The role of different slug species in damage to oilseed rape bordering on sown wildflower strips

Damage caused by different slug species on above and below ground parts of young oilseed rape bordering on sown wildfower strips was studied. Slug densities and damage were recorded in the field and damage rates for each slug species were measured in the laboratory. Severe slug damage was observed in rape areas 1 m from the wildflower strips. Damage rates of slug species feeding above ground were distinctly higher than those feeding below ground. The estimated damage caused by above-ground feeding in all four study fields ranged between 72% and 89 % and was always distinctly higher than damage caused by below-ground feeding (11% to 28 %). The estimated damage caused by Arion lusitanicus above ground was between 54% and 69 %, followed by Deroceras reticulatum (3% to 26 %). Thus A. lusitanicus was responsible for the majority of damage in the rape crops studied.     

Predation by the Carabid Beetles Pterostichus melanarius and Poecilus cupreus on Slugs and Slug Eggs

Predation on slugs, Arion lusitanicus (Mabille) and Deroceras reticulatum (Müller), and their eggs by the carabid beetles Pterostichus melanarius (Illiger) and Poecilus cupreus (L.) was investigated in the laboratory. Slugs of different size and slug eggs were offered to the beetles in petri dishes with and without several alternative prey. Pterostichus melanarius destroyed eggs of D. reticulatum and A. lusitanicus, with a clear preference for D. reticulatum eggs. The availability of some alternative prey types adversely affected feeding on D. reticulatum eggs by P. cupreus and feeding on A. lusitanicus eggs by P. melanarius. Yet consumption of D. reticulatum eggs by P. melanarius was not significantly influenced by any alternative prey. Only P. melanarius killed small D. reticulatum in the presence of alternative prey. This suggests that P. melanarius and P. cupreus may have the potential to reduce slug populations in the field by destroying slug eggs and, in the case of P. melanarius, killing freshly hatched slugs.     

Size-specific susceptibility of the pest slugs Deroceras reticulatum and Arion lusitanicus to the nematode biocontrol agent Phasmarhabditis hermaphrodita

The nematode Phasmarhabditis hermaphrodita is a commercially available biocontrol agent against slugs. This product is especially interesting for use in organic farming, where products containing metaldehyde or carbamates cannot be used for controlling pest slugs. We investigated the potential of P. hermaphrodita for the control of the pest slugs Deroceras reticulatum and Arion lusitanicus. These two species are the most harmful slug pests in Switzerland. At different times of the year, we collected slug specimens of different weight and assessed their susceptibility to P. hermaphrodita in the laboratory. Batches of five slugs were subjected to five different doses of nematodes plus an untreated control and replicated three times. During six weeks, feeding and survival of the slugs were recorded. D. reticulatum was strongly affected by increasing nematode doses, irrespective of the slugs' body weight. In small specimens of A. lusitanicus, feeding and survival were strongly affected by the nematodes, while larger specimens remained almost unaffected. Because A. lusitanicus has an asynchronous development in Switzerland, it seems difficult to control the entire population with a single nematode application. To what extent nematodes will be used in practice for slug control depends on their effectivity against the pest slugs of major importance, on the longevity of the molluscicidal effect and on the price of nematodes.     

Feeding deterrent effect of carvone, a compound from caraway seeds, on the slug Arion lusitanicus

The feeding deterrent effect of carvone on the slug Arion lusitanicus was investigated. Carvone, a natural compound from caraway seeds, was incorporated into mulch to reduce its inherent volatility. In a laboratory choice experiment, boxes were filled on one side with carvone‐treated mulch and on the other side with untreated mulch. At carvone concentrations ranging from 0.03–0.75 ml litre^?1 mulch, slugs ate significantly more lettuce on the untreated side. In a laboratory based no‐choice experiment, carvone concentrations of 0.25 and 0.75 ml litre^?1 mulch significantly reduced slug feeding in comparison with the untreated control. Moreover at the highest concentration of carvone (0.75 ml litre^?1 mulch) 50% mortality was recorded over a period of 5 days, indicating a clear molluscicidal effect. Due to its volatility carvone did not decrease plant defoliation by A. lusitanicus when applied directly onto lettuce. Subsequent field evaluation showed 0.75 ml litre^?1 mulch to partially reduce slug feeding damage. However, this effect was not sufficient to significantly increase lettuce yield. The incorporation of a higher carvone concentration into mulch is still to be tested to confirm whether carvone‐treated mulch can be recommended as an effective alternative approach to chemical slug control.     

