Evaluation of carabids as predators of slugs in arable land
An Enzyme-Linked Immunosorbent Assay (ELISA) was developed which detected slug antigens in postmortem gut analysis of carabid beetles. The ELISA was used to identify beetles which fed on slugs in three fields of oilseed rape and winter wheat in the Tyne valley, Northumberland. Generalist species such as Harpalus rufipes, Pterostichus melanarius, Pterostichus nladidus, Anlara silnilata and Nebria brevicollis fed on slugs in the field. Molluscan specialists such as Carabus violaceus and Cychrus caraboides also fed on slugs in the field. Laboratory studies indicated that many large and medium sized carabids were able to predate small slugs. Some beetle species did not eat slugs but exposure to the beetles increased slug mortality. Therefore, postmortem investigations may underestimate the impact that carabids exert on slugs as they do not measure the number of slugs killed. Slug mucus affected the locomotory activity of generalist and specialist beetle species. Beetles foraged longer, covered greater distances, made more turns, walked slower and spent more time stationary on soil covered in slug mucus compared to control areas. Abax parallelepipedus, P.melanarius, Pterostichus niger and H.rufipes all reduced slug damage to a chinese cabbage crop in a miniplot experiment compared with unprotected plots. However, these differences were not significant. A.parallelepipedus was most effective at reducing slug damage to the chinese cabbage but was rare in arable land. H.rufipes was least effective at reducing slug damage but was abundant in arable land in both years of the study. A high proportion of H.rufipes beetles fed on slugs in the field. None of these four species occurred at densities in the field which reduced slug damage in the miniplot experiment.