Deciphering the factors that govern diversity and number of trophic levels in a community, or “community structure,” is one of the fundamental goals of community ecologists. Community ecology models and empirical studies have provided a framework for understanding how population density at various trophic levels responds to variation in the relative strength of top-down (consumer driven) and bottom-up (resource driven) forces. This framework can be applied to understanding variation in insect diversity at different trophic levels. In North-Central Colorado we sampled grazed and ungrazed grasslands to quantify the relative strengths of direct and indirect interactions between plants and the arthropod community. This allowed us to determine how diversity within trophic levels affects overall plant and arthropod community structure. We found that plant abundance and diversity was higher on grazed pasture versus unmanaged fields. Structural equation models revealed strong effects of herbivore diversity on diversity of other trophic levels. Top-down forces were important in grazed fields, with enemy diversity depressing herbivore diversity, which in turn depressed plant diversity. Bottom-up forces dominated in unmanaged fields, with plant diversity causing increased herbivore diversity, which in turn increased enemy diversity. For all fields, detritivore diversity was enhanced by overall arthropod diversity. Increasing productivity caused increases in detritivore numbers, but lower diversity. These results support hypotheses from other empirical studies that changes in diversity of a single trophic level can cascade to effect diversity at other, nonadjacent trophic levels. The patterns uncovered in this study are the basis for current experimental tests of diversity cascades.