Slug activity density increases seed predation independently of an urban–rural gradient

Post-dispersal seed predation by slugs is increasingly being acknowledged as a potentially important contribution to this ecosystem function. However, specific drivers of predation rates in different landscape contexts are still unknown. We assessed the role of slugs as facultative seed predators along an urban–rural gradient and identified scale-dependent anthropogenic drivers that might affect either slugs or their function as seed predators.We used a combination of seed cafeterias and pitfall traps in grassy areas of eleven schoolyards and five field margins surrounded by different land-use types to assess slug activity density and seed predation rates and quantified urbanization, habitat heterogeneity and microhabitat structure.We show that slugs are important seed predators regardless of anthropogenic land use. Their activity density was a significant predictor for seed predation but increases in woody vegetation and bare soil also increased seed predation. This indicates that the magnitude of seed predation might also be affected by slug foraging activity and feeding behaviour, which might be influenced by habitat features such as the availability of vegetation and bare soil. Our results suggest that not only assessing the activity density (as proxy for relative abundance) of seed predators but also identifying effects on their feeding patterns and behaviour might increase our mechanistic understanding of relationships between land-use changes and seed predation and their impact on cultivated and wild plant species.     

The significance of facultative scavenging in generalist predator nutrition: detecting decayed prey in the guts of predators using PCR

Gut-content analyses using molecular techniques are an effective approach to quantifying predator-prey interactions. Predation is often assumed but scavenging is an equally likely route by which animal DNA enters the gut of a predator/scavenger. We used PCR (polymerase chain reaction) to detect scavenged material in predator gut homogenates. The rates at which DNA in decaying slugs (Mollusca: Pulmonata) and aphids (Homoptera: Aphididae) became undetectable were estimated. The detectability of DNA from both carrion types in the guts of the generalist predator Pterostichus melanarius (Coleoptera: Carabidae) was then determined. The effects of carrion age and weight, as well as beetle sex, on detection periods, were quantified. Laboratory trials measured prey preference of beetles between live and decaying prey. Further experiments measured, for the first time, feeding by P. melanarius on dead slugs and aphids directly in the field. In both field and laboratory, P. melanarius preferentially fed on dead prey if available, but preference changed as the prey became increasingly decayed. Disappearance rates for slug carrion in wheat fields and grasslands were estimated and P. melanarius was identified as the main scavenger. Comparison of the retention time for dead slugs in the field, with the detection period for decaying slug material in the guts of the predators, showed that PCR-based techniques are not able to distinguish between predated and scavenged food items. This could potentially lead to overestimation of the impact of predation on slugs (and other prey) by carabids. Possible implications of facultative scavenging by invertebrate predators for biocontrol and food-web research are discussed.     

Daily activity rhythm and use of shelter in the slugs Deroceras reticulation and Arion distinctus under laboratory conditions

Daily activity of slugs, Deroceras reticulatum and Arion distinctus, was studied in the laboratory in relation to the presence of shelters so as to define optimal conditions for using traps to forecast crop damage. Under constant temperature and humidity, activity of slugs began with the lights off. Its arrest occurred after a period of activity with the lights on. Slugs rested most frequently under a shelter on bare earth and rarely used the same shelter for more than two consecutive days. When food was placed under the shelter, the number of slugs found under the shelter was more constant throughout the 24 h period, but lower during diurnal rest. The presence of 4% methiocarb pellets under the shelter led to an increased occupation by slugs, due to the poisoning of some of them. Acts of aggression were more numerous in A. distinctus than in D. reticulatum. In D. reticulatum the smallest slug was the least aggressive and suffered more attacks from the other slugs. In A. distinctus the numbers of attacks suffered or provoked varied little with the size of the slug, but the smallest slug showed less interactions with other slugs.     

