Influence of slug herbivory on the vegetation development in an experimental wildflower strip

Wildflower strips along arable fields are currently being created on a large scale to increase natural enemies of crop pests and to conserve insect diversity on farmland. Slugs can affect the vegetation development of these strips considerably. This study examines the influence of herbivory by the slugs Deroceras reticulatum and Arion lusitanicus on the development of seven plants, which provide a diverse vegetation structure in wildflower strips soon after sowing. The total plant density was significantly reduced by either of the slug species compared with a control free of slugs. In contrast, the total biomass, percentage cover and number of inflorescences did not differ significantly among the three treatments. Three of the seven plant species were affected adversely by one or both slug species. Centaurea cyanus was considerably reduced by Deroceras and completely destroyed by Arion. The density of Fagopyrum esculentum and density and coverage of Papaver rhoeas were significantly reduced by Arion. Biomass and coverage of Agrostemma githago increased significantly in the Arion treatment. Borago officinalis, Malva sylvestris and Sinapis alba remained unaffected by either of the slug species. The survival of Centaurea, known to be a particularly attractive plant to several flower visiting insects, was drastically reduced by slug herbivory. Therefore, it is recommended to increase the quantity of seeds of plants that are of particular ecological significance to guarantee the survival of wildflower strip plants which are particularly susceptible to slug herbivory.