Submitted to: Crop Protection Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/18/2010
Publication Date: 2/1/2011
Citation: Hardke, J., Leonard, R., Huang, F., Jackson, R.E. 2011. Damage and survivorship of fall armyworm (Lepidoptera: Noctuidae) on transgenic field corn expressing Bacillus thuringiensis cry proteins. Crop Protection Journal. 30(2):168-172. Interpretive Summary: Fall armyworm has never been a primary target of commercial Bt cotton and corn lines. However, results from this study demonstrated that some Bt corn lines, particularly those that produce the Cry1F protein, could be utilized in management systems in areas within the Southern United States where fall armyworm is a consistent pest of field corn in an effort to reduce damage caused by this pest. Fewer fall armyworm larvae survived on Cry1F-producing corn hybrids, and subsequent damage was also reduced by the lines expressing Cry1F. There is a concern, however, with potential Bt resistance development in fall armyworm in the Southern United States to the Cry1F protein. Single-gene Cry1F-producing corn hybrids and Bt cotton varieties that express Cry1F are available to at least two generations of fall armyworm. This has increased exposure of the fall armyworm population to this technology, which could lead to issues with resistance development. With documented Cry1F resistance in fall armyworm populations in the Caribbean, efforts should be made to ensure the sustainability of this technology for fall armyworm control. The commercialization of pyramided-gene Bt corn hybrids (those expressing multiple Bt proteins) should delay Bt resistance development in these populations, which lends to the need for additional research with these new technologies.
Technical Abstract: Field corn, Zea mays L. plants expressing Cry1Ab and Cry1F insecticidal crystal (Cry) proteins of Bacillus thuringiensis (Bt) Berliner are planted on considerable acreage across the Southern region of the United States. The fall armyworm, Spodoptera frugiperda (J. E. Smith), is an economically important pest during the mid-to-late season on non-Bt and some commercial Bt corn hybrids. The objective of this study was to quantify foliage injury and survivorship of fall armyworm on transgenic corn lines expressing Cry1Ab and Cry1F Bt proteins. Corn lines/hybrids expressing Cry1Ab, Cry1F, and a conventional non-Bt cultivar were evaluated against artificial infestations of fall armyworm in field trials. Larvae (second instars) of fall armyworm were placed on corn plants (V8-V10 stages). Leaf injury ratings were recorded 14 d after infestation. Hybrids expressing Cry1F had significantly lower feeding injury ratings than non-Bt plants. Development and survivorship of fall armyworm on Bt corn lines/hybrids were also evaluated in no-choice laboratory assays by offering freshly harvested corn leaf tissue to third instars. Transgenic corn hybrids expressing Cry1Ab and Cry1F significantly reduced growth, development, and survivorship of fall armyworm compared to those offered non-Bt corn tissue. However, 25-71% of third instars offered Bt corn leaf tissues successfully pupated and emerged as adults. These results suggest Cry1Ab has limited effects on fall armyworm; whereas Cry1F demonstrated significant reductions in foliage injury and lower survivorship compared to that on non-Bt corn tissues. Although fall armyworm is not considered a primary target for IRM by the U.S. Environmental Protection Agency, these levels of survivorship could impact selection pressures across the farmscape, especially when considering transgenic Bt cotton cultivars are expressing similar Cry (Cry1Ac or Cry1F) proteins.