Slug Deroceras Reticulatum Research Articles

Parametric intensity and the spatial arrangement of the terrestrial mollusc herbivores Deroceras reticulatum and Arion intermedius

Summary 1. Parametric intensity and spatial arrangement analyses were used to investigate the spatial pattern of the slugs Arion intermedius and Deroceras reticulatum. 2. The spatial lag of sampling (distance between sampling points) was shown to be unimportant in the intensity analyses. Rather, the 0·25 m grain scale was imposed on the whole sampling. The observed slope of the variance to mean relationships was common to both species, possibly determined by egg laying in batches at 0·25 m. However, the variance of the sample, for a given mean, was lower in summer. This corresponded with a reduction in the proportion of zero counts, which could be due to slug movement, possibly increased by predator activity, acting at the 0·25 m scale. 3. By contrast with the intensity analyses, the lag scale was important for spatial arrangement. At 0·25 m, in March 1997, the A. intermedius and D. reticulatum juveniles were aggregated, presumably about where egg batches were laid. At higher scales, the arrangements of D. reticulatum became spatially random, and A. intermedius resolved to a patch arrangement at the 16 m scale. 4. Over time, the D. reticulatum spatial arrangements remained random and independent of the previous sampling date. From March to July 1997, the A. intermedius patch persisted. A crash in abundance of both species, between July and October 1997, appeared to destroy the patch, but subsequent association suggested that the patch persisted until March 1998. The arrangements of the species were independent of one another on all sampling dates. 5. These species‐specific spatial arrangements were independent of all measured environmental factors and consistent with differences in the local reproduction, survival and migration of A. intermedius and D. reticulatum. 6. This comparative study indicates that the terms aggregated, random and regular should have separate definitions for parametric intensity and spatial arrangement. Furthermore, spatial scale has different meaning in intensity and arrangement analyses. Spatial arrangements are not described by parametric intensity. Spatial arrangements change with spatial scale. Temporal changes in intensity need not manifest as changes in spatial arrangement.

The effects of trophic structure and soil fertility on the assembly of plant communities: a microcosm experiment

Using closed, ventilated outdoor microcosms, plant communities were allowed to assemble from a pool of 48 herbaceous species comprising a wide range of plant functional types. The experiment involved factorial manipulation of soil fertility, invertebrate herbivores (slugs, grass aphids) and their predators (ground beetles, ladybirds). In the absence of herbivores the vegetation on soils of high, moderate and low fertility was dominated by plant species which under natural field conditions are restricted to fertile soils. At high fertility, the rate of competitive exclusion was rapid compared with communities persisting at lower fertility which remained species‐rich with high densities of individuals. The effects of herbivory were profound and attributable mainly to the slug Deroceras reticulatum. At moderate and low soil fertility the main effect of herbivores was to change the ranking of plant species; palatable grasses (e.g. Poa annua, Poa trivialis and Lolium perenne) were suppressed and plant species of slower growth rate (e.g. Festuca rubra, Anthoxanthum odoratum, Festuca ovina) were promoted. More subtle impacts of herbivory altered the size structure of plant populations suggesting the preference, by slugs, for seedlings and small (suppressed) plants. Although ladybirds and their larvae persisted in low numbers in some microcosms, carnivory was more strongly in evidence (lower densities of D. reticulatum and reduced consumption of lettuce discs) in relation to the activities of the ground beetle Pterostichus melanarius. Only in the low fertility treatment, however, was this potential translated into effects on vegetation; for several plant species the frequency of large individuals increased in the presence of P. melanarius. We conclude that outdoor microcosms provide a valuable ecological tool and, in particular, allow investigation of (a) the role of herbivores in promoting slow‐growing plant species in the vegetation of infertile habitats and (b) the protection of palatable plants against herbivores by carnivores.

