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Shifting to ‘refuge-in-the-bag

As compliance with refuge requirements for planting Bt corn hybrids declines, the landscape is shifting for a new approach to insect resistance management. Several seed companies are seeking regulatory approvals for the concept known as “refuge-in-a-bag,” or RIB for short. The companies say the RIB technology will make it easier and more convenient for farmers to plant refuges in the future.

Corn rootworm control is the latest trait to be added into stacked-trait technology in corn. Photo by Ralph Pearce.

The current management approach requires farmers to plant a structured refuge of non-Bt hybrids to reduce the risk of insects developing resistance to the Bt traits. The minimum refuge area is 20 percent or five percent, depending on the technology. Despite being aware of the need to plant refuges, fewer North American farmers are complying with the regulations. Whether the reasons are related to inconvenience, confusion or concerns about reduced productivity in the refuge areas, a trend toward lower levels of compliance has been emerging in both Canada and the United States.

The idea behind the RIB approach is to mix the right amount of Bt and non-Bt seeds, based on the refuge requirement, in the same bag so that the seed is interspersed in the field. While RIB has not been approved in Canada, and has only received limited approval in the US, it is poised to become the foundation of future insect resistance management in Bt corn.

“I think we’re at the point now where producers are clearly receptive to a new approach, that approach being refuge-in-a-bag seed mixtures,” says Dr. Mike Gray, University of Illinois professor and interim assistant dean for Agriculture and Resources Extension. “I think there are some signs that policy makers may be interested in that approach as it obviously does ensure compliance. I think we have some new transgenic tools in the marketplace at this point that should benefit, not only in terms of crop protection, but also have some benefits with regard to resistance management,” says Gray, referring to the pyramided corn hybrids that express multiple traits of the Cry proteins to control European corn borer and corn rootworm.

Gray says regulators took a big step when they allowed the commercialization of the SmartStax hybrids. This newer technology, developed by Monsanto and Dow AgroSciences, still requires farmers to plant a structured refuge, but the level is reduced from 20 percent to five percent.

Gray says another significant move came when the US Environmental Protection Agency (EPA) granted the registration of the Optimum AcreMax 1 insect protection in corn hybrids from Pioneer Hi-Bred. It is hailed as the first approval of an “in-the-bag” solution for refuge management corn rootworm. The in-the-bag product contains 90 percent of a Pioneer-brand hybrid with Herculex XTRA that includes protection against both corn rootworm and corn borer, and 10 percent of a Pioneer hybrid with the Herculex 1 trait for corn borer protection. Because Herculex 1 does not contain protection against corn rootworm, the 10 percent blend provides the refuge for this pest. Growers, however, are still required to plant a 20 percent refuge for European corn borer. According to the product’s information, the technology allows growers to plant the separate refuge field up to a half mile away. Meanwhile, Pioneer’s parent company, DuPont, has plans for Optimum AcreMax 2 to provide a refuge-in-a-bag solution for both corn rootworm and corn borer.

With more seed companies petitioning regulators to approve RIB, Gray believes it will be important to find the right mix of non-transgenic seed that is not only suitable for managing insect resistance but will also be acceptable to the farmers. He says most producers seem to be interested in a blend of 95 percent of Bt and five percent non-Bt. “Once you start to move into the six to 10 percent range of non-traited seed, the receptiveness goes down because growers believe that it’s a lot of plants that could be exposed to potential insect injury,” says Gray.

Questions still remain
The other side of the equation is the size of the refuge area. Is five percent enough to deter the insects from developing resistance over the long term? Gray expects the question will be a significant issue for the EPA (and Canadian Food Inspection Agency in Canada) during the registration review.

One of the keys of the “refuge-in-the-bag” technology is the protection it provides below the ground, as seen in this root mass comparison.     Photo courtesy of Pioneer Hi-Bred.

Larry Robertson, Dow AgroSciences’ North American project manager for RIB, says the 95-5 blend is the “sweet spot” for maximizing the growers’ opportunity for yield as well as the durability of the trait. The key, he says, for reducing the risk of insect resistance is the multiple modes of action for pest control, both above and below the ground. “Everything we have done from a scientific perspective tells us that it is going to be a very effective method to help improve the durability and longevity of those traits from a couple of different perspectives,” explains Robertson. “One is the level of performance. The second is the level of compliance, which is obviously a concern the industry has: that the growers are actually planting adequate levels of refuge in the right location on their farm. So this drives both of those very well to significantly improve the durability of the trait versus not having a refuge-in-the-bag system in place.”

Robertson says Dow submitted its application for approval in both Canada and the US in December 2009. While he is hesitant to put a timeline on a possible Canadian registration, Robertson hopes the company will hear about its American registration in 2011.

Monsanto is one of several other companies that have submitted applications. Chris Anderson, the company’s Canadian stewardship lead, says Monsanto is seeking permission to use the RIB concept for products such as Genuity SmartStax and Genuity VT YieldGard Double Pro.

He also does not believe that reducing the refuge to five percent, when using multiple modes of action, will increase the risk of insects developing resistance. “We’ve got something in the order of 10 years of research behind the refuge-in-a-bag concept, comparing a structured refuge – where you plant a discreet portion of the field, where it’s a separate field, a block or separate strips in the field – to an unstructured refuge, which is a refuge where the Bt and non-Bt seeds are mixed together. We’ve spent a lot of time and research dollars investigating how to make a concept like this work,” says Anderson. “So we feel quite confident that this is going to provide a good, long-term management practice to protect against the development of insects that might be resistant to Bt products.”

For Anderson, the simplicity goes beyond the idea of one bag. “You know the right amount of refuge is in the bag and you don’t have to consider particular configuration issues or how far a second field (non-Bt) is away. Those things just make it so much easier for a producer to make use of the technology and be compliant with the Insect Resistance Management (IRM) requirements at the same time,” he says.

As regulators consider the future of RIB and the new approach to insect resistance management, the Canadian crop protection industry says compliance with current requirements remains vital. Although Janice Tranberg, acting executive director of biotechnology for CropLife Canada, says the likelihood of RIB coming to Canada is fairly high, she tempers that assessment with a note of caution. “The CFIA has also told us that it is very important that we have control of the current technologies if we want to have access to new technologies,” says Tranberg. “And that’s why it is very important for us to bring this awareness and to get farmers to realize that it’s important to keep compliant to the refuge areas.”

Tranberg says raising that awareness while avoiding confusion over refuge requirements in the short term will be a big challenge for the industry in the months ahead. “We have a 20 percent refuge for the current technology, we have five per cent for SmartStax, or we could have refuge-in-a bag (if approved),” says Tranberg. “Each one has a little bit of a different requirement and I think it’s going to be important that farmers understand the different requirements for their different technologies.”