Characterization of corn root factors to improve artificial diet for western corn rootworm (Coleoptera: Chrysomelidae) larvae

Authors: HUYNH, MAN - University Of Missouri; BERNKLAU, ELISA - Colorado State University; COUDRON, THOMAS - Retired ARS Employee; Shelby, Kent; BJOSTAD, LOUIS - Colorado State University; Hibbard, Bruce

Submitted to: Journal of Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/9/2019
Publication Date: 4/6/2019
Citation: Huynh, M.P., Bernklau, E.J., Coudron, T.A., Shelby, K., Bjostad, L.B., Hibbard, B.E. 2019. Characterization of corn root factors to improve artificial diet for western corn rootworm (Coleoptera: Chrysomelidae) larvae. Journal of Insect Science. 19(2):1-8. https://doi.org/10.1093/jisesa/iez030.
DOI: https://doi.org/10.1093/jisesa/iez030

Interpretive Summary: The western corn rootworm is a serious insect pest of maize in the U.S Corn Belt and parts of Europe. An artificial diet that supports WCR development similar to larval feeding on maize roots would facilitate new research toward management of this pest. Previous efforts to develop an artificial diet for larvae of the western corn rootworm highlighted the role of corn root powder, which had a significant positive impact on larval development. Unfortunately, this ingredient is not commercially available. To formulate a diet for western corn rootworm larvae with all ingredients readily accessible, we evaluated whether essential growth factors for larval development could be extracted from corn root powder and included in the formulation to improve the performance of diet without corn root powder. Corn roots apparently contain factors that assist in larval growth. These factors were not fully extracted by methanol and remained on the remnants of the extracted root, suggesting the primary corn root components improving rootworm performance cannot be extracted with methanol. Additionally, we demonstrated that whole corn root powder on its own was not a suitable sole nutrition source and was was best when used in combination with all the other nutritional sources in the published WCR formulation. This information will be important for the long-term goal of an artificial diet for western corn rootworm rearing.

Technical Abstract: The western corn rootworm, Diabrotica virgifera virgifera LeConte, is an important economic pest of maize (Zea mays L.) in North America and Europe. Previous efforts to formulate an artificial diet for western corn rootworm larvae highlighted an important role of corn root powder, which had a significant positive impact on several larval developmental traits. Unfortunately, this ingredient is not available for purchase. To formulate a diet with all ingredients readily accessible, we evaluated whether essential growth factors for larval development could be extracted from corn root powder and included in the formulation to improve the performance of diet without corn root powder. For all experiments, multiple life history parameters (survival, weight, and molting) were recorded from 15-day diet bioassays. Corn roots apparently contain factors that assist in larval growth, but unfortunately, and these factors were not fully extracted by methanol and remained on the extracted root. Methanolic extracts significantly increased molting to 2nd instar, but did not significantly increase survival, dry weight, or molting to 3rd instar, suggesting the primary corn root substituents affecting these factors cannot be extracted or other extraction methods may be utilized to extract the essential factors in corn roots. Additionally, we showed that whole corn root powder was best when used in combination with all the other nutritional sources in the published WCR formulation and corn root powder made from proprietary seed and Viking seed has similar value.