Effect of predator size and temperature on the predation of Deroceras reticulatum (Muller) (Mollusca) by carabid beetles

Twenty-one carabid species were used in a laboratory study to determine the effect of beetle size and temperature on the predation of one day old Deroceras reticulatum (Muller) slugs. The beetles were caught in arable land at the study site. None of the five small-sized beetle species killed slugs, whereas five of the seven medium-sized beetle species and eight of the nine large-sized beetle species killed slugs. Four of the most abundant beetle species at the study site were used to assess the effect of temperature on the predation of 1-day-old slugs. There were significant differences in the proportion of beetles predating slugs at the different temperatures. Regression analysis showed that there was a significant increase in the proportion of Pterostichus madidus (Fabricius) and Harpalus rufipes (Degeer) beetles predating slugs as temperature increased. Nebria brevicollis (Fabricius) inflicted its highest level of slug mortality at 8°C and its larvae were the only predators to significantly increase slug mortality at 4°C, the lowest experimental temperature. Harpalus aeneus (Fabricius) inflicted significant levels of slug mortality at 20°C, the highest experimental temperature. It appeared that the predatory activity of these beetle species at the five experimental temperatures reflected their annual activity periods in the field.     

Predation by the carabid beetle Harpalus rufipes on the pest slug Deroceras reticulatum in the laboratory

The Harpalini species Harpalus rufipes, as many other generalist carabids, consume a wide variety of prey and it is known to feed on pest slugs such as the grey field slug Deroceras reticulatum, but quantitative data about the predatory activity of H. rufipes on slugs are very scarce. In laboratory experiments, we assessed the capability of male H. rufipes to kill eggs and different‐sized slugs of the pest species D. reticulatum in either the absence or the presence of alternative live prey (dipteran larvae and aphids). We also investigated the preference of H. rufipes for eggs and hatchlings of D. reticulatum in a choice experiment. H. rufipes killed considerable amounts of eggs and small juveniles (≤5.0 mg) of D. reticulatum, both in no‐choice and in choice situations. Medium‐sized juvenile slugs (10–20 mg) were seldom killed only in no‐choice situations, and no large juveniles (50–60 mg) were killed. Dipteran larvae and aphids were killed also in no‐choice and in choice situations. The type of alternative prey presented with slug eggs affected the survival of the eggs to H. rufipes predation. The presence of dipteran larvae as alternative prey did not affect the survival of juvenile slugs. When eggs and small juvenile slugs were offered together, the survivals of both items were similar. The obtained results under laboratory conditions suggest that the generalist predator H. rufipes might realise an important contribution to the control of pest slugs.     

Cell Movements and Mechanical Force Distribution During the Migration of Dictyostelium Slugs

Migration of Dictyostelium discoideum slugs results from coordinated movement of their constituent cells. It is generally assumed that each cell contributes to the total motive force of the slug. However, the basic mechanisms by which mechanical forces (traction and resistive forces) are transmitted to the substrate, their magnitude and their location, are largely unknown. In this work, we performed detailed observations of cell movements by fluorescence microscopy using two-dimensional (2D) slugs. We show that 2D slugs share most of the properties of 3D ones. In particular, waves of movement propagate in long 2D slugs, and slug speed correlates with slug length as found in 3D slugs. We also present the first measurements of the distribution of forces exerted by 2D and 3D slugs using the elastic substrate method. Traction forces are mainly exerted in the central region of the slug. The large perpendicular forces around slug boundary and the existence of parallel resistive forces in the tip and/or the tail suggest an important role of the sheath in the transmission of forces to the substrate.     

Nature and distribution of the morphogen DIF in the Dictyostelium slug

The Dictyostelium slug contains a simple anterior-posterior pattern of prestalk and prespore cells. It is likely that DIF, the morphogen which induces stalk cells, is involved in establishing this pattern. Previous work has shown that a number of distinct species of DIF are released by developing cells and that cell-associated DIF activity increases rapidly during the slug stage of development. In this paper we describe a comparison of the DIF extracted from slugs with the DIF released into the medium. Analysis by high-pressure liquid chromatography (HPLC) using different solvent systems shows that the major species of DIF activity extracted from slugs coelutes with DIF-1, the major species of released DIF and is similarly sensitive to sodium borohydride reduction. Since DIF specifically induces the differentiation of prestalk cells, the anterior cells of the slug, it could be anticipated that DIF is localized in the prestalk region. We have therefore determined the distribution of DIF within the slug. Migrating slugs from strain V12M2 were manually dissected into anterior one-third and posterior two-third fragments and the DIF activity extracted. Surprisingly, we found that DIF was not restricted to the prestalk fragment. Instead there appears to be a reverse gradient of DIF in the slug with at least twice the specific activity of total DIF in the prespore region than in the prestalk region.     

