Larval movement of sugarcane borer, Diatraea saccharalis (F.) in a seed mixture: Implications for resistance management

Insect movement among Bt and non-Bt plants in the field is a common concern in regard to resistance management. The seed mixture or refuge in the bag (RIB) is currently available for some pyramided corn events. In a structured refuge, the dispersal of adults is an important matter while, in RIB strategy, the movement of larvae is a point of concern. We evaluated larval movement and occurrence of sugarcane borer (SCB), Diatraea saccharalis (F.), in four seed mixture planting patterns of non-Bt plants and Bt plants containing pyramided Bt traits, SmartStax^TM. The four patterns of planting were: T1) pure Bt corn, T2) a non-Bt corn plant surrounded by Bt corn plants, T3) pure non-Bt corn, and T4) a Bt corn plant surrounded by non-Bt corn plants. Each treatment consisted of three rows and 9 plants in each row. Independent trials were conducted both in the open field and in the greenhouse by infesting 50 ready-to-hatch SCB eggs on the center plants. The number of live SCB and length of stalk tunnels in each plant were checked after 21 days after egg infestation. There were no significant differences in number of larvae/pupae observed between the central non-Bt plants in T2 and T3. Similarly, in all trials no larvae were found in the center Bt plant in both T1 and T4. A limited number of larvae moved from center non-Bt /Bt plants to adjacent non-Bt plants. Larval feeding injury in terms of stalk tunneling was directly related to the interplant movement pattern. Overall, larvae had ability to move at least to 4-plants away from the center plant and movement varied among planting patterns. Results of this study suggest that refuge plants in the seed mixture may provide an equivalent refuge population of SCB as structured refuge planting.