Better use of molluscicide pellets for improved management of slugs

Ph. D. Thesis.The grey field slug, Deroceras reticulatum, is one of the most important pests of agriculture, with an estimated 59% and 22% of total planted oil seed rape and wheat respectively affected by slugs in the UK annually. It is estimated that without molluscicides, the cost to the UK’s agricultural industry from loss of crop yield due to slug damage could be in excess of £100 million per year. Metaldehyde is the most commonly used molluscicide in UK agriculture however it presents a large water pollution risk and threat to non-target organisms, in addition, control of slugs by metaldehyde is often inefficient. Understanding how Deroceras reticulatum’s behaviour is affected by the presence of slug pellets with different molluscicide concentrations, and how these pellets affect locomotion, feeding and the health of a slug once a pellet is consumed will help develop more effective slug pellets. The pest-pellet interaction is a key process in successful slug control and can only be effective if slugs accept and consume a pellet when encountered. This research indicated that the concentration of metaldehyde in pellets does not impact on D. reticulatum’s foraging activity, however the presence of a molluscicide may impact on foraging behaviour compared to non-molluscicide pellets. D. reticulatum was more likely to accept and feed on a pellet of lower concentration (1%) compared to higher concentrations (3% and 5%). Paralysis due to the effects of molluscicide is likely to be a key factor in successful slug control. Slugs poisoned with 1% or 3% metaldehyde were more likely to be paralysed after exposure to pellets when compared to higher concentrations, however, were more likely to recover after exposure to 1% pellets. This research has demonstrated that slugs are highly sensitive to metaldehyde. D. reticulatum can detect metaldehyde that has been incorporated using inorganic Controlled Release Technology, with as little as 0.28% metaldehyde content. Controlled release technology involving molluscicides is still in its infancy, however, has potential as a future focus for improved pellet design.Institute for Agri-Food Research and Innovation (IAFRI