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Title: INFLUENCE OF WITHIN-FIELD AND LANDSCAPE FACTORS ON APHID PREDATOR POPULATIONS IN WHEAT (REVISE RECORD--ADD ACCEPT DATE, REVISE TITLE)

Author
item Elliott, Norman - Norm
item Kieckhefer, Robert
item LEE, J - USDA-OICD
item French, Bryan

Submitted to: Landscape Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/27/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: It may be possible to manipulate agricultural landscapes to improve control of crop pests. One possibility is to manipulate the composition of the landscape in a way that improves the survival and reproduction of natural enemies of crop pests, thereby improving biological control. At the present time there is not enough information on the effects of landscape structure on natural enemies to indicate whether or not manipulations would have a significant effect on biological control. The purpose of this study was to determine if landscape structure was important in determining the abundance of cereal aphid predators in wheat fields. Specifically, we studied the influence of prey density, within-habitat vegetation, and landscape composition on the abundance of predatory insects in wheat fields in eastern South Dakota. Aphids, aphid predatory insects, and within-habitat vegetation were sampled in 104 fields over a three year period, 1988-1990. The composition and patchiness of the landscape surrounding each field was determined from high altitude aerial photographs. Predator species richness and species diversity in wheat fields were related to landscape variables. Abundance of most predator species was influenced by variability in the structure of the landscape. Overall, predator abundance and species diversity increased with increasing amounts of semi-natural land, and with the patchiness of the surrounding landscape. Results suggest that landscape structure is an important factor determining the abundance of cereal aphid predators in wheat fields. Thus, there may be potential for improving biological control via landscape manipulation.

Technical Abstract: The influence of prey density, within-habitat vegetation, and the landscape matrix on the abundance of aphid predatory insects in wheat fields was studied in eastern South Dakota, United States. Aphids, aphid predatory insects, and within-habitat vegetation were sampled in 104 fields over a three year period, 1988-1990. The composition and patchiness of the landscape surrounding each field was determined from high altitude aerial photographs. Landscape variables were aggregated at three spatial scales ranging from 2.59 km**2 to 582 km**2. Regression models incorporating within-field and landscape matrix variables accounted for 27 to 49% of the variance in aphid predator abundance in wheat fields. Landscape variables were included in regression models more frequently, and generally accounted for a greater percentage of variability in abundance than within-field variables. Predator species richness and species diversity were also related to within-field and landscape matrix variables. Some predator species were strongly influenced by variability in the structure of the landscape matrix occurring at a particular spatial scale, and the importance of variability at a particular spatial scale varied among species. Overall, predator abundance and species diversity increased with increasing vegetational diversity within wheat fields and increasing amounts of semi-natural lands and patchiness of the surrounding landscape.