Influence of within-field and landscape factors on aphid predator populations in wheat

The influence of prey density, within-field vegetation, and the composition and patchiness of the surrounding landscape on the abundance of insect pre dators of cereal aphids was studied in wheat fields in eastern South Dakota , USA. Cereal aphids, aphid predators, and within-field vegetation were sam pled in 104 fields over a three year period (1988-1990). The composition an d patchiness of the landscape surrounding each field were determined from h igh altitude aerial photographs. Five landscape variables, aggregated at th ree spatial scales ranging from 2.6 km(2) to 581 km(2), were measured from aerial photographs. Regression models incorporating within-field and landsc ape variables accounted for 27-49% of the variance in aphid predator abunda nce in wheat fields. Aphid predator species richness and species diversity were also related to within-field and landscape variables. Some predators w ere strongly influenced by variability in the composition and patchiness of the landscape surrounding a field at a particular spatial scale while othe rs responded to variability at all scales. Overall, predator abundance, spe cies richness, and species diversity increased with increasing vegetational diversity in wheat fields and with increasing amounts of non-cultivated la nds and increasing patchiness in the surrounding landscape.