Bt Corn Refuge...In a Bag

Researchers know that without a refuge to provide susceptible individuals in the population, genetically resistant CRW are more likely to mate with each other causing wide-spread resistance to the Bt protein to evolve in the CRW population much quicker.  Due to the need for a refuge and to ensure that growers comply with refuge requirements, scientists have developed the Refuge-in-a-Bag (RIB) concept.

Figure 7: Ears of corn at harvest. (Lynn Betts, NRCS)

RIB is a mixture of rootworm-protected Bt corn seed and non-Bt corn (can be Bt corn for controlling lepidopteran insects) seed in the same bag.  The bag contains the required percentage of non-Bt corn and ensures that farmers plant the refuge at the same time they plant the Bt corn.   A benefit of this approach is that the non-Bt plants will be spread throughout the field which may provide better distribution of survivors from the refuge to mate with beetles emerging from rootworm Bt corn compared to block refuges that are planted in one area of the field.  Researchers are using simulation modeling techniques to compare RIB versus block refuge scenarios under a variety of conditions to identify key factors that influence potential rates of resistance evolution. 

Before answering the following question, watch this video presentation on selection pressure, refuge in a block vs. Refuge-in-a-Bag, and the occurrence of resistant CRW populations to rootworm Bt corn.  



Question:  Does the Refuge in a Bag increase selection pressure on the population?

Looks Good! Correct: …but it depends. If farmers are not planting the required refuge, the Refuge in a Bag (RIB) reduces selection pressure because the farmer will be forced to plant some non Bt plants. However, if CRW feed on the non Bt refuge plants, get bigger, then move to neighboring Bt plants, they can consume a sub-lethal dose of Bt and still survive. This CHANGES the way the rootworm Bt proteins are applying selection pressure for resistance on the CRW population. So RIB may decrease selection pressure in some instances and increase selection pressure in others.