Land use and field edges drive movements of spiders in soybean agroecosystems

Intensification of agricultural production has altered land use patterns in North America. At the landscape level, diversity and prevalence of specific land classifications alter arthropod populations within crop fields. Locally, edge effects alter arthropod populations by providing food and harborage. Therefore, edges need to be considered in addition to broad landscape effects in relation to use of natural enemies for biological control. Spiders are an important component of the natural enemy community within agricultural systems since they navigate efficiently in complex landscapes, rapidly adjust to environmental changes or prey availability, subsist on alternative prey and disperse rapidly into new habitats. Since spiders readily respond to environmental cues, landscape patterns have the potential to alter spider and prey populations within crop fields.

This study focused on how land use at both landscape and field levels impacted spider communities and their movement within soybean fields. The surrounding land use was analyzed at a distance of 5 km for landscape diversity using GIS. Additionally, composition of field edges directly adjacent to soybean fields was analyzed in relation to spider abundance and within-field movement patterns analyzed using Spatial Analysis by Distance IndEs (SADIE). Spiders, other arthropod predators, soybean pests, and alternative prey items were collected using pitfall, quadrat, and sweep net sampling from ten Kentucky soybean fields. Forested areas at the landscape and field levels had a positive impact on spider populations, while crops had variable influences depending on scale. These results indicate that multiple scales need to be analyzed to monitor arthropod populations.