||A factorial field experiment was conducted in native tallgrass prairie of eastern Kansas in which pesticides were applied to reduce numbers of below and/or above- ground arthropods on small plots sited within enclosures containing varying densities of the prairie vole Microtus ochrogaster. The numbers of aboveground sucking phytophagous insects were particularly sensitive to the application of below and aboveground pesticides. Au- chenorrhyncha (leafhoppers and planthoppers) increased in number on plots treated be- lowground with isofenphos and ethoprop, suggesting that these insects may interact com- petitively with belowground arthropods. Sternorrhyncha (primarily aphids) and chewing phytophagous insects (primarily grasshoppers and beetles) did not respond to the soil pesticide treatment. Application of carbaryl to foliage resulted in a decrease in Auchenorrhyncha and an increase in Sternorryncha but no consistent change in numbers of other aboveground arthropods, which apparently migrated readily among the small (9 m2) experimental plots. Varying mammal density did not result in any significant variation in density of aboveground arthropods, and no significant interactions with mammal density were detected in above- ground arthropod responses to either below or aboveground chemical treatment.