Changes in ground beetle (Coleoptera:Carabidae) assemblages in farming systems bordered by complex or simple roadside vegetation

Evidence suggests that vegetative diverse plant communities support diverse and abundant insect natural enemy communities. Vegetation both in and surrounding agricultural fields may be used to enhance natural enemy populations. The effects of roadside vegetation diversity on abundance and species richness of ground beetles (Coleoptera: Carabidae) were investigated. Populations and communities were compared in agricultural ecosystems bordered by complex prairie vegetation with those bordered by simple communities dominated by smooth brome grass (Bromus inermis Leysser). Pitfall traps were placed in 10 experimental roadsides and 10 and 15 m into their adjacent corn fields. Beetles trapped during two corn growth stages, before corn canopy closure and following corn canopy closure, were compared between complex and simple agricultural systems. Before canopy closure, carabid species richness was significantly greater in complex than in simple agricultural systems. Following canopy closure, carabid abundance was significantly greater in simple than in complex agricultural systems. The Bray-Curtis similarity index showed that carabid communities in complex and simple agricultural systems decreased to similar extents from before to after canopy closure of the corn. Carabid distribution was compared between experimental roadsides and their adjacent corn fields. Carabids were more abundant in roadsides than in corn fields before canopy closure and more abundant in adjacent corn fields than in roadsides following canopy closure. The Bray-Curtis similarity index showed that carabid communities in complex roadsides and their adjacent corn fields decreased to similar extents from before to after canopy closure of the corn. Carabid communities in simple roadsides and their adjacent corn fields became increasingly different before and after canopy closure of the corn. Results indicate that both complex and simple agricultural landscape are beneficial for carabids, and that carabid abundance and diversity changes between roadsides and adjacent corn fields in response to changing field conditions.