Larval movement and survival of Helicoverpa zea (Boddie) in seed blends of non-Bt and Bt maize containing Agrisure Viptera® trait: Implications for resistance management

Abstract

A seed blend refuge has been used to host susceptible insects for Bt maize insect resistance management (IRM) in the U.S. Maize Belt. One major concern in the use of seed blends is that larval movement among non-Bt and Bt plants could cause additional mortalities of susceptible insects. To address this concern, three caged-field trials were conducted to evaluate larval movement and survival of the corn earworm, Helicoverpa zea (Boddie), in eight seed blends of Cry1Ab/Vip3A maize with 0–30% non-Bt refuges. Each plot consisted of five rows and 21 plants in each row. Each plot was infested on the ear silks of the central plant at R1 stage with 35 F1 neonates produced from field-collected H. zea. After 9–13 d, no live larvae or kernel damages were observed on all Bt plants across all planting patterns and trials. In pure non-Bt plantings, 64.8% of the total larvae recovered moved away from the infested ears and survived on other plants, but most of the recovered larvae (86.8%) were located within a distance of three plants from the originally infested plants, and all live larvae were found on the originally infested or its adjacent rows. Larval survival and distribution were similar among seed blends with non-Bt plants in the centers of the plots, in which larvae predominantly located on the central plants (85.7% of the total recovered) with 100% being found on the central rows. Overall, larval recovery from central non-Bt plants in seed blends was 27.5% less than that from the pure non-Bt plantings. Kernel damage levels followed similar patterns as the number of larvae recovered in the plants, and larvae recovered developed similarly across treatments. Results of the study should have value in understanding the larval movement behavior of H. zea, assessing resistance evolution risk, and refining Bt maize IRM modeling for managing this pest. Additional studies are needed to determine the extent to which the reduction of refuge populations in seed blends influences resistance development of the pest to the Bt maize.