Intraspecific and interspecific competition among northern corn rootworms,Diabrotica barberiSmith&Lawrence, and western corn rootworms,Diabrotica virgifera virgiferaLeConte, were investigated under greenhouse conditions. Densities of both species were varied on potted corn seedlings to determine the effects of competition on adult emergence. The results depended on the initial larval densities of the two species. Intraspecific and interspecific competition significantly affected in adult emergence of both species. Western corn rootworm adult emergence was influenced more by intraspecific competition than interspecific competition, but females were effected by northern corn rootworm densities. Northern corn rootworm was very sensitive to both intraspecific and interspecific competition.