A symposium at Canterbury Christ Church University College, Kent, UK, on 8-9 September 2003 jointly organised by the British Crop Protection Council and The Malacological Society of London

In his introduction as Chairman, Georges Dussart pointed to two factors that give slugs and snail an edge: they are good invaders and they flourish in association with the activities of humans. Evidence of schistosomiasis in Egyptian mummies indicates a long-standing medical impact. The serious agricultural problems they pose seem to be a twentieth century development, linked to modern reduced tillage agriculture and the demand for top quality produce. The symposium, the third on the subject organised by BCPC and MLS, broadened the remit over those in 1989 and 1996 to include conservation issues and veterinary problems.

The program was organised around six sessions over two days: five sessions with five talks in each, and a poster session with 28 contributions. (In the summaries which follow, most posters have been re-located to an appropriate oral session.) The University College of Christ Church Canterbury is a pleasant, modern campus set within strolling distance of the delightful mediaeval town centred around the historic cathedral. The organizing committee had done its work, well backed by the experience and clear guidance of BCPC, and Georges Dussart is to be congratulated for his efforts. The Proceedings were issued at registration – a tight schedule in the run up, but no typescripts to write, edit or format afterwards! There was only one hiccup – the poster boards were 1.15 m wide x 1.75 m high, the posters were 1.75 m wide x 1.15m high. Some would-be participants were put off by the all-in price, but students got a good discount, and about 140 delegates attended, representing around 20 countries.

The need to find methods of control which are both effective and environmentally safe was clear in many of the talks. Many presentations considered the use of botanical pesticides (more available to some countries than conventional ones), alongside biological control and crop husbandry. Yet the no-longer-new molluscicides remain the standard control in many cases, and provide an important comparison standard for new techniques, especially in the complex environment of the field trial. The studies which the Symposium encompassed ranged from laboratory trials to field trials. Few of the promising ideas from the laboratory make it past the field trial. As modern molecular approaches start to show promise (for example fusion proteins or protease inhibitors), it is clear that we will also need a more detailed understanding of the compensatory abilities of the animals’ physiology, such as its immune responses and xenobiotic metabolising enzymes. Environmental monitoring and the integration of control methods were addressed to a limited extent. We shall also need powerful models to predict population changes which encompass both time and space. Examples, currently limited in their scope, were described. One of the under-appreciated aspects of meetings such as this is the transfer of methodology – from a new link in a biochemical approach to simple but effective ways of studying the animals in the field.

Session 1: Introduction

Organiser Bill Symondson: chairman Gordon Port

The opening session set the scene for the rest of the meeting, starting with a talk by invited speaker, Les Noble (Aberdeen), on the increasingly important role of molecular biology in the study of molluscs and their interactions with humans. Increasing parasite resistance and unpredictable control of crop pests prompt new genomic approaches to elucidate the molecular basis of host-parasite and pest-chemical interactions, to suggest more targeted control methods. Ciara Dodd (Cardiff) and coworkers then demonstrated the application of molecular ecology techniques using monoclonal antibodies and amplification of slug DNA from the gut of carabid beetles to study the control of slugs in agriculture by predators. Improved prediction and integrated control of slugs in winter wheat and oil-seed rape was the theme for David Glen (Styloma Research & Consulting, Cheddar) and collaborators. Traps baited with chicken layers mash gave a reliable evaluation of damage risk. Field experiments suggested that seedbed consolidation and delayed slug pellet treatment could cope with slugs returning to the surface after ploughing.

Christian Altaba (Balearic Islands) documented the explosive diversification and extensive endemism of freshwater molluscs – unionoid mussels in eastern USA and Mediterranean, melanospid snails in the Mediterranean, hydrobiid spring-snails in Europe, N America and Australia, the Mekong pomatiopsids and African planorbids. Many of these are threatened by habitat destruction and pollution (72% of N American unionoids are extinct or imperiled), in some cases as non-targeted victims of molluscicides. Yogeshkumar Naik (Bulawayo) and D Livingstone (Plymouth Marine Lab) highlighted the potential of freshwater snails as biomarkers of chemical pollution. Dose-dependent reduction of esterase activities were recorded within hours of exposing aquatic snails to organophosphate and carbamate pesticides . Xenobiotic metabolizing enzymes (XMEs) play an important role in the metabolism and excretion of various xenobiotics, and his accompanying poster showed that the activity of XMEs in four aquatic snails was altered by exposure to molluscicides. Understanding the interaction of these XMEs would allow the development of safer and more effective molluscicides for the control of snail-borne diseases.

