At which scale should conservation of non-crop habitat take place to sustain such important ecosystem services as the control of crop pests? To help understanding the consequences of land-use decisions, Ben Werling and Claudio Gratton examined the impact of local and broad scale landscape structure on the predation of two insect pests of potatoes in Wisconsin, the Colorado potato beetle, Leptinotarsa decemlineata, and the green peach aphid, Myzus persicae.
At a local scale (meters), potato fields of different sizes were bordered by different areas of uncultivated grassy field margins. At a broad scale (kilometers), potato fields and grassy margins were set in landscapes composed of varying percentages of non-crop habitat. The Predation of both investigated species was significantly impacted by non-crop habitats, but this relationship occurred at different scales for each pest and interacted differently with habitat type. The predation of exposed egg masses of L. decemlineata was greater in field margins than in the potato crop and increased in both habitats when field margins were large relative to the area of potatoes while that predation was less affected by the amount of non-crop habitat within kilometers. In contrast, the suppression of aphid population growth by predators increased with the area of non-crop habitat within kilometers of fields, but was less affected by the field margin area.
As a potential mechanism for the differential impact of local and broad scale landscape structure on predation of these pests, Ben and Claudio suggested that the two pests are attacked by natural enemies with different dispersal abilities. Aphid predators may move across the landscape at broader scales than predators that attack L. decemlineata eggs. Alternatively, the same predators may attack both pests, but respond to landscape structure differently in June, when L. decemlineata egg abundance peak and August when Aphids are present.
Ben and Claudio quoted that the influence of non-crop habitats on predation the potato beetles is due to the movement of natural enemies between resource-providing field margins and potatoes. Consequently small field sizes could reduce the travel distance and increase the ability of organisms to access resources in non-crop habitats. The oppositional patterns of M. persicae suppression suggest that aphidophagous predators move between non-crop habitats at the scale of kilometers. Because even a single ecosystem service, such as pest predation, can be influenced by landscape structure at multiple scales, the authors emphasize that it may be necessary to conserve heterogeneity both at the levels of individual farms and entire mosaic landscapes to maintain ecosystem services.