Wednesday, August 6, 2008: 2:10 PM
102 D, Midwest Airlines Center
Ben P. Werling, Entomology, Michigan State University, East Lansing, MI and Claudio Gratton, Department of Entomology, University of Wisconsin - Madison, Madison, WI
Background/Question/Methods Predaceous arthropods have limited impact on populations of insect herbivores in most annual crops. This may be because crop habitats lack key resources that limit the abundance and diversity of these predators. Conserving natural areas outside of crops may be one way to increase the impact of predators on herbivorous pests and reduce the need to use insecticides, since natural habitats may provide diverse resources that enhance the abundance and diversity of predators. We examined if the presence of natural areas in the landscape surrounding potatoes affects predation on eggs of the Colorado potato beetle (CPB), Leptinotarsa decemlineata, a key pest of potatoes. To accomplish this, we compared predation on CPB eggs in potato fields set in landscapes that varied at both local and large spatial scales. At a local scale, we hypothesized that the grassy field margins that border potato fields are reservoirs of predators that enter the crop and attack pests. We expected predation to be greater in field margins than potatoes and to be greater in potato fields surrounded by large amounts of field margin. At a larger scale, we hypothesized that predation in both potatoes and field margins would be positively related to the percentage of the surrounding 1.5 km composed of uncultivated habitat.
Results/Conclusions Our results suggest that local habitats like field margins do harbor predators of CPB eggs: 10% more eggs were killed by predators in field margins compared to potatoes. Furthermore, predation within the crop increased from 0 to 10% as the area of field margin surrounding potatoes increased; however, this increase in predation only occurred when potato fields were small in area compared to field margin habitats. In contrast, we found no evidence that predation on CPB is affected by the amount of uncultivated habitat within 1.5 km of potatoes and field margins. Overall, our results suggest that off-crop natural areas do support predators that attack pests in potatoes, but that the influence of these predators becomes significant only when potato fields are small and all parts of the crop are relatively close to field margin.
