Entomology, Department of


First Advisor

Joe Louis

Date of this Version

Spring 5-2022


Betancurt, J.D. 2022. First Line Of Defense: Role Of Surface Waxes In Sorghum Defense Against Aphids. M.S. thesis, University of Nebraska-Lincoln.


A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Entomology, Under the Supervision of Professor Joe Louis. Lincoln, Nebraska: April 2022

Copyright © 2022 Juan David Betancurt Cardona


Since 2013, the sugarcane aphid (SCA; Melanaphis sacchari) has become a devastating pest in sorghum (Sorghum bicolor) in the United States. Efforts to mitigate this pest and contain its rapid population growth have increased recently. Host plant resistance (HPR) is an effective and environmentally friendly strategy to reduce aphid populations in this crop. Many factors make SCA a challenging pest to control. For example, SCA can overcome drastic climatic changes, which allows them to successfully colonize sorghum plants at different developmental stages.

Epicuticular waxes (EW) constitute the first point of contact between plants and their environment. EW differ in their structure and composition at different developmental stages in sorghum. In addition, EW are known to be involved in protecting plants from external stresses. However, the role of EW in sorghum-SCA interactions is not fully understood. To elucidate the role of EW in the SCA-sorghum interactions, we used the Electrical Penetration Graph (EPG) technique to monitor the SCA feeing behavior at different developmental stages of sorghum BTx623 plants and, in sorghum wild-type and bloomless (wax-depleted) plants. Additionally, through no-choice and choice assays, we determined whether the EW influence the SCA survival (antibiosis) and behavior (antixenosis) in sorghum plants and how the wax composition is related with plants responses against SCA.

We found that aphids prefer to feed longer in the sieve elements of six-week-old plants compared to two-week-old plants. However, the SCA proliferation was higher on two-week-old plants compared to six-week-old plants. Our EPG results revealed that the aphids spent more time feeding in the xylem phase and preferred to settle in the bloomless plants compared to wild-type plants. The abundance of α-amyrin and isoarborinone, both belonging to the triterpenoid family, increased after aphid infestation in six-week-old plants compared to six-week-old plants. The total amount of 16-monoacyglycerols and 32C-alcohols was higher in bloomless plants compared to the wild-type plants.

Results from this study helped us to further understand the role of epicuticular waxes play in aphid-plant interactions and will contribute to the understanding of the mechanisms involved in plants defenses and their association with waxes in plants.

Advisor: Joe Louis