SLUG DAMAGE AND NUMBERS OF SLUGS IN OILSEED RAPE BORDERING ON GRASS STRIPS

In 1995, slug damage and numbers of slugs were estimated intwo grass strips and adjacent rape fields. Investigations beganas soon as rape seedlings emerged and lasted for five weeks.Slug damage to rape plants 1 m from the grass strips was significantlyhigher than at greater distances from the strips. Derocerasreticulatum was the most abundant slug species recorded in bothgrass strips and adjacent rape fields. Arion lusitanicus andArion fasciatus were much less abundant than D. reticulatum.In one field, D. reticulatum declined steadily with increasingdistance from the grass strips and therefore appeared to havecaused the majority of severe damage to rape plants close tothe strips. This finding was surprising because until now severeslug damage in oilseed rape beside semi-natural habitats hasbeen observed only where A. lusitanicus was abundant. (Received 12 November 1997; accepted 26 January 1998)     

The influence of temperature on life history traits in the Iberian slug,Arion lusitanicus

The slug Arion lusitanicus is an invasive species which has recently become established in many European countries and is considered a serious pest, both in agriculture and private gardens. The effect of temperature on growth rate, survival, egg developmental time and hatchability of the slug are reported. The growth rate was positively correlated with temperatures up to 20°C and A. lusitanicus continued (on average) to grow until they die. A model describing how growth depends on temperature was developed, and a field survey found that the predicted growth matched the observed with reasonable accuracy. This study confirms the assumption that A. lusitanicus die after egg laying. Free‐ranging A. lusitanicus has an annual life cycle, but our data show that slugs also possess the ability to live for up to 3 years. The egg developmental time was, like growth, positively correlated with temperature and was shortest at 20°C, but the optimum temperature for egg development, when regarded as the temperature with highest hatchability was found to be 10°C. In conclusion, this study has shown that growth and the life‐history traits, egg developmental time and hatchability, of A. lusitanicus are highly influenced by temperature. However, data also show that temperatures within the range 2–20°C did not influence survival rates to any large degree, and that A. lusitanicus can quickly adjust to changes in temperature. The study provides a number of basic parameters which contribute to the understanding of the population dynamics of A. lusitanicus.     

Daily activity of the pest slug Arion lusitanicus under laboratory conditions

The daily activity of the slug Arion lusitanicus was studied using time‐lapse video analysis in the laboratory. Under constant temperature (18°C) and 16–h photoperiod, the activity of slugs was measured in half‐hourly periods as locomotor activity, feeding or resting. Track lengths were determined using image analysis. Locomotion of A. lusitanicus was greatest at 5:30, 1.5 h after sunrise, and at 20:30, 1 h after sunset; least locomotor activity occurred between 13:00 and 14:00. The mean distance travelled by A. lusitanicus in 24 h was 10.8 m. The largest slug was the most active and the smallest the least. Slugs spent 68% of 24 hours resting, mainly under artificial shelter traps, 27% in locomotion and 4% feeding. Feeding occurred mainly during the hours of dakness (76%). All categories of behaviour investigated varied greatly between individuals and also between times of day. Homing to artificial shelters and other roost sites was regularly observed within 24 h (41%), but decreased considerably thereafter. The behavioural patterns proved to be in agreement with those found in a previous field investigation and are therefore also discussed with a view to their importance in pest control.     

Arion slugs as nest predators of small passerine species – a review

Arionid slugs have been reported to attack nestlings of some ground‐ or shrub‐nesting passerine birds, mainly in Europe. We review these reported cases and consider their effects. The slugs can cause grave or even fatal injuries to the nestlings. Surprisingly, no brood defence by the parents has been described. The information on the frequency of slug predation in bird populations is scanty, and the scale of the phenomenon is unknown. The expansion of the invasive Arion vulgaris Moquin‐Tandon, 1855 (synonymously A. lusitanicus or A. lusitanicus auct. non Mabille, 1868) in Europe may result in an increase of the negative influence of slugs on the breeding success of some passerines in the near future.     

