Degree Type


Date of Award


Degree Name

Master of Science





First Advisor

Bryony C. Bonning


Soybean aphid poses a significant threat to soybean agriculture in North America. Current management strategies are heavily dependent on chemical insecticides, which while presently effective, may have negative side effects. Bt toxins have been successfully used in various transgenic crops for almost 20 years to manage lepidopteran and coleopteran pests. However, this strategy has not been used in the management of aphids and other hemipterans due to their low susceptibility to Bt toxins, potentially arising from a lack of binding to the hemipteran gut. To circumvent this limitation in soybean aphids, a phage display library was screened in vivo against the soybean aphid gut to identify candidate gut binding peptides to add to a Bt toxin. The in vitro binding capacity of candidate gut binding peptides was characterized. The candidate with the strongest gut binding was used to engineer the Bt toxin Cry4Aa by insertion of the peptide sequence at five sites in the toxin, the N-terminus, loop 2 and loop 3 of domain II, and the loops formed between B12-B13 and B15-B16, of domain III. Four of the seven engineered toxins maintained stability upon activation and native toxicity against Culex pipiens larvae. The four remaining toxins are currently being tested against soybean aphid.

Copyright Owner

Benjamin Robert Deist



File Format


File Size

91 pages