Multidimensional approach to formulating a specialized diet for northern corn rootworm larvae

Authors: MAN, HUYNH - University Of Missouri; Hibbard, Bruce; Lapointe, Stephen; Niedz, Randall; French, Bryan; Pereira, Adriano; FINKE, DEBORAH - University Of Missouri; Shelby, Kent; Coudron, Thomas

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/29/2019
Publication Date: 3/6/2019
Citation: Man, H.P., Hibbard, B.E., Lapointe, S.L., Niedz, R.P., French, B.W., Pereira, A.E., Finke, D.L., Shelby, K., Coudron, T.A. 2019. Multidimensional approach to formulating a specialized diet for northern corn rootworm larvae. Scientific Reports. 9:3709. https://doi.org/10.1038/s41598-019-39709-x.
DOI: https://doi.org/10.1038/s41598-019-39709-x

Interpretive Summary: The northern corn rootworm (NCR) is an important pest of maize in the United States. This pest has developed resistance to insecticides and crop rotation. The recent increases in NCR populations in some areas cause a growing concern for farmers, regulatory agencies, the seed industry, and researchers about the adaptation of NCR to transgenic crops. Missing is an artificial diet that can be used in diet bioassays as a tool for evaluating the resistance of NCR populations to transgenic toxins. Since no artificial diet has been developed specifically for NCR larvae, we first compared all 5 available rootworm diets for NCR larval performance to identify the best diet. We then identified key diet ingredients in the best diet and explored new protein sources to formulate an optimized blend for NCR. This resulted in a NCR diet formulation that supports approximately 97% survival and molting, and a 150% increase in larval weight compared with larvae reared on the best previous diet after 10 days of feeding. This diet is ideal for use in resistance bioassays and it is reasonable to expect extensive application of the diet both for monitoring and for developing new management technologies.

Technical Abstract: The northern corn rootworm (NCR), Diabrotica barberi Smith & Lawrence, is a major pest of maize (Zea mays L.) in several regions of the United States Corn Belt. This pest has developed resistance to insecticides and crop rotation as observed for the western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte. Damage caused by this pest will increase should resistance to Bacillus thuringiensis (Bt) become common, as it has for WCR. This possibility heightens the importance of monitoring for resistance to maize varieties derived through traditional methods or genetic modification with exogenous toxins. Toxicity bioassays using artificial diet have proven to be valuable for monitoring resistance in WCR to toxins produced by Bt. No artificial diet has been developed specifically for NCR larvae, so we first evaluated known Diabrotica diets. The best artificial diet for NCR to date has been a diet developed for the WCR. We developed a specialized diet for NCR using an iterative approach. Screening designs including 8 diet components were performed to identify the principal nutritional components contributing to multiple developmental parameters (survival, weight, and molting). We then applied mixture designs coupled with response surface modeling to optimize a blend of those components. Finally, we validated an improved NCR diet formulation that supports approximately 97% survival and molting, and a 150% increase in larval weight after 10 days of feeding compared with the best previously published artificial diet. This formulation appears suitable for use in diet bioassays as a tool for evaluating the resistance of NCR populations to insecticides.