Sea‐slug invasion of the land

Invasion of the land has been a considerable challenge for aquatic organismal lineages, primarily because of desiccation and lack of physical support in air. Gastropod molluscs are among the most successful animals in this habitat shift because of their hard exoskeleton, whereas land slugs, regarded as descendants of land snails, gradually lost their shells in sheltered, moist environments. We present solid evidence of terrestrial invasion by a lineage of sea slugs; this invasion is represented by a newly discovered species, Aiteng marefugitus (Panpulmonata: Acochlidia), from a humid tropical rainforest on a small island in the Republic of Palau, western Pacific. The slug lineage seems to have invaded the forest habitat directly from the upper littoral zone in the Cenozoic.     

Dispersal movements of non-native and native terrestrial slugs in an urban environment

Animal movement varies from undirected dispersal to directed migration. Movement rates may have implications for conservation and resource management, as well as pest control, and they play a key role in invasion success. In slugs, long-distance dispersal is typically passive, whereas active movement is critical for local dispersal and determines access to resources such as food and shelter. Telemetry has recently been used to study individual slug movements in the wild, whereas movement in arena tests has explored mechanisms of interspecific competition and invasiveness in slugs. Studies that relate the performance of individual slugs in arena tests to their post-release behavior in nature are lacking. We measured individual short-term movement speed of commonly occurring native and non-native slugs of the genera Arion and Limax in arena tests and tracked their post-release dispersal movements in a garden by PIT telemetry. We demonstrate clear differences in movement behavior among the species, but non-native slugs did not display higher movement rates than their native congeners. In the arena test, slugs of the genus Limax displayed a higher short-term speed than slugs of the genus Arion, whereas in the field, individuals of Limax maximus showed lower dispersal rates compared to the other slug species. Moreover, there was a positive correlation between short-term speed in the arena test and movement in the field among individuals of L. cinereoniger, indicating the possible existence of behavioral syndromes in slugs, which may link movement ecology, animal personality, and the invasion ecology of pest species.     

Activity of platelet-activating factor (PAF) acetylhydrolase in plasma from patients with ischemic cerebrovascular disease

Platelet-activating factor (PAF) is metabolized by a specific enzyme, PAF acetylhydrolase, which may play an important role in the manifestation of the biological activities of PAF in vivo. The activity of PAF acetylhydrolase in plasma of patients with ischemic stroke was higher than that in healthy controls. The incidence of irreversible platelet aggregation in response to PAF, as well as to ADP, was found to be higher in patients than in controls. The patients whose platelets responded with irreversible aggregation to PAF displayed a higher activity of plasma PAF acetylhydrolase than those with only reversible aggregation. In controls, PAF acetylhydrolase activity correlated positively, although weakly, with LDL-cholesterol, which may reflect the major role of LDL in carrying this enzyme. However, since there was no significant difference in plasma levels of lipids and apoproteins between patients and controls (except for apo B) and there was no significant relationship between the enzyme activity and the levels of other lipids and apoproteins, it is unlikely that increased plasma level of PAF acetylhydrolase activity in stroke patients is accounted for by an abnormality of lipoprotein metabolism. Platelet hyperfunction may be associated with augmented generation of PAF, which, in turn, may bring about the induction of the inactivating enzyme, PAF acetylhydrolase.     

A cell type-specific effect of calcium on pattern formation and differentiation in dictyostelium discoideum

Spatial gradients of sequestered and free cellular calcium (Ca2+) exist in the slug of Dictyostelium discoideum (Maeda and Maeda, 1973; Tirlapur et al., 1991; Azhar et al., 1995; Cubitt et al., 1995). When we vary intracellular Ca2+ with the help of calcium buffers and the ionophore Br-A23187, there are striking effects on slug morphology, patterning and cell differentiation. In the presence of a calcium ionophore, high external Ca2+ levels lead to an increase of intracellular sequestered and free Ca2+, the formation of long slugs, a decrease in the fraction of genetically defined prespore cells and 'stalky' fruiting bodies. Conversely, a lowering of external Ca2+ levels results in a decrease of intracellular Ca2+, the formation of short slugs, an increase in the prespore fraction and 'spory' fruiting bodies. We infer that Ca2+ plays a significant morphogenetic role in D. discoideum development, by selectively promoting the prestalk pathway relative to the prespore pathway.     

