondrial lineage, S1 sensu Pinceel et al. (Genetica 125: 155–171, 2005). This result was corroborated by a parallel analysis of a 655 bp COI DNA barcode. The 16S rDNA S1 haplotype (S1-03) of the Californian specimens is hitherto known only from the northeastern U.S. Hence, it is likely that populations may have been introduced to California from the northeastern states, rather than directly from the native area of the S1 haplogroup in Europe.

Predation, vegetation and habitat-specific survival of terrestrial eggs of a diadromous fish, Galaxias maculatus (Jenyns, 1842)

Mortality from predation during the early life-stages of most teleost fishes can be extreme, and many species have developed specialized spawning strategies to reduce predation. In the diadromous fish Galaxias maculatus there is terrestrial development of eggs which restricts aquatic predation, but exposes them to terrestrial predators and a more extreme physical environment. We hypothesised that exotic slugs ( Milax gagates, Deroceras panormitanum and D. reticulatum) and mice ( Mus musculus) reduce the survival of developing eggs and tested this using laboratory and field predation experiments and sampling. We also tested the effects of riparian vegetation composition and density on egg survival. We found that exotic slugs ( M. gagates and D. panormitanum) reduced the survival of eggs in laboratory experiments, but that neither slugs nor mice affected egg survival in field experiments. Egg densities were positively associated with the stem density of riparian vegetation and the thickness of the aerial root-mat. Egg survival was also positively associated with stem density and aerial root-mat thickness, but was not density-dependent. Although predation by mice and slugs did not appear to be a major cause of egg mortality in our study locations, mortality dynamics could be different in areas with greater densities of predators. Abiotic factors are important in egg survival and these are heavily modified by the height and density of riparian vegetation. It is likely that G. maculatus egg survival, therefore, co-varies with the composition of riparian vegetation.

An analysis of spatial distribution in the exotic slug caterpillar Parasa lepida (Cramer) (Lepidoptera: Limacodidae) at an urban coastal site in central Japan

The slug caterpillar Parasa lepida (Lepidoptera: Limacodidae) is an introduced pest to urban trees in western Japan. The spatial distribution pattern of P. lepida cocoons was examined on cherry trees along an urban coastal avenue with reference to the effects of distance from the sea, dieback of trees, and avian predation. Stepwise multiple regression analysis revealed that cocoon density increased and tree dieback decreased with distance from the sea. These results suggest that salt spray from the sea and the resulting plant stress may negatively affect the moth. Avian predation rate increased with cocoon density per tree, suggesting density-dependent predation. Also, the predation rate was higher on cocoons between 0.5 and 1.5 m above ground, where the twigs were cleared and prop wood was fixed. These spatial distribution patterns are discussed with regard to pest control.

Slug control in Australian canola: monitoring, molluscicidal baits and economic thresholds

Exotic slugs have become serious pests of canola, at establishment, in Southern Australian high-rainfall cropping zones. Slugs were monitored using relatively inexpensive 300 mm x 300 mm terracotta tiles acting as refuges. An investigation was made of the effects of the time of application of chelated iron baits on the slug species Deroceras reticulatum Müller and Lehmannia nyctelia Bourguignat. Baits reduced the number of surface-active slug species. A single application at sowing provided greater efficacy than one application before sowing, and efficacy was comparable with that of two applications. Canola seedling densities showed a negative response to D. reticulatum numbers; the presence of even one individual per refuge trap reduced seedling numbers below optimum densities. Thistles and other vegetation were associated with increased numbers of slugs. European guidelines for slug monitoring and damage appear to be at least partly applicable to Australian conditions.

The Slugs (Gastropoda :Pulmonata) of Oklahoma and Kansas with New Records

Less is known concerning the ecology and taxonomy of the pulmonates called in Kansas, Oklahoma and the western Ozarks in general, than of any of the other terrestrial mollusks of this region. Leonard (1959) recorded only three species from Kansas and Branson (1959a) ten from Oklahoma. However, there are several other forms heretofore unrecorded from either state. Furthermore, recent research has necessitated changes which need to be incorporated into the existing body of information. Four families of slugs have representatives in this area, only the first two of which are native: Philomycidae, Limacidae, Arionidae and Veronicellidae. All of the Philomycids and one limacid, Deroceras laeve, naturally occur here; the others are exotic. The Limacidae are primarily European, Eurasian and North African in distribution; arionids are Holartic, i. e., western North America, Asia, Europe and Africa; and the Veronicellidae are tropical (Burch, 1961). Including one species reported below, there are 13 exotic slugs known from the United States; five of them have been found in Kansas and Oklahoma.