Degree Type


Date of Award


Degree Name

Doctor of Philosophy



First Advisor

Leslie C. Lewis


Entomopathogenic nematodes in the genus Steinernema are promising biological control agents of soil insect pests. Two factors which may influence efficacy of biological control applications are virulence and dispersal of nematodes. This research examined the influence of fertilizers on the virulence of nematodes and the effects of earthworm presence on nematode dispersal;The virulence of Steinernema carpocapsae (Weiser) was determined in soil amended with fertilizer treatments of fresh cow manure, composted manure, and urea. Urea and fresh manure reduced nematode virulence in laboratory experiments. Field experiments, however, only indicated reduced nematode virulence in soil amended with fresh manure. Soil amended with composted manure did not affect nematode virulence;The effects of fertilizers on the ability of S. carpocapsae to control the black cutworm, Agrotis ipsilon (Hufnagel), were determined in a corn ecosystem. Fertilizer treatments included fresh cow manure, composted manure, and urea. Except in soil amended with high rates of fresh manure, nematode applications resulted in reduced cutworm damage relative to a control (no nematodes or fertilizers added). Analysis of black cutworm damage may be an efficient method to study effects of other biotic and abiotic factors on the efficacy of entomopathogenic nematodes in biological control;Vertical dispersal of S. carpocapsae, S. feltiae (Filipjev), and S. glaseri (Steiner) was determined in the presence and absence of the earthworm Lumbricus terrestris (L.). Nematode dispersal was evaluated through a bioassay and through direct extraction of nematodes from soil. Dispersal of S. carpocapsae and S. feltiae was increased in the presence of earthworms. Dispersal of S. glaseri was reduced in the presence of earthworms relative to absence of earthworms. The differences in effects of earthworms among nematode species may have been due to interspecific differences in dispersal behavior. In soil void of earthworms, dispersal of S. glaseri was greatest followed by dispersal of S. carpocapsae and then S. feltiae. The presence of earthworm burrows did not affect nematode dispersal. Therefore a phoretic relationship between the earthworms and nematodes is likely.



Digital Repository @ Iowa State University,

Copyright Owner

David Ian Shapiro



Proquest ID


File Format


File Size

110 pages