Slug damage and control of field slug (Deroceras reticulatum (Müller)) by carvone in stored potatoes

After a wet autumn and harvesting under wet conditions, slugs brought into potato stores via clods and soil adhering to tubers may cause substantial damage by feeding on the tubers. A carvone sprout inhibitor, Talent®, applied in the potato stores at a dose of 50 ml per tonne potatoes, controlled slugs within a few days. A dose of 25 ml carvone was insufficient. Using a laboratory box test, the slug (Deroceras reticulatum) affected only wounded tubers and, although slime was present on the unwounded potatoes, they were not damaged by slugs.

The causes of over-winter plant losses of autumn-sown white lupins (Lupinus albus) in different regions of the UK over three seasons

A series of experiments were carried out at 14 sites in the major arable areas of the UK, in the years 1993–94, 1994–95 and 1995–96 to determine the causes and extent of over-winter plant losses of two autumn-sown cultivars of white lupin (Lupinus albus L.).Over the three seasons frost was the major cause of plant losses. Two mechanisms (one known and one not previously reported in the UK) of frost tolerance under field conditions were identified: (i) lignification of the root parenchyma early in the life of the seedling, and (ii) a large vernalization requirement of the main-stem apex, which delays stem elongation in older plants. A model was developed that could be used to predict the susceptibility of these lupin cultivars to the first severe frost of the winter using accumulated thermal time (above a base temperature of 3 °C).The effect of sowing at the beginning or end of a sowing window, calculated to optimize plant architecture the following summer, therefore varied with the weather during the autumn/winter period. A combination of cool autumn weather and late sowing (outside of the sowing window) resulted in plant losses due to a lack of lignification of the root parenchyma. In unusually warm autumn conditions (1994–95 and 1995–96) plants sown at the beginning of the sowing window were well developed before the first frosts occurred, with consequent stem elongation and plant losses.Although losses due to pests were not severe (c. 3 to 5 plants/m2), plants were attacked during the autumn by grey field slugs (Deroceras reticulatum Muller), bean seed flies (Delia platura Meigen), and probably thrips (Thrips angusticeps Uzel, Noctuidae), although this has not been confirmed. The fungal pathogens Fusarium spp. and Botrytis cinerea Pers. caused losses in conjunction with frost damage.

SUSCEPTIBILITY OF THE EGGS OF THE PEST SLUG DEROCERAS RETICULATUM TO CONTACT WITH METAL SALTS

Laboratory research is reported in which eggs of the pest slug Deroceras reticulatum were incubated on filter paper moistened with solutions of cupric sulphate, aluminium sulphate, ferric chloride and zinc sulphate at different concentrations. After four or more days exposure, the median lethal doses (LD50) were below 10 � g metal ion/cm 2 for the four metals tested. Copper showed the highest toxicity with LD50 values below 5 � g metal ion/cm 2

Effects ofPhasmarhabditis hermaphrodita on non-target molluscs

Two field experiments were done in which plots of oilseed rape, immediately adjacent to the field margin, were left untreated or treated with the slug-parasitic rhabditid nematode Phasmarhabditis hermaphrodita. Nematodes were applied at a rate of 3 × 10 9 ha -1 . Slug populations within plots were low and nematode application had little detectable effect on slug numbers, biomass or slug damage to the crop. There was a large snail community in the field margin in both experiments, but P hermaphrodita had no detectable effect on the abundance of any of the nine snail species recorded. The susceptibility of seven common hedgerow species (Monacha cantiana, Cepaea hortensis, Cepaea nemoralis, Pomatias elegans, Oxychilus helveticus, Clausilia bidentata and Discus rotundatus) to P hermaphrodita was tested in the laboratory. Snails were kept confined for three weeks on soil without nematodes, or with P hermaphrodita applied at the recommended application rate or five times this rate. Soil treatment with the recommended rate of nematodes caused significant mortality only for the snail M cantiana and the susceptible slug Deroceras reticulatum. Soil treatment with five times the recommended rate caused significant mortality of the slug D reticulatum and the snails M cantiana and C hortensis, but not any other species. Reasons why application of P. hermaphrodita to arable crops in Britain is unlikely to pose a substantial threat to non-target molluscs are discussed.

