Insects such as the black cutworm are a major pest of seedling corn in Corn Belt states. Both the nematode Steinernema carpocapsae and the fungus Beauveria bassiana are potential biological control agents of this pest Because their survivability depends on moisture and they are affected adversely by nitrogen compounds, this project studied the effects of various fertilizers (fresh cow manure, composted cow manure, and urea) on these insect-killing organisms. Results showed that S. carpocapsae is more active in soils with no fertilizer amendment or with composted manure than with fresh manure or chemical fertilizer; B. bassiana is adversely affected by fresh manure. Investigation of factors that may enhance dispersal (which in turn may be a determining factor in the success of biological control) found that dispersal of two species of insect-killing nematodes was increased in the presence of earthworms.