Mini-plot field experiments on slug control using biological and chemical control agents

In three field experiments, the rhabditid nematode Phasmarhabditis hermaphrodita was applied one or more times at the standard rate (3 × 10⁹ ha^?1) or half the standard rate to protect crops from slug damage under experimental conditions. Expt 1 was done in a field planted with the ornamental Polygonatum japonica. The treatments were: infective juveniles of the nematode at the standard field rate, metaldehyde pellets at the recommended field rate, and ioxynil (a herbicide with molluscicidal properties) at 90 mg m^?2. The treatments were repeated every 2 wk. Arion ater agg. caused most of the damage to P. japonica. There were no significant differences in damage between treatments during the 3 wk after first application, but plants on plots treated with metaldehyde or nematodes had significantly less damage than plants on untreated plots in the fourth and fifth weeks. Expts 2 and 3 were done on the same site, the first with leaf beet and the second with lettuce. The treatments in these experiments were: nematodes applied to the planted area at the standard field rate 3 days prior to planting, with or without previous application of cow manure; nematodes at half standard rate applied twice, 6 days apart, to the planted area or to the surrounding area; metaldehyde pellets and iron phosphate pellets, both applied at the recommended rate to the planted area immediately after planting. In both experiments, the two chemical molluscicides and nematodes applied once to the planted area at the standard field rate without previous application of cow manure, or twice at half standard rate, were able to reduce slug damage. Nematodes applied after manure did not reduce slug damage. None of the treatments reduced the numbers of slugs contaminating the harvested plants. Slug populations were assessed by means of soil sampling before and after Expts 2 and 3. Only after Expt 3 was there a significant effect of treatment on slug numbers, with significantly fewer in metaldehyde treated plots than in untreated plots.     

Mini‐plot field experiments using the rhabditid nematode Phasmarhabditis hermaphrodite for biocontrol of slugs

The nematode Phasmarhabditis hermaphrodita, a parasite of slugs, was cultured in vitro and applied as a drench in two outdoor mini‐plot field experiments to test the capacity of the nematode to protect Chinese cabbage seedlings and wheat seeds from damage by the field slug Deroceras reticulatum. The first experiment compared a single dose of nematodes (2 X 10¹⁰ ha^‐1) with methiocarb pellets added at the recommended field rate (5.5 kg.product ha^‐1 ) and untreated plots. Plots treated with either nematodes or methiocarb pellets had significantly less slug damage than untreated plots and, from the third week onwards, there was significantly less slug damage on plots treated with nematodes than on methiocarb‐treated plots. At the end of the experiment, 6 weeks after treatment, both slug numbers and biomass were significantly higher in untreated plots than in either methiocarb‐treated or nematode‐treated plots. In the second experiment, six nematode doses ranging from 1 X 10 ⁸ to 2 X 10¹⁰ ha^‐1 were compared with a standard rate application of methiocarb pellets and untreated plots. Plant protection improved with increasing nematode dose between 1 X10⁸ and 8 X 10⁸ha^‐1, but showed little or no further improvement at higher doses. Plant protection similar to that given by methiocarb pellets was provided by nematode doses of 8 X 10⁸ ha^‐1 and above.     

Influences of preceding cover crops on slug damage and biological control using Phasmarhabditis hermaphrodita

In a replicated field experiment, ryegrass, vetch and red clover were grown or the soil was kept bare over a 2–month period in summer to compare the effects of these treatments on slug damage to the following crop (Chinese cabbage) and on the efficacy of nematodes (Phasmarhabditis hermaphrodita) applied as biological control agents to the soil at planting time to protect this crop. Slug damage was significantly (c. two times) greater after red clover or vetch than after ryegrass. Damage on plots without cover crop was intermediate and not significantly different from either extreme. Slug damage was reduced by about one‐third by the nematode treatment. The preceding cover crop did not influence nematode efficacy. Numbers of slugs on harvested plants (mainly Deroceras reticulatum and Deroceras panormitanum) were influenced by an interaction between cover crop and nematode treatment. On subplots without nematodes, more slugs were recorded with than without a preceding cover crop. No such differences were found on nematode‐treated subplots. Soil samples were collected at intervals from 0–99 days after nematode treatment to monitor nematode survival and infectivity in bioassays with D. reticulatum. No significant effects of cover crops were detected in bioassays. Moreover, there were no significant effects of nematodes on slug survival. Their effects on slug food consumption were mostly insignificant and any effects were transient and not consistent. However, significantly more slug cadavers contained nematodes when slugs were exposed to nematode‐treated soil. The implications of these results are discussed.     

