Blended versus block refuges: Comparison of production of ECB and SWCB larvae on refuge plants

We compared the production of European corn borers from single non-Bt plants next to Bt plants (blended refuge) with production from non-Bt plants next to other non-Bt plants (block refuge) for insect resistance management (IRM). When the infestation was heavy (50 larvae/plant on all refuge and adjacent plants) the blended refuge plants produced 44% of the larvae produced by block refuge plants (second generation). When the infestation was more natural on 20% of the plants) the blended refuge plants produced 20 % of the larvae produced in the block refuge. We also found that 60% of larvae moved off the plant where they were placed. Therefore a blended refuge plant loses 60% of larvae when they move onto Bt plants. This suggests that there is a significant reduction in the production of ECB and SWCB larvae on blended refuge plants relative to production on block refuge plants. This will need to be incorporated in IRM models used to evaluate the blended refuge in Bt corn.