Environmental factors shaping generalist ground beetle communities and populations of associated slug prey

Slugs are a difficult pest to manage in conservation agriculture, where reduced soil disturbance and increased ground cover create ideal conditions for slug population growth, but also an opportunity to promote natural suppression by ground-dwelling arthropods. However, it remains unclear which predatory arthropod species are associated with depressed slug abundance and how environmental factors shape this predatory community composition. Here we examined relationships between ground-dwelling arthropods (ground beetles, spiders, harvestmen), weather, and land cover on slug activity-density, measured over two years from commercial corn and soybean fields in the US Mid-Atlantic. We found that slug and ground beetle activity-density were slightly positively correlated. At the same time, spiders and harvestmen showed no association, suggesting that this ground beetle community may be opportunistically preying upon slugs. Sites within landscapes dominated by soybeans harbored the most slugs and ground beetles. Within the field, ground beetle species richness was highest whenever there was corn-based cover, while slugs and ground beetle activity-density did not respond to a particular cover type. We found two species that were associated with decreasing slug activity-density (Anisodactylus sanctaecrucis and Scarites quadriceps) and three that were positively associated (A. punctiforme, C. tricolor, and P. chalcites). Though we found a robust community of ground beetles persisting in these intensively managed agricultural landscapes, their apparent contribution to slug suppression may be limited by these beetles’ generalist life histories. Still, efforts to maintain ground beetle habitat and reduce prophylactic insecticide use will likely promote the knock-on effect of natural slug suppression.