Growth of cropland, loss of natural habitat to blame
The continued growth of cropland and loss of natural habitat have increasingly simplified agricultural landscapes in the Midwest.
In a study supported in part by the National Science Foundation’s (NSF) Kellogg Biological Station Long-Term Ecological Research (LTER) site in Michigan – one of 26 such NSF LTER sites around the world – scientists concluded that this simplification is associated with increased crop pest abundance and insecticide use.
“This research suggests that there are simple ecological solutions – such as preservation or restoration of semi-natural lands within large agricultural regions – that could reduce the need for insecticides and contribute to agricultural economies,” says Nancy Huntly, NSF program director for the network of LTER sites.
While the relationship between landscape simplification, crop pest pressure and insecticide use has been suggested before, it has not been well supported by empirical evidence, scientists say.
Results of the study, published in this week’s issue of the journal Proceedings of the National Academy of Sciences, are the first to document a link between simplification and increased insecticide use.
“When you replace natural habitat with cropland, you tend to get more crop pest problems,” says lead author Tim Meehan, an entomologist at the University of Wisconsin-Madison (UW-Madison).
He and other authors are affiliated with the Great Lakes Bioenergy Research Center, one of three U.S. Department of Energy Bioenergy Research Centers, and with NSF’s Kellogg Biological Station LTER site.
“Two things drive this pattern,” says Meehan. “As you remove natural habitats, you remove habitat for beneficial predatory insects, and when you create more cropland you make a bigger target for pests – giving them what they need to survive and multiply.”
Because landscape simplification has long been assumed to increase pest pressure, Meehan and colleagues were not surprised to find that counties with less natural habitat had higher rates of insecticide use.
One striking finding was that landscape simplification was associated with annual insecticide application to an additional 5,400 square miles – an area the size of Connecticut.
Although simplification of agricultural landscapes is likely to continue, the research suggests that the planting of perennial bioenergy crops – like switchgrass and mixed prairie – can offset some negative effects.
“Perennial crops provide year-round habitat for beneficial insects, birds, and other wildlife, and are critical for buffering streams and rivers from soil erosion and preventing nutrient and pesticide pollution,” says Doug Landis, a Michigan State University entomologist and landscape ecologist who’s affiliated with the Kellogg Biological Station LTER site.
Perennial grasslands that can be used for bioenergy could also provide biodiversity support, especially beneficial insect support, says Claudio Gratton, a UW-Madison entomologist.
“If we can create agricultural landscapes with increased crop diversity, then perhaps we can increase beneficial insects, reduce pest pressure and reduce the need for chemical inputs into the environment,” Gratton says.
“We are at a junction right now,” he believes.
“There is increased demand for renewable energy, and one big question is: where it will come from? We hope that these kinds of studies will help us forecast the impacts that bioenergy crops may have on agricultural landscapes.”