Copine A is expressed in prestalk cells and regulates slug phototaxis and thermotaxis in developing Dictyostelium

Copines are calcium-dependent membrane-binding proteins found in many eukaryotic organisms. We are studying the function of copines using the model organism, Dictyostelium discoideum. When under starvation conditions, Dictyostelium cells aggregate into mounds that become migrating slugs, which can move toward light and heat before culminating into a fruiting body. Previously, we showed that Dictyostelium cells lacking the copine A (cpnA) gene are not able to form fruiting bodies and instead arrest at the slug stage. In this study, we compared the slug behavior of cells lacking the cpnA gene to the slug behavior of wild-type cells. The slugs formed by cpnA- cells were much larger than wild-type slugs and exhibited no phototaxis and negative thermotaxis in the same conditions that wild-type slugs exhibited positive phototaxis and thermotaxis. Mixing as little as 5% wild-type cells with cpnA- cells rescued the phototaxis and thermotaxis defects, suggesting that CpnA plays a specific role in the regulation of the production and/or release of a signaling molecule. Reducing extracellular levels of ammonia also partially rescued the phototaxis and thermotaxis defects of cpnA- slugs, suggesting that CpnA may have a specific role in regulating ammonia signaling. Expressing the lacZ gene under the cpnA promoter in wild-type cells indicated cpnA is preferentially expressed in the prestalk cells found in the anterior part of the slug, which include the cells at the tip of the slug that regulate phototaxis, thermotaxis, and the initiation of culmination into fruiting bodies. Our results suggest that CpnA plays a role in the regulation of the signaling pathways, including ammonia signaling, necessary for sensing and/or orienting toward light and heat in the prestalk cells of the Dictyostelium slug.     

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.     

Platelet-activating factor acetylhydrolase increases during macrophage differentiation. A novel mechanism that regulates accumulation of platelet-activating factor

Monocytes and macrophages produce bioactive lipids, such as platelet-activating factor (1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine, PAF), that mediate inflammation. These cells synthesize PAF following their activation, but not constitutively. Previous studies have demonstrated that PAF accumulation is regulated by the activity of the synthetic enzymes. We observed that the accumulation of PAF in stimulated human monocytes decreased by 90% as they differentiated into macrophages. There was no decrease in the activities of the synthetic enzymes; however, the activity of the degradative enzyme, PAF acetylhydrolase, increased 260-fold. The increase in PAF acetylhydrolase activity appeared to result from a net increase in the synthesis of a new enzyme. These studies demonstrate a novel mechanism in which an increase of the degradative enzyme regulates the accumulation of PAF. This may be an important mechanism by which macrophages modulate inflammatory responses.     

Effects of metaldehyde and methiocarb on feeding preferences and survival of a slug predator (Pterostichus melanarius (F.): Carabidae,Pterostichini)

The potential for reducing slug populations in crops through predation by generalist carabid beetles is well documented. However, few studies have considered interactions between biological and chemical control agents of slugs. Laboratory assays supported previous findings that the consumption of metaldehyde by slugs (Deroceras reticulatum) leads to increased duration of feeding bouts by carabid beetles (such as Pterostichini) on sub‐lethally affected individuals. However, a similar effect was not found for Pterostichus melanarius exposed to slugs fed on the other widely applied pelleted molluscicide formulation (methiocarb). Examination of beetle survival after consumption of slugs containing molluscicides demonstrated the strong biocidal properties of methiocarb, whereas metaldehyde consumption (ingested through slug predation) did not differ from control slugs killed by freezing. Beetle avoidance of slugs containing a more toxic molluscicide compound and the interaction between slug mucus production and beetle attack rates are discussed.     

Regulation of the synthesis of platelet-activating factor and its inactive storage precursor (1-alkyl-2-acyl-sn-glycero-3-phosphocholine) from 1-alkyl-2-acetyl-sn-glycerol by rabbit platelets

