Geographic distribution of Bacillus thuringiensis Cry1F toxin resistance in western bean cutworm (Lepidoptera: Noctuidae), populations in the United States

Authors: Coates, Brad; Abel, Craig; Swoboda, Katharine; Palmquist, Debra; MONTEZANO, DEBORA - University Of Nebraska; ZUKOFF, SARAH - Kansas State University; WANG, YANGZHOU - Academy Of Military Medical Sciences; BRADSHAW, JEFFREY - University Of Nebraska; DIFONZO, CHRISTINA - Michigan State University; SHIELDS, ELSON - Cornell University; TILMON, KELLY - The Ohio State University; HUNT, THOMAS - University Of Nebraska; PETERSON, JULIE - University Of Nebraska

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/12/2020
Publication Date: 8/2/2020
Citation: Coates, B.S., Abel, C.A., Swoboda, K.A., Palmquist, D.E., Montezano, D.G., Zukoff, S.N., Wang, Y., Bradshaw, J.D., DiFonzo, C.D., Shields, E., Tilmon, K.J., Hunt, T.E., Peterson, J.A. 2020. Geographic distribution of Bacillus thuringiensis Cry1F toxin resistance in western bean cutworm (Lepidoptera: Noctuidae), populations in the United States. Journal of Economic Entomology. 113(5):2465-2472. https://doi.org/10.1093/jee/toaa136.
DOI: https://doi.org/10.1093/jee/toaa136

Interpretive Summary: Feeding damage to corn by pest insect species is a major cause of yield and grain quality loss in the United States and worldwide. Larvae of the western bean cutworm (WBC) are a perennial pest of corn that inflicts damage to ears and kernels. WBC damage occurs in its native range within the High Plains, as well as across a range expansion zone around the Great Lakes region. WBC larvae have become resistant to transgenic corn hybrids containing the Bt (Bacillus thuringiensis) Cry1F toxin meant to control WBC populations. However, it is unclear how common resistance has become with WBC populations and the geographic range of resistant populations. A study by ARS scientists and university collaborators compared the level of WBC resistance to Cry1F toxins across locations in the Midwest and Great Lakes regions of the United States using laboratory bioassays. Results of this two-year study demonstrated high levels of resistance with WBC populations across all sampled locations, although resistance levels varied across locations. Regardless of weight data showed that WBC larval feeding on Cry1F toxin had slower growth and development, likely indicating an impact on overall health and fitness. These results are of interest to regulatory, university, industry stakeholders and corn producers interested in the evolution of Bt resistance in insects and issues related to the control of WBC in corn production systems.

Technical Abstract: The western bean cutworm (WBC), Striacosta albicosta (Lepidoptera: Noctuidae), is a sporadic yet severe pest of transgenic corn in the High Plains and Great Lakes regions of North America, including on hybrids expressing the Bacillus thuringiensis (Bt) Cry1F toxin. The level and geographic distribution of Cry1F resistance is not completely known. Neonate S. albicosta from 10 locations between Nebraska and New York state were subjected to dose-response trypsin-activated native Cry1F toxin overlay bioassays. In 2017, the mean estimated lethal concentration causing 50% larval mortality (LC50) was high (range 15.1 µg Cry1F cm-2 to 18.4 µg Cry1F cm-2), and not significantly different among locations. In 2018, LC50 estimates at Scottsbluff, NE (22.0 µg Cry1F cm-2) and Watertown, NY (21.7 µg Cry1F cm-2) were significantly higher when compared to locations in Michigan (15.8 µg Cry1F cm-2). Significantly lower 14-day larval weight among survivors was correlated with higher Cry1F dose, indicating the potential for fitness effects among field-exposed larvae. Results from this study indicate that S. albicosta resistance to the Bt Cry1F toxin is high, and relatively evenly distributed across the areas of native and range expansion areas where seasonal field infestations typically occur.