Susceptibility of third-instar western corn rootworms, Diabrotica virgifera virgifera LeConte, to the Agriotos, All, Breton, and Mexican strains of the entomogenous nematode Steinemema feltiae was compared based on concentration-mortality regressions. Larvae were most susceptible to the Mexican strain, less susceptible to the Agriotos and Breton strains, and least susceptible to the All strain. The Mexican strain was 22 times more virulent than the Allstrain. Rootworm larvae encapsulated invading nematodes of all strains, but the frequency of encapsulation was lower for the Mexican and Agriotos strains. Apparently, the defensive response of encapsulation had only a minor effect on larval susceptibility. Frequency of encapsulation and larval susceptibility were not consistently related.