We have established previously that 1-alkyl-2-acetyl-sn-glycerol (alkylacetyl-G) can be converted into at least six metabolites by rabbit platelets, including alkylacetyl-sn-(glycero-3-phosphocholine) (-GPC), i.e. platelet-activating factor (PAF) and 1-alkyl-2-acyl-sn- (alkylacyl)-GPC. Since part of the biological functions of alkylacetyl-G can be explained by its metabolic conversion to PAF and also to alkylacyl-GPC as an inactive storage precursor of PAF, the present study focused on the regulation of the synthesis of PAF and alkylacyl-GPC from alkylacetyl-G. Our results document the presence of a specific dithiothreitol (DTT)-insensitive cholinephosphotransferase in saponin-permeabilized rabbit platelets and show that DTT potentiates the production of PAF from alkylacetyl-G but inhibits the formation of phosphatidylcholine from diolein. We also demonstrated that the availability of CDP-choline controls the generation of PAF from alkylacetyl-G. Furthermore, when CTP: phosphocholine cytidylyltransferase is activated to produce more CDP-choline through the translocation of this enzyme from the cytosol to membranes by incubating the rabbit platelets with 0.2 mM sodium oleate, the production of PAF from alkylacetyl-G is increased 5-fold. More importantly, our experiments reveal the presence of two metabolic pathways that are responsible for the synthesis of alkylacyl-GPC from alkylacetyl-G, with each producing a unique molecular species composition of the stored PAF precursor, alkylacyl-GPC. The latter is enriched in polyunsaturates (70.7-78.5% 20:4) when formed through the remodeling pathway of PAF cycle via alkylacetyl-G (DTT-insensitive cholinephosphotransferase)----alkylacetyl-GPC----alkyllyso-GPC---- alkylacyl-GPC . Alkylacyl-GPC containing saturated species (71.8% 16:0) is generated by the retroconversion/de novo pathway according to the reaction scheme of alkylacetyl-G----alkyl-G----alkyllyso-glycero-3-phosphate (-GP)----alkylacyl-GP----alkylacyl-G (DTT-sensitive cholinephosphotransferase)----alkylacyl-GPC. Inactivation of PAF through the remodeling/PAF cycle can generate alkylacyl-GPC at both low (1.75 x 10(-7) M) and high (10(-6) M) concentrations of PAF whereas the conversion of alkylacetyl-G to alkylacyl-GPC via PAF through the remodeling pathway only occurs at a low concentration (1.75 x 10(-7) M). At a high concentration (10(-6) M), alkylacetyl-G is converted to alkylacyl-GPC via the retroconversion/de novo route. These data suggest that the formation of PAF by the DTT-insensitive cholinephosphotransferase activity limits the amounts of alkylacyl-GPC produced from alkylacetyl-G through this remodeling pathway (PAF cycle).(ABSTRACT TRUNCATED AT 400 WORDS)     

The effects of crop development upon slug distribution and control by Abax parallelepipedus (Coleoptera: Carabidae)

The polyphagous carabid beetle Abax parallelepipedus has been shown to be capable of controlling slugs within a lettuce crop in previous studies. This report describes experiments undertaken in plots within a polythene tunnel. Field slugs, Deroceras reticulatum, were introduced to plots containing either large or small lettuce plants, at 30 slugs per plot. The plots were further subdivided into those with or without six beetle predators. Slug numbers were assessed after two weeks, and were found to be affected by plant size, both with and without the presence of predators. These two factors had an additive effect, with both small plant size and the presence of beetles causing significant reductions in slug numbers. Plots with beetles contained either males or females, and females were shown to be significantly better at reducing slug numbers than males, particularly within plots of small plants. The four principal treatments (combinations of two plant sizes and the presence/absence of beetles) generated four distinct patterns of slug distribution within the plots. The potential of the residual slug populations to inflict further damage was measured in a subsequent crop of seedling lettuces. It appeared that the beetles were generally incapable of capturing slugs within large lettuce plants, but were effective predators at soil level. Possible reasons for the survival of fewer slugs in plots with small plants, both with and without the presence of predators, are discussed.     

Activities of Enzymes Involved in the Metabolism of Platelet-Activating Factor in Neural Cell Cultures During Proliferation and Differentiation