Session 2: Physiology and Function

Organiser Bill Bailey; chairman Georges Dussart

The physiology of molluscs provides necessary insights into the control of pests and vectors, species conservation and pollution monitoring. Steve Dungey (Environment Agency, Wallingford) considered the implications of using aquatic snails to monitor a weak environmental oestrogen, bisphenol-A. This has no adverse hormone-mediated effect on fish below 16 µg l-1, but in the tropical ramshorn snail Marisa cornuarietis stimulates egg production and is lethal at very low concentrations. Adverse effects are absent only below a few nanograms per litre. Jesus Tsurruka and colleagues(Bilbao) described the massive redeployment of materials from the body wall of the slug Arion ater to the reproductive organs and then to the eggs during reproductive maturation. Villi Flari (CSL, York) showed that snowdrop lectin (GNA) fed to slugs is transferred to the haemolymph. It might be used as a carrier molecule for neuropeptides which inhibit reproduction or development. A poster presentation from Evan Mulligan and colleagues (Newcastle and CSL York) describes an attempt to use recombinant DNA technology to produce a crop expressing a foreign protease inhibitor to increase resistance to slug damage. However, juvenile Deroceras reticulatum survived and developed better on oil-seed rape expressing oryzacystatin-1 than a control group. Tony Walker and colleagues (Kingston) have detected MAPK and PKC homologues in Lymnaea stagnalis, indicating similarities in cell signalling in the innate immune responses to pathogens of molluscs and vertebrates. Further work may reveal molecular targets for mollusc control. Finally, Rita Triebskorn (Steinbeis-Transfer Centre, Rottenburg, Germany) and Heinz-R Köhler (Tübingen) showed that assay of the stress protein hsp70 provides a rapid and sensitive measure of the impact of heavy metal pollutants and molluscicides, while histological and cytological studies give a better understanding of mode of action. Heinz-R Köhler presented a poster giving details of 3 isoforms of the hsp70 stress protein in Deroceras, and Katja Bader, Beate Linder, Heinz-R Köhler and Rita Triebskorn presented a poster detailing the combined effects of the pesticides Polyram and Sufran and temperature on terrestrial gastropods.

Session 3: Poster Presentations

Organizers: Brigitte Grimm and Robert Cameron

Posters covering a wide range of topics linked to the oral sessions were displayed throughout the Symposium, and poster authors were present to discuss their work during this session. Most posters have been moved to the appropriate oral session, except for two on heliciculture - and one on culturing slugs - and four on snail population biology, which are better dealt with here.
Athanasios Gogas, Maia Hatzioannou and Maria Lazaridou (Thessaloniki) described the commercial rearing of Helix aspersa from the Pelepponese on a mixed rearing programme, with reproduction and hatching in controlled conditions and fattening in poly-tunnels. Mercedes Ortega, I Rodriguez and Jesus Txurruka (Bilbao) found that Helix aspersa had highest food conversion ratios on low moisture content diets and a mean potential biomass increase of 27 mg d-1. K Christensen, G Schnydrig and Markus Bieri (Lonza, Switzerland) bred Deroceras reticulatum under standard conditions as a prerequisite for controlled efficacy tests of molluscicides. Egg laying starts at 120–140 d.

Fred Naggs and colleagues (Natural History Museum, London) described the faunal change and survivorship of Sri Lanka’s snail fauna. L Dvorak (Sumava National Park, Czech Republic) described the extension of range of Cepaea nemoralis in the Czech Republic since its first record in the 1890s, possibly related to human activity. Alois Honek and Zdenka Martinkova (Crop Production RI, Drnovska, Czech Republic) compared the persistence and shell band morph frequencies of the widespread native Cepaea hortensis with that of introduced C nemoralis which occurs in the north west in areas affected by human activities. Jane Ward Booth and Georges Dussart (Canterbury) discussed problems in inferring age from size histograms in a population of Monarcha cantiana where local migration occurred from a favourable habitat to one where growth was slower.