Biocontrol of Slugs in Protected Lettuce Using the Rhabditid Nematode Phasmarhabditis hermaphrodita

In two experiments, the rhabditid nematode Phasmarhabditis hermaphrodita, a parasite of slugs, was cultured in vitro and applied as a drench to soil at four dose rates (3 108, 1 109, 3 109 and 1 1010 ha-1) 1 or 4 days before planting lettuce seedlings in a polythene tunnel. The effects of the four nematode doses on slug damage during the first 3 weeks after planting and on the numbers of slugs found within and below lettuce plants at harvest were measured. Results were then compared with untreated plots and with plots where methiocarb pellets were applied at the recommended field rate. In the first experiment, methiocarb pellets significantly reduced the percentage of plants damaged by slugs, but the nematode did not. In the second experiment, methiocarb pellets and the second highest dose of nematodes significantly reduced the percentage of plants damaged by slugs. The different effect of the nematode in the two experiments may have resulted from differences in the timing of nematode application and/or differences in the pattern of slug damage between experiments. At the end of the first experiment, the highest two doses of nematodes and methiocarb pellets had significantly reduced the number of slugs found within lettuce plants at harvest and on the soil surface below the plants. At the end of the second experiment, analysis of variance showed no significant effects of any treatment on slug numbers or biomass, but regression analysis showed significant negative relationships between nematode dose and total slug numbers, numbers of Arion ater agg. and biomass of Deroceras reticulatum. In both experiments, increasing nematode dose significantly reduced the numbers of slugs found contaminating the harvested lettuce. At the end of the second experiment, the mean weight of individuals of A. ater agg. increased with rising nematode dose.     

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.     

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.     

Spatiotemporal Analysis of Predation by Carabid Beetles (Carabidae) on Nematode Infected and Uninfected Slugs in the Field

The dynamics of predation on parasites within prey has received relatively little attention despite the profound effects this is likely to have on both prey and parasite numbers and hence on biological control programmes where parasites are employed. The nematode Phasmarhabditis hermaphrodita is a commercially available biological agent against slugs. Predation on these slugs may, at the same time, result in intraguild predation on slug-parasitic nematodes. This study describes, for the first time, predation by carabid beetles on slugs and their nematode parasites on both spatial and temporal scales, using PCR-based methods. The highest nematode infection levels were found in the slugs Deroceras reticulatum and Arion silvaticus. Numbers of infected slugs decreased over time and no infected slugs were found four months after nematode application. The density of the most abundant slug, the invasive Arion vulgaris, was positively related to the activity-density of the carabid beetle, Carabus nemoralis. Predation on slugs was density and size related, with highest predation levels also on A. vulgaris. Predation on A. vulgaris decreased significantly in summer when these slugs were larger than one gram. Predation by C. nemoralis on slugs was opportunistic, without any preferences for specific species. Intraguild predation on the nematodes was low, suggesting that carabid beetles such as C. nemoralis probably do not have a significant impact on the success of biological control using P. hermaphrodita.     

Field Test Using the Nematode Phasmarhabditis hermaphrodita for Biocontrol of Slugs in Spain

An experiment was carried out between May and July 1999 in Galicia (North-West Spain) to test the capacity of the nematode Phasmarhabditis hermaphrodita to protect field grown lettuces from slug damage in our field conditions. The experiment compared a single dose of nematodes (3 ×109 ha -1) with mini-pellets containing 5% metaldehyde, applied at the recommended field rate (3 g pellets m -2), and untreated plots. Slug damage for each lettuce head was estimated on six dates during the first 4 weeks after planting. At harvest, each lettuce head was weighed, scored as marketable or not by weight and external aspect, and inspected for slugs. Metaldehyde significantly reduced slug damage to lettuce plants from the first day after planting to the third week. Nematodes significantly reduced slug damage from the second to the third week. At harvest, 6 weeks after planting, the mean weight of the lettuce heads and the number of marketable heads in the nematode plots were as good as in the metaldehyde plots, and both treatments were significantly better than the untreated plots. The number of slugs within the harvested plants was significantly reduced only with the metaldehyde treatment.     

