Eight-legged eaters: Defining the influence of spider populations on insect pest control in soybeans

The contribution of spiders to biological control in annual cropping systems can be relatively low but remains poorly defined. For farmers dedicated to integrated pest management, one would expect that spiders can contribute substantially to biological control, but the influence of generalist predators, like spiders, on biological control remains unclear due to interguild and intraguild predation. To clarify the potential role of spiders on biological control in an annual crop, we conducted a field experiment in soybeans in which we depleted, augmented, or left unchanged populations of web-building and foliage-dwelling spiders (Infraorder: Araneomorph). We then quantified their abundance and diversity and assessed their contributions to biological control in soybeans. We assessed these contributions via sweep net collection and counts of insects and spiders as well as by quantifying soybean leaf damage at the plot level. We hypothesized that augmented spider populations would result in decreased populations of insect pests. Our experiment provides valuable insight into the contributions of spiders to pest control in a common annual crop. This information will help us build pest control programs that better account for the needs of spiders, including adjusting insecticide regimes to help spider populations grow.