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Corn Insects and Resistance to Bt Corn – Newsflash (05/30/19)

Northern corn rootworm (NCR) resistance to Bt corn hybrids expressing the Cry3Bb1 (Yieldgard Rootworm) and Cry34/35Ab1 (Herculex CRW) proteins was documented for first time in the U.S. from populations collected in southeastern North Dakota.

Northern corn rootworm (NCR) resistance to Bt corn hybrids ent.1expressing the Cry3Bb1 (Yieldgard Rootworm) and Cry34/35Ab1 (Herculex CRW) proteins was documented for first time in the U.S. from populations collected in southeastern North Dakota. Adults of NCR were collected from five locations (Arthur, two fields at Page, Sargent county, and Ransom county). Populations of NCRs from Arthur, Page, Ransom, and Sargent were found to have resistance to Bt corn hybrids expressing the Cry34/35Ab1 protein. The NCR population of Arthur also was resistant to Bt corn hybrids expressing the Cry3Bb1 protein. No cross-resistance was evident between the Cry3Bb1 and Cry34/35Ab1 proteins for any NCR populations tested.

In addition, western corn rootworm (WCR) adults collected from Ransom county showed resistance to Bt corn hybrids expressing the Cry3Bb1 protein. No WCR populations were observed at the other locations. The low density of WCR is probably due to the cold winter of 2013-2014 that may have caused significant egg mortality (overwintering life stage).

Increased survival of NCR and WCR to Bt pyramided (Cry3Bb1 + Cry34/35Ab1 or SmartStax) corn was also observed in some populations. The reduced susceptibility of both corn rootworm species to the Bt pyramid corn could be attributed to increased tolerance of these populations to Cry3Bb1 and/or Cry34/35Ab1 proteins. However, not all corn rootworm populations tested were resistant and some were still susceptible to Bt corn expressing either or both Cry34/35Ab1 and Cry3Bb1 proteins in ND.

This research was recently published in the 2019 Journal of Economic Entomology. The abstract is available at https://academic.oup.com/jee/advance-article-abstract/doi/10.1093/jee/toz111/5494710

The following are some guidelines for growers to help reduce the risk of corn rootworm populations developing resistance to Bt corn hybrids in North Dakota.

  • Rotate fields (crop rotation) annually between corn and non-host crops such as soybean, flax, sunflowers, or wheat.
  • Control volunteer corn that could serve as hosts for local Bt-resistant rootworm populations.
  • Plant non-Bt corn hybrids with a soil insecticide instead, especially when low rootworm pressure is expected.
  • Plant the structured refuge corn (non-Bt corn) according to guidelines of the chosen Bt corn.
  • Rotate fields with Bt corn hybrids that have different modes of action each year.
  • Plant Bt pyramided corn hybrids. These hybrids have two or multiple Cry proteins with different modes of action for control of corn rootworms.
  • Scout your field for corn rootworm adults, and assess larval root-feeding injury during late summer.
  • If you experience higher pressure of corn rootworms in your field, contact and report to your local seed company representative and your local county extension agent / extension entomologist.

For more information, consult the NDSU Extension publication E1852 Integrated Pest Management of Corn Rootworms in North Dakota at:

www.ag.ndsu.edu/publications/crops/integrated-pest-management-of-corn-rootworms-in-north-dakota

Thanks to the North Dakota Corn Utilization Council for supporting this research on corn rootworms in ND.

 

EUROPEAN CORN BORER (ECB) resistance ent.2to a Bt corn hybrid expressing the Cry1F (Herculex 1) protein was confirmed for the first time for multiple populations of ECB in Nova Scotia, Canada in 2018 (Source: J. Smith and A. Schaafsma, University of Guelph). In order to reduce the risk of geographic expansion of field-evolved resistance of ECB to Bt corn hybrids, growers should avoid planting Bt corn hybrids expressing the single protein Cry1F or Cry1Ab, and pyramid corn hybrids in which one of the proteins is Cry1F. Resistance of ECB to Cry has not been observed in North Dakota or in nearby states. Always be vigilant in planting the refuge requirement that accompanies the chosen Bt corn hybrid. If you experience unexpected damage or heavy infestation of ECB adults or/and larvae in your corn fields, then immediately contact your local seed company representative and your local county extension agent / extension entomologist.

 

Veronica Calles-Torrez                                                                                                                                   Janet J. Knodel

Post-Doctoral Scientist                                                                                                                   Extension Entomologist

 

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