Pathogenicity of Moraxella osloensis, a Bacterium Associated with the Nematode Phasmarhabditis hermaphrodita, to the Slug Deroceras reticulatum

Moraxella osloensis, a gram-negative bacterium, is associated with Phasmarhabditis hermaphrodita, a nematode parasite of slugs. This bacterium-feeding nematode has potential for the biological control of slugs, especially the grey garden slug, Deroceras reticulatum. Infective juveniles of P. hermaphrodita invade the shell cavity of the slug, develop into self-fertilizing hermaphrodites, and produce progeny, resulting in host death. However, the role of the associated bacterium in the pathogenicity of the nematode to the slug is unknown. We discovered that M. osloensis alone is pathogenic to D. reticulatum after injection into the shell cavity or hemocoel of the slug. The bacteria from 60-h cultures were more pathogenic than the bacteria from 40-h cultures, as indicated by the higher and more rapid mortality of the slugs injected with the former. Coinjection of penicillin and streptomycin with the 60-h bacterial culture reduced its pathogenicity to the slug. Further work suggested that the reduction and loss of pathogenicity of the aged infective juveniles of P. hermaphrodita to D. reticulatum result from the loss of M. osloensis from the aged nematodes. Also, axenic J1/J2 nematodes were nonpathogenic after injection into the shell cavity. Therefore, we conclude that the bacterium is the sole killing agent of D. reticulatum in the nematode-bacterium complex and that P. hermaphrodita acts only as a vector to transport the bacterium into the shell cavity of the slug. The identification of the toxic metabolites produced by M. osloensis is being pursued.     

Behavioural avoidance by slugs and snails of the parasitic nematode Phasmarhabditis hermaphrodita

The nematode Phasmarhabditis hermaphrodita has been developed as a biological control agent for slugs and snails. Slugs avoid areas where P. hermaphrodita is present. We investigated whether behavioural avoidance of P. hermaphrodita is a common feature of slugs and snails by exposing eight species to P. hermaphrodita. We showed that slugs generally avoided P. hermaphrodita, whereas snails did not. We also showed that slugs specifically avoided the commercial strain and a natural isolate of P. hermaphrodita and were not deterred by other nematodes such as Steinernema kraussei or Turbatrix aceti. We also showed that slugs avoided the dauer stage of P. hermaphrodita and not mixed-stage cultures. Furthermore, slugs do not avoid dead P. hermaphrodita or exudates from live nematodes. Taken together, we have unravelled further factors that are essential for slugs to avoid P. hermaphrodita in soil, which could have important implications for the biological control of slugs and snails.     

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.     

Effects of seed-bed conditions on slug numbers and damage to winter wheat in a clay soil

In a field experiment three levels of consolidation were combined with three seed-bed tilths, to produce nine different types of seed-bed. The soil properties of each combination of tilth and consolidation were measured and effects on the numbers and biomass of slugs in the top 10 cm of soil and on damage to wheat seeds and seedlings were assessed. Eight species of slug were present, with three species predominating (Deroceras reticulatum, Arion distinctus and Arion subfuscus). Between 3% and 33% of seeds and seedlings were killed by slugs (recorded at Growth Stage 12). Contrary to expectation, most damage occurred on consolidated seed-beds of fine or medium tilth, least on loose seed-beds of the same texture; intermediate damage occurred on cloddy seed-beds, where consolidation had little effect. The level of damage occurring on different types of seed-bed was directly related to the biomass of slugs in the top 10 crn of soil, and was inversely related to depth of sowing and the percentage of fine soil in the seed-bed. These three factors together accounted for 94–97% of the variance in slug damage. Consolidation was associated with increased slug damage probably because of its effects on these three factors: slug biomass was greater and seed was at shallower depth in consolidated than loose seed-beds and consolidation, whether before or after drilling, failed to break down clods of soil into finer particles. This is the first experimental evidence in the field of the effects of seedbed conditions on slug numbers and damage to winter wheat and represents a significant step towards forecasting and avoiding slug damage in this crop.     

