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Sponsored: Corn Rootworm Traits: Are Our Tools Showing Signs of Wear?
In recent years, we have been blessed that corn rootworm (CRW) damage to our corn crop hasn’t been widespread or severe. Still, CRW is one of the most economically important pests to prevent because even moderate root feeding can seriously diminish yields. The latest research suggests CRW may be poised for a comeback, but I recommend we don’t throw it a “welcome back” party.
Let’s take a step back and review the traits we currently have for managing CRW. The first trait for CRW utilizing the Bacillus thuringiensis (Bt) toxin was the Cry3Bb1 protein in YieldGard® VT RW. It was developed by Monsanto and registered in 2003. Next came Herculex® RW (Cry34/35Ab1), registered in 2005 by Dow AgroSciences and DuPont Pioneer. Then, Syngenta registered Agrisure® RW (mCry3A) the following year. The most recent is Agrisure Duracade™ (eCry3.1Ab) which debuted in 2014 but still lacks import approval from China.
That’s quite an impressive list of tools to keep rootworms at bay, but here is where the issue arises. The efficacy of the CRW traits in the market is weakening. Resistance to rootworm traits was initially identified by Dr. Aaron Gassmann, Iowa State University entomologist, in 2009. The rootworms in that study were found to be resistant to YieldGard VT RW.(1) You might say, “that is nothing new, what’s the big deal?” Well, the real issue is the rapid pace at which resistance has progressed since then.
- In 2011, nine fields in eight different Iowa counties were identified as having resistant rootworm populations. This time, resistance to both YieldGard VT RW and Agrisure RW was documented. Crossresistance between YieldGard VT RW and Agrisure RW was also discovered.(2)
- In 2015, resistance to YieldGard VT RW was identified in Nebraska and cross resistance between YieldGard VT RW and Agrisure RW was documented.(3)
- In April 2016, cross resistance between YieldGard VT RW, Agrisure RW, and Agrisure Duracade was found in Minnesota.(4)
- In May 2016, resistance to YieldGard VT RW only was documented in Illinois. Resistance to Agrisure RW and cross resistance have yet to be been found in Illinois.(5)
- In June 2016, cross resistance between YieldGard VT RW, Agrisure RW, and Agrisure Duracade was documented in Iowa.(6)
The one trait not on this list is Herculex RW. It has been tested and its control has remained robust, until now. Unfortunately, this summer Dr. Gassmann published results from a study that shows the first occurrence of rootworm adapting to survive Cry34/35Ab1, the Bt toxin in Herculex RW.7 Cross resistance between the novel Cry34/35Ab1 (Herculex RW) protein and the other Cry3 (YieldGard VT RW, Agrisure RW, Agrisure Duracade) proteins has not yet been found. This indicates that the Herculex RW resistance likely occurs through a different mechanism and lessens the likelihood of cross resistance, but further research is needed.(8)
What does this mean for your farm? Not every rootworm in every field has resistance, but in order to preserve what effectiveness we have in our rootworm traits, adjustments should be made. The timeline above is a high level view of the current state of rootworm traits. It is evident that rootworm traits are showing signs of wear while the next rootworm trait is still several years out.
In the meantime, a good strategy for managing rootworm should not only include rotating pyramided rootworm traits, but also insecticide use and crop rotation. Relying on Herculex RW (Cry34/35Ab1) to do all the heavy lifting in controlling rootworm year after year will only put more selective pressure on it and shorten its effective life span.7 Rotating rootworm traits is paramount to maintaining the utility of our current traits. Beck’s is uniquely positioned to allow customers to rotate rootworm traits without jumping from one seed supplier to another (see table above). Talk with your local Beck’s field agronomist, seed advisor or dealer for a tailored recommendation for your operation.
Greg Shepherd, CCA | Field Agronomist
- Gassmann AJ, Petzold-Maxwell JL, Keweshan RS, Dunbar MW (2011) Field-evolved resistance to Bt maize by western corn rootworm. PLoS ONE 6(7): e22629.
- Gassmann AJ, Petzold-Maxwell JL, Clifton EH, Dunbar MW, Hoffman AM, Ingber DA, and Keweshan RS (2014) Field-evolved resistance by western corn rootworm to multiple Bacillus thuringiensis toxins in transgenic maize. Proc. Natl. Acad. Sci. USA. 111:5141-5146.
- Wangila DS, Gassmann AJ, Petzold-Maxwell JL, French BW, and Meinke LJ (2015) Susceptibility of Nebraska western corn rootworm populations (Coleoptera: Chrysomelidae) to Bt corn events. J. Econ. Entomol. 108: 742-751.
- Zukoff SN, Ostlie KR, Potter B, Meihls LN, Zukoff AL, French L, Ellersieck MR, Wade French B, Hibbard BE (2016) Multiple Assays Indicate Vary Levels of Cross Resistance in Cry3Bb1-Selected Field Population of the Western Corn Rootworm to mCry3A, eCry3.1Ab, and Cry34/35Ab1. J. Econ. Entomol. 2016 Apr 22. pii: tow073 (Epub ahead of print).
- Schrader PM, Estes RE, Tinsley NA, Gassmann AJ, and Gray ME (2016) Evaluation of adult emergence and larval root injury for Cry3Bb1-resistant populations of the western corn rootworm. J. Appl. Entomol. doi:10.1111/jen.12329
- Jakka S, Shrestha RB, and Gassmann AJ (2016) Broad-spectrun resistance to Bacillus thuringiensis toxins by western corn rootworm (Diabrotica virgifera virgifera). Scientifi c Reports. doi:10.103/srep27860.
- Gassmann AJ, Shrestha RB, Jakka S, Dunar MW, CliftonEH, Paolino AR, Ingber DA, French BW, Masloski KE, Dounda JW, and St. Clair CR. (2016) Evidence of Resistance to Cry34/35Ab1 Corn by Western Corn Rootworm (Coleoptera: Chrysomelidae): Root Injury in the Field and Larval Survival in Plant-Based Bioassays. J. Econ. Entomol. 2016, 109 (4) 1872-1880.
- Li H, Olson M, Lin G, Hey T, Tan SY, and Narva KE. (2013) Bacillus thuringiensis Cry34/35Ab1 interactions with western corn rootworm midgut binding sites. PLoS ONE 8:e53079.
SmartStax®, YieldGard VT Rootworm/RR2® and YieldGard® are trademarks of Monsanto Technology LLC. Herculex® is a registered trademark of Dow AgroSciences LLC. Agrisure®, Agrisure Duracade® and Agrisure Viptera® are trademarks of a Syngenta Group Company. ®Optimum and AcreMax are registered trademarks of Pioneer. All other trademarks are the property of their respective owners.