Further evidence that seed blend refuges may accelerate resistance evolution in Lepidoptera

This was an exploratory field experiment to assess how seed blend refuge might differ from block refuge in terms of insect productivity and selection for resistance to Bt toxins. Larvae avoid feeding on kernels in seed blend refuge ears. Larvae on seed blend refuge ears may be developmentally delayed. Seed blend refuges result in shorter corn earworm pupae and significant mortality in fall armyworm. The resistance management plan for Lepidoptera on Bt corn has always relied on a high dose being present for target pests. Dose for some other pests such as corn earworm and fall armyworm was not as high prior to the introduction of pyramid toxin corn. Field studies show very low survival of these species on pyramided corn, especially that which contains Vip3a in combination with other toxins. However, seed blend refuge ears in pyramided corn effectively lower the dose and they destroy the security provided by pyramiding toxins. Thus seed blend refuges may provide a distinct advantage for heterozygous resistant insects and they may actually accelerate the rate of resistance evolution.