Feeding Activity and Survival of Slugs,Deroceras reticulatum,Exposed to the Rhabditid Nematode,Phasmarhabditis hermaphrodita: A Model of Dose Response

The slug, Deroceras reticulatum (Stylommatophora: Limacidae), was exposed to different concentrations of infective dauer juveniles of the rhabditid nematode Phasmarhabditis hermaphrodita, in a two-stage bioassay, at 10°C. Slugs were exposed in groups of 10 or 12 to nematodes in plastic boxes filled with soil aggregates for 3 or 5 days and then transferred individually to petri dishes each containing a disk of Chinese cabbage leaf as food. Subsequently, slug food consumption and survival were measured for 10 to 13 days. Models were developed to describe the way that exposure to the nematode caused inhibition of slug feeding followed by death. Both effects were related to nematode concentrations and time after exposure to the nematode. Following exposure to high concentrations (300,000 dauer juveniles per box), slugs were killed rapidly, within a few days after the end of the exposure period. Following exposure to low concentrations of nematodes (7000 or 15,000 per box), substantial numbers of slugs survived until the end of the bioassay, but feeding activity by these slugs was strongly inhibited. It is suggested that inhibition of slug feeding is important for the success of this nematode as a biocontrol agent.     

Effects of soil incorporation on the efficacy of the rhabditid nematode, Phasmarhabditis hermaphrodita, as a biological control agent for slugs

The effects of soil cultivation immediately after application of the rhabditid nematode, Phasmarhabditis hermaphrodita , to the soil surface were investigated in two field experiments. The first experiment was done in mini-plots separated by barriers, with an artificially introduced population of slugs ( Deroceras reticulatum ). Nematodes were applied as a drench at a rate of 3 times 10⁹ ha^-1 in one of two application volumes and then left undisturbed or incorporated into the soil by cultivation to 2 cm or 10 cm depth. Moist soil conditions were maintained by irrigation throughout the experiment. Nematode application significantly reduced slug damage to Chinese cabbage seedlings throughout the 7 wk duration of the experiment and the population of D. reticulatum in soil 7 wk after treatment. However, soil cultivation had no effect and did not interact with the effect of nematodes. In the second experiment, in a crop of winter wheat, nematodes were applied to soil by hand-lance at a rate of 3 times 10⁹ ha^-1 and left undisturbed on the soil surface or incorporated by spring-tine cultivation to a depth of 2, 5 or 10 cm. In this experiment, nematodes were applied to dry soil. Cultivation alone had no effect. Nematode application reduced slug damage to wheat plants in plots where nematodes were incorporated into the soil, but not where they were left on the surface. There was no detectable impact of nematodes on slug populations in the wheat experiment.     

The effect of intraspecific competition on the development and quality of Phasmarhabditis hermaphrodita (Rhabditida: Rhabditidae)

The effect of intraspecific competition on the development and reproduction of the slug parasitic nematode Phasmarhabditis hermaphrodita was studied in a series of laboratory experiments. Different inocula concentrations (1, 10, 25, 50, 100, 250, 500 and 1000) of P. hermaphrodita dauer juveniles (DJ) were applied to 0.02 g of homogenised slug Deroceras reticulatum on agar in multi-well plates and the development time, yield, lipid content, and body length of females and DJs were recorded. There was an inverse relationship between dose and recorded female length or lipid content. In newly emerged DJs the body length and lipid content were relatively invariable up to a dose of 250 DJs (ranging between 850 and 925 µm, 6.8 and 7.4, respectively), and decreased at higher doses (500 and 1000 DJs). The yield increased with increasing dosage to its optimum at a dose of 100 (200,000 DJs per 1 g of substrate) DJs and thereafter decreased. In the treatment with the highest dose (1000 DJs), only a minor portion of the inoculum developed to adult stage and completed their reproduction cycle while the rest remained at the larval stage. It might, therefore, be concluded that P. hermaphrodita tolerates intraspecific competition to a certain level at which crowding becomes too severe and a part of the inoculum do not develop and probably leave the site to avoid the fatal overcrowding. In conclusion, we show that intraspecific competition negatively affects the yield and quality of DJs of P. hermaphrodita, but it seems that this nematode can partly prevent overcrowding by avoiding occupied sites.     

The rhabditid nematode Phasmarhabditis hermaphrodita as a potential biological control agent for slugs

A nematode, Phasmarhabditis hermaphrodita, known to be associated with slugs but not previously thought to be parasitic, was shown to be a parasite capable of killing the pest slug Deroceras reticulatum. The parasite infects slugs in the area beneath the mantle surrounding the shell, causing a disease with characteristic symptoms, particularly swelling of the mantle. Infection leads to death of the slug, usually between seven and 21 days afterwards. The nematode then spreads and multiplies in the cadaver. In an experiment where individual D. reticulatum were exposed to different numbers of P. hermaphrodita, a significant positive relationship was found between nematode dose and slug mortality. In two experiments on host range, the nematode was found to infect and kill all pest slug species tested: Deroceras caruanae, Arion distinctus, Arion silvaticus, Arion intermedius, Arion ater, Tandonia sowerbyi and T. budapestensis, in addition to D. reticulatum.     

