Here, Mitch Teich, host of the Lake Effect on Milwaukee Public Radio, talks with Tim about how characteristics of the landscape affect natural pest control by beneficial insects.
Agricultural landscapes provide us with a variety of valuable services. These include provisioning of food, fiber, feed, and fuel; regulation of greenhouse gases, water quality, and soil quality; and support of biodiversity and biodiversity services.
Our lab studies how ecosystem services are affected by land use and land management in agroecosystems. We take a landscape perspective in our work and focus on services provided by mobile organisms, such as crop pollinators and natural enemies of crop pests.
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.
We all have an intuitive understanding that organisms interact with one another, through such events as predation, parasitism, and even mutualism. It is easy for us to relate to plants and animals this way because we too are often focused on direct interactions between ourselves and the people and things around us. Less often do we consider how we are indirectly linked to one another; that is, how two things influence each other through a shared intermediary.
Field ecologists are often interested in multiple species that are connected to one another through a third living thing, including some in the Gratton Lab at theUniversityofWisconsin-Madison. Steve Hong and his colleagues have been studying how two pests of the important crop soybean affect the plant and one another. Soybean has historically fallen victim to tiny worms called nematodes that attack the plant below the surface. Above ground the plant is fed upon by tiny insects known as aphids which have been introduced to Wisconsin only in the last decade.
Experiments in the laboratory and the field with soybean and its above and below-ground pests have revealed the complicated relationships among them. Winged aphids have been shown to prefer soybeans that are uninfected by the nematodes, both in the lab and in the field. However aphid growth and reproduction were not reduced on plants infected by nematodes versus those that were not infected. However yield and seed production were reduced in the field by nematodes and aphids respectively.
Hong, SC, A MacGuidwin, C Gratton. In review. Soybean aphid (Aphis glycines Matsumura) and soybean cyst nematode (Heterodera glycines Ichinohe) interactions in the field and effects on soybean yield.