Evaluation of plant-based Western corn rootworm bioassays for cost effectiveness and detection of resistance to Bt traits

The western corn rootworm (WCR) is the most important insect pest of corn in the United States. Given a history of developing resistance, a reasonable concern exists that WCR will develop resistance to newer management tactics.  To delay resistance development of insect pests to Bt crops, the U.S. Environmental Protection Agency (EPA) has mandated that an insect resistance management (IRM) plan must be in place prior to registration of any Bt product.  One component of current IRM plans is resistance monitoring plans.  The EPA is currently considering replacing diet bioassays for all WCR toxins with on-plant assays. We evaluated a single-plant assay and a seedling mat assay for their respective abilities to detect resistance to four different single Bt traits and for cost effectiveness.  WCR populations with resistance to each trait were included along with control populations.  Initial studies suggest that each bioassay has advantages and disadvantages, depending on the protein being evaluated and cost effectiveness.