Baseline susceptibility of a laboratory strain of northern corn rootworm, diabrotica barberi (coleoptera: chrysomelidae) to bacillus thuringiensis traits in seedling, single plant, and diet-toxicity assays

Authors: PEREIRA, ADRIANO - University Of Missouri; HUYNH, MAN - University Of Missouri; SETHI, AMIT - Corteva Agriscience; MILES, ASHLEY - Corteva Agriscience; French, Bryan; ELLERSIECK, MARK - University Of Missouri; COUDRON, THOMAS - University Of Missouri; Shelby, Kent; Hibbard, Bruce

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/27/2020
Publication Date: 8/12/2020
Citation: Pereira, A.E., Huynh, M.P., Sethi, A., Miles, A.L., French, B.W., Ellersieck, M.R., Coudron, T.A., Shelby, K., Hibbard, B.E. 2020. Baseline susceptibility of a laboratory strain of northern corn rootworm, diabrotica barberi (coleoptera: chrysomelidae) to bacillus thuringiensis traits in seedling, single plant, and diet-toxicity assays. Journal of Economic Entomology. 113(4):1955–1962. https://doi.org/10.1093/jee/toaa107.
DOI: https://doi.org/10.1093/jee/toaa107

Interpretive Summary: The northern corn rootworm (NCR) is one of the most important corn pest in the U.S. Corn Belt. The larvae of this pest cause significant damage to corn roots that can lead to significant yield loss. NCR resistance evolution to transgenic corn hybrids has been reported in corn fields of North Dakota and Minnesota. The Environmental Protection Agency (EPA) has mandated resistance monitoring programs, but for multiple reasons, this has not been possible in the past. Here, we report the susceptibility of a laboratory population of NCR to all current transgenic toxins in plant and diet assays. As a result of this study and other work, the methods are now in place to address the EPA mandate to monitor field populations of NCR for resistance to transgenic corn.

Technical Abstract: The northern corn rootworm (NCR), Diabrotica barberi Smith & Lawrence, is an economic pest of maize in the U.S. Corn Belt. The objective of this study was to determine the baseline susceptibility of a laboratory NCR strain to Bt proteins eCry3.1Ab, mCry3A, Cry3Bb1, and Cry34/35Ab1 using seedling, single plant, and diet-toxicity assays. Plant assays were performed in greenhouse using corn hybrids expressing one of the Bt proteins and each respective near-isoline. Diet-toxicity assays, consisting of Bt proteins overlaid onto artificial diet were also conducted. In both plant assays, significantly more larvae survived Cry34/35Ab1-expressing corn compared with all other Bt-expressing corn, and larvae that survived eCry3.1Ab-expressing corn had significantly smaller head capsule widths compared with larvae that survived Cry34/35Ab1-expressing corn. In seedling assays, larvae surviving eCry3.1Ab-expressing corn also had significantly smaller head capsule widths compared with larvae that survived mCry3A-expressing corn. Additionally, larvae that survived mCry3A-expressing corn weighed significantly more than larvae surviving eCry3.1Ab- and Cry34/35Ab1-expressing corn. In single plant assays, no significant differences in larval dry weight was observed between any of the Bt-expressing corn. In diet assays, LC50s ranged from 0.14 (eCry3.1Ab) to 10.6 µg/cm2 (Cry34/35Ab1), EC50s ranged from 0.12 (Cry34/35Ab1) to 1.57 µg/cm2 (mCry3A), IC50s ranged from 0.08 (eCry3.1Ab) to 2.41 µg/cm2 (Cry34/35Ab1), and MIC50s ranged from 2.52 (eCry3.1Ab) to 14.2 µg/cm2 (mCry3A). These results establish the toxicity of four Bt proteins to a laboratory diapausing NCR strain established prior to the introduction of Bt traits and are important for monitoring resistance evolution in NCR field populations.