Aspects of Feeding in the Grey Field Slug (Deroceras reticulatum)

Abstract

Gastropod damage to crop plants has a significant economic impact on the United Kingdom’s agriculture and horticulture industries, with the Grey Field Slug (Deroceras reticulatum) being particularly culpable. The main form of crop protection employed by farmers are pellets containing the active ingredient, metaldehyde. During rainfall events or with poor application, metaldehyde can leach into the water system, thus preventing or limiting it from entering the water system is a high priority. Greater understanding of the interaction between slugs and slug pellets could reveal an area of vulnerability or potential manipulation to be targeted by molluscicides. Improved slug pellet formulations could reduce risks to water. The main objective was to discover if novel formulations improved molluscicide efficiency (increased feeding and mortality) in comparison to commercially available molluscicides. Bioacoustics experimental work enabled comparison of feeding patterns between pellet types by recording the number and length of bites. Bioassay experiments aimed to compare mortality differences between pellet types over 3 to 5 days. Secondary questions aimed to discover if novel formulations would slow or reduce leaching of metaldehyde out of the pellet and to explore the commercial viability of the novel formulations. Soil column type experiments were used to compare leaching of metaldehyde between formulations. Mixed methods were used to discuss the viability of a novel pellet, with a focus on previous molluscicide sale and use in the UK. Overall, the novel formulations tested did not increase mortality or reduce leaching when compared to currently commercially available pellets. Due to changes in legislation during the project, work shifted from a metaldehyde focus to ferric phosphate towards the end of the project. The improved methodologies and discussion will be useful to the development of future molluscicides, as metaldehyde is still in use in over 30 countries.