Electrophysiological and pharmacological characteristics of buccal smooth muscle of the pest slug Deroceras reticulatum

Buccal mass muscle of the pest slug Deroceras reticulatum was examined by conventional tension recording and the sucrose-gap electrophysiological technique. Elevated potassium salines induced dose-dependent depolarisations accompanied by tonic contractures with superimposed rapid twitch contractions. The latter were suppressed at over 40 mmol · l−1 external potassium, where depolarisation-induced inactivation of voltage-sensitive calcium channels may have occurred. Acetylcholine caused significant dose-dependent depolarisations and tonic contractures, while 5-hydroxy tryptamine induced lower depolarisations accompanied by phasic contractile activity superimposed on low level tonic force. Of the purines examined only guanosine triphosphate caused significant mechanical activity above a threshold of 0.1 μmol · l−1. The tetrapeptides inhibited buccal muscle spontaneous activity, but the related small cardioactive peptide B was weakly excitatory. The amino acids glutamate and gamma-aminobutyric acid were weakly excitatory on buccal muscle while the molluscicides metaldehyde and methiocarb disrupted normal mechanical activity of the feeding musculature. Acetylcholine and 5-hydroxytryptamine appear to have major roles in regulating feeding muscle activity, seemingly modulated by guanosine triphosphate and inhibited by phenylalanine-methionine-arginine-phenylalanine-NH2 and phenylalanine-leucine-arginine-phenylalanine-NH2.

Experimental infections of muskoxen (Ovibos moschatus) and domestic sheep with Umingmakstrongylus pallikuukensis (Nematoda: Protostrongylidae): parasite development, population structure, and pathology

Three captive muskoxen (Ovibos moschatus) were successfully infected with third-stage larvae of Umingmakstrongylus pallikuukensis digested or emerged from the slugs Deroceras reticulatum and D. laeve, for the first time completing the life cycle of this parasite under experimental conditions. The course of parasite development and patency was followed for 26 months post infection (p.i.) using fecal examinations and radiography. The prepatent periods in two of the muskoxen were 91 and 95 days and the patent period in one extended for 23 months. Larval production peaked 13-14 months p.i. On postmortem of two of the muskoxen at months 14 and 26 p.i., adult parasites were found only within pulmonary cysts and cysts were randomly distributed between left and right lungs. Cyst dimensions were positively correlated with the number of adult parasites they contained. On postmortem of the third muskox at day 97 p.i., not all adult parasites were within typical cysts; two were found free in interlobular septa. First-stage larvae were recovered from lung cysts of this animal but not from feces. Lung pathology in all three muskoxen appeared localized and associated with the adult nematodes. Infection of two sheep with third-stage larvae of U. pallikuukensis did not result in parasite establishment.

Targeting Biocontrol with the Slug-Parasitic Nematode Phasmarhabditis hermaphrodita in Slug Feeding Areas: A Model Study

The nematode Phasmarhabditis hermaphrodita was applied to soil in an outdoor miniplot experiment to protect Chinese cabbage seedlings from damage by the field slug Deroceras reticulatum. The aim was to investigate the possibility of reducing the numbers of nematodes applied by only partially spraying soil in the area where slug control was needed. Nematodes sprayed as overall applications were compared with band applications along plant rows and spot applications around individual plants, in plots with nine or 18 plants. Band and spot applications were applied at two rates, designated the full rate (same number of nematodes per plot as in the overall application) and the area rate (same number of nematodes per unit area comprising 43% (band) and 18% (spot) of the overall application). In plots with 18 plants, where spot-treated plant alternated with untreated plants, no significant difference in damage was found between spot-treated plants and untreated plants. This indicates that slugs were not repelled from nematode-treated areas and that any effects in reducing slug damage were not due to repellency. All nematode treatments resulted in a significant reduction in the mean level of slug damage to seedlings from six or more days after treatment. However, there were significant interactions between nematode treatment, the number of plants per plot, the position of plants within plots (edge or middle) and time after treatment. The effect of time after treatment was modelled. The log time to 50% reduction in slug damage (t 50 ) was related to the area treated and the dose applied. In plots with band or spot treatments at the full dose, there was a relatively small increase in t 50 with declining area treated. In plots treated with band or spot treatments at the area dose, t 50 increased consistently with declining relative area treated. The final level of damage, expressed as a percentage of damage on untreated plots (P), was influenced by both the dose and area treated. Final damage was greatest on spoti treated plots where half the plants were untreated. We conclude that partial treatment of soil around all plants to be protected from slug damage is a potentially valuable method of reducing the overall nematode dose required for control of slug damage, provided that some damage can be tolerated.

Slugs (Deroceras reticulatum and Arion ater agg.) Avoid Soil Treated with the Rhabditid Nematode Phasmarhabditis hermaphrodita

A series of experiments was done to determine whether the pest slugs Deroceras reticulatum and Arion ater agg. (Mollusca: Gastropoda: Stylommatophora) could detect the presence of and avoid soil treated with the parasitic nematode Phasmarhabditis hermaphrodita (Nematoda: Rhabditidae). One-half of the surface area of moist soil in experimental boxes was treated with infective juveniles of P. hermaphrodita at a density of 120/cm2. The other half of each box was left untreated. Five discs of Chinese cabbage leaf were placed in each half of each box. Slugs (D. reticulatum or A. ater agg.) were added to each box and food consumption and resting sites were recorded over a 12-day period. Both slug species were more likely to rest and feed on untreated soil than on nematode-treated soil. A series of boxes was also prepared with one-half untreated and the remaining half treated with 1, 4, 12, 38, or 120 nematodes/cm2. Slugs were less likely to rest or feed in the treated half of boxes containing 38 or 120 P. hermaphrodita/cm2 but showed no preference between the untreated and the nematode-treated soil at lower nematode densities. A final experiment showed that there was little movement of P. hermaphrodita from the treated half to the untreated half of each box.

Comparison of seedling and adult palatability in annual and perennial plants

1.The relative palatabilities of the seedlings and adults of a range of British herbaceous plant species (14 annuals and 15 perennials) were compared using a generalist native herbivore (the slugDeroceras reticulatum) in a food‐choice experiment. A palatability index (0 to 1) was devised.2.A general linear model analysis showed that, overall, there was a highly significant difference between seedling and adult palatability.3.In the majority of cases, seedlings were more palatable than adults. However, in species with highly palatable adults the opposite tended to be the case.4.No consistent difference between annual and perennial species was seen with respect to the relative palatabilies of adultsvsseedlings.5.No evidence of a trade‐off between seedling palatability and relative growth rate was found.6.In view of the role that selective seedling predation may play in determining species composition in the field, the results of this experiment indicate the need for caution in making ecological inferences from the exclusive use of adult material in palatability tests.

Bacteria associated with the digestive system of the slug Deroceras reticulatum are not required for protein digestion

Bacteria were isolated from the crop, digestive glands and salivary glands of the field slug Deroceras reticulatum (Müller). The digestive gland was the most densely populated organ with about ×3 and ×400 more bacterial colony forming units (CFU) mg −1 of tissue than in the crop and salivary glands, respectively. Growth on plate-count agar incorporating gelatin showed that 34, 16 and 3% of the total numbers of CFU present in the salivary gland, digestive gland and crop, respectively, secreted extracellular proteinases that degraded gelatin. Administration of antibiotics (chloramphenicol or tetracycline plus chlortetracycline) to slugs in an artificial diet reduced the numbers of total and proteolytic CFU present by 98–99%. Although proteinase-secreting bacteria were present in all organs studied, only the crop possessed significantly greater proteolytic activity (×3 at pH 8.0) when slugs were not fed on diet containing antibiotics.

Palatability of weeds from different European origins to the slugs Deroceras reticulatum Müller and Arion lusitanicus Mabille

Abstract As part of a study on the significance of seed provenances in schemes to enhance biodiversity in agricultural habitats, juvenile plants of Cichorium intybus, Daucus carota, Leucanthemum vulgare and Silene alba of different European origins were exposed to grazing by two slug species, Deroceras reticulatum and Arion lusitanicus . Living plants were offered in trays, either in a glasshouse ( Deroceras ) or outdoors ( Arion ). The amount of herbivory was origin-dependent, with higher losses for all four species from German and Hungarian provenances compared with English and Swiss plants. The main trend was similar for both slug species except in the case of Daucus , and there was a significant ‘origin × plant species’ interaction. We found strong correlations between provenance-specific herbivory and certain climatic characteristics of the corresponding regions, i.e. winter minimum temperatures, and dryness in spring and late summer, which are crucial for the development of slugs. The results can be interpreted in terms of a SW-NE European climatic gradient and may be a consequence of differences in the need for plant defences against herbivory by slugs. Additionally, the data on palatability were compared with susceptibility towards two parasites which occurred in a field experiment, a leaf miner on Leucanthemum vulgare and a rust fungus on Silene alba . While specific leaf mining frequencies on Leucanthemum contrasted with the palatability of the different provenances to slugs, the rust infection on Silene was low on local and German plants, and higher on the more distant provenances from England and Hungary.

Detection of iron in tissues from slugs (Deroceras reticulatum Müller) after ingestion of iron chelates, by means of energy-filtering transmission electron microscopy (EFTEM)

Detection of iron in tissues from slugs (Deroceras reticulatum Müller) after ingestion of iron chelates, by means of energy-filtering transmission electron microscopy (EFTEM)

Laboratory Food Choice Trials to Explore the Potential of Common Weeds to Reduce Slug Feeding on Oilseed Rape

ABSTRACT Food choice trials with the slug pests Arion lusitanicus and Deroceras reticulatum were carried out in the laboratory, using seedlings of rape, Brassica napus and several weed species. The attraction of the weeds to the slugs was compared with rape and, subsequently, the potential of the presence of weeds to reduce slug feeding on young rape was assessed. Capsella bursa-pastoris and Taraxacum officinale (only for A. lusitanicus) were very attractive weeds and rape was not significantly more defoliated than C. bursa-pastoris and T. officinale when tested with these two weed species. Moreover Veronica persica (A. lusitanicus) and C. bursa-pastoris (D. reticulatum) reduced the number of killed rape plants significantly. Therefore these weeds, sown in high quantities into fields of oilseed rape, could potentially prevent young rape plants from severe slug damage.

Detection of iron in tissues from slugs (deroceras reticulatummüller) after ingestion of iron chelates, by means of energy-filtering transmission electron microscopy (EFTEM)

Two iron chelates, one toxic (iron 'butan') and the other not (iron 'octan'), were ingested by slugs (Deroceras reticulatum) at either a low (5 g kg -1 diet) or a high (100 g kg -1 diet) dose rate. In tissue sections of the digestive gland and body wall, iron was detected by energy-filtering transmission electron microscopy (EFTEM), using electron spectroscopical imaging (ESI) and electron energy-loss spectroscopy (EELS). The strongest signals for iron were obtained in secondary lysosomes of the resorptive cells in the digestive gland of slugs treated with a low dose of either compound, or with the high dose of iron 'octan'. At the cell apices of these cells, in endocytotic vesicles and in apically located lysosomes, iron was detected only in slugs fed with either dose of iron 'octan'. In slugs fed with the high dose of iron 'butan', iron could clearly be localised in the epithelial and mucus cells of the skin. The results are discussed with respect to differences in the toxicity of the two iron chelates.