Overall Versus Band Application of the Nematode Phasmarhabditis hermaphrodita With and Without Incorporation into Soil, for Biological Control of Slugs in Winter Wheat

In two concurrent field experiments, the effects of three types of soil cultivation and two patterns of nematode application were studied in order to investigate their effects on damage to winter wheat by slugs (assessed at Zadoks Growth Stage 12). In experiment 1, infective juveniles (IJs) of the nematode Phasmarhabditis hermaphrodita were applied to soil as an overall spray or as a band spray (8-cm wide), centred on the drill rows (16.7-cm apart). Nematodes were either left undisturbed on the soil surface or harrowed into the soil immediately after application. The control provided by nematodes was compared with that provided by metaldehyde and methiocarb pellets broadcast at the recommended rate immediately after drilling. In this experiment, winter wheat on plots treated with IJs showed significantly less slug damage than on wheat plots treated with metaldehyde or methiocarb pellets or untreated plots. There was no significant difference in plant damage between plots treated with band and overall spray applications of IJs, nor was there any significant difference between plots with and without harrowing. There was also no significant difference between untreated plots and plots treated with metaldehyde or methiocarb pellets, probably because rainfall shortly after treatment rendered the pellets ineffective. In experiment 2, nematodes were applied as an overall spray or plots were not treated with nematodes before soil was cultivated with tines, Roterra or Dutzi cultivators. Nematode application before soil cultivation using tines or Roterra reduced the number of plants damaged significantly. However, nematodes applied before Dutzi cultivation appeared to be rendered ineffective. Damage to winter wheat was lowest in plots that had been sprayed with nematodes and subsequently cultivated with tines or Roterra.     

Nematode associates and susceptibility of a protected slug (Geomalacus maculosus) to four biocontrol nematodes

The impact of selected entomopathogenic nematodes and Phasmarhabditis hermaphrodita on the European-Union-protected slug Geomalacus maculosus and the sympatric Lehmannia marginata was investigated. There was no significant difference in mortality between slugs treated with nematodes and their controls. The presence of P. hermaphrodita in two G. maculosus cadavers may be the result of necromenic behaviour. This study constitutes the first record of P. californica in Europe.     

Impact of soil suppressiveness on various population densities of Heterodera schachtii

Infectivity of second‐stage juvenile (J2) populations of Heterodera schachtii was assayed with radish.The numbers of J2 in three‐day‐old seedlings were proportional to the numbers of J2 in two differently textured soils.In a microplot trial with a known H.schachtii‐supprcssivc soil, half of the plots contained untreated suppressive soil, the other half contained the same soil, but methyl iodide‐fumigated and therefore conducive.Both soils were infested with cysts introducing the equivalents of 0, 30, 60 or 120 H.schachtii eggs g‐¹ soil, kept moist for 2 months, and then planted to Swiss chard.The numbers of J2 in radish roots were proportional to the numbers of H.schachtii eggs introduced into the microplots, at a low level of detection in suppressive soil and at a high level in conducive soil.Growth of Swiss chard was not different at increasing infestation levels in suppressive soil, but growth was reduced in conducive soil proportionally to increasing nematode infestation level.     

15N stable isotope labelling of slugs (Gastropoda: Pulmonata)

Stable isotope tracers are a promising tool for investigating the ecology of terrestrial slugs, including predator‐prey relationships, migration behaviour, nutrient turnover and dietary routing. The objective of the present feasibility study was to label two economically important slug groups, Deroceras reticulatum and keeled slugs (families Limacidae and Milacidae, respectively), with the stable isotope ¹⁵N under controlled laboratory conditions. Significant isotopic enrichment in slug tissue was detected after 4 days and persisted for at least 10 days after slugs had been fed on ¹⁵N enriched food for a period of 15 days. The time course of ¹⁵N uptake into slug tissues and its relation to food consumption were well described mathematically. Estimated mean ¹⁵N assimilation efficiencies from labelled maize mixed with unlabelled wheat bran were 30% and 38%, respectively, for the species groups studied. These findings suggest that slugs can be readily and efficiently labelled and that it is feasible to devise protocols for producing large numbers of isotopically labelled slugs for use in ecological studies. A simple method is described for the collection and analysis of cutaneous mucus from individual slugs which can be used to test uniformity of isotopic labelling.