Effect of seed blends and soil-insecticide on western and northern corn rootworm emergence from mCry3A + eCry3.1Ab Bt maize

Authors: FRANK, DANIEL - West Virginia University; KURTZ, RYAN - Cotton, Inc; TINSLEY, NICHOLAS - University Of Illinois; GASSMANN, AARON - Iowa State University; MEINKE, LANCE - University Of Nebraska; MOELLENBECK, DANIEL - Dm Crop Research Group, Inc; GRAY, MICHAEL - University Of Illinois; BLEDSOE, LARRY - Purdue University; KRUPKE, CHRISTIAN - Purdue University; ESTES, RONALD - University Of Illinois; WEBER, PATRICK - Iowa State University; Hibbard, Bruce

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/13/2015
Publication Date: 6/5/2015
Publication URL: http://handle.nal.usda.gov/10113/61077
Citation: Frank, D., Kurtz, R., Tinsley, N.A., Gassmann, A.J., Meinke, L.J., Moellenbeck, D., Gray, M.E., Bledsoe, L.W., Krupke, C.H., Estes, R.E., Weber, P., Hibbard, B.E. 2015. Effect of seed blends and soil-insecticide on western and northern corn rootworm emergence from mCry3A + eCry3.1Ab Bt maize. Journal of Economic Entomology. 108(3):1260-1270.

Interpretive Summary: The effectiveness of refuge strategies for delaying resistance in populations of an insect pest to transgenic crops that expresses their own insecticide (a protein knows as Bt toxin) relies on production of sufficient numbers of non-resistant insects from plants that do not have the insecticide in order to reduce the frequency of mating between resistant insects. The refuge strategy also depends on the farmer to plant areas of non-transgenic crops in the right proportion and close to the transgenic crop. To assist in this effort companies have proposed the use of blended seed, a mixture of transgenic and non-transgenic seeds in the correct ratio for effective control of resistance development. This study was aimed at assessing the effectiveness of such a strategy for corn rootworm. Blended seed mixtures containing various ratios of transgenic Bt maize and non-Bt maize were deployed alone and in combination with a soil applied insecticide (tefluthrin) were used to evaluate the survivability of the western corn rootworm in a total of nine field environments across the Midwestern United States in 2010 and 2011. Northern corn rootworm emergence was also evaluated in four of these environments. As expected, both western and northern corn rootworm beetle emergence from all Bt treatments was significantly reduced when compared with beetle emergence from "refuge" treatments. When evaluating western corn rootworm beetle emergence from various blends, more beetles emerged from the blends than from the non-blended transgenic crop and more beetles emerged as the blend favored a higher percentage on non-transgenic corn. Insecticide delayed the number of days to 50% beetle emergence in western corn rootworms more so in the non-blended transgenic crop than in the blended treatments, suggesting the latter is better for resistance management in corn. This information is necessary to assess the usefulness of blended seed strategies for insect pest control in the US.

Technical Abstract: Blended seed mixtures containing various ratios of transgenic Bt maize expressing the mCry3A + eCry3.1Ab proteins and non-Bt maize (near-isoline maize) were deployed alone and in combination with a soil applied insecticide (Force CS) to evaluate the survivorship of the western corn rootworm, Diabrotica virgifera virgifera LeConte, in a total of nine field environments across the Midwestern United States in 2010 and 2011. Northern corn rootworm, Diabrotica barberi Smith & Lawrence emergence was also evaluated in four of these environments. Both western and northern corn rootworm beetle emergence from all Bt treatments was significantly reduced when compared with beetle emergence from near-isoline treatments. When evaluating western corn rootworm beetle emergence from various ratios of mCry3A + eCry3.1Ab:near-isoline, 2.6, 4.2, and 6.7 fold more beetles emerged from 95:5, 90:10, and 80:20 blended seed treatments, respectively than from the 100:0 treatment when data from all environments were averaged together. Similar data from the northern corn rootworm resulted in 2.8, 3.2, and 4.2 fold more beetles than from the 100:0 treatment. The addition of Force CS (tefluthrin) significantly reduced western corn rootworm beetle emergence for each of the three treatments to which it was applied. Force CS also significantly delayed the number of days to 50% beetle emergence in western corn rootworms. Time to 50% beetle emergence in the 100% mCry3A + eCry3.1Ab treatment with Force CS was delayed 13.7 d when compared with western corn rootworm beetle emergence on near-isoline corn. These data are discussed in terms of rootworm resistance management.