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Why GMO refuge is still crucial

If you wondered why it was so important to put out refuge acres as required for Bt GMO products, you don’t need to wonder any longer. It’s critical to follow the refuge rules, and it will remain critical even after refuge-in-a-bag corn becomes more common on the market.

Key Points

Following refuge requirements is more important now than ever.

A break in resistance to rootworms documented in certain Iowa fields.

Not all Bt technologies are affected by this break.

Recently, questions arose about the possible discovery of Bt rootworm resistance feeding in corn in Iowa. Christian Krupke, an Extension entomologist at Purdue University, recently answered questions about this situation.

Here are his answers to key questions. Find his full commentary at Find 2011 newsletters, then go to the Aug. 5 edition.

IPF: Why is stewardship particularly crucial for rootworm traits?

Krupke: Corn rootworm Bt toxins are not high-dose toxins. Many larvae survive exposure and reach adulthood on each acre of these hybrids. This is one reason that the refuge is so critical in stewardship of this valuable Integrated Pest Management tool.

IPF: Why is the issue so timely now?

Krupke: Iowa State University entomologist Aaron Gassman published research findings following up on persistent reports of high damage to Bt corn in northeastern Iowa. After collecting adults and eggs and rearing larvae from the area, he concluded the larvae were able to survive on Bt corn hybrids expressing the Cry3Bb1 toxin at levels similar to survival on non-Bt corn.

IPF: Are all Bt rootworm events affected?

Krupke: No. Hybrids expressing the toxin included those formerly labeled as Yieldgard RW and VT3 hybrids. This toxin is also one of the proteins found in SmartStax hybrids. The good news is that the study tested the other major toxins deployed in North America against the pest. These are found in Herculex hybrids targeting rootworms and in SmartStax hybrids. Gassman found no enhanced survival of larvae exposed to other toxins.

In other words, no cross-resistance between the two toxins was found, which is another good thing.

IPF: What does this mean for corn producing areas?

Krupke: It certainly isn’t good news, but it is not a total disaster either. It demonstrates again what a remarkably adaptable pest the western corn rootworm is. There is no “putting the genie back in the bottle” and resistance in areas where it’s documented isn’t likely to diminish. It’s an alert to keep our eyes open for occurrences elsewhere. However, the vast majority of Bt corn continues to perform well.

IPF: Could this happen in other places, like Indiana?

Krupke: Yes. Rootworms are the key pest of corn here, and there is no reason why we could not see resistance occur at some point, either to this or other toxins.

IPF: What should farmers watch for?

Krupke: Fields to watch are those where pressure on the insect to develop resistance is the highest — continuous Bt corn in areas of high rootworm pressure. Some northwestern and north-central Indiana fields may fit this description, but in general Indiana has a more diverse cropping system than Iowa, with a large percentage of fields rotating to soybeans.


Rootworm warning: Published reports indicate some western corn rootworm larvae in Iowa have dveloped resistance on one of the earlier Bt rootworm toxins.

This article published in the September, 2011 edition of INDIANA PRAIRIE FARMER.

All rights reserved. Copyright Farm Progress Cos. 2011.