Population densities ofEmpoascaleafhoppers and their major natural enemies (Anagrus parasitoidsandErigone spiders) were compared on squash in pure and mixed stands. Adult leafhoppers were more abundant in monoculture than on squash in polyculture, but squash in polyculture harbored more nymphs than did plants in monoculture. Therefore total leafhopper densities as prey were similar on squash in monoculture and on squash intercropped with cowpea and corn. These results are consistent with general theory on the response of polyphagous herbivores to vegetational diversity. The specialist parasitoid was not enhanced in mixed stands, but the generalist predator exhibited greater densities on intercropped squash. Thus, host range or range of prey might be important for predicting enemy response to vegetational diversity, as is host plant range for predicting the effects of plant diversity on herbivore densities.