Responses of ground-dwelling spiders to four hedgerow species on sloped agricultural fields in Southwest China

Spiders are important predators in agroecosystems and contribute to the control of agricultural pest populations. Habitat management such as the creation of new semi-natural habitats around or within fields enhances spider abundance and species diversity. Using pitfall traps, we investigated the effects of four hedgerow plant species, which serve as undisturbed and permanent semi-natural habitats, on ground-dwelling spider activity density (a parameter of population density and relative activity) and species richness. Samples were collected over two winter wheat and two summer maize growing seasons during 2005–2007 in trial field 1 (slope gradient of 20%) and field 2 (slope gradient of 12%) at the Ziyang Experimental Site in Sichuan Province, China. The hedgerow species evaluated were Amorpha fruticosa (field 1), Vetiveria zizanioides (field 1), Eulaliopsis binata (field 2), and Medicago sativa (field 2). Compared to control plots, hedgerow plots had significantly higher activity density and species richness of ground-dwelling spiders within strips in both fields 1 and 2 during the wheat growing season. The presence of hedgerow strips did not augment the activity density and species richness of ground-dwelling spiders within the crop fields during the wheat or maize growing seasons. The ground-dwelling spider activity density within hedgerow strips was significantly higher in the Vetiveria than in the Amorpha plots and in the Medicago than in the Eulaliopsis plots, and the species richness was significantly higher in the Vetiveria than in the Amorpha plots during the wheat season. Our results suggest that hedgerows may serve as important overwintering sites for ground-dwelling spiders during the wheat growing season. In addition, the diversification of agroecosystems by using hedgerow strips may be a viable strategy for maintaining ground-dwelling spider populations in agricultural areas. However, ground-dwelling spiders did not move into adjacent crop fields; therefore, future work should address the mechanisms of attracting spiders into crop fields, thereby contributing to the bio-control of pests.