Action of Extracts of Apiaceae on Feeding Behavior and Neurophysiology of the Field Slug Deroceras reticulatum

A systematic examination was made of the plant family Apiaceae (Umbelliferae) in which extracts of 33 species, representing 32 genera, were screened for antifeedant activity against the field slug Deroceras reticulatum by using an electrophysiological recording assay. In this assay, the olfactory sensory epithelium of the posterior tentacle of the slug was exposed to volatile components of the plant extracts presented in an airstream, and any subsequent activity of the olfactory nerve was recorded. Extracts of 22 species elicited a range of nervous activity in the preparation. A feeding bioassay was used to measure any change in consumption when extracts were added to a standard food. Statistical analysis of data obtained from both electrophysiological traces and the feeding bioassays identified extracts of Petroselinum crispum, Conium maculatum, and Coriandrum sativum as being the most neuroactive as well as the most antifeedant.

Transgenic Arabidopsis leaf tissue expressing a modified oryzacystatin shows resistance to the field slug Deroceras reticulatum (Müller).

Transgenic Arabidopsis thaliana has been developed which expresses the oryzacystatin mutant OC-I delta 86, which is an inhibitor of the major proteinase present in the digestive gland of the slug, Deroceras reticulatum. When fed on leaf tissue from plants expressing this inhibitor the growth of juvenile slugs was significantly reduced by 31% compared with those feeding on control leaf tissue. Furthermore, while surviving slugs did not individually consume less when feeding on leaf tissue expressing OC-I delta 86, the total amount of leaf tissue eaten was 50% less, due to reduced survival of slugs. The synthetic cysteine proteinase inhibitors E-64 and leupeptin also significantly reduced slug weight gain (by at least 40%) and digestive gland cysteine proteinase activity when administered in an artificial diet, indicating that their antimetabolic effects are due to direct inhibition of gut proteolytic activity. These results suggest that transgenic crop plants expressing phytocystatins could be used to suppress the growth rates of slug populations in the field.

Low Temperatures Suppress Growth of the Ciliate Parasite, Tetrahymena rostrata , and Pathogenicity to Field Slugs, Deroceras reticulatum

The slug parasitic ciliate protozoan, Tetrahymena rostrata , was isolated from the slug Deroceras reticulatum and used in bioassays against D. reticulatum at 10 and 17oC and in in vitro growth experiments at a range of temperatures. The parasite reproduced, and significantly reduced the life span of juvenile D. reticulatum at 17oC, but not at 10oC.

Assessment of the cytotoxic impact of heavy metals on soil invertebrates using a protocol integrating qualitative and quantitative components

Slugs (Deroceras reticulatum), isopods (Porcellio scaber), diplopods (J ulus scandinavius), and collembola (Tetrodontophora bielanensis) were exposed to cadmium, lead or zinc at differing concentrations under constant laboratory conditions. Ultrastructural alterations of monitored tissues (for diplopods and collembola, midgut epithelium; for slugs and isopods, midgut gland epithelium) were recorded qualitatively and quantitatively by transmission electron microscopy. In order to combine both qualitative and quantitative aspects of the observed responses into a proposed easy-to-handle ‘impact index’, we developed a protocol according to the physiological basis for the ultrastructural responses. Using this protocol, the data clearly showed the different susceptibilities (1) of organelles to the respective metal, (2) of the investigated species to particular metals, and (3) of the monitored tissue to increasing metal concentration. Moreover, the construction of matrices of impact indices for single symptoms allows the description and analysis of complex syndromes in a mathematical way. Cluster analysis of the present data on controlled laboratory experiments utilizing single contaminants revealed similar patterns of cellular responses to the tested metals in the investigated tissues of P. scaber and J. scandinavius and species-specificity for T. bielanensis and D. reticulatum monitored tissues. Some of the highest metal concentrations seemed to affect the homogeneity of these specific reponse patterns, and did not fit the respective clusters.