Platelet-Activating Factor (PAF) is a potent lipid mediator involved in physiological and pathological events in the nervous tissue where it can be synthesized by two distinct pathways. The last reaction of the de novo pathway utilizes CDPcholine and alkylacetylglycerol and is catalyzed by a specific phosphocholinetransferase (PAF-PCT) whereas the remodelling pathway ends with the reaction catalyzed by lyso-PAF acetyltransferase (lyso-PAF AcT) utilizing lyso-PAF, a product of phospholipase A₂ activity, and acetyl-CoA. The levels of PAF in the nervous tissue are also regulated by PAF acetylhydrolase that inactivates this mediator. We have studied the activities of these enzymes during cell proliferation and differentiation in two experimental models: 1) neuronal and glial primary cell cultures from chick embryo and 2) LA-N-1 neuroblastoma cells induced to differentiate by retinoic acid (RA). In undifferentiated neuronal cells from 8-days chick embryos the activity of PAF-PCT was much higher than that of lyso-PAF AcT but it decreased during the period of cellular proliferation up to the arrest of mitosis (day 1–3). During this period no significant changes of lyso-PAF AcT activity was observed. Both enzyme activities increased during the period of neuronal maturation and the formation of cellular contacts and synaptic-like junctions. The activity of PAF acetylhydrolase was unchanged during the development of the neuronal cultures. PAF-PCT activity did not change during the development of chick embryo glial cultures but lyso-PAF AcT activity increased up to the 12th day. RA treatment of LA-N-1 cell culture in proliferation decreased PAF-PCT activity and had no significant effect on lyso-PAF AcT and PAF acetylhydrolase indicating that the synthesis of PAF by the enzyme catalyzing the last step of the de novo pathway is inhibited when the LA-N-1 cells are induced to differentiate. These data suggest that: 1) in chick embryo primary cultures, both pathways are potentially able to contribute to PAF synthesis during development of neuronal cells particularly when they form synaptic-like junctions whereas, during development of glial cells, only the remodelling pathway might be particularly active on synthesizing PAF; 2) in LA-N-1 neuroblastoma cells PAF-synthesizing enzymes coexist and, when cells start to differentiate the contribution of the de novo pathway to PAF biosynthesis might be reduced.     

Predation on the slug Deroceras reticulatum by the carabid beetles Pterostichus madidus and Nebria brevicollis in the presence of alternative prey

1 Slugs are important pests in many agricultural crops and potential biological control agents are being studied as an alternative to molluscicides. Carabid beetles may be able to reduce slug populations, but their role as control agents may be influenced by the presence of alternative prey. 2 Attacks on the pest slug Deroceras reticulatum (Müller) by the carabid beetles Pterostichus madidus (Fabricius) and Nebria brevicollis (Fabricius) were investigated in the presence of alternative prey (earthworms and Calliphora fly larvae). Consumption of slug eggs and aphids was also investigated. 3 All five prey types were consumed to varying degrees during the experiments. Both beetle species showed a significant preference for Calliphora larvae over slugs. Pterostichus madidus showed a significant preference for earthworms over slugs. No preference was shown between earthworms or Calliphora larvae by P. madidus females or N. brevicollis. However, P. madidus males showed a significant preference for Calliphora larvae over worms. Pterostichus madidus showed no preference between slug eggs and aphids; N. brevicollis showed a significant preference for aphids over slug eggs. 4 The results from this study indicate that generalist beetles will often attack other prey in preferences to adult slugs. Slugs may not be preferred because of their mucus. Other prey items occur frequently in arable soils and generalist carabids may ignore slugs altogether and may only feed on them when slug density is high or other prey are unavailable.     

The role of parasite release in invasion of the USA by European slugs

Several species of European slugs are invasive in the USA, threatening native species and damaging agricultural and horticultural crops. One possible explanation for the success of these invaders is parasite release. To test this hypothesis we collected European slugs in part of their native range (United Kingdom) and in the USA and compared prevalence, distribution and species richness of their nematode parasites. All slugs were dissected and examined for the presence of nematodes. In the UK, nematodes were present at 93% of study sites and 16.4% of all slugs examined were associated with nematodes whereas in the USA the respective figures were 34% of sites and 5.4% of slugs. Nematode species richness was greater in the UK with 12 species being found, seven of which were thought to be truly parasitic as opposed to being phoretic or necromenic. Nine species of nematode were found in the USA, four of which were truly parasitic. Four of the ten European slug species examined in the USA, were entirely free of truly parasitic nematodes whereas all were infected by nematodes in some sites in the UK. There was a significant difference in the prevalence of truly parasitic nematodes in five of these species when comparing their home versus invasive range. A significant difference in parasite prevalence was observed when comparing native and introduced slug species in the USA, however, this was not significant in the UK. Our data support a role for parasite release during the invasion of the USA by European slugs.