Session 4: Prospects for Control

Organizer David Glen, chairman Bill Symondson

Slugs are major pests of a wide range of agricultural and horticultural crops. Richard Meredith (Bayer CropScience, Cambridge) described how, after decades of research, agriculture still uses three active ingredients (metaldehyde, methiocarb and thiodicarb), although integration of chemicals with other methods are useful such as preparation of a firm seedbed and monitoring of slug activity. Effects on non-target organisms (carabid beetles, earthworms and vertebrates) were put in perspective. Markus Bieri (Lonza, Switzerland) described the environmental profile of metaldehyde – its degradation to CO2 and water, its lack of phytotoxicity, and absence of adverse effects on beetles, bees, insects used for biological control, earthworms, fish or aquatic crustaceans. Using 14C labelled metaldehyde in collaboration with Rita Triebskorn, Bieri found radioactivity in almost every organ 5 minutes after oral administration. R C Hollingsworth (US Pacific Basin ARC, USDA) described how the efficacy of caffeine, a potential new molluscicide, is enhanced by a corn flour/sugar adjuvant as a feeding inhibitor of the slug Veronicella cubensis.. The suitability of caffeine was critically assessed by Louise Simms and Michael Wilson (Aberdeen): it appears to be more toxic to mammals and some earthworms than metaldehyde. A poster by M Vuksa, S Djedovic (ARI, Serbia and Montenegro) and B Stojnic (Belgrade) described the successful use of iron-pyrophosphate-hydrate against Arion lusitanicus, a recent invader which is becoming a major pest.

In recent years, aquatic snails have become serious pests of sewage treatment plants, consuming biofilm so fast that the autotrophic nitrifying bacteria are wiped out. As a result ammonia remains in the effluent. D Thomas (Thames Water) and Georges Dussart presented a poster showing an invasion of Lymnaea peregra causing the failure of a sewage works was successfully eliminated by copper sulphate. Jiaqian Jiang (Surrey) and colleagues from Thames Water and Canterbury described a novel cost-effective wastewater treatment process which promises to overcome this problem. The poster from F-H Wei, X-J Xu, S Cai, J Lui, Y Fu, M Cao (Hubei Institute of Schistosomiasis Control, China) and Georges Dussart (Canterbury) showed that a mixture of nicotinanilide and niclosamide gave good control of the amphibious snail Oncomelania hupensis, the vector of schistosomiasis to buffalo and humans in China, and was much cheaper than nicotinanilide alone.

Andre Chabert (ACTA, France) and colleagues from Bayer CropScience described the Activ+ Limaces decision-aid system to assess the risk of slug damage by means of a climate model and agronomic factors, which over 80% of farmers who use it regard as a useful and user-friendly tool. Control continues to rely heavily on the use of molluscicidal bait pellets. Three posters also presented modelling. Jenna Willis, David Bohan, Y Choi, M Semenov (Rothamsted), V K Brown (Reading) and E Gussin (De Sangosse, Romney) tested simulations of slug population dynamics at 5 UK sites to understand how rainfall and temperature affect populations and how changes in climate may affect abundance and invasiveness of pest species throughout Europe. Y H Choi, D A Bohan, M A Semenov (Rothamsted), R P J Potting (Wageningen, Netherlands) and David Glen described a model of temporal and spatial dynamics of slug and nematode populations and their interaction which is a powerful tool for observing control success in different scenarios of nematode application. X-J Xu, J-B Liu, F Wei , W Chen (Hubei Institute) and Georges Dussart studied the distribution of Oncomelania in irrigation systems and the sedimentation rate of snails and eggs to develop and test systems for snail control.

Session 5: Behaviour and Ecology

Organizer Richard Cook, chairman Bill Bailey

Knowledge of the behavioural responses of snails and slugs to chemicals and predators leads to an understanding of the factors that influence their presence and abundance, and to improved biological and chemical control of pest species.
Clare Armsworth (Rothamsted) with Bill Symondson (Cardiff) and David Glen showed that the slug Deroceras reticulatum avoided paper previously walked over by the predatory carabid Pterostichus melanarius, but in mini-plots of winter wheat, newly hatched slugs did not alter their dispersion rates if the beetles were present. lbon Cancio and colleagues (Bilbao) found that Helix aspersa from the abandoned copper mine on Parys Mountain accumulated black silver deposits in digestive cell lysosomes, but no cell type replacement was seen. Sally Howlett and Gordon Port (Newcastle), video-tracking Deroceras in arenas containing broadcast or drilled pellets, found that they fed on the first pellet encountered, and that happened much sooner in the broadcast plots. Soil contamination of pellets, such as occurs in heavy rain, did not reduce their efficacy. Claudia Gerard (Rennes) and Georges Dussart discussed the new environmental niche available to the freshwater invader Potamopyrgus antipodarum in France, and the niche available to a helminth parasite Sanguincola within the snail. Ingo Schüder and Gordon Port (Newcastle) presented details of a fully automated video system for tracking slugs and snails and recording their behaviour, and Angela Lush (South Australian Research and Development Institute) and G Baker (CSIRO, Canberra) described a novel method of tracking small cryptic snails (Microxeromagna armillata) in citrus orchards using the mucus stain alcian blue on flagging tape.

