Evolution confirmed of field resistance to Cry3Bb1
Gray is particularly concerned about the escalation of soil insecticide usage with Bt hybrids for corn rootworm protection. This practice is seemingly becoming very common in many Corn Belt states. Many will recall that a primary benefit touted when rootworm Bt hybrids entered the marketplace (2003) was the reduction or potential elimination of soil insecticides. Even though commodity prices have increased, so have seed costs, and now many producers are adding yet another input cost--a soil insecticide.
Another very strong concern that Gray and many of his entomology colleagues hold is the increased selection pressure being placed on the Cry34/35Ab1 protein in areas of the Corn Belt where resistance to the Cry3Bb1 protein has been confirmed. Pyramided hybrids that are being used in these areas continue to work reasonably well; however, in effect, one protein (Cry34/35Ab1) is providing the primary control. And the required refuge for these pyramided Bt hybrids has been reduced from 20% to a 5% seed blend. Even though a seed blend (refuge-in-a-bag) is a preferred resistance management strategy for corn rootworms, the reduction in refuge is a lingering concern for Gray.
The western corn rootworm remains a versatile insect foe. It has adapted to many classes of insecticides, to crop rotation, and to this relatively new transgenic technology. Producers will need to employ a well-conceived integrated pest management approach to stay one step ahead of this insect.