Environmental factors shaping generalist carabid 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 likely promote natural suppression by ground-dwelling arthropods. However, it remains unclear which predatory arthropod species are associated with reduced slug abundance and how environmental factors shape this predatory community composition. Here, we examined relationships among ground-dwelling arthropods (carabid beetles, spiders, harvestmen), weather, and land cover and their effects on slug activity density, which was measured over 2 years across 37 commercial corn and soybean fields in the US Mid-Atlantic. We found 21 carabid species, and a positive relationship between slug and carabid beetle activity density, suggesting that this carabid beetle community may be preying upon slugs opportunistically. Slug activity density was reduced with tillage, higher temperatures, and a high proportion of corn in the landscape, while carabid activity density in crop fields decreased where there was greater surrounding land cover diversity. Neither neonicotinoid seed treatment nor foliar insecticides significantly affected slugs or carabid beetles. Carabid community composition was shaped by temperature, rainfall, and tillage, while carabid species richness was unrelated to within-field cover or landscape composition. Although we did not assess predation rates, our findings suggest great potential to promote natural suppression of slugs within conservation agriculture systems where diverse carabid assemblages persist. Our study further underscores the need and opportunity for targeted management of ground cover in and around crop fields to maintain robust carabid beetle communities and encourage slug predation amidst landscapes dominated by corn and soybean.