Three posters were concerned with slug behaviour in relation to control. Bill Bailey and colleagues (Manchester) showed that Deroceras inoculated with Phasmarhabditis ceased feeding, courtship and movement (in that order) within 3 days, and was more rapid in smaller individuals. Parasitised slugs no longer confined their activity to the night time. Brigitte Grimm (Natural History Museum, London) and K Schaumberger (Graz) found that Arion lusitanicus was most active after dusk and dawn, and moved 10.8 m in 24 h. 76% of feeding occurred during darkness. In the study covered by their poster, Jan Hagnell, C Schander (Göteborg) and Ted von Proschwitz (NHM, Göteborg) found that Arion ater native to Sweden, Arion rufus, introduced there ca 150 y ago, and ater x lusitanicus hybrids respire faster than other slugs, but Spanish A. ater and the recently arrived A. lusitanicus do not. They interpret this as an adaptation to the cold Swedish climate which may herald the appearance of a ‘Super Slug’.

Fig. Stark Landscape of old copper mine on Parys Mountain, Anglesey, Wales, the site for Cancio and co-workers study of metal uptake in Helix

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Session 6: Integrated Pest Management

Organizer Gordon Port; chairman David Glen

This session examined novel approaches to management of mollusc pests and how these approaches can be integ rated with other measures to minimise pest damage.

Megan Leyson, D Hopkind &and S Charwat (South Australian R D I) and G Baker reported on the release and establishment of Sarcophaga penicillata, an exotic biological control agent for the introduced snail Cochlicella acuta, a major contaminant of grain. Gordon Port and colleagues (Newcastle) discussed progress in the integrated control of slug damage in horticultural field crops. Ingo Schuder (Newcastle) identified Deroceras panormitanum (D. Caruanae) and Oxyloma pfeifferi as the key pests in hardy ornamental plant nurseries. Control with a copper-impregnated matting reduced snail activity and suppressed egg laying. Cinnamamide, copper ammonium carbonate, ureaformaldehyde and Phasmarhabditis also gave promising results. Albert Ester and colleagues (PPO, Lelystad) achieved protection of Brussels sprouts, which slugs damage by deformation, rot and sliming, using the indigenous nematode Phasmarhabditis hermaphrodita. Ahmed Ali (Cardiff) presented results from screening two African plants, myrrh and opoponax, showing successful repellency to slugs, and in a poster described further results showing molluscicidal and repellent properties of African plants.

Two posters also described results with nematodes and botanical products, and a further two reported reduction of slug damage when weeds provided an alternative food supply. Albert Ester, K van Rozen (PPO, Lelystad) and A Hazendonk (PPO, Aalsmeer) achieved successful protection of orchid flowers from slug damage using Phasmarhabditis, metaldehyde, iron III phosphate or caffeine. Dinka Grubisic and colleagues (Zagreb) obtained good control of slugs in vegetable crops with Phasmarhabditis: other treatments tried included botanicals based on lavender and rosemary. Kenneth Evans and S Henderson (SAC, Edinburgh) assessed the potential of five common weeds to reduce grazing by slugs on winter wheat seedlings. Slugs preferred all the weeds to the wheat seedlings, and the presence of dandelion or oil seed rape weeds significantly reduced slug damage to seedlings. AS Brooks, Mitch Crook, A Wilcox (Harper Adams) and Richard Cook (Kingston) showed that in lab trials, red clover was as effective as metaldehyde at reducing slug damage to wheat seedlings. It was also the most palatable legume tested and had the least effect on wheat survival.

Bill Bailey

Copies of the proceedings: Slugs & Snails – Agricultural, Veterinary and Environmental Perspectives (Chaired by G B J Dussart, September 2003, ISBN 1 901396 80 0, ISSN 0306-3941: No. 80) at £35 may be ordered from BCPC Publications sales, 7 Omni Business Centre, Omega Park, Alton, Hampshire, GU34 2QD, Uk. Tel: +44(0)1420 593 200, Fax: +44(0)1420 593 209, Email: publ...@bcpc.org, or via the BCPC website at www.bcpc.org/bookshop

Scenes from the Campus, Town and the Poster Session: