Degree Type


Date of Award


Degree Name

Doctor of Philosophy





First Advisor

Erin W. Hodgson

Second Advisor

Aaron J. Gassmann


Farmers can benefit from tools that are applied at planting and can still manage pest populations throughout the growing season. To meet these demands, some of the tools include host-plant resistance and seed-applied pesticides. However, prophylactic applications of pesticides in a seed treatment may not always be needed to preserve yield. The complex biology of induced plant defenses could also be exploited to make crops more tolerant to pest injury. Here we focus on two major soybean pests: soybean aphid, Aphis glycines Matsumura, and soybean cyst nematode, Heterodera glycines Ichinohe.

One field study was conducted in multiple years and locations with experimental plots to compare the effects of host-plant resistant cultivars and pesticidal seed treatments on soybean aphid, soybean cyst nematode, and soybean yield. Complementary studies were performed in the greenhouse with the same treatments. Host-plant resistance effectively suppressed both soybean pests; however, pesticidal seed treatments were inconsistent.

A laboratory study was performed to explore inducible host plant defenses and its potential impacts on soybean aphid. Fungal entomopathogens were used as plant inoculum and molecular tools to identify isolates of these fungi that naturally occur in agricultural fields. Fungal entomopathogens could establish as endophytes in soybean, but the fungus Metarhizium brunneum actually increased populations of soybean aphid on inoculated plants. All of the fungal isolates were Metarhizium robertsii, which confirms its prevalence throughout North American soils.


Copyright Owner

Eric Harold Clifton



File Format


File Size

140 pages