Conserving natural areas to enhance biological control of Wisconsin potato pests: A multi-scale landscape study

The research reported in this thesis examined the impact of natural areas in local and broad-scale landscapes on biological control in Wisconsin potatoes. At a local scale, I examined the impact of grassy field margins within 200 m of the crop on biological control. At a broad scale, I examined the impact of non-crop habitats within 1.5 km of potato fields. To examine the impacts of these habitats on biological control, field studies addressed two questions: (1) do non-crop habitats influence the diversity of natural enemies in potatoes, and at what scale? and (2) at what scale is predation of the potato pests Leptinotarsa decemlineata (Say) and Myzus persicae (Sulzer) impacted by non-crop habitats? To address the first question, predatory ground beetles (Coleoptera: Carabidae) were sampled in 19 commercial potato fields and grassy field margins in 2005. This study showed that beetle diversity in potatoes increased with the area of non-crop habitat within 1.5 km. Grassy field margins supported more species than potatoes, but there was no evidence these habitats influenced diversity in the crop. Secondly, predation of Leptinotarsa decemlineata (Say) and Myzus persicae (Sulzer) were measured in potato fields in 2005 and 2006. Results suggest that predation of these two pests is differentially influenced by local- and broad-scale landscape structure. To complement broad-scale studies, I also conducted small-scale experiments. The first study asked the question: Is it important to conserve diverse predators that attack different life stages of L. decemlineata? Results suggest that the importance of conserving functionally diverse predators depends on prey density. A second experiment examined the impact of planting native warm-season grasses on predation of L. decemlineata eggs. Predation of eggs was elevated in potatoes surrounded by grasses, and this appeared to be due to increased abundance of harvestmen (Opiliones). Overall, this research shows that conserving non-crop habitats can influence predator diversity and predation of potato pests. However, the appropriate scale of habitat conservation and the importance of conserving diverse predators are highly dependent on the biology of the organisms involved.