Ground Beetle (Coleoptera: Carabidae) Assemblages and Slug Abundance in Agricultural Fields Under Organic and Low-Input Conventional Management Within a Long-Term Agronomic Trial in Central Italy

Ground Beetle (Coleoptera: Carabidae) Responses to Cattle Grazing, Grassland Restoration, and Habitat across a Precipitation Gradient

Simple Summary

Beneficial insect numbers have sharply declined in recent years, and these declines negatively impact (1) food crops due to reduced pollination services, and (2) wildlife and birds due to reduced food sources. In part, agricultural intensification and habitat fragmentation have led to these declines. In the United States, one conservation effort is the Conservation Reserve Program (CRP), which provides financial assistance for replanting agricultural land to restored habitat to improve environmental health and quality. Common CRP grassland restorations are CP2 (“native grass” seed mix) and CP25 (“rare and declining habitat” seed mix). We examined the response of ground beetles, a group that is important for wildlife, to CRP restoration and management across three grassland habitats, and 108 sites. We examined two restoration types (CP2, CP25), and the grazing or absence of grazing by cattle. Our findings indicate that ground beetle communities are not negatively impacted by moderate levels of cattle grazing. Additionally, we found that cattle grazing might have positive effects on ground beetle abundance, biomass, and diversity in tallgrass habitats. The positive impact of cattle grazing may provide an additional incentive for CRP restorations that would enhance beneficial insect populations.

Abstract

Grasslands in North America have declined by over 70% since industrialization of settlements due to the conversion of natural habitats to cropland and urban centers. In the United States, the federally supported Conservation Reserve Program (CRP) was created to improve water quality, reduce soil erosion, and increase native habitats for wildlife. Within these restored grasslands, ground beetles (Coleoptera: Carabidae) are a keystone invertebrate group that fill several crucial niches and may serve as bioindicators of successful land management strategies. To understand the impact of land management on ground beetles, we examined carabid beetle community responses to a grazing treatment and two plant restoration treatments with low and relatively high initial plant diversity over two field seasons. We used pitfall traps at 108 CRP sites across a 63.5 cm precipitation gradient, encompassing three grassland types. Overall, grazing and restoration treatment did not have detectable effects on carabid abundance, biomass, or diversity. Carabid communities, however, responded differently to grazing within grassland types—all three community measures increased in response to grazing in tallgrass sites only. Our short-term study suggests that moderate levels of cattle grazing do not negatively affect carabid communities and might have positive effects on abundance, biomass, and diversity in tallgrass regions.

Slug Monitoring and Impacts on the Ground Beetle Community in the Frame of Sustainable Pest Control in Conventional and Conservation Agroecosystems

In conservation agriculture, slugs are considered significant pests and their monitoring is a key option in the integrated pest management framework. Together with molluscicide applications, predators such as ground beetles can offer a tool for slug control in the field. Through the evaluation of slug and ground beetle monitoring strategies, this work compared their presence in conventional and conservation agricultural plots. The invasive Deroceras invadens was the dominant slug species to occur in all sampling periods. Among Carabidae, Poecilus cupreus and Pterostichus melas were the most abundant species, and Bembidion spp., Brachinus spp., and Harpalus spp. were also common. Beer-baited pitfall traps, whatever their alcoholic content, caught more slugs and ground beetles than wooden boards used as shelters. Slugs were more abundant in conventional plots than in conservation plots, possibly due to the lower presence of natural enemies such as ground beetles. Despite possible impacts on Carabidae, beer-baited pitfall traps should be considered a useful tool for slug monitoring and for the planning of molluscicide applications. Soil management such as minimum- or no-tillage and the presence of cover crops are important elements influencing both slug and ground beetle presence, possibly playing a key role in the maintenance of natural enemy populations.