Low temperature survival in different life stages of the Iberian slug, Arion lusitanicus

The slug Arion lusitanicus Mabille (Gastropoda: Pulmonata: Arionidae) is an invasive species which has spread to most parts of Europe. The area of origin is unknown, but A. lusitanicus seems to cope well with the local conditions in the countries to which it has migrated. It spreads rapidly, occurs often in high densities and has become a serious pest in most European countries. Therefore there is an urgent need for better knowledge of the ecophysiology of A. lusitanicus, such as the influence of climatic conditions, in order to develop prognostic models and strategies for novel pest management practises.The aim of our study was to investigate the influence of subzero temperatures in relation to winter survival. A. lusitanicus is shown to be freeze-tolerant in some life stages. Most juveniles and some adult slugs survived being frozen at −1.3 °C for 3 days, but none of the slugs survived freezing at −3 °C. The eggs survived subzero temperatures (down to −2 °C) probably by supercooling. Juveniles and adults may also survive in a supercooled state (down to −3 °C) but are generally poor supercoolers. Therefore, the winter survival of A. lusitanicus depends to a high degree on migration to habitats protected from low winter temperatures, e.g. under plant litter, buried in the soil or in compost heaps.     

Drought tolerance in eggs and juveniles of the Iberian slug, <Emphasis Type="Italic">Arion lusitanicus</Emphasis>

The spread of invasive species is an increasing problem world wide. The invasive slug Arion lusitanicus has spread to most parts of Europe, where it often is considered as a serious pest. There is a need for better knowledge of its ecophysiology to be able to predict the effect of climatic factors, such as temperature and humidity on the population dynamics and abundance. The aim of the present study was to assemble data on the water balance and drought tolerance of eggs and juveniles of A. lusitanicus. Both eggs and juveniles had little capacity to prevent evaporative water loss and lost water when the ambient humidity fell below 99.8 and 99.5%, respectively. The water conductance of the cuticle of juveniles was 242 μg cm⁻² h⁻¹ mmHg⁻¹ and resembles that of other slug species. Both eggs and juveniles of A. lusitanicus tolerate a substantial water loss. There was no difference in water loss resistance between eggs and juveniles, but the eggs were slightly more tolerant to water loss than the juveniles. The percent water loss causing 50% mortality was 72% for the juveniles and 81% for the eggs. Despite A. lusitanicus’ tolerance of substantial water loss, its survival depends on humid habitats.     

SLUG DAMAGE AND NUMBER OF SLUGS (GASTROPODA: PULMONATA) IN WINTER WHEAT IN FIELDS WITH SOWN WILDFLOWER STRIPS

Previous observations have shown that slugs found favourableconditions for reproduction in wildflower strips and that theycaused high damage to oilseed rape adjacent to the strips. Inthe current study slug numbers and damage were estimated inwildflower strips and at different distances from the stripsinto winter wheat crops, from 1994 to 1996. Slug damage wasestimated using an index of defoliation and slug numbers andactivity were measured using wheat bran traps. Investigationsbegan when winter wheat seedlings emerged and lasted for fiveweeks. Slug damage was never severe in any of the fields studied.In most fields, slug damage was higher close to the wildflowerstrips than at greater distances from the strips. The decliningslug damage with increasing distances from the wildflowers stripswas related to the distribution pattern of juvenile Arion lusitanicus,suggesting that this species was responsible for the higherdamage near the strips. Other slug species (Deroceras reticulatum,Arion fasciatus, Deroceras laeve) were more or less evenly distributedover the field or were almost entirely confined to the wildflowerstrips. Results showed that winter wheat was not at risk fromslug feeding in spite of the establishment of wildflower stripsand that therefore the application of molluscicide along thestrips is unnecessary. (Received 23 June 1997; accepted 17 October 1997)     

A method to study slug predation on seedlings in the field

Dandelion is a common Asteraceae species that populates disturbed sites and gaps within swards where it becomes an important competitor of grasses. The natural control against dandelion includes seedling predation, with slugs, particularly Arion lusitanicus, being the most important in the Czech Republic. However, the study of slug seedling consumption is difficult because naturally established seedlings are not always available. Therefore, we developed a method of exposing laboratory‐grown seedlings as bait for slug predation. Dandelion seeds were sown in plastic cups containing a bottom layer of moist substrate. The emerged seedlings were thinned to 20 and displayed in an open area. During 2008–2010, the seedling baits were placed at 15 sites at 1 month intervals throughout the dandelion vegetative season, in parallel with plasticine baits that monitored slug feeding activity. For each 1 month interval, seedling survival was observed for a period of 8 days, and the estimated time to death was calculated; the percentage of surviving seedlings was then recorded. This method of seedling presentation demonstrated that local and temporal variation in seedling survival is correlated with slug feeding activity. The advantage of this technique is that the seedlings in baits may be presented at any place and time, as required by the experimental design; however, we found that the estimated time to seedling death was shorter for the exposed baits than for the naturally established seedlings. The method is suitable for the study of plant species other than dandelion, and also for aims other than the study of spatiotemporal trends in seedling consumption by slugs.     

Ingestion and excretion of two transgenic Bt corn varieties by slugs

The release of transgenic Bacillus thuringiensis (Bt) corn expressing various Cry endotoxins has raised concern that these endotoxins are disseminated in the food web and may adversely affect non-target beneficial organisms, such as predators and organisms of the decomposer food web. We therefore investigated in a laboratory study, whether the Cry1Ab and Cry3Bb1 protein from Bt corn could potentially be transferred to such organisms by measuring the Cry protein content in the two common agricultural slug pests Arion lusitanicus and Deroceras reticulatum and their feces. We measured Cry1Ab and Cry3Bb1 protein concentration in leaves, intestines, and feces of corn leaf-fed slugs using ELISA and determined how much of the ingested protein is excreted by the slugs. Cry3Bb1 concentration in leaves of DKC5143Bt corn was significantly higher than Cry1Ab concentration in leaves of N4640Bt corn. While slugs were feeding on corn leaves, the Cry3Bb1 and Cry1Ab proteins were found in intestines and feces of both slug species. Bt protein concentrations in intestines of Cry3Bb1 corn-fed slugs were in both slug species higher than in Cry1Ab corn fed slugs, whereas no differences between Cry3Bb1 and Cry1Ab protein in feces were found. After slugs had ceased feeding on Bt corn, Cry1Ab was detectable in fresh slug feces for a significantly longer time and often in higher amounts than the Cry3Bb1. Our results indicate that both Cry proteins are likely to be transferred to higher trophic levels and to the decomposer food web. Since different Bt proteins seem to vary in their degradation, they have different transfer probabilities. This should be considered in risk assessments for non-target arthropods.     

Body size and the colonisation of cereal crops by the invasive slug Arion lusitanicus

The invasive slug Arion lusitanicus lives in undisturbed stands of grass or herbaceous plants from where it disperses into crops. Factors that determined the dispersal of slugs from a grassy orchard (O) into an adjacent cereal stand were investigated. Slug‐feeding activity, abundance and body weight were established along a 120 m transect across an orchard and a cereal crop. Slugs in the source population in the orchard were more abundant and lighter in 2008 than 2009. The slugs that left the orchard and moved into the cereal crop were heavier than those that remained in the orchard and the distance they travelled was positively correlated with their weight. The abundance of slugs in the cereal crop decreased with the increase in the distance from the source population, more so in 2008, when slugs were light in weight and accumulated near the edge of the orchard, than in 2009 when the slugs were heavier and distributed more evenly. The feeding activity of the slugs leaving the orchard and distance they dispersed also increased during the course of the season. Long distance dispersal is achieved by crawling, the speed of which increased with slug size. Seasonal and annual variation in body size thus affected the distribution of slugs in the cereal crop and the distance they dispersed.     

The effect of different growing substrates on the development and quality of Phasmarhabditis hermaphrodita (Nematoda: Rhabditidae)

The effect of different growing substrates on the development of the slug parasite Phasmarhabditis hermaphrodita has been studied in a series of laboratory experiments. Wild, laboratory and Nemaslug strains of P. hermaphrodita and their monoxenic counterparts with Moraxella osloensis (CCM 5605T) were reared on homogenised pig kidney, Deroceras reticulatum, Arion lusitanicus, and Galleria mellonella, the faeces of D. reticulatum and A. lusitanicus, or leaf compost. Development time, yield, lipid reserves and the body length of nematodes were assessed. All P. hermaphrodita strains were able to grow and reproduce on all tested substrates; however, yields were markedly higher on invertebrate media. Lipid content and body size varied across the substrates and strains. A uniform response of all nematode strains and the most dramatic differences among substrates were recorded in yields, which could indicate that the quality of the substrate is expressed mainly in yield. Monoxenized strains had higher yield, length, lipid content and shorter development time. In general, the strain differences between the observed parameters were most likely due to different bacterial associates. The dramatic differences in yields on invertebrate substrates, in comparison to the others, illustrate the evolutionary advantage of the association of nematodes with invertebrates.     

Quantitative comparison of chemical, biological and mechanical induction of secondary compounds in Pinus pinaster seedlings

Chemical elicitors and mechanical treatments simulating real insect herbivory have been increasingly used to study induced defensive responses in woody plants. However, simultaneous quantitative comparisons of plant chemical defences elicited by real and simulated herbivory have received little attention. In this paper we compared the effects of real herbivory, simulated herbivory using two chemical elicitors, and mechanical damage treatments on the quantitative secondary chemistry of Pinus pinaster juveniles (namely on non-volatile resin in the stem and total phenolics in the needles). The real herbivory involved phloem wounding by Hylobius abietis and defoliation by Brachyderes lusitanicus (two pine weevils); the chemical elicitors to simulate herbivory induction were 40 mM methyl jasmonate (MJ) and 20 μM benzothiadiazole (BTH); and the mechanical treatments included phloem wounding and needle clipping. We also performed an additional experiment for assessing at what extent insect extracts could increase plant responses over mechanical damage. Chemical induction with MJ, mechanical wounding and real phloem herbivory by H. abietis all produced quantitatively similar results, increasing the concentration of resin in the stem and total phenolics in the needles by equivalent magnitudes. Exogenous application of BTH increased the concentration of phenolic compounds in pine needles, but did not show the same effect on stem resin. Contrastingly, we did not find significant changes in the concentration of resin in the stem or phenolics in the needles after needle clipping and B. lusitanicus feeding. Mechanical damage followed by the application of extracts from the insects B. lusitanicus and H. abietis on the injured tissues did not increase the responses in comparison to mechanical damage alone. The fact that strong induced responses elicited by phloem wounding insects are equally elicited by phloem injuries suggests that defences in pine trees are raised with low specificity regarding biotic enemies. Results from this paper support future methodological approaches using chemical elicitors and mechanical damage as simulated herbivory treatments for the experimental induction of conifer defences.     

Evaluation of the synergistic antimicrobial effect of folk medicinal plants with clindamycin against methicillin-resistant Staphylococcus aureus strains

Antibiotic resistance has become a major worldwide priority, and identifying natural antimicrobial compounds may help overcome this problem. In this study, ethanolic extracts of 12 plants commonly used in traditional medicine were tested against two strains of methicillin-resistant Staphylococcus aureus (ATCC 33591 and ATCC 43300) in terms of minimum inhibitory concentrations (MICs). Furthermore, the effect of combining plant extracts with clindamycin antibiotic was also investigated using the checkerboard method. Among the tested plants, Camellia sinensis, Thymus vulgaris, Rosmarinus officinalis and Salvia officinalis exhibited potent inhibitory activity against both strains with MICs ranges (125–500 µg ml⁻¹). Synergistic activity was confirmed for the four plants combined with clindamycin with fractional inhibitory concentration index <0·5. However, no antagonistic activity was found for these combinations. Our findings suggest that using an antibiotics-plants combination might be a successful technique to reduce antibiotic consumption, which would overcome the antibiotics resistance or delay its onset.     

Phylogeny of slug species of the genus Arion: evidence of monophyly of Iberian endemics and of the existence of relict species in Pyrenean refuges

The Iberian Peninsula contains the majority of the Paleartic land slug species of the genus Arion, which exhibits diverse taxonomic problems. The present study investigated Arion taxonomy on the basis of analyses of the mitochondrial ND1 gene and nuclear internal transcribed spacer 1 (ITS1) sequences. The Iberian endemic species were monophyletically clustered in two divergent sister clades. The topotype specimens of Arion lusitanicus and the closely related species Arion nobrei and Arion fuligineus, as well as Arion hispanicus and Arion flagellus, were grouped into an ‘Atlantic’ clade, whereas Arion baeticus, Arion gilvus, Arion anguloi, Arion wiktori and Arion paularensis were included in a ‘Continental–Mediterranean’ clade. Calibration of mutation rate in the ND1 gene suggested that the divergence of these two clades occurred around the Pliocene–Pleistocene boundary, with subsequent speciation events during the Pleistocene. A group of ancestral and divergent endemic species with distribution centred in the Pyrenean mountain range (Arion molinae, Arion lizarrusti, Arion antrhacius and Arion iratii) arose in the Pliocene and survived through the Pleistocene in geographically confined small populations. Arion lusitanicus showed up to be polyphyletic: specimens, sampled outside the geographic range of the topotype in the north‐western Iberian Peninsula, were included in a non‐monophyletic clade together with the widely distributed species Arion ater and Arion rufus. The divergent species with a wide European distribution (Arion subfuscus, Arion hortensis, Arion fagophilus and Arion intermedius) were located in basal positions in all topologies. The evolutionary history of these slug species (highly sensitive to climatic factors, with capacity for both outcrossing and selfing, and with low dispersal ability) appears to have been moulded by Pliocene–Pleistocene climate events and by the rugged topography of southern Europe, giving rise to repeated cycles of population isolation during periods of glaciation alternating with interglacial expansions limited by geographic barriers.     

Factors restricting the feeding of the cabbage stem flea beetle (Psylliodes chrysocephala)

The feeding acceptability of 40 different plants to Psylliodes chrysocephala L. (Coleoptera: Chrysomelidae) was determined using leaf disc consumption tests for the adult, and stem or petiole penetration tests for the larvae. Only plants that contained glucosinolates were accepted as food, but addition of the glucosinolate sinigrin to rejected food plants did not make them acceptable to adults. Of the 34 plants that contained glucosinolates, nine were either totally or mostly rejected. Solvent extracts of the rejected plants applied to oilseed rape inhibited feeding by adults. The feeding of P. chrysocephala within the group of plants tested is influenced by the presence or absence of glucosinolates, which may act as feeding stimulants, and other, unidentified chemicals which act as feeding inhibitors.     

Is palatability of a root-hemiparasitic plant influenced by its host species?

Palatability of parasitic plants may be influenced by their host species, because the parasites take up nutrients and secondary compounds from the hosts. If parasitic plants acquired the full spectrum of secondary compounds from their host, one would expect a correlation between host and parasite palatability. We examined the palatability of leaves of the root-hemiparasite Melampyrum arvense grown with different host plants and the palatability of these host plants for two generalist herbivores, the caterpillar of Spodoptera littoralis and the slug Arion lusitanicus. We used 19 species of host plants from 11 families that are known to contain a wide spectrum of anti-herbivore compounds. Growth of M. arvense was strongly influenced by the host species. The palatability of the individual host species for the two herbivores differed strongly. Both A. lusitanicus and S. littoralis discriminated also between hemiparasites grown with different host plants. There was no correlation between the palatability of a host species and that of the parasites grown on that host, i.e., hemiparasites grown on palatable host species were not more palatable than those grown on unpalatable hosts. We suggest an interacting pattern of specific effects of chemical anti-herbivore defences and indirect effects of the hosts on herbivores through effects on growth and tissue quality of the parasites.