Western corn rootworm larval movement in SmartStax™ seed mix scenarios

The Environmental Protection Agency (EPA) has mandated that all registrants of Bt crops submit an insect resistance management (IRM) plan prior to registration of any Bt crop. IRM can extend the lifetime of management options, but depends on extensive knowledge of the biology of the pest species involved for an optimal plan. Recently, the EPA registered a seed mix refuge for one of the Bt products targeting the western corn rootworm. Insect movement between Bt and isoline plants in row crops can speed the development of resistance of high dose Bt products. Upon hatch, larval western corn rootworm will move through the soil and seek out host roots. In isoline corn, the larvae move between plants to access new roots when the initial host source is depleted. To assess the movement of the larvae between Bt and isoline plants, we planted four configurations of Bt and isoline plants each consisting of combinations of SmartStax (Bt) and isoline roots. One or two plants in each replicate were infested with 1500 viable western corn rootworm eggs, depending on the treatment. The infested plant and neighboring plants were sampled throughout the study for larval recovery to track the movements of the western corn rootworm between plants. Plant damage and adult emergence data were also collected on separate plots. Overall, Smartstax performed extremely well except when infested isoline plants surrounded the Bt plant on both sides. These plants had late occurring damage and significantly higher adult emergence than any other plant (including isoline plants).