Evaluating western corn rootworm (Coleoptera: Chrysomelidae) emergence and root damage in a seed mix refuge

Resistance management is essential for maintaining the efficacy and long-term durability of transgenic corn engineered to control western corn rootworm (Diabrotica virgifera virgifera Le Conte). Theoretically, a refuge can be provided by growing susceptible (refuge) plants in either a separate section of the field adjacent to resistant (transgenic) plants, or as a seed mixture. We examined the effects of varying the structure of a 10 and 20% refuge between currently approved structured refuges (block or strip plantings), as well as deploying the refuge within a seed mix, on adult emergence timing and magnitude, root damage and yield. Our 2-yr field study used naturally occurring western corn rootworm populations and included seven treatments: 10 and 20% block refuge, 10 and 20% strip refuge, 10 and 20% seed mix refuge, and 100% refuge. Beetles emerging from refuge corn emerged more synchronously with those emerging from transgenic (Bacillus thuringiensis [Berliner] Bt-RW) corn in seed mix refuges when compared with block refuges. The proportion of beetles emerging from refuge plants was significantly greater in a block and strip refuge structure than in a seed mix refuge. More beetles emerged from Bt-RW corn plants when they were grown as part of a seed mix. We discuss the potential benefits and drawbacks of a seed